GEOLOGICAL SURVEY CIRCULAR 861 

Geological Studies of the 

COST Nos. G-1 and G-2 Wells, 

United States North Atlantic 

Outer Continental Shelf 

Geological Studies of the 

COST Nos. G-1 and G-2 Wells, 

United States North Atlantic 

Outer Continental Shelf 

By Peter A. Scholle and Chiye R. Wenkam, Editors 

G E 0 L 0 G I CAL S U R V E Y C I R C U LA R 861 

1982 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Free on application to the Branch of Distribution, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
CONTENTS 

Page 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Geologic setting of the Georges Bank basin, by JohnS. Schlee and Kim D. Klitgord . . . . . . . 4 

Lithology and petrography of COST Nos. G-1 and G-2 wells, by Michael A. Arthur . . . . . . . 11 

Calcareous nannofossil biostratigraphy and paleoenvironment of the COST Nos. G-1 

and G-2 wells in the Georges Bank basin, by Page C. Valentine...................... 34 

Foraminiferal and seismic stratigraphy, paleoenvironments, and depositional cycles in the 

Georges Bank basin, by C. Wylie Poag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

Significance of the Mesozoic carbonate bank-reef sequence for the petroleum geology of 

the Georges Bank basin, by Robert E. Mattick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 

Organic geochemistry of the Georges Bank basin COST Nos. G-1 and G-2 wells, by R. E. 

Miller, H. E. Lerch, G. E. Claypool, M. A. Smith, D. K. Owings, D. T. Ligon, and S. B. 

Eisner . . . . . . . . . . . . . . . . . . -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 

Thermal history of the Georges Bank basin, by Michael A. Arthur . . . . . . . . . . . . . . . . . . . . . 143 

Geophysical studies of the COST Nos. G-1 and G-2 wells, by David J. ~aylor and R. C. 

Anderson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 

Basement structure, sedimentation, and tectonic history of the Georges Bank basin, by 

Kim D. Klitgord, JohnS. Schlee, and Karl Hinz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 

Figures 

ILLUSTRATIONS 

Page 

1-4. Maps showing: 

1. Locations of Georges Bank and COST wells Nos. G-1 and 

G-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

2. Locations of COST wells Nos. G-1 and G-2, USGS core 

hole 6001, and multichannel seismic reflection 

profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

3. Isopachs of Upper Triassic and younger sedimentary rocks 

in the Georges Bank basin . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

4. Tectonics and structure of the Georges Bank area.. . . . . . . . 6 

5-7. Charts showing: 

5. Lithologic logs of COST Nos. G-1 and G-2 wells and the 

Nantucket Island well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

6. Geophysical logs, lithology, and ages for the COST No. G-1 

well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

7. Correlation between rocks of COST Nos. G-1 and G-2 

wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

8-9. Graphs for the COST No. G-1 well showing: 

8. Porosity versus depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

9. Porosity versus permeability . . . . . . . . . . . . . . . . . . . . . . . . . 18 

10. Chart showing geophysical logs, lithology, and ages for the COST No 

G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

iii 
Page 

Figures 11-12. Graphs for the COST No. G-2 well showing: 

11. Porosity versus depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

12. Porosity versus permeability .. _... . . . . . . . . . . . . . . . . . . . . 24 

13-14. Charts showing calcareous nannofossil biostratigraphy and paleoenvironments in: 

13. COST No. G-1 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

14. COST No. G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

15. Map of well and core sites and reflection profiles . . . . . . . . . . . . . . . . . . . . . 43 

16. Stratigraphic column of COST No. G-1 well......................... 44 

17. Geologic column of COST No. G-1 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

18. Diagram showing interpreted structure and stratigraphy along seismic 

line 77-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 

19. Stratigraphic column of COST No. G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . 50 

20. Seismic profile of line 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

21. Diagram showing interpreted structure and stratigraphy along seismic 

line 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 

22. Geologic column of COST No. G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 

23. Graph showing sediment accumulation rates for the G-1, G-2, and 

other COST wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

24. Chart showing correlation between Shell Mohican I-100 and COST No. 

G-2 wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 

25. Diagram showing interpreted structure and stratigraphy along seismic 

line 204 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 

26. Geologic column of ASP corehole 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

27-28. Charts showing: 

27. Paleoenvironments of COST Nos. G-1 and G-2 wells, compared with relative sea level and global supercycles . . . . . . 8~ 

28. Comparative stratigraphy of Georges Bank and the adjacent North American Basin . . . . . . . . . . . . . . . . . . . . . . . . . 89 

29. Map showing locations of CDP profiles on the northern and central U.S. 

Atlantic margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 

30. Chart showing COST No. G-2 well data plotted alongside seismic data 

from profile 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

31-34. Parts of seismic profiles across the outer shelf and slope in the Georges 

Bank basin: 

31. Seismic profile 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

32. Seismic profile 20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9f' 

33. Seismic profile 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9~ 

34. Seismic profile 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10(' 

35. Part of seismic profile 22 across the Long Island platform . . . . . . . . . . . . . . 101 

36. Diagrammatic sketch showing construction of continental shelf during 

the Jurassic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10~ 

37. Map of shelf margin positions during Middle Jurassic, Late JurassicEarly Cretaceous, and present time . . . . . . . . . . . . . . . . . . . . . . . . . . . 10~ 

38. Diagrammatic sketch of carbonate reef and bank facies . . . . . . . . . . . . . . . . lOr 

39. Gas chromatograms of saturated paraffin-naphthene hydrocarbons in 

lignosulfonate and in an asphalt-like substance and a solid black 

hydrocarbon from the COST No. G-2 well . . . . . . . . . . . . . . . . . . . . . . 114 

40-41. Charts summarizing organic-richness analyses of: 

40. COST No. G-1 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 

41. COST No. G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 

42-50. Gas chromatograms of saturated paraffin-naphthene hydrocarbons of: 

42. Cretaceous rocks of the COST No. G-1 well . . . . . . . . . . . . . . 120 

43. Upper Jurassic through Tertiary rocks of the COST No. 

G-2 well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

44. Upper Jurassic rocks of the COST No. G-1 well . . . . . . . . . . 124 

45. Upper and Middle Jurassic rocks down to 12,540 ft 

(3,822 m) in the COST No. G-2 well . . . . . . . . . . . . . . . . . . . 125 

46. Middle Jurassic rocks from 13,500 to 17,540 ft (4,115 to 

5,346 m) in the COST No. G-2 well................... 126 

iv 
Figures 42-50. Gas chromatograms-Continued 

47. Middle Jurassic rocks from 17,470 to 20,010 ft (5,325 to 

6,099 ml in the COST No. G-2 well .................. . 

48. Middle Jurassic rocks from 20,480 to 21,540 ft (6,242 to 

5,565 ml in the COST No. G-2 well .................. . 

49. Middle Jurassic rocks from above 13,000 ft (3,962 ml in the 

COST No. G-1 well ............................... . 

50. Middle Jurassic, Lower Jurassic, and Cambrian rocks of the 

COST No. G-1 well ............................... . 

51-57. Summary profiles showing: 

51. Types of organic matter versus depth in COST No. G-1 

well ........................................... . 

52. C1 to C7 hydrocarbon analyses for COST No. G-1 well ..... . 

53. Maturation versus depth in COST No. G-1 well ......... . 

54. Types of organic matter versus depth in COST No. G-2 

well ........................................... . 

55. Maturation versus depth in COST No. G-2 well ......... . 

56. C1 to C7 hydrocarbon analyses for COST No. G-2 well ..... . 

57. Temperature, vitrinite reflectance, and thermal alteration 

indices versus depth for COST Nos. G-1 and G-2 wells ... 

58-59. Charts showing: 

58. History of basement subsidence and sedimentation at 

COST No. G-2 well ............................... . 

59. Model of thermal history at COST No. G-2 site .......... . 

60-62. Graphs showing vitrinite reflectance for samples from COST Nos. G-1 

and G-2 wells: 

60. Versus thermal alteration indices ..................... . 

61. Versus present temperature gradient (linear plotl ........ . 

62. Versus present temperature gradient (semilog plotl ....... . 

63-64. Graphs of average velocity and root-mean-square velocity versus twoway traveltime for: 

63. COST No. G-1 well ................................ . 

64. COST No. G-2 well ................................ . 

65. Graph showing two-way traveltime as a function of depth for COST Nos. 

G-1 and G-2 wells ....................................... . 

66. Map showing locations of seismic lines 77-1 and 77-2 ................ . 

67. Seismic profile of line 77-1 and synthetic seismogram from COST No. 

G-1 well ............................................... . 

68. Seismic profile of line 77-2 and synthetic seismogram from COST No. 

G-2 well ............................................... . 

69-70. Charts showing core log data and synthetic seismograms versus time for: 

69. COST No. G-1 well ................................ . 

70. COST No. G-2 well ................................ . 

71. Map showing locations of multichannel seismic profiles in the Georges 

Bank region ............................................. . 

72. Cross-section and magnetic anomaly profile for the Georges Bank basin 

based on CDP line 19 ..................................... . 

73-7 4. Maps of the Georges Bank area showing: 

73. Magnetic anomalies ................................ . 

7 4. Depth to magnetic basement ........................ . 

75. Magnetic anomaly and seismic reflection profiles across Step #1 ........ . 

76. Maps of gravity anomalies in the Georges Bank area ................. . 

77. Two-dimensional gravity model for CDP line 5 ...................... . 

78-79. Seismic profiles of: 

78. Part of CDP line 19 showing landward-dipping reflectors .. . 

79. Part of CDP line 1 showing buried steps ............... . 

80. Interpretive cross sections of Georges Bank basin ................... . 

81-86. Seismic profiles of parts of: 

81. CDP line 5 across prerift or synrift basins .............. . 

82. CDP line 1 across the Jurassic shelf edge showing buried 

benches ........................................ . 

v 

Page 

127 

128 

129 

130 

131 

133 

134 

136 

139 

140 

144 

148 

149 

151 

151 

152 

153 

153 

154 

155 

156 

157 

158 

159 

161 

162 

164 

166 

167 

168 

170 

171 

172 

173 

175 

175 
Page 

Figures 81-86. Seismic profiles-Continued 

83. CDP line 5 across the Jurassic shelf edge . . . . . . . . . . . . . . . . 177 

84. BGR line 209 across central Georges Bank basin (with interpretation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 

85. Line 20 across west central Georges Bank basin (with interpretation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 

86. Line 18 between shot points 1360 and 1900 . . . . . . . . . . . . . . 180 

87-88. Isopach maps of the Georges Bank basin showing: 

87. Synrift deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 

88. Cretaceous and Jurassic postrift sediments . . . . . . . . . . . . . . 183 

89. Paleogeographic maps showing Early and Middle Jurassic reconstructions of the Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 

Plate 1. Thin-section photomicrographs of carbonate rocks from COST No. G-2 well . . . . . 30 

2. Thin-section photomicrographs of clastic rocks from COST Nos. G-1 and G-2 

wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

TABLES 

Page 

Table 1. Lithologic descriptions of COST No. G-1 well cuttings used for organic 

geochemical analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

2. Lithologic descriptions of COST No. G-2 well cuttings used for organic 

geochemical analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 

3. Organic carbon and extractable organic matter, COST No. G-1 well . . . . . . . . . . . . 112 

4. Organic carbon and extractable organic matter, COST No. G-2 well . . . . . . . . . . . . 113 

5. Organic carbon and thermal analysis data for samples from the COST No. G-1 

well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 

6. Organic carbon and thermal analysis data for samples from the COST No. G-2 

well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 

7. Geothermal gradients on passive continental margins . . . . . . . . . . . . . . . . . . . . . . . 146 

8. Data used and results of calculations of basin subsidence at the COST No. G-2 

well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 

9. Time-temperature indices for representative horizons in the COST No. G-2 well . . 150 

Use of brand names in this report is for descriptive purposes only and 

does not constitute endorsement by the U.S. Geological Survey. 

vi 
Geological Studies of the COST Nos. G-1 and G-2 Wells, 

United States North Atlantic Outer Continental S.,elf 

By Peter A. Scholle and Chiye R. Wenkam, Editors 

ABSTRACT 

The COST Nos. G-1 and G-2 wells (fig. 1) are the second and 

third deep stratigraphic test wells drilled in the North Atlantic Outer Continental Shelf of the United States. COST 

No. G-1 was drilled in the Georges Bank basin to a total 

depth of 16,071 ft (4,898 m). G-1 bottomed in phyllite, slate, 

and metaquartzite overlain by weakly metamorphosed dolomite, all of Cambrian age. From approximately 15,600 to 

12,400 ft (4,755 to 3,780 m) the strata are Upper Triassic(?), 

Lower Jurassic(?), and Middle Jurassic, predominantly red 

shales, sandstones, and conglomerates. Thin, gray Middle 

Jurassic beds of shale, sandstone, limestone, and dolomite occur from 12,400 to 9,900 ft (3,780 to 3,018 m). From 9,900 to 

1,030 ft (3,018 to 314 m) are coarse-grained unconsolidated 

sands and loosely cemented sandstones, with beds of gray 

shale, lignite, and coal. The microfossils indicate the rocks 

are Upper Jurassic from 10,100 ft (3,078 m) up to 5,400 ft 

(1,646 m) and Cretaceous from that depth to 1,030 ft (314m). 

No younger or shallower rocks were recovered in the drilling 

at the COST No. G-1 site, but an Eocene limestone is inferred 

to be disconformable over Santonian strata The Jurassic 

strata of the COST No. G-1 well were deposited in shallow 

marine, marginal marine, and nonmarine environments, 

which changed to a dominantly shallow marine but still nearshore environment in the Cretaceous. 

The COST No. G-2 well was drilled 42 statute miles (68 km) 

east of the G-1 site, still within the Georges Bank basin, to a 

depth of 21,874 ft (6,667 m). The bottom 40ft (12m) of salt 

and anhydrite is overlain by approximately 7,000 ft (2,134 m) 

of Upper Tri~sic(?), Lower Jurassic(?) and Middle Jurassic 

dolomite, limestone, and interbedded anhydrite from 21,830 

to 13,615 ft (6,654 to 4,153 m). From 13,500 to 9,700 ft (4,115 

to 2,957 m) are Middle Jurassic limestones with interbedded 

sandstone. From 9,700 to 4,000 ft (2,957 to 1,219 m) are 

Upper Jurassic and Cretaceous interbedded sandstones and 

limestones overlain by Upper Cretaceous unconsolidated 

sands, sandstones, and calcareous shales. Pliocene, Miocene, 

Eocene, and Paleocene strata are disconformable over Santonian rocks; uppermost Cretaceous rocks are missing at this 

site, as at G-1. The sedimentary rocks in the COST No. G-2 

well were deposited in somewhat deeper water, farther away 

from sources of terrigenous material than those at G-1, but 

still in marginal marine to shallow marine environments. 

Data from geophysical logs and examination of conventional cores, well-cuttings, and sidewall cores show that 

below 10,000 ft (3,048 m), the strata in both wells have 

moderate porosities (< 20 percent) and low to moderate 

permeabilities (< 100 mD) and are thus considered adequate to 

poor reservoir rocks. Above 10,000 ft (3,000 m) the porosities 

range from 16 to 39 percent, and the permeabilities are highly 

variable, ranging from 0.01 to 7,100 mD. 

Measurements of vitrinite reflectance, color alteration of 

visible organic matter, and various organic geochemical properties suggest that the Tertiary and Cretaceous strata of the 

COST Nos. G-1 and G-2 are not prospective for oil and gas. 

These sediments have not been buried deeply enough for 

hydrocarbon generation, and the kerogen and evtractable 

organic matter in them are thermally immature. However, 

the Jurassic rocks at the G-1 site do contain smal' amounts 

of thermally mature gas-prone kerogens. The Jura~sic rocks 

at COST No. G-2 are also gas-prone and are slightly richer in 

organic carbon and total extractable hydrocarbons· than the 

G-1 rocks, but both sites have only poor to fair o~, and gas 

source-rock potential. 

INTRODUCTION 

Until the COST Nos. G-1 and G-2 wells were 

drilled, the only subsurface information on the 

geology of Georges Bank came from multichannel 

seismic lines and extrapolation of the stratigraphy from wells on the Scotian shelf, eastern 

Canada Although rocks recovered fr'lm the 

COST Nos. G-1 and G-2 wells are ea"ilY correlated with named formations on the Scotian 

shelf, there are differences in the development of 

the sedimentary section on Georges Bank that affect petroleum source and reservoir poteiJ tials. 

The COST No. G-1 well was drilled between 

April 6 and July 26, 1976, by Ocean Prcvluction 

Company acting as operator for 31 participating 

companies. The well was drilled by the s~misubmersible rig SEDCO-J in 157ft (48 m) of water in 

the southwestern part of the Georges Bark basin 

at lat 40°55'52.108" N., long 68°18'18.917" W. A 

total section of 16,071 ft (4,898 m) was drilled. 

The COST No. G-2 well was drilled 42 statute 

miles (68 km) east of COST No. G-1 between 

January 6 and August 30, 1977, by OcE'm Production Company acting as operator for 19 participating companies. G-2 was drilled ir 272 ft 
66°W 

MASS. 

"'A 

• ~a ~Nantucket M.artha's Island 

Vmeyard 

c:> COST NO. G-2 

COST NO. G-1 ° 

0 50 100 STATUTE MILES 

I•'• II I\ Ill I I II I I I I 

0 50 100 KILOMETERS 

FIGURE !.-Locations of the COST No. G-1 and G-2 wells in the Georges Bank area Bathymetric contou .. s in meters. 

(83 m) of water by the semisubmersible rig Ocean 

Victory at lat 40°50'11.410' N., long 

67°30'29.784' W. A total section of 21,874 ft 

(6,667 m) was drilled. 

This circular summarizes data from previously 

released reports (Amato and Bebout, 1980, for 

the COST No. G-1 well and Amato and Simonis, 

1980 for the COST No. G-2 well) and contains 

2 

new data on the lithology, stratigraphy, geochemistry, geology, and geophysicr of these two 

wells from studies by the USGS. 

The data presented in the nine different papers 

were obtained from well cuttings, r'dewall cores, 

conventional cores, electric logs, core descriptions, and multichannel seismic profiles. All well 

depths are relative to the Kelly Pushing (KB), 
which was 98ft (30m) above mean sea level and 

255ft (78 m) above the sea floor for the COST No. 

G-1 well; KB was 79 ft (24 m) above mean sea 

level and 351ft (107m) above the sea floor for the 

COST No. G-2 well. Units are reported in the primary system of measurement with English or 

metric equivalents in parentheses. Thus, for 

depths in the wells, primary units are in feet (with 

meters as a secondary conversion); for seismic 

lines, primary measurements are in kilometers or 

meters (with miles or feet as a secondary conversion). Only the primary units are reported to a 

valid number of significant figures. 

The COST Nos. G-1 and G-2 wells were drilled 

intentionally off structure in blocks 79 and 141 

respectively of North Atlantic Outer Continental 

Shelf tracts that were part of Lease Sale No. 42, 

held December 18, 1979. The public disclosure 

provision of Federal leasing regulations stipulates that the U.S. Geological Survey release all 

geologic data from deep stratigraphic test wells 

60 days after a lease is granted within 50 nautical 

3 

miles of such a test site. Blocks adjacent to 79 

and 141 were leased on February 1, 1980. 

ACKNOWLEDGMENTS 

Piero Ascoli kindly provided samples from the 

Scotian basin. Raymond Hall and Doris Lew prepared the foraminifera samples. Invaluable technical assistance was provided by Patty For1"estal, 

Thomas McClurg, Jane Murphy, JoAnn Taylor, 

and Jeffery Zwinakis. The authors ben~fitted 

from discussions with F. G. Adinolfi, illiam 

Dillon, Jurgen Fritsch, John Grow, Leigh Price, 

D. R. Shaw, and E. K. Simonis. Elazar Uchupi 

and J. M. Hunt of Woods Hole Oceanographic 

Institution and C. Wylie Poag, Kim Klitgord, 

John Schlee, and Elizabeth Winget read various 

chapters and provided valuable suggestions. 

0. W. Girard, Jr., and W. H. Butler review')d the 

entire manuscript; their comments and suggestions are much appreciated. 
Geologic Setting of the Georges Bank Bar'n 

John S. Schlee and Kim D. Klitgord 

The COST No. G-1 and G-2 wells were drilled 

on Georges Bank (fig 2), a broad, shallow platform that extends east of New England. The 

Georges Bank (25,862 mP; 67,000 km2

) is part of 

the U.S. Continental Shelf and is flanked on the 

north by the Gulf of Maine (Uchupi, 1966). The 

northern one-third of Georges Bank is covered by 

shallow, north-trending sand shoals, and the 

remainder is a flat-floored shelf covered with 

rippled sand. The southern side is indented by 

several submarine canyons and numerous smaller 

gullies and ravines. Two shr llow channels 

separate the bank from the other parts of the 

shelf. To the west, the Great South Channel 

separates Georges Bank from N a"'ltucket Shoals, 

and to the east, the Northeast c~·annel (722 ft; 

220 m deep) provides a deep-water entrance to the 

Gulf of Maine. 

25 50 miles 

25 50 kilometers 

Bathymetry '" meters 

68° 

FIGURE 2.-Locations of COST wells Nos. G-1 and G-2, USGS core hole 6001, and the grid of multichannel seismic reflection 

profiles. Bathymetry is in meters. Bracketed sections of seismic profiles are shown in Klitgord and ott ~rs (this volume). 

4 
STRUCTURE 

Georges Bank is underlain by a wedge of 

Triassic and younger sedimentary rock that 

overlies rifted basement (fig. 3). Tectonically, 

Georges Bank is a collection of smaller subbasins, 

some of which are linear grabens that trend 

northeast (Ballard, 1975; Austin and others, 

1980; Mattick and others, 1981; Schlee and 

Jansa, 1981). Collectively they are termed the 

Georges Bank basin, and structurally they are 

situated between the LaHave platform to the 

northwest, the Gulf of Maine platform to the 

north, and the Long Island platform to the west. 

The basement deepens seaward from the platforms in a series of steps (half-grabens) (fig. 4). A 

western set of steps seaward of the Long Island 

platform can be clearly distinguished as small 

grabens or subbasins, while an eastern set of 

steps southeast of the Gulf of Maine platform, 

can be defined as grabens or subbasins on only 

some of the seismic lines (figs. 3 and 4). Steps #1 

and #3 (fig. 4), landward of the Yarmouth arch, 

appear to be grabens or half-grabens. Seismic 

reflection and magnetic data show that these 

structures trend N. 30 o E. There is a high 

magnetic anomaly along the edge of each graben 

and a low magnetic anomaly over the graben. The 

most landward of these grabens (step #1, fig. 4) is 

a shallow structure that lies along the northern 

edge of Georges Bank (Ballard and Uchupi, 1972; 

Oldale and others, 1974). An unconformity over 

the top of these grabens corresponds approximately to the breakup unconformity of Falvey 

(1974), and it increases in depth from less than 

0.5 km (0.3 mi) below sea level adjacent to the 

Gulf of Maine to more than 10 km (6.2 mi) beneath the center of the bank. Beneath the southeastern part of the bank is a broad subbasin that 

lies between the Yarmouth arch and the East 

Coast magnetic anomaly (ECMA) (fig. 4); this 

subbasin extends to the northeast where it 

71° 7Cf 4~ 69° 68° .---~~~--~~~--~~~~--~~----~--------------~------~------~67° 

68" 

FIGURE 3.-Isopach map of Upper Triassic and younger sedimentary rocks in the Georges Bank basin. Thicknesses in 

kilometers. Dots show where thickness was measured along the profiles and indicate the control. 

5 
a72"W 

~PALEO SHELF 

TTT'TT' SCARP-EDGE 

--BENCH 

EDGE 

69" W 

nmmn DROP IN BREAKUP UNCONFORMITY 

- - MAJOR TECTONIC BOUNDARY 

T T T DEEPENING BASEMENT INFERRED FROM 

~~ - - --4 ()(J(!m 

STATUTE MILES 

0 22 40 ffl 20 40 60 80 100 

KILOMETERS 

64"W 

TTTTTT1 DEEPENING 

~ BASEMENT 

MAGNETICS 

BASEMENT 

HIGH 

63"W 

FIGURE 4.-Tectonic-structural map of the Georges Bank region showing the stable, shallow platforms of Paleozoic continental crust, areas of 

block- faulted crust (subbasins or grabens), steps (half-grabens) and intervening basement highs, and Jurassic oceanic crust. The East Coast 

magnetic anomaly and the ancient Jurassic shelf edge are indicated at the boundary between the block-faulted zone and the oceanic crust. 

The New England Seamounts and possible intrusive volcanic bodies are also shown. The lines indicate locations of multichannel seismic 

profiles. 

4 2"N 

41 • N 
merges with the Scotian Basin beneath the Canadian shelf. This subbasin may be situated on 

volcanic crust of Early Jurassic age formed in the 

area of continental separation; the other subbasins or steps are probably underlain by continental crust of Triassic age or older. The COST 

No. G-1 well was drilled into a small structural 

high that may be the southwestward extension of 

the Yarmouth arch and the COST No. G-2 well 

was drilled into the southeasternmost subbasin, 

mentioned above. 

The New England Seamount chain intersects 

the Georges Bank region near lat 40° N., long 

68° W., where there is a major gap in the ECMA. 

Bear Seamount is located at this intersection and 

its low magnetic dipole signature may mask the 

continuity of the ECMA across this gap. Within 

the Georges Bank basin, three buried seamounts 

or intrusive bodies are inferred to be present from 

distinctive magnetic anomaly patterns. All three 

are just landward of the ECMA and have high 

oval-shaped magnetic anomalies associated with 

them. Two of these bodies are located near the 

shelf edge just west of the Great South Channel 

(about lat 40° N., long 70° W.) within the zone of 

subbasins formed by grabens. The third and 

largest body is within the southernmost subbasin 

about 12.4 mi (20 km) southeast of the COST No. 

G-2 well (lat 40°8' N., long 67°20' W.). 

Acoustic basement has a variable character 

across the margin and only in certain places does 

it correspond with the base of the sediment fill. 

The rugged acoustic basement along the northern 

edge of Georges Bank probably reflects the Paleozoic metamorphic and igneous rocks along the 

edges of the grabens. Seismic penetration is variable in this area and also farther south where the 

grabens are at greater depths. The basement surface on some seismic profiles coincides with inferred Paleozoic rocks, and on other profiles the 

surface of the dipping rift sediments (post-rift 

unconformity) forms acoustic basement. Acoustic basement between the Yarmouth arch and the 

ECMA has a shingled aspect that probably represents the top of a carbonate bank complex near 

the Jurassic shelf edge. Oceanic crust can be 

traced landward almost to the ECMA on most of 

the seismic profiles off Georges Bank (Schlee and 

others, 1976; Grow and others, 1979; Klitgord 

and Grow, 1980). In this region acoustic basement is a series of small hyperbolic echoes that 

are typical of oceanic crust. 

7 

STRATIGRAPHY 

Rocks recovered from COST No. G-1 and G-2 

wells provide information on the deep stratigraphy of Georges Bank (fig. 5). The G-1 well 

(Lachance, 1980; Scholle, Krivoy, and Hennessy, 

1980) encountered a sequence mostly o~ sandstone, shale, and siltstone of Late Jurassic to 

early Tertiary age, that overlies sandstone, anhydrite, and dolomite of Early Jurassic(?) to Middle 

Jurassic age. The well penetrated Paleozoi n. metamorphosed dolomite, quartzite, and phyllite at 

15,600 ft (4,755 m) and reached a total depth of 

16,071 ft (4,898 m). At the COST No. G--2 site, 

42 mi (67 km) to the east, the total section is 

thicker and contains more carbonate roc1

·"'S and 

evaporites. The Upper Jurassic through T·~rtiary 

section contains abundant sandstone anrl mudstone and also has thick beds of limestone toward 

the base of the Cretaceous. These limestones are 

probably equivalent to strata sampled in Heezen 

Canyon by Ryan and others (1978) in 4,100 to 

4,265 ft (1,250 to 1,300 m) of water, ar'1 Neocomian in age, and were deposited in a reefal environment. Oxfordian and older rocks are dominantly limestone, dolomite, and anhydrite in the 

COST No. G-2 hole; the well bottomed in salt at 

21,874 ft (7,612 m) total depth (Simonis, 1980; 

Scholle, Schwab, and Krivoy, 1980). The. other 

deep (1,686 ft; 514 m) hole, AMCOR #6001, was 

drilled on Nantucket Island (Folger and others, 

1978). This well encountered poorly conso~idated 

nonmarine and marine shelf silts and clay of Late 

Cretaceous and Tertiary age and bottomed in 

weathered basalt approximately 183 ±8 m .y. old 

(Early Jurassic). 

Several trends are shown by these three holes. 

The Cretaceous strata apparently thicken and 

become finer grained and more calcareous toward 

the COST No. G-2 well. The Jurassic rocks are 

present only at the Georges Bank sites, where 

they thicken and become more carbonate-rich to 

the southeast over the main part of the basin. 

Multichannel seismic reflection profiles n(Jt only 

here, but off the mid-Atlantic states af well, 

support inferences that the rocks become more 

carbonate- and evaporite-rich with ag~ and 

toward the southeast (Schlee and others, 1976, 

1979; Mattick and others, 1981). The carl''lnate 

rocks are inferred to extend beneath the cortinental slope where they form a platform front rnd interfinger with deep-sea deposits of equivale"'lt age 
~---126 km {78mi)--------l~ ... ,.. ____ 70 km {43 mi) ----1 .. ~ 

WEST NANTUCKET COST COST 

0~--~oo~.o~·?o~~~~~~~.PL~E~IST~O~CE~NE~~~~;=~G;-~f~~DD~~~==r=G=-2~--~ EAST 

I f - -~UPPER CRETACEO~USTERTIARY ··.:~-.~{c£ TERTIARY 

r+- u c ----:---.----;;--~ 

L LOWER ~*..~~~ R E UPPER :~ __:_~ -~ 

0 

2 -

JURASSIC. B ::.~·.:.~··:-· T A L ~~~__: 

BASALT w ~-~ ~"' C E 0 · ~ - -

(f)2 r0:: 

w 

1-

w 

~3 - 0 

_j 

-

:::::s:::: 

z 

:::r:4 -

1-

0.... 

w 

0 ~ GRAVEL AND SAND 

5 1- lill SHALE, MUDSTONE 

CJ SANDSTONE 

~ CARBONATE ROCK 

CJ EVAPORITE ROCK 

~ -~ .- - 0 ~ - - . 

--~- USR ~~=~ --~~~ ·- -_ -;:"""'= 

J 

u 

R 

A 

s 

s 

I 

c 

--~ :__._,_ ---, u - . -

p~ __:____. __ 

p 

E -

Rl-.,:____-~ 

M~~ 

I 

D 

D 

L 

E 

- 4 

1-

6 

w - w 

I..J._ 

I..J._ 

- 8 0 

(f) 

0 

- 10 z 

<( 

(f) 

~ 

- 12 0 

:::r: 

1-

-I 4 z 

:::r: 

1-

-I 6 0.... 

w 

0 

-I 8 

J 

20 

22 

FIGURE 5.-Lithologic logs of the COST Nos. G-1 and G-2 wells and the Nantucket Island well (6001). Mod~fied from Scholle, 

Krivoy, and Hennessy (1980); Scholle, Schwab, and Krivoy (1980); Judkins and others (1980); and Folger a"1'd others (1978). 

in the North Atlantic oceanic basin (Schlee and 

others, 1979). Our multichannel seismic profiles 

reveal that the seaward edge of the carbonate 

platform may be expressed as a distinct break in 

slope (Schlee and others, 1979, fig. 6) or as a 

shingled offlap of reflectors that are presumably 

part of a seaward prograding platform (Schlee 

and others, 1979, fig. 7). Most of the profiles show 

a sharp break in slope, but line 20 (figs. 2 and 4) in 

the western part of the basin reveals a distinctly 

prograded arrangement of reflectors that appears 

to indicate that the shelf was built seaward 

12.4 mi (20 km) over older slope and rise deposits. 

These two types of shelf edge are paleoenvironmentally significant because they are related to 

the amount of deltaic outbuilding that occurs on 

8 

the shelf. Eliuk (1978, fig. 8) has c~scribed these 

two types of seismic signatures f'lr profiles collected across the Scotian shelf northeast of 

Georges Bank. He has tied the ge~physical data 

to the lithologic logs from sever~l holes drilled 

there and found that the progradei arrangement 

of reflectors resulted from the formation of a 

large delta complex nearby that caused the carbonate platform to build seaward of earlier ones. 

Away from the influence of the delta, a welldefined "platform type" shelf bre,.:~'k bounds the 

seaward side of the Scotian carrf)nate buildup 

(Abenaki Formation). Eliuk drew analogies to the 

present-day Great Bahama Bank for the platform 

type of shelf edge and to the Pleistocene deposits 

of the Florida Bay for the prograding deltaic 
type. The Great Bahama Bank is a sharply defined carbonate platform of bioclastic detritus far 

from an area of terrigenous input. The Florida 

Keys deposits show the input of deltaic sand on 

the ancestral platform near Miami. 

The Georges Bank seismic stratigraphy has 

been tied to Canadian offshore stratigraphy by 

Wade (1977) and Austin and others (1980) using 

multichannel seismic reflection profiles. Judkins 

and others {I 980) and Poag (this volume) have 

tentatively correlated formations and key 

markers from the stratigraphic section set up for 

the Scotian margin by Mel ver (1972), Jansa and 

Wade (1975a), Gradstein and others (1975), 

Ascoli (1976), and Given (1977). This correlation 

was facilitated by presence on Georges Bank of 

the same major vertical and lateral stratigraphic 

trends that are seen on the Scotian margin. These 

trends are an increase in carbonates and evaporites with age in outer shelf holes and an increase 

in clastic sedimentary rocks, particularly for the 

Jurassic, at inshore sites. 

The oldest rock sequences encountered in the 

COST Nos. G-1 and G-2 wells are probably 

equivalent to the Iroquois Formation (dolomite 

and anhydrite), the Argo Formation (salt at very 

bottom of the COST No. G-2 well), and the 

Mohican Formation (sequence of sandstones and 

shale of early Middle Jurassic to Early Jurassic 

age present in the COST No. G-1 well). The 

limestones of Middle Jurassic to earliest 

Cretaceous age beneath Georges Bank probably 

correlate with the Abenaki Formation platform 

limestone and shale sequence on the Scotian 

shelf: both there and under Georges Bank, the 

Abenaki Formation or its equivalent changes inshore to the MicMac and Mohawk Formations 

and consists of shelf sandstone, shale and thinbedded limestone. 

Utilizing Canadian outer shelf holes, Judkins 

and others (1980, pl. 3) have also correlated formations of Cretaceous age with the lithologic units of 

the COST Nos. G-1 and G-2 wells. Their correlations show a major change in the total thickness of 

the Jurassic and Cretaceous rocks from the central 

Scotian basin to the area of COST G-wells. The 

Cretaceous rocks are thinner on Georges Bank 

(4,100-4,600 ft; 1,250-1,400 m) than in the northem Scotian basin (9,000-10,000 ft; 2,750-3,050 m), 

but equivalent age units in the Jurassic System 

(from the top of the Jurassic to the top of the Argo 

Formation) are thicker beneath the Georges Bank 

9 

basin: 15,995 ft vs. 5,496 ft (4,875 m vs. 1,675 m). 

This difference in thickness, which is seen in 

both G-1 and G-2 holes, is a result of rapid sediment accumulation during the Jurassic and lower 

rates after that time. At least 15,995 ft (4,875 m) 

of rock accumulated during the first 54 m.y. of 

basin development at the COST No. G-2 well, 

whereas only 5,742 ft (1,750 m) of sediment accumulated in the last 141 m.y., and 79 percent of 

that accumulated during the Cretaceous (141-

65 m.y. B.P.). The overall trend is similar to that 

shown by Poag (1980b, fig. 28) for the COPT No. 

B-2 and No. B-3 wells in the Baltimore Ct•11yon 

trough on the outer continental shelf. 

SUMMARY 

The Georges Bank basin is similar in w~tonic 

setting and sedimentary fill to other basinr along 

eastern North America (Schlee and Jans&r 1981; 

Grow and Sheridan, 1981). Like the E~otian 

margin, it was built over a complexly faulted 

basement whose continued movement duri,g the 

early stages of basin development probal, ly influenced sedimentary facies and thickness 

(Klitgord and others, this volume; Eliuk, 1978). 

The deepest, most restricted part of the basin 

may contain as much as 26,250 ft (8.6 1~m) of 

Lower Jurassic and older nonmarine clastic rocks 

and evaporite deposits. Both COST wells c!lpear 

to have penetrated a part of this sequence. 1' "iddle 

and Upper Jurassic nonmarine clastic roclrs and 

marine carbonate and evaporitic rocks 0 to 

13,100 ft (0 to 4 km) thick were the initial 

deposits in the subsidence phase of basin development and signify a transition to an oper~shelf 

environment. Buildup of the carbonate rocks 

probably started on elevated basement ]'l()Cks 

and eventually formed a massive platfonr that 

covered much of the southern half of the bar~n. In 

the western part of the basin, the platfor:-n appears to have prograded seaward 12.4 mi (20 km), 

perhaps in response to deltaic sedimentation. 

During the Cretaceous, transgressive and r~~gressive marine and nonmarine clastic sedimentary 

rocks and thin limestone buried the earlier platform as the broad pattern of basin subsidence 

continued at a diminished rate. The Cenozoi~ Era 

was marked by periodic cutback of the cont,inental slope and an even slower rate of sedimel"'t accumulation on the bank. As in other eastern 
North American basins, the interval of basin 

development spans the Late Triassic(?) to the 

present. The Georges Bank basin like others has 

accumulated more than 32,800 ft (10 km) of sediment in several subbasins, and it shows the 

10 

change from early rift deposits to a complex carbonate buildup during the early subsidence 

phase, and later burial by sand, silt, and clay as 

sea level reached its maximum in the Late 

Cretaceous and early Tertiary. 
Lithology and Petrography of the COST Nos. 

G-1 and G-2 Wells 

By Michael A. Arthur 

The following generalized lithologic descriptions for the sedimentary rocks recovered in the 

COST Nos. G-1 and G-2 wells in the Georges 

Bank basin are based on initial descriptions of 

core materials prepared by the Ocean Production 

Company and on subsequent studies by Lachance 

(1980) for the G-1 well and Simonis (1980) for the 

G-2 well. In addition, selected cuttings and thin 

sections of cuttings from 142 intervals in the G-1 

well and 81 intervals in the G-2 well (an average 

of 10 cuttings per section) have been examined for 

this study. These observations have been supplemented by descriptions of thin sections of 

conventional and sidewall cores provided by Core 

Laboratories, Inc., because the cuttings are 

inadequate for a complete description of the lithofacies in a well. A total of 190 sections of sidewall 

cores were described for the G-1 well and 131 sections of sidewall cores were studies for the G-2 

well. The boundaries of lithologic units are based 

on all available lithologic descriptions and data 

from geophysical logs. 

The descriptions of lithology and petrography 

are given from the bottom of each well to the top 

in order to facilitate interpretation of the succession of sedimentary environments. All depths are 

given in feet (meters) below the Kelly Bushing. 

Ages of lithologic units are based on determinations given in Valentine (this volume) and Poag 

(this volume). 

DESCRIPTION OF COST NO. G-1 SEQUENCE 

The COST No. G-1 (fig. 6) sequence is informally divided in this paper into four major lithologic units (fig. 7), which are further divided on 

11 

the basis of minor lithologic changes. These 

lithologies are discussed stratigraphically from 

bottom to top in the well. 

UNIT 4 (16.071-15.650 n: 4.898-4.770 M) 

PALEOZOiq?) BASEMENT 

The COST No. G-1 well bottomed in black, 

fissile, graphitic slate, schist, and phyllite 

(550-450 m.y. old, on the basis of K/Ar dating 

techniques; Steinkraus, 1980). The material is 

highly fractured and the fractures are filled with 

sparry dolomite or calcite and a fibrous s~ricitic 

mica The rock is carbonaceous and consists of 

foliated quartz and dolomite (including is'llated 

rhombs), euhedral pyrite, and sericite. Seccndary 

overgrowths were detected on many ouartz 

grains. About 20 ft (6 m) of this low-grade metamorphic basement rock was recovered in a conventional core (Core 6) from the bottom of the 

hole. The average dip of these strata appears to 

be about 25 o, and the cutting samples in ~icate 

there is another 50 ft (15 m) of schist anc" slate 

above this core. An additional 400 ft (122 m) of 

dolomite and sandy, argillaceous dolomitP. that 

overlies the schistose rocks has also apparently 

been metamorphosed because much of the dolomitic rock is highly recrystallized and se:'icitic. 

The dolomitic rocks are dense, light to dark gray, 

unfossiliferous, and range from clean to ~rgillaceous, silty, and sandy. Much of the dolomite is 

micritic and has no discernible original sedimentary structures, but sparry patches and vei,s are 

common; some samples exhibit intense reci-ystallization. Angular quartz and pyrite are conmon, 

and some anhydrite-filled voids occur. 
DEPTH 

FEET METERS 

KELL~KB~~HING 0 ~T gEA LEVEL 

1000 

500 

2000 I 

3000 I 

.... 11000 to.) 

4000-l 

5000 ~l 1500 

6000l 

-2000---

7000 -~ 

8000 I 

I 

I 

f 

SPONTANEOUS 

POTENTIAL 

(mollivolts) 

20 mv -~ -+ 

~I 

bl 

~ I I I 

I il I II 

f-~~1 i 

~ ~~~I I 

I ~--L j 

I ~~ I 

~ 

CONDUCTIVITY 

(millimhos/m) 

~ ~ ~ 

II ~ 

II I~ 

II I .... 

II 1A 

I 

I 

H- ~~-I 

~~ l 

II ~ I 

~1~1 

II ~ I 

COMPENSATED 

FORMATION 

DENSITY (g/cm') 

1~ 1~ 1~ 200 2~ 2~ 2~ 300 

I I 

I I I l m:::: I I I 

I afj I 1 

~ j 

- ~ l~ j ;m I I 

I I 5 4 j 

I ~ 

I + I I ~ I I 

I --= I 

SYSTEMS, SERIES, 

AND (OR) STAGE 

h ~ 011 . ,., .... -""' ......... 

U'J 

:::> a:O CONIACIAN ww 

a..U a..<( TURONIAN :::>f-w 

a: 

u 

CENOMANIAN 

TO 

I APTIAN 

APTIAN 

U'J 

:::> a:O 

ww 

;s:u 

o<C ..Jtu a: BARREMIAN u TO 

BERRIASIAN 

u 

u; 

en 

<( 

a: 

::> 

..., 

a: 

w 

D.. 

D.. 

::> 

~ 

~ a: 

w 

..... 

?; 

Cl 

z 

a: 

0 

u 

> 

Cl 

0 

0 

~ ::::; DESCRIPTION 

KELLY BUSHING IK B.l 

SEA LEVEL 198ft; 30m below K. B. I 

SEA FLOOR 1255 ft; 78 m below 

K. B.l 

~ t.;..o ,o ~~ ,o0 •J 

Poorly consolidated gray~whote 

sands and gra\lels woth shell 

~~-;_.>.;·~-~ fragments and hgnitoc stringers 

·:··=·· o.~ or beds 

~ Interbedded sand and shale 

Gray shale 

• • 

"~-"~! .:;_; .' ·.i....· . .:_ """""''-·"""00- graoned, calcareous sand and 

· .., ·•· .• .; ~ ~ gravel wtth subordinate tnter-

. --f-: -:-. -~ .~bedded, \l&roco~ored ·~·~-

-':-L~-t~ Argillaceous dolomite 

Tan, coarse-grd.ned sandstune, 

thick, reddish shale interbeds 

·~ -:.; .. .' ::~: : Unconsolidated, coarse-graoned 

:....:....:-~- sands 

:__. -...:.·. Unconsolidated, coarse-graoned ---;-,' 

pebbly sands and thick, soft 

-

- claystone ~.- .. ........ :- ·- .. Medium11raoned, calcareous 

sandstone; calcareous shales; 

thon dolomite beds 

Tan11ray shale; fin&- to coarseFr.-~-"""":! grained sandstone 

~ 1--'~- ~ -_:~ c. .. ~~ '-w mod"m· .....L,.- grained, poorly consolidated 

. . to moderately cemented sand~ 

....C.. · 4- stone and red-brown shale 

~I . ..L. _i_ 
CN 

DIV)I) 

~I I ~ 

2500 u Red-brown. soft shale 

iii 

en 

<( Thock, poorly consolidated 

a: sandstones and shales :::::> 

...., 9000--j f j~j I I a: 

w 

CL 

CL 

:::::> graoned sandstone 

3000 -- t ijfj t II j j 1 t t 't -j j -I t L~-1---==-= 10,000 1 

Gray, fossollferous, microtoc 

limestone, sandstone and 

-~ shale interbeds 

-~ 

Red-brown shale, very tone 

11.000 I I r-1 i I II lail I I rf=====:l graoned sandstone· tan, 

mocrotoc limestone 

Tan, mocritic, sandy limestone 

3500 I ~ I II f.---11 u 

(/) Thon-bedded sandstone and (/) 

<( shale 

IX: 

12,000 1 I I I ~ I I II I I~ I I I ::) Lomestone and dolomote -, Thock-bedded sandstone and w shale ...J 

0 

0 

13.000 I I I I Yl I II I ~I I I I I Jrl .. I ~ Loght gray-buff, fonely crystallone 

dolomote, numerous thon 

anhydrite beds 

4000 

Sandstone, anhydrote; dolomite 

14,000 1 l ftl I I II ~~ I I I I I m I l. J ______ . lif-:+~ _ ~ _ ''"'""'" anhydrite onclusions '·~~-

u Thin-bedded red shale; solty, 

4500 

I I fl I I II J frJ l ) ) - ) ) ltl l I 

(/) fine-grained, red sandstone; (/) anhydrite layers <( 

15,000 1 IX: Red sandstone and conglom- ::) 

-, erate 

IX: 

w Limestone, shale, and sandstone 

s: in thin beds 

0 

...J 

Light gray-white, sandy and 

16,ooo I I I 114 I II ~~ ~ ~ t t I -- stoaly dolomite 

Black slate 

2 3 "BASEMENT"? 4 Total depth of well 

-5000 16,071 feet below K. B 

FIGURE ~.-'Geophysical logs, lithology, anJ ages for the 003T No. G-1 well. Modified from Scholle, Krivoy, and Hennessy (1980). Stratigraphic 

boundaries were based on preliminary data and do not match those shown elsewhere in this volume. 
-J=o,. 

LITHOLOGIC UNITS COST NO. G-1 WELL COST NO. G-1 WELL COST NO. G-2 WELL LITHOLOGIC UNITS COST NO. G-2 WELL 

DEPTH (KM) DEPTH (FT) 

Uo" < (<,030 <o 9,940 ft, 3<4 <o 3,000 m) ~ TERTIARY . .. -0 ------Unot 1 (1,100 to 9,700 ft; 335 to 2,957 m) 

Subunot 1A (1,030-1,870 ft;) ·: ·~-~~.··· ·:_,_ ._ ~·~ Subunot 1A (1,100-1 550 ft·) :..:..'=::::-:::_:__--' UPPER CRETACEOUS -:.;:;:-~.,_~., . . 

Subunot 18 (1 ,870-5,150 tt,) J:~:::=-o:r [·.,:- ,.-'"' t- 2000 Subunot 18 (1,550-2,500 ft;) 

Subunot.1C (2,500-6,900 ft,) 

:::;...~...;.~'-- t~~-~c' 4000 Sooooo< <C (5 <50-B.<oo H l l -r-:~·::: LOWER CRETACEOUS ~:-;,-~~ Subunit 1D (8,100-9,940 ft;) · .· _.-. · · -: .-.·~ Subunot 1D (6,920-9,700 ft,) 

Unot 2 (9,940 to 12,360 ft: 3,030 to 3,767 m)~ 2 _j~· .. ··:.::~ .. ~.-} 1-SOOO ~Uo" 2 (9 700 <o <3,625 H 2,957 <o 4,<53 m) 

Subunot 2A (9,940-11,460 ft,) :i..~~.:.L~' UPPER JURASSIC -__,:--_~_ / Subunot 2A (9,700-11,780 ft;) 

Subunot 28 (11,460-12,360 ft) ::.,:~.:.,...-.., ~ -~- -~~ 8090 Subunot 28 (11,780-13,625 ft;) 

c-~-~~1 ~. I ;- . - / /r---Unot 3 (13,625 to 21,830 ft; 4,153 to 6,654 m) 

Subunit 38 (14,125-14,925 ft,) 

Unot 4 (15,650 to 16,071 ft;) ------------

~ 

~ 

1~==1 

~ 

~ 

~ 

~ 

GRAVEL AND SAND 

SHALE, MUDSTONE 

SANDSTONE 

CARBONATE ROCK 

EVAPORITE ROCK 

' 

6-

?-

~ 

~- / 10000 // Subunit 3A (13,625-18,720 ft,) 

~ / 

~¥~A / -;-..--,._·- 12000 

5/ 

MIDDLE JURASSIC Subunot 38 (18,720-21 ,830 ft;) 

Unot 4 (21,830 to 21,872 ft; 6,654 to 6,667 m) 

:'<~~oC";~-14000 

~ii ~~16000 

f7:%f,'~ 

~..:.._,_.~ Iii 18000 

~~~;~~ I ',L<,~.ry-~L~"- 20000 

-~15' ~ ~ 

15'~: -~- ~ 

c -22000 

FIGURE 7.-Lithologic correlation between rocks from the COST Nos. G-1 and G-2 wells. 
UNIT 3 (15,650-12,360 n: 4,770-3,767 M) 

UPPER TRIASSIC TO LOWER JURASSIC 

Unit 3 consists of varying proportions of sandstone, conglomerate, shale, dolomite, and anhydrite with minor amounts of limestone. It has arbitrarily been divided into 3 parts: subunit 3C 

consists of sandstone, conglomerate, conglomeratic sandstone, shale, and minor limestone; 

subunit 3B is composed of shale, sandy shale, 

sandstone, and thin interbedded dolomite and 

anhydrite layers; and in subunit 3A dolomite and 

anhydrite prevail and have variable amounts of 

interbedded sandstone and shale. 

SUBUNIT 3C (15,650-14,925 FT; 4,770--4,549 M) 

The dolomite of unit 4 is overlain by 150 ft 

locally as blebs and nodules in shale and in a few 

beds of chickenwire structure. 

SUBUNIT 3B (14,925-14,125 FT; 4,549-4,305 M) 

This subunit consists largely of interbedded 

red-brown to dark-gray shale and fine- to meiiumgrained sandstone. Some sandstone beds ar~~ conglomeratic, and dolomite beds and anh~rdrite 

nodules and beds occur locally. The sandstones 

have little or no porosity and are similar in composition and texture, but are generally n ()t as 

coarse grained as those of subunit 3C. Suburit 3B 

appears to have been deposited in a nonmarne to 

highly restricted marginal marine (sabkah ·type) 

environment. 

(46 m) of pink to red, coarse- to very coarse- SUBUNIT 3A (14,125--12,360 FT; 4,30~,767 M) 

grained sandstones and interbedded red-brown 

shales with traces of lignite. Above this interval Subunit 3A is composed largely of dol 'lmite 

is about 350 ft (1 07 m) of similar rocks containing and anhydrite and has lesser amounts of sandbeds of light- to medium-gray limestone and stone and shale. The lower 800 ft (244 m) of 

dolomite. The proportion of conglomerate and subunit 3A, which is transitional to 3B, consists 

conglomeratic sandstone increases upsection, and largely of pink to red fine- to medium-grained 

the uppermost 225 ft (69 m) consists of red to red- sandstone and dark-gray to red-brown shale interpink conglomerate, conglomeratic sandstone, bedded with buff to dark-gray dolomite and anhysandstone, and subordinate amounts of shale. drite. The shale and dolomite contain vzrying 

The sandstones range in composition from amounts of anhydrite as blebs, pore fillingr, and 

lithic arenites to quartz wackes and arenites, nodules. Dolomite beds become more abundant 

which range from poorly to well sorted. Subangu- towards the top of 3A. The upper 965 ft (294 m) of 

lar to angular quartz predominates in most subunit 3A consists almost entirely of buff to 

samples with minor amounts of metamorphic light- to dark-gray dolomite and interbedded thin, 

rock fragments (< 15%), potassium feldspar white to gray anhydrite layers. 

(< 5%), and plagioclase(< 1 %). Many of the feld- The sandstones in the lower part of th~ unit 

spars are highly altered to clay minerals (sericite range from feldspathic lithic wacke to lithic 

and kaolinite). The low porosity of these sand- arenite and from feldspathic quartzarenite to 

stones is probably due to compaction and forma- wacke. Most sandstones are fine to mE'Qium 

tion of carbonate-clay-iron mineral cements. grained (grains are angular to subangular\, but 

Dolomite is the most common cement and occurs some coarse-grained sandstone and conghmeras irregular patches, replacements of framework atic (mainly granitic, based on descriptions of 

grains, and as isolated rhombs. Ferruginous clay cores) sandstone is present. Quartz is the domimatrix cements are also common. nant mineral, ranging from 5 to 20 percent in the 

Most of these sediments appear to have been samples examined. Plagioclase and micr'lCline 

deposited in a nonmarine to marginal marine equal about one-half the total feldspar in some 

environment. The limestones in the middle of sub- samples, but potassium feldspars are the most 

unit 3C are medium to light gray and slightly common. Rock fragments vary in abundancr~, and 

argillaceous, and commonly contain pellets, many are difficult to identify because of their 

mollusk fragments, and dolomite as isolated similarity to the framework grains. Granitic rock 

rhombs or patches and as zones of replacement of fragments are the most common and usually comlimestone. The limestones appear to have no pose 5 to 10 percent of the framework grains. 

primary or secondary porosity. Anhydrite occurs Fine-grained schistose and slaty fragments and 

15 
reworked carbonate and mudstone rock fragments are also present. Some of the sandstones 

contain up to 20 percent of clay-hematite matrix. 

Dolomite, siderite, and anhydrite cements and 

pore fillings commonly occur in the same sample. 

Quartz overgrowths are also quite common and 

result in sandstones with a tight, interlocking, or 

sutured fabric. Cementation and compaction 

have reduced porosity to less than 5 percent. 

Framework feldspars and those in granitic rock 

fragments are commonly altered to sericitic clay 

and kaolinite, but dolomite and anhydrite replacements of feldspar have eliminated most of the 

secondary porosity that may have resulted from 

the alteration. 

The sedimentary sequence in subunit 3A 

records a change in depositional environment 

from fluctuating restricted marine and nonmarine at the base to largely restricted marine 

and shallow marine in the upper part. The 

dolomites in the upper part of the subunit are 

primarily micritic, but may exhibit patchy 

recrystallization. Veins or fractures are also filled 

with sparry dolomite, and anhydrite vein and 

pore fillings and nodules are also common. In a 

few samples, micritic dolomite exhibits a relict 

pelletal texture, and there are ghosts of replaced 

ostracod and mollusk fragments in other samples. Algal laminations are also present in some 

dolomite-anhydrite intervals. The dolomites are 

probably mostly primary, but dolomite replacement of original intertidal to subtidal carbonate 

mud probably also occurred. 

UNIT 2 (12,360-9,940 n: 3,767-3,030 M) 

LOWER JURASSIC (LOWER PLIENSBACHIAf,.) TO 

MIDDLE JURASSIC (BAJOCIAN) 

The lower boundary of unit 2 represents a sharp 

lithologic change (also seen in the geophysical 

logs) from the dolomite-anhydrite interval of 

subunit 3A to predominantly sandstone and 

shale with some interbedded dolomite and limestone. Two subunits are defined: subunit 2B 

(12,360-11,460 ft; 3,767-3,493 m) comprises 

interbedded fine- to medium-grained sandstone 

and shale with some interbedded dolomite and 

limestone; subunit 2A (11,460-9,940 ft; 3,493-

3,030 m) consists of interbedded limestone and 

dolomitic limestone, shale, and some siltstone to 

fine-grained sandstone. Predominantly carbonate 

16 

and predominantly clastic intervals seem to alternate or intertongue on the order of thousands 

of feet (several hundreds of meters) in both 

subunits. 

Subunit 2B contains interbedded thin- to thickbedded, tan to pink or red, very fine- to mediumgrained sandstone and gray to red-brown, somewhat silty or sandy shale. Thin beds of dense, 

buff to light-gray micritic dolomite and limestone 

also occur locally, and a relativE'Jy thick interval 

of dolomite and limestone occurr between 11,900 

and 11,975 ft (3,627 and 3,650 m). A few thin 

lignitic or coaly beds are also prnsent. 

The carbonate intervals are micritic; limestone 

and dolomite occur together as interbedded or interlaminated strata and dolomite as a limestone 

replacement. These carbonate units are argillaceous, silty, or sandy, and are usually closely 

associated with clastic rocks. All gradations from 

silty and sandy carbonate rocks to dolomite- and 

calcite-cemented siltstone and sandstone are 

present. Anhydrite as rare laminae or blebs was 

noted in association with the carbonate rocks in 

subunit 2B. A few slightly fossiliferous (mollusk 

debris), pelletal carbonate mudstones were noted, 

but most beds are dense, micritic, and unfossiliferous. Little or no primary or se,~ondary porosity 

appears to exist at these depths in the well. 

Sandstones and siltstones are similar in composition and texture to those ir unit 3, and are 

predominantly very fine-grain~d to mediumgrained feldspathic quartz wackes or feldspathic 

lithic wackes. Clay-hematite CE''llents are very 

common, and in some samples r~condary quartz 

overgrowths are visible. Most sandstones and 

siltstones, including the more pc ()rly sorted ones, 

are cemented with dolomite, siderite, or calcite. 

Porosity is usually less than 5 P'~rcent. 

This subunit consists largeJ.~r of interbedded 

buff to gray limestone and dolo~te; tan to pink 

siltstone; fine-grained sandstone; and red-brown, 

green, and gray shale. It is distinguished from 

subunit 2B by the predominance of carbonate 

rocks, particularly in the lower 300 ft (91 m) and 
the uppermost 150 ft (46 m). Limestone is more 

abundant than dolomite, and shale and sandy 

shale are the most common clastic rocks. Beds of 

lignite or coal occur locally. 

The limestones are argillaceous and usually 

contain less than 10 percent fine sand- or siltsized quartz. Most carbonate intervals are pyritic. Micritic textures are common, particularly 

in the lower part of this subunit, but pelletal 

calcareous mudstones also occur. Dolomite is 

common in the middle part of the unit in association with minor anhydrite pore fillings in the 

dominantly micritic dolomite. The uppermost 

limestone strata are much more fossiliferous: 

they contain fragments of mollusks, ostracods, 

benthic foraminifers, and echinoderms (crinoids). 

In addition, pellets and oolites are common constituents. Textures and compositions vary from 

pelletal calcareous mudstone to pellet-oolite 

packstone and fossiliferous calcareous packstone. 

The limestones have little primary or secondary 

porosity; sparry calcite or dolomite spar fills 

most void spaces, and micrite has apparently 

undergone patchy recrystallization to sparry calcite. There is little compaction or breakage 

evident in the constituents of packstones and 

grainstones, which suggests that cementation occurred early in the history of the carbonates of 

this subunit. 

The siltstones and sandstones are similar in 

composition (feldspathic wacke to feldspathic 

quartz wacke and subordinate arenites) and texture to those of 2B, and have relatively poor 

reservoir characteristics. 

The lithology of unit 2 records the transition 

from the prol9nged restricted marine sabkah and 

tidal-flat conditions of subunit 3A to more open 

shallow marine (subtidal-intertidal) conditions in 

the lowest part, to alternating nonmarine and 

shallow marine, and back to shallow marine conditions at the top in lignitic, oolitic, pelletal, and 

fossiliferous limestone. 

UNIT 1 (9,940-1,030 n: 3,030-314 M) 

MIDDLE JURASSIC (BAJOCIAN(?)) TO UPPER CRn ACEOUS 

(SANTONIAN) 

The base of unit 1 is marked by the sudden 

disappearance of the fossiliferous limestone of 

subunit 2A. Lithologic unit 1 contains mostly 

pebbly sandstone and shale, but has some lignite 

17 

or coal beds and minor amounts of limestcne and 

dolomite. The abundance, coarseness, an 1 composition of the sands change through the r~ction, 

and four lithologic subunits are defined on the 

basis of these changes. Subunit 1D consists of interbedded, thick-bedded, tan to red-browr sandstone and shale and minor thin limestone beds. 

Subunit 1 C contains more tan to red-brm"''ll and 

gray thin-bedded and pebbly sandstone~ sandstone with fewer shale interbeds than subunit 1D, 

and some interbedded coal. Subunit 1B is composed of coarse- to very coarse-grained, commonly pebbly sand and lesser amounts of bedded 

gray shale, lignite, marlstone, limeston~, and 

dolomite. Subunit 1A consists almost entirely of 

pebbly, fossiliferous, glauconitic, poorly consolidated quartz sand. 

SUBUNIT 10 (9,940--8, 100FT; 3,030-2,469 M) 

This subunit is made up of light-gray to tan, 

pink, and light red, fine- to coarse-grained, mostly 

poorly to moderately sorted sandstone interbedded with red to red-brown and tan to gray 

micaceous silty shale and shale. Coal ir fairly 

abundant in the sequence, and there are a few 

thin, light-gray to buff, micritic, argillaceous 

limestone beds. 

The sandstone beds range from lightly cemented to poorly consolidated. The porosity is as 

high as 25 percent, but permeabilities (figr. 8 and 

9) are low, in part because most of the sanrlstones 

are feldspathic quartz wackes, consisting of 60 to 

80 percent quartz, 10 to 15 percent fl'~ldspar 

(about equal amounts of K-feldspar and plagioclase), and small percentages of rock fr~~ents. 

Plant fragments, muscovite, and pyrite ani other 

heavy minerals are trace constituents. Fe~qspars 

are commonly altered to clay minerals or rnplaced 

by carbonate minerals. The sandston~s are 

cemented by silica-clay mixtures, much of which 

was probably original matrix material, or by 

calcite and dolomite. The degree of conso1~iation 

generally decreases upward. 

The shale and limestone beds are app<:<~~ntly 

unfossiliferous and typically silty or sandy. Limestones are buff-tan to light gray, argillaceo·ls, and 

micritic in texture. Because of the absonce of 

fossils and the association of coal, oxidized sands, 

and shales, the sedimentary rocks of subt·nit lD 

are interpreted as having been deposited ir a nonmarine, possibly deltaic, environment. 
CORE POROSITY (percent) 

or----5r----1~o ____ ,~5 ____ 2~o ____ ~25 ____ ~3o _____ 35 

! : ~ ~ 8 f.-

! 9 ~ 

§ 12 ::~ 13 

14r 

151 

.. 

:' ... . . .. 

.. 

. ·:; . 

. . . .. 

.. 

· . 

·. 

.. 

... 

. . 

· . 

16L_--~----~--~----~--~----~--~ 

FIGURE B.-Porosity versus depth for the COST No. G-1 well, 

from measurements on sidewall cores. After Lachance and 

Amato (1980); data from Core Laboratories, Inc. 

SUBUNIT 1C (8, 100--5,150 FT; 2,469-1,570 M) 

The sediments of this lithologic subunit differ 

little from those of subunit lD, except that the 

sandstone and shale are apparently more thinly 

bedded and more frequently interbedded in subunit 1 C, and that the sandstone beds are medium 

to very coarse grained and commonly pebbly as 

well. Coal is present in subunit lC, but not as 

abundant as in subunit lD. Limestone beds are 

relatively uncommon, but much of the sandstone 

is calcareous. The interbedded shales are redbrown to about 6,500 ft (1,983 m), but above that 

level they are tan to gray and green. 

These feldspathic quartz wacke sandstones are 

similar in composition to those in subunit lD. 

The porosity and permeability vary depending on 

the degree of sorting, but some sandstones with 

good reservoir potential are present in the interval between 8,000 and 7,000 ft (2,430 and 

2,134 m). Carbonate cements are common in some 

intervals. 

The sedimentary rocks of subunit lC record 

deposition under nonmarine conditions at the 

base of the unit and shallow marine conditions 

near the top, possibly in a deltaic environment. 

18 

CORE POROSITY (percent) 

10.

000 or--__ __,5'------'-T1o'------'-T15=-----'=T2o'--__ ~25~ __ ~30::__~35 

5000 

1000 

500 

.. ·. .. : .· 100 . : 

50 

.. \ . . 10 

•. • I • • •: 

·. 1.0 

0.5 

0.1 L__ __ ____]__ __ __jl___ __ __[__ __ _____l ____ __L_ __ __J_ __ ____l 

FIGURE 9.-Porosity versus permeability for the COST No. 

G-1 well, from measurements on sid ~wall cores. After 

Lachance and Amato (1980); data from Core Laboratories, 

Inc. 

SUBUNIT 1B (5, 150--1,870 FT; 1,571--570 M) 

Thin to thick, tan to buff, mecium- to coarsegrained sands with interbedded gray to reddish 

shales and marls and some beds of light-gray-buff 

argillaceous dolomite characterize lithologic 

subunit lB. The sands are poor1

y consolidated 

and have porosities up to 35 perCE''lt and variable 

but often high permeabilities (figs. 8 and 9). Sand 

or sandstone is prevalent from 4,800 to 4,100 ft 

(1,463 to 1,250 m) and from 3,fl)0 to 2,400 ft 

(1,097 to 731 m), whereas shale dominates theremainder of the subunit. 

Lignite or coal is common in many parts of the 

sequence, and there is pyrite in ~~~th shales and 

sands. Above 3,650 ft (1,112 m) the sands contain 

calcareous worm tubes, mollusk fragments, gastropods, foraminifers, bryozoa, ar-1 abundant organic (terrestrial plant?) matter. A thick, fossiliferous, sandy dolomite bed occurs between 3,540 

and 3,570 ft (1,079 and 1,088 m). 
Sands and sandstones are commonly coarse to 

very coarse grained and poorly sorted, but some 

very well-sorted beds are present. Grains are 

angular to subrounded. Quartz pebbles occur in 

many intervals. The degree of cementation is 

variable, and calcite, siderite, and dolomite 

cements are present. The sands and sandstones 

range from feldspathic quartz wacke to quartzarenite. The feldspar content seems to generally 

decline upsection as the degree of sorting 

increases. 

The sediments of subunit 1B were deposited 

primarily under shallow marine conditions, but 

intervals of nonmarine deposition are possible. 

SUBUNIT 1A (1,870-1,030 FT; 570-314 M) 

This subunit consists almost entirely of pebbly, 

poorly to well sorted, poorly consolidated quartz 

sand. Pebbles are usually quartzose and the sand 

is micaceous, glauconitic, pyritic, and fossiliferous, containing numerous fragments and whole 

skeletons of bryozoans, planktic and benthic foraminifers, and Inoceramids and other mollusks. 

Clay and calcite or siderite compose the matrix 

(or cement, when present). Porosities are commonly greater than 25 to 30 percent and permeability is moderate to high (fig. 8). Some glauconitic and sideritic shale is also present in the 

section. Lignite beds and pyritic, carbonaceous 

shale occur between 1,500 and 1,575 ft (457 and 

480 m). The sequence represents predominantly 

marine shelf deposition. No cuttings were obtained from above 1,300 ft (396m). 

washing. However, the presence of salt is inferred 

from a sudden increase in penetration rate during 

drilling, a large increase in the salinity of drilling 

mud, and the very clear anhydrite crystals. The 

salt unit is tentatively correlated to the Argo Formation of Early Jurassic age on the Scotia"l shelf 

(Bielak and Simonis, 1980). 

UNIT 3 (21,830-13,625 n: 6,654-4,153 M) 

LOWER TO MIDDLE JURASSIC (HETTANGIAN(f~ 

TO BATHONIAN(?)) 

This unit is composed of dolomite anc limestone, interbedded with anhydrite, and rar~ fineto very fine-grained sandstone and shale beds. 

The sedimentary rocks of unit 3 were depofdted in 

restricted marine and marginal marine environments. Two subunits have been defined: s~Ibunit 

3B of dolomite and anhydrite with some interbedded limestone, siltstone, sandstone, and shale; 

and subunit 3A of limestone and dolomite with 

interbedded anyhydrite. 

The organic carbon contents of rocks in unit 3 

(Miller and others, this volume) are low, zveraging about 0.2 to 0.3 weight percent, ar1 the 

hydrocarbon source potential of the entire unit 

appears low. Porosity and permeability (figs. 11 

and 12) are also low, suggesting very poor reservoir quality. 

SUBUNIT 3B (21,830-18,720 FT; 6,654-5,706 M 

(LOWER JURASSIC(?)) 

The lower part of this subunit consists of interbedded anhydrite and dolomite with all interDESCRIPTION OF THE COST NO. G-2 WELL gradations of the two lithologies. The dolmnite is 

SEQUENCE light to medium gray and brown and is micritic to 

The 21,872 ft (6,667 m) of sedimentary section 

penetrated in the COST No. G-2 well (fig. 10) in 

the Georges Bank basin is here divided into four 

major lithologic units (fig. 7). These are described 

from the bottom to the top of the well. 

UNIT 4 (21,872-21,830 n: 6,667-6,654 M) 

UPPER TRIASSIC (RHAOIAN?) OR LOWER JURASSIC 

sparry. Although some vugs and intercrystalline 

pores up to 0.5 mm in diameter were noted. these 

probably resulted from preparation of the sections; remnants of anhydrite or halite(?) were 

found in many of the pores. Much of the do1()mite 

is massive and micritic or exhibits patchy r~crystallization to sparry dolomite (or dolomitA pore 

fillings). In a few zones in the lower part of subunit 3B, dolomite has replaced original oolitic and 

pelletal limestone. The open and uncompacted 

structure of the original oolites and pellets sugUnit 4 consists of halite with anhydrite inclu- gests early dolomitization. 

sions. No cuttings of salt were recovered, prob- Limestone is rare in the lower part of subunit 

ably because it dissolved during drilling and 3B, but becomes more abundant upward. There 

19 
~ 

DEPTH 

FEET I METERS 

SPONTANEOUS 

POTENTIAL 

(millivolts) 

30 mv 

-H+ KEU Y BUSHING 0 

(K.B.I O SEA LEVEL r-~""T"""--r---.---. 

1000 ~ 

< 

500 

2000 

i 

i% 

3000 

1000 ) 

~ 

4000 

1500 

5000 

CONDUCTIVITY 

(millimhos/m) 

~~ ~ ~ ~ 

ltr 

-

I 

'1:::5 

m 

COMPENSATED 

FORMATION 

DENSITY (gm/cmJ) 

1 5 1 75 2.0 2.25 2.5 2 75 3 0 3.25 3.5 

~ 

s 

I 

1-

t-

>-

a: >- <: a:oz 

~za: 

~<:~ w <: 1- :::> 

0 

(/) 

:::> a:O 

ww a..U 

a..<: :::>1- w 

a: 

u 

(/) 

:::> 

0 

w 

u 

<: 1-

w 

a: 

u 

a: 

w 

~ 

0 

~ 

(/) 

...J 

~ a: 

w 

1-

~ 

SYSTEM, (.!) 

SERIES, AND ~ 

(OR) STAGE o 

u 

~ 

(.!) 

0 

...J 

0 

J: 

1-

~ 

t"Y--t~-:: =-~ 

SANTONIAN 

CONIACIAN 

APTIAN 

BARREMIAN 

TO 

BERRIASIAN 

_._ _._ ...... 

...;.. 

~ 

-. f!

-·-··-· 

DESCRIPTION 

Kelly Bushong (K.B I Sea level (79 ft below K B. I 

Sediment-water Interface (351 ft 

below K.B I 

Fnable, gray to tan sands and silts 

Light-gray, glaucomte-bearing, calcareous shales and calc1silt1tes 

Foss1llferous limestone 

Gray, calcareous, fine- to coarsegrained sandstones and thick, 

gray, calcareous, silty shales; occasional. thon limestone beds 

Gray silty shale, calcareous shale, 

limestone, and thon sandstone 

beds 

White, chalky limestone; shale 

Poorly consolidated, light-gray 

sandstone, subordinate shale and 

siltstone. and a few thin limestone 

beds 

I -~ Soft light-gray shale with th1n. por-

~ .!__I ...!. 0 ous sandstone and I imestone beds 

7000 

\ ~ Ill~ IIIII IIIII I ~Ill f~~ ll.. a: 

i ii:~~M~,~Im-•~l"'"~'''' - _- -=.. shale, and siltstone Interbeds =>=> ---- -, .: -'-__.__ ...L: Gray, calcareous shal" .c:: 

\ Thick, interbedded, light-gray, .;halky 

limestones, dark-gray calcareous 

shales; thon sandstone beds 
~ 

7000 

8000 

9000 

10,000 

11,000 

12,000 

13,000 

14,000 

15,000 

2500 

" < 

--

~ 

I 

~ 

~ 

~ 

I 

I~ 

!:t 

~ 

~ 

u 

en 

en 

~ 

a: 

:::> 

., 

a: 

w 

~ 

~ 

:::> 

f-=r-= 

f---:...,_---,-_-

r--':_-_:::: 

Interbedded red and gray. s1lty. very 

fine to med1um-grained sandstone 

and vancolored shale; occasional. 

th1n limestone beds 

t=~~:st" Ooht1c, skeletal, and m1cr1tic lome3000 --~~~-f:;'tl-lllllit-IT-IIr"T•~~F-1-T-t--t----t------ift;;;;;::::;:;;;;t- ~:~~s~~~~st~~=eous, mlca3500 ~ 

IW 

~;;;;;;;j- Thon-bedded sandstones and limestones 

< ' ) Mass1ve. ool1t1c. pelletal, and m1cnt1c '7 .- - - limestones, subordinate 

-'- _ sandstone and shale 

I., 

I~ 1------

I~ 

-'-- _._ -l... Gray micaceous, calcareous shales; 

onterbedded sandstones and 

~ __~_ lomestones _L 

T-r 

?77?77l777i 

~~~~T;-

~~-~~---:-~-~ 

~:.....:...~..:..__-=-:-

Gray-brown, dense, arg1llaceous, 

m1cnt1c to calcaren1tic limestone; 

Interbedded shale, m1nor 

sandstone and anhydrite 

4000---L-LJLJL~~~~~-t~--~~--~~~~--t-1--t--t-----t-------tt~~:t-----------------

< 

; 

4500 

\ 

u 

en 

en 

~ 

a: 

:::> 

., 

w 

~ 

0 

0 

~ 

~ 

~M 

Fine-grained sandstone, Siltstone, 

shale, and limestone 

M1cnt1c lomestone: subordmate 

anhydrite, dolom1te, shale, and 

sandstone 

"Ch1cken-wire" anhydrite; numerous oolit1c-m1critic limestone and 

dolomite interbeds 

Micritic oolitic. and pelletal, wh1te, 

brown or gray limestone with 

numerous anhydrite beds and 

some very finely crystalline dolomite replacement 

FIGURE 10.-Geophysicallogs, lithology, and age for the COST No. G-2 well. Modified from Scholle, Schwab, and Krivoy (1980). Stratigraphic 

boundaries were based on preliminary data and do not match those shown elsewhere in this volume. 
....., 

....., 

DEPTH 

FEET I METERS 

15,000 

16,000 

5000 

17,000 

18,000 5500 

19,000 

6000 

20,000 

21,000 

6500 

22,000 

SPONTANEOUS 

POTENTIAL 

(millivolts) 

30 mv 

+--l+ 

I 

I? 

I> 

D 

~ 

( ~ f----~lr ,Ls ~ 

J 

'! 

~ 

-6. 

' ~ 

-~ 

l? 

---;; 

2 

..,- ~ 

.R ~--

- ·'" '--

l.--~ 

"""b 

,-

!~ e--~ 

p-

~ 

-

CONDUCTIVITY 

(mtlhmhos/m) 

~~ ~ ~ § I 

I 

-f-.~ 

( 

~ 1-=; 

2 

COMPENSATED 

FORMATION 

DENSITY (gm/cm3) 

15 175 20 225 25 2.75 3.0 3.25 35 

~~ .....:::.-

.......... ~ 

~ -

- - ~ s 

fs 

-~ ~ 

~~ 

~~ 

~=--

<::: 

~ 

~ ;_ 

- ~ - ~ ~ < 

~ ~ ~ 

~ t- H 

I-= 

-=: ~ """"":; 

1 

~ 

---; ,___. 

~ 

~ 

~ 

-

- t-= ~ 

g 

31 

r-= ~~ 

3 

u 

fJ) 

fJ) 

< a: 

:::J 

..., 

w 

...J 

c 

c 

~ 

~--7---

u 

u; 

(J) 

~ 

cc 

1-

cc 

w 

a.. 

a.. 

:::> 

z 

<( 

I 

1-

cc 

w 

a 

_J 

0 

1-

0 

z 

>- _J 

co 

<( 

co 

0 

cc 

a.. 

~ 

> a: 

w 

.... 

~ 

SYSTEM, <!l 

SERIES, AND ~ 

lORI STAGE ~ u -

~ 

;; 

~ 

~ 

! 

~ .. ... 

>-

<!) 

0 

...J 

0 

:X: 

1-

:::::i 

-

- "':"'T--

7 / 

/ / 

7 / 

= / / 

4 

FIGURE 10.-Geophysicallogs, lithology, and age for the COST No. G-2 well-Continued 

DESCRIPTION 

Mocntoc, calcarenotoc, or oolltoc, 

whote-gray limestone with subordonate anhydrote and dolomote 

Mocntoc limestone, mocrocrystalllne 

dolomite, and anhydnte 

loght·gray sandstone, oolltoc-pelletal 

limestone. and soltstone 

Dark-gray solty lomestone 

Argillaceous gray-brown dolomite 

and limestone. anhydrote 

Anhydrote. dolomotoc limestone, red 

shale, and sandstone 

Massive, brown-gray argollaceous 

dolomote and white-gray anhydrite 

Gray, succrosoc dolomote and anhydrote woth thon sandstone beds 

Halite and anhydnte 

Total depth of well 21,872 ft below 

KB. 
-+-' 

Q) 

Q) 

!t:. 

:I: 

I-

~ 

w 

Q 

00 

[> 

6000 

• 

8000 

XliK xxxx~x•xx x x X X 

10,000 

Core 2 [> 

[> 

Core 3 [> 0 

[> [> 

• • Core 4 [> 

• 

• 

+ Core 5 

[> 

16,000 

[> 

[> [> 

18,000 

[> [> 

Core 6 

[> 

20,000 

Core 7 

• Core 8 

• • 

• • • 

• 

• •• 

• 

•• • 

• 

• • •• • • 

. . ' 

• 

30 35 

I 

• 

• • .. • • ' 

• •• • • 

• • • f/1 • • • • • • • 

• • •• • • 

• 

• •• • ...... • • 

• • • ••• 

XX X XX>CX1X,l X I ... • Core 1 • • 

• • • • • 

• 

• • • • 

• • 

• 

• 

CONVENTIONAL CORES 

x Sandstone 

+ Shale 

o Limestone 

• Dolomite 

c Anhydrite 

SIDEWALL CORES 

• Sandstone 

A Limestone 

40 

22,0oo~o~c~o ____ ~>~------~~----~------~------~------~------~------~ 

FIGURE H.-Porosity versus depth for the COST No. G-2 well, from measurements on sidewall cores. After Malinowski (1980); 

data from Core Laboratories, Inc. 

23 
0 

10,000 

5000 

1000 

500 

0 

E 

>- 1-

...J 100 - al 

<{ 

w 

~ 

a: 

w 

c.. 

w 

a: 

0 

u 

5 

t 

1.0L 

f0.5 

cr 

CORE POROSITY (percent) 

5 10 15 20 25 30 

I 

• •• • 

• 

CONVENTIONAL CORES 

x Sandstone 

. ' . • • 

+ Shale 0 Limestone 

Dolomite • .. 

0 Anhydrite 

SIDEWALL CORES .. • Sandstone 

6. Limestone • • 

• 

X I 

• • • • • • • • * • • • • • • 0 X • X 

X 1-x . ,, .. X_ • •• • 

X X • • )()( • • • • • •• • X .. • • 

• • X 

• • • • • • • 

• X • • • 

• X 

• 

• 0 • • 

• • • 

• 

• • • X • .. .. X X 

0.1 ~X~tX X)(J(l<~x 40 ... MIn 6.&& ....... 

0.05 

35 40 

I 

• ~ 

• ~ 

• J 

• 

FIGURE 12.-Porosity versus permeability for the COST No. G-2 well, from measurements on sidewall cores. After 

Malinowski (1980); data from Core Laboratories, Inc. 

24 
are several layers of oolite or pellet packstones 

and grainstones, but calcareous mudstones or 

dolomitized calcareous mudstones are most common. Some samples suggest the presence of interbedded boundstone layers as well. These algal 

laminates contain silt-sized subangular quartz 

and appear to be rich in organic matter. Many of 

the calcareous mudstones contain fractures or 

vugs filled with anhydrite. A few fossiliferous 

calcareous wackestones are also present in subunit 3B, containing fragments of ostracods, large 

benthic foraminifers, echinoderms, and mollusks. 

Oolites and calcareous fossils are commonly 

micritic. 

The few sandstones in this subunit are highly 

compacted, well cemented, fine- to very finegrained arkosic wackestones and feldspathic 

quartz wackestones. Feldspars are commonly 

chloritized and the framework quartz grains have 

sutured contacts with one another. Clay, micas, 

and dolomite usually make up the intergranular 

matrix. A few thin, brown to gray, calcareous and 

silty shales also occur interbedded with the sandstones and dolomitic sandstones. The upper 60ft 

(18 m) of subunit 3B consists of dolomitic sandstones and silty to sandy dolomite. Clastic grains 

are mostly quartz and reworked carbonate particles such as pellets and fossil fragments. 

Simonis (1980) noted a green tuffaceous shale 

layer at 18,960 ft (5, 779 m). 

SUBUNIT 3A (18,720-13,625 FT; 5,700-4,153 M 

(LOWER TO MIDDLE JURASSIC) 

calcareous packstone and wackestone or dolomitized versions of these textures. Some grainstones are also present. Some of these intervals 

are fossiliferous and contain fragment.s of 

ostracods and other mollusks. Many of the calcareous fossil constituents are recrystallized or have 

micritic envelopes. There is little or no porosity 

remaining in most intervals. The generall:T uncompacted textures suggest early cement~tion, 

dolomitization, and filling of vugs by anhydJ..;te or 

carbonate spar. Little secondary porosity has 

been formed. 

UNIT 2 (13,625-9,700 n: 4,153-2,957 M) 

MIDDLE AND UPPER(?) JURASSIC 

(BA THONIAN(?)-OXFORDIAN(?) ) 

Unit 2 differs from the underlying unit in that it 

is composed almost entirely of limestone with 

minor interbedded sandstones and very rare intervals of dolomite and anhydrite. Unit 2 repres~nts a 

change from carbonate-evaporite depositk10J. in 

restricted marginal-marine and high-energy, openmarine shelf conditions to deposition in a more 

open carbonate shelf setting of variable energy. 

SUBUNIT 2B (13,625-11,780 FT; 4,153-3,590 M) 

BATHONIAN(?)-CALLOVIAN(?) 

The lower 265 ft (81 m) of subunit 2F are 

brown-red sandstone and silty hematiticlimonitic mudstone and shale. The sandstones are 

poorly to moderately sorted, very fine- to 

medium-grained feldspathic quartz wackes. The 

Subunit 3A comprises tan to medium-gray sandstones are highly compacted and have 

limestone interbedded and intergradational with sutured grain contacts, some dolomitic cenent, 

dolomite and anhydritic dolomite, and light-gray, and dolomite rhombs replacing feldspar. The 

white, and translucent, nodular to laminated mudstone and shale are slightly calcareous· and 

anhydrite. Sandstone and siltstone beds are rare contain disseminated silt-sized quartz. This part 

in the lowermost 50 ft (15 m) of the subunit, of the unit probably represents a tongue of nonwhere it is transitional to the sandy dolomites marine clastic sediments deposited after 

and dolomitic sandstones of upper subunit 3B. restricted marine deposition of carbonates and 

The limestone and dolomite are variable in tex- evaporites and before the limestones formf'q in 

ture. Calcareous mudstones, argillaceous calcare- more open marine environments. 

ous mudstones, and massive dolomicrites are the Brown to medium-gray micritic limestoner premost common. There is patchy recrystallization dominate in the remainder of subunit 2B, l'~lt a 

to anhedral sparry calcite or dolomite in some few beds of pellet and oolite calcareous packr+..one 

samples. Vugs and other original intercrystalline and grainstone also occur, as do thin laye:":"s of 

pore spaces are commonly filled with anhydrite, gray, calcareous, silty mudstone. Many of the 

particularly in the dolomite beds. Small amounts calcareous mudstones are burrow-mottled and 

of disseminated silt-sized quartz are common. A contain pellets, articulated ostracod fragm<:\uts, 

second kind of texture is pelletal or oolitic and fine-grained disseminated quartz silt. r~me 

25 
beds may be classified as boundstones on the 

basis of laminated algal texture. Pyrite and 

disseminated wisps of organic matter are also 

common. Original or secondary pores are filled by 

sparry calcite, and some calcareous mudstones 

exhibit a dismicritic texture. Stylolitic seams are 

common, as are spar-filled fractures. Rare dolomite rhombs and anhydrite were noted in some 

samples. 

The pelletal and oolitic packstone beds are also 

tightly cemented, and original voids are filled 

with sparry calcite. Ostracod fragments, quartz 

silt, echinoderm plates, and benthic foraminifers 

are common to abundant in some of the reworked 

carbonates, which were deposited in an apparently high-energy environment. 

Fragments of altered, green, tuffaceous(?) claystone were also found between 11,720 and 

12,100 ft (3,572 and 3,688 m). The fragments are 

vesicular and have a felted, devitrified groundmass surrounding elongate altered feldspar(?) 

phenocrysts. 

SUBUNIT 2A (11,780-9,700 FT; 3,590-2,957 M) 

CAllOVIAN-OXFORDIAN(?) 

The rocks of this subunit, including the 

limestones, exhibit a more clastic character, indicated by the prevalent angular to subrounded 

quartz sand and silt grains in mudstone and limestone, and by the abundance of intraclast and 

oolitic-pelletal limestones. Moderately sorted, 

fine- to medium-grained sandstone beds of quartz 

wacke occur in the lower part of the subunit and 

are somewhat thicker and more common in the 

upper part. These sandstones are commonly interbedded with argillaceous calcareous mudstones near the base of the subunit and algal 

intraclast boundstones, intraclast packstones, 

and pellet or oolite lime mudstones to packstones 

in the upper part. Some fossiliferous packstones 

also occur. Most of the limestones are tightly 

cemented with calcite spar or silty clay filling the 

original void space, but some samples have 

porosities as high as 15 percent. Fragments of 

ostracods are common throughout 2A, and echinoderm plates and spines, mollusk and brachiopod fragments, benthic foraminifers, rare coral 

and bryozoan fragments, and calcareous algae 

are also present. Individual grains are usually 

micritized. 

26 

Sandstone beds range from poo~ly sorted argillaceous types to moderately sorted calcitecemented varieties in which the c~ment encloses 

framework grains, resulting in poikilotopic 

texture. There is an apparent incr,.~ase in porosity 

of the sandstone beds at the top of subunit 2A. 

Shale and silty mudstone occur in some parts of 

the section. The shale and mudstone range from 

calcareous, gray to black intervals to hematitic, 

red, silty, nonfossiliferous zoner, The organiccarbon and pyrite content of shales in the upper 

part of subunit 2A is high, corunonly greater 

than 0.6 weight percent. 

The depositional environment of subunit 2A 

sediments apparently varied from high-energy 

shallow marine to nonmarine, anc"l the proportion 

of terrigenous clastic sediments increases upward 

in the section. 

UNIT 1: (9,700-1, 100 n: 2,957-335 M) 

MIDDLE AND UPPER JURASSiq?) (CALLOVIAN AND 

OXFORDIAN) TO TERTIARY (MIOCENE AND PLIOCENE) 

The sediments of unit 1 are doninantly marine 

clastics but have intervals of interbedded limestone and a few nonmarine sand stone-coal-shale 

sequences. The sedimentation rat.es decrease upward, and shallow-marine conwtions prevailed 

from the Late Cretaceous through the Cenozoic. 

The sands of this unit possess good reservoir 

characteristics. 

SUBUNIT 1D (9,700--0,920 FT; 2,957-2,109 M) 

CALLOVIAN AND OXFORDIAN TO UPPER KIMMERIDGIAN 

Interbedded white to red sandstone, gray to 

tan oolitic and algal intraclast limestone, and 

gray to red and maroon shale with thin coal 

stringers make up most of subuiJit 1D. The sediments are predominantly rec" to 7,840 ft 

(2,390 m). The sandstones are p~marily fine to 

medium grained and moderately to well sorted, 

and they vary in degree of cemeiJ tation. Some intervals are more silt- and cla:"-rich. Porosity 

ranges from less than 10 percent in fairly tightly 

calcite-cemented zones to as muc~ as 30 percent 

in more friable intervals. The sandstones are 

feldspathic quartz wackes to Frenites. Framework grains are angular to subangular and consist of 60 to 90 percent quartz, less than 15 
percent feldspar (K-feldspar and plagioclase), and 

muscovite, chlorite, some carbonate rock fragments, and a variety of heavy minerals. The feldspars are commonly altered to clay minerals. 

Dispersed organic material is relatively 

abundant. 

The shales or mudstones are calcareous and 

silty and have high organic carbon contents (0.5 

to 1.2 weight percent), especially in the gray 

shales within the upper part of the subunit. The 

more organic-rich intervals, which include thin 

coal or lignite interbeds, are also pyritic. Darkgray shales are commonly interbedded with the 

limestone intervals, whereas red shales are interbedded with tan to red sandstones in the lower 

part of subunit lD. 

Limestone beds are present throughout the section, but their total thickness is less than that of 

the sandstone. The limestones are oolitic and 

pellet packstones and grainstones, algal intraclast packstones and boundstones, and some 

pellet calcareous mudstones to algal lime mudstones. Relatively little primary or secondary 

porosity was noted in thin sections of the limestones. Nearly all packstones and grainstones 

have sparry calcite fillings of void spaces. 

Ostracod and mollusk fragments, echinoderm 

plates, and benthic foraminifers are the most 

common faunal constituents. Apparent laminae 

of blue-green algae bind some intraclast limestones. Many of the limestone beds are silty and 

contain variable amounts of organic matter and 

pyrite. 

The depositional environment of subunit lD 

apparently varied from a nonmarine delta to a 

shallow marine, high-energy, mixed carbonateclastic shelf. 

SUBUNIT 1C (6,900-2,500 FT; 2,103--762 M} 

UPPER KIMMERIDGIAN TO APTIAN AND ALBIAN 

Subunit 1 C consists of a mixture of lithologies 

deposited mainly in marginal marine to shallow 

marine environments. Limestone intervals are 

sandwiched between sandstone-shale-coal sequences. Porosity reaches as much as 35 percent, 

but is quite variable from one interval to another. 

The lower 1,200 ft (366 m) of subunit lC consists of fossiliferous calcareous mudstone and 

chalky mudstone with minor quartz sand and silt 

27 

and some interbedded gray calcareous shale. 

Articulated and fragmented ostracods, gastropods, bivalves, echionoderm plates and spines, 

and benthic foraminifers are common fr·unal 

constituents. 

Thick-bedded, coarse- to very coarse-grrined, 

poorly consolidated quartzarenites predominate 

from about 5,740 to 4,500 ft (1,750 to 1,372 m). 

These are interbedded with dark-gray to browngray, somewhat organic-rich shale or mud~· tone, 

coal, and lignite. Fine- to medium-grained, wellsorted sandstone beds also occur, but thes~ are 

usually tightly cemented by calcite or rllica. 

Calcite cements predominate near the bott<'~ of 

this interval in transition to the lime::;otone 

sequence. The proportion of calcareous mudstone 

beds also increases in the lower part of this 

interval. 

Limestone beds characterize the interval from 

about 4,500 to 3,950 ft (1,372 to 1,204 m). These 

are primarily argillaceous, glauconitic, cl' qjky 

mudstone, but include some fossiliferous O'llitic 

wackestone, packstone, and grainstone beds. 

Primary or secondary porosity in these beis is 

fairly high. Glauconitic sandstone and gray calcareous shale is interbedded in the upper pr-.:t of 

this interval, and silty calcareous mudstone predominates up to about 300ft (91 m) in the section. 

Sandstone, interbedded with gray, glauconitic 

silty mudstone, composes the upper 500 ft 

(153m) of subunit lC. The sands range from 

those that are tightly cemented with calcite to friable, fine- to coarse-grained, granular, moder~tely 

to well sorted, subangular to subrounded quartz 

wackes to arenites. Glauconite is common, a~ are 

mollusk fragments, lignite, and foraminifers .. 

SUBUNIT 1B: (2,500--1,550 FT; 762-472 M} 

APTIAN AND ALBIAN TO LOWER SANTONIAN 

Argillaceous to silty calcareous mudstone and 

chalk compose the bulk of subunit lB. These sediments were deposited in an open marine, possibly 

outer shelf environment. Glauconite, ostra~ods, 

planktic and benthic foraminifers, Inoceramid 

fragments, molluscan shell fragments, quartz silt 

and sand, organic matter, and pyrite are conunon 

constituents. The degree of induration and 

cementation by calcite varies, but most coarser 

grained intervals are fairly tightly cemented. 
SUBUNIT 1A: (1,550--1, 100FT; 472-335 M) 

LOWER SANTONIAN TO MIOCENE 

This subunit is characterized by unconsolidated marine clastic sediment, predominantly 

tan to white, fine- to coarse-grained, moderately 

to well sorted, granular to pebbly quartzarenite 

interbedded with gray, silty, glauconitic calcareous mudstone and glauconitic siltstone. 

SUMMARY 

The COST No. G-1 well was drilled on a basement high to a depth of 16,071 ft (4,898 m) and is 

located in shallower water, farther inshore than 

the COST No. G-2 well, which was drilled to a 

depth of 21,874 ft (6,667 m). The G-1 well reached 

Paleozoic basement, consisting of black slate, 

phyllite, and metadolomite unconformably overlain by Early Jurassic and younger carbonate and 

clastic rocks. The G-2 well bottomed in a 

dolomite-evaporite sequence of possible Late Triassic or Early Jurassic age. The sedimentary 

rocks in both wells reflect deposition primarily in 

a shallow marine setting. It appears that the 

strata at G-1 were deposited in shallower water 

nearer a source of clastic detritus than the strata 

at G-2, which contain more carbonate rocks deposited in an inner- to outer-shelf setting. Overall 

subsidence and sediment accumulation rates during the Jurassic and Early Cretaceous at G-1 

were lower than those of the shelf in the vicinity 

of the G-2 well. 

Nearly 3,900 ft (1,189 m) of Upper Triassic and 

Lower Jurassic strata were penetrated in the G-2 

well. These consisted mainly of interbedded dolomite and anhydrite and subordinate amounts of 

limestone, shale, and siltstone or sandstone. The 

lithologies suggest deposition in a restricted 

marginal marine setting characterized by net 

evaporation. Environments ranged from supratidal (indicated by nodular anhydrite, dolomite, 

and sand), to shallow subtidal (indicated by 

pelletal calcareous mud and oolitic wackestone to 

packstone). Triassic rocks probably do not exist 

in the vicinity of the G-1 well, but about 2,100 ft 

(640 m) of Lower Jurassic interbedded red shale, 

sandy-silty shale, red sandstone and conglomerate, sandy dolomite, dolomite, and minor 

anhydrite were penetrated. These lithologies 

reflect deposition in nonmarine to restricted 

marginal-marine environments. 

Middle Jurassic strata are pres~nt in both the 

G-2 (6,500 ft; 1,981 m thick) anc G-1 (3,900 ft; 

1,189 m thick) wells. Interbedded dolomite, anhydrite, and micritic, calcarenitic, and oolitic limestone compose most of the sequence at the G-2 

well (plate 1), except for some more sandy, silty 

and argillaceous beds in the upper part of the 

Middle Jurassic sequence, ag~in suggesting 

shallow-shelf to restricted margill al-marine depositional environments. The Middle Jurassic at 

G-1 is characterized by fine-grained dolomite and 

subordinate anhydrite beds at the base, which 

give way upward to mainly thin-bedded sandstone, shale, and sandy limestone. 

The Upper Jurassic sequence at the G-1 well is 

about 4,400 ft (1,341 m) thick and consists largely 

of medium- to coarse-grained sane stone beds and 

thick intervals of red to tan shple and silty to 

sandy shale. Sandstones in the upper part are 

cemented with calcite or dolomite but are poorly 

consolidated and more argillaceo·1s in the lower 

part. The Upper Jurassic at the G-2 well is about 

5,800 ft (1,768 m) thick and much more calcareous 

than that at the G-1 well. Limestones, including 

oolitic, calcarenitic, and micritic types, predominate in the lower and upper portk~s of this interval, but sandy limestone, calcarnous shale, and 

fine- to medium-grained calcare0us sandstones 

also occur, particularly in middle and upper intervals. The contrast between litholc'!ies at the G-1 

and G-2 wells suggests a pred"lminantly nonmarine or marginal marine-deltaic environment in 

the vicinity of G-1 and shallow-marine deposition 

at G-2. 

28 

About 3,400 ft (1,036 m) of LC'wer Cretaceous 

strata were penetrated at the G-2 well. These 

units consist largely of micritic limestone, chalk, 

silty and calcareous shale, and squdstone. Glauconite is common in all strata The G-2 well 

encountered about 2,500 ft (762 r') of Lower Cretaceous coarse-grained pebbly sands, coarsegrained calcareous sands, and tl'in, interbedded 

claystone, as well as some argillr"!eous dolomite. 

Upper Cretaceous strata are 1,40(] to 1,600 ft (427 

to 488 m) thick at both wells. Coarse-grained 

sands, gravels and shales predominate at the G-1 

well, whereas mainly glauconitic cltalks, argillaceous chalks, and fine-grained sands and silts occur 

in the G-2 well. The lithologic t.t·ends of Cretaceous sediments reflect a more nE'qrshore, clasticdominated depositional envirorment for the 

vicinity of the G-1 well and O:"Jen shelf, even 
pelagic, conditions near the G-2 well. The little 

sediment of Tertiary age recovered from both 

wells consists mainly of sand. 

Reservoir quality is apparently poor in both 

wells below about 10,000 ft (3,048 m). This can be 

seen both in a sharp decline in porosity and permeability measured on sidewall core samples 

(figs. 8, 9, 11, and 12) and from petrographic 

study of sidewall core and cutting samples. Limestone and dolomite beds in both wells are extremely tight (plate 2); no significant secondary 

porosity was observed in any samples, and much 

recrystallization is evident. In the G-2 well, 

many of the sandstones and siltstones inter29 

bedded with calcareous sequences below 10,000 ft 

(3,048 m) are either highly compacted, exhil,~ting 

sutured grain contacts, or tightly cemented with 

dolomite or calcite. Above 10,000 ft (3,048 m) 

most samples were calcite cemented; cementation 

appears to have been relatively early, ~~fore 

significant compaction. Poikilotopic texture:~ are 

common. Sandstones above 10,000 ft (3,048 m) in 

the G-1 well are commonly argillaceous and 

typically cemented by hematite, ankerite or 

siderite, or, less commonly, calcite. However, 

some primary porosity is preserved in many of 

the better sorted sands. 
PLATE 1 

Thin-section photomicrographs of characteristic carbonate rocks recovered in the COST No. G-2 

well (all with crossed nicols; field of view approximately 0.5 mm, except in D, which is 2 mm). 

Figure A. Pellet packstone containing pyrite, ostracod fragments, echinoderm plates and fragments, 

angular quartz grains, and sparry calcite void filling. From 12,140 ft (3,700 m). 

B. Dolomitized oolitic grainstone showing relatively loose packing and remznent concentric 

structure of original oolites; void space filled by dolospar. From 12,770 ft (3,892 m). 

C. Tight anhedral to euhedral mosaic of dolomite crystals containing no recognizable fossil 

constituents. Abundant wisps of organic matter. From 21,500 ft (6,553 m). 

D. Dark, organic-rich, dolomitic lime mud with void space that had been filled by anhydrite 

(now dissolved during making of thin section). 

30 
31 
PLATE 2 

Thin-section photomicrographs of representative clastic sedimentary rocks from the COST Nos. 

G-1 and G-2 wells (all with crossed nicols; field of view in A and D approximately 2mm; all others approximately 0.5 nun). 

Figure A. Sandy or silty lime mudstone containing angular sand- and silt-sized quartz grains, 

glauconite, benthic foraminifers, Inoceramid prisms, and echinoderm fragments set in 

lithified chalk matrix. From 1,320 ft (402 m) in well G-2. 

B. Fine-grained quartz sandstone with poikilotopic calcite cement. From 7,570 ft (2,307 m) in 

well G-2. 

C. Hematite-cemented (dark areas), medium- to fine-grained quartz sandstone. From 9,910 ft 

(3,020 m) in well G-1. 

D. Slightly argillaceous, fine-grained quartz sandstone; sutured grain contacts, no pore-filling 

cement (porosity is 5-10 percent), and chloritized feldspars. From 9,190 ft (2,801 m) in 

well G-1. 

E. Iron-stained quartz siltstone to fine-grained sandstone. Some hematite cement is present, 

but grains are tightly packed and have sutured contacts; feldspar grains are chloritized. 

From 13,490 ft (4,112 m) in well G-2. 

F. Fine-grained arkosic sandstone with dolomite and calcite cement in some parts, sutured 

grain contacts in others; no primary or secondary porosity; feldspar chloritized. 

32 
33 
Calcareous Nannofossil Biostratigraphy and 

Paleoenvironment of the COST Nos. G-1 and G-2 

Wells in the Georges Bank Basin 

Page C. Valentine 

The oldest sedimentary rocks sampled in the 

COST Nos. G-1 and G-2 wells are not fossiliferous and are of questionable Early Jurassic to 

Late Triassic age. During Jurassic and Early 

Cretaceous time, most of the sediments in the 

Georges Bank basin were deposited in a fluctuating nonmarine to shallow marine environment. Within this sequence, however, there is 

evidence that deeper marine shelf conditions occurred during the Berriasian at both well sites 

and also during Valanginian and Hauterivian 

time at the G-2 site. Marine shelf environments 

existed during most of the Late Cretaceous, except during the Cenomanian, when there was 

shallower water over the COST No. G-1 site. 

There is a hiatus at the Cretaceous-Tertiary 

boundary, and Campanian and Maestrichtian 

strata are missing from both sections. There may 

be other major hiatuses, but the lack of microfossils in some parts of the section makes it difficult to accurately define them. Study of samples 

of Tertiary strata shows that a marine carbonate 

shelf province existed in the Georges Bank basin 

during the Eocene. 

from individual rock fragments representing each 

of the lithologic units present in a single cutting 

sample. The oldest assemblage identified in a 

sample was used to determine the age of the 

strata at that level. In all, 296 samples from 97 

levels in the well were analyzed. Sample depths 

are relative to the Kelly Bushing, which was 98 ft 

(30 m) above sea level and 255 ft (79 m) above the 

sea floor. Selected information from the reports 

on the COST No. G-1 well by International Biostratigraphers, Inc. (1976) and Amato and 

Bebout (1980) has been incorporated into the 

present study. The highest and lowest occurrences of stratigraphically important calcareous 

nannofossil species were determined frorn this 

study and from the study by International Biostratigraphers, Inc. (1976) (fig. 13). 

EOCENE (972 FT: 296 M) 

Casing was set at 972 ft (296 m), apparently in 

Eocene strata that form a prominent seismic 

horizon that is widespread beneath Georges Bank 

(Oldale and others, 197 4, figs. 4, 8). This horizon 

was cored in the Franklin Basin on the northwest 

BIOSTRATIGRAPHY AND PALEOENVIRONMENT flank of Georges Bank and dated as Eocene 

OF THE COST NO. G-l WELL (Hathaway and others, 1979). In the COST No. 

G-1 well, sidewall cores and cuttings were colThe COST No. G-1 well was drilled to a depth lected starting below the casing, and calcareous 

of 16,071 ft (4,898 m). Calcareous nannofossil nannofossils are comn1on and moderately 

biostratigraphy is primarily based on the study preserved in limestone cuttings from samples 

of rotary drill cuttings collected over 10- to 30-ft from 1,060 and 1,090 ft (323 and 332 m) that are 

(3- to 9-m) intervals. The cutting samples from probably cavings. The nannofloras are middle to 

1,030 to 2,710 ft (314 to 836 m) were studied at late Eocene in age and contain, among other 

intervals of 90 ft (27 m) or less; from 2,710 to species, Chiasmolithus grandis, Cyclococ2,443 ft (826 to 745 m), samples were studied at colithina formosa, Dictyococcites scrippsae, 

60- to 120-ft (18- to 37-m) intervals, and from Neococcolithes dubius, and Reticulofenestra um8,010 to 15,310 ft (2,441 to 4,666 m) at 290-ft bilica. The limestone was deposited on a marine 

(88-m) intervals or less. Smear slides were made carbonate shelf. 

34 
DEPTH 

(BELOW KB) 

METERS FEET 

I 

-

• 

-

• • • • 

-I 

-

--

• 

• 

-

-

• 

• 

-

• 

-

-

• 

-

--

-

• -

AGE 

SANTONIAN 

and 

CONIACIAN 

CENOMANIAN 

and en 

ALBIAN 5 

w 

u 

3417 1--- <(· 

rw 

a: 

APTIAN U 

to 

VALANGINIAN 

5070 1- - --

BERRIASIAN 

5410'-- -

J,'~~oE~~~fA~ u 576o~-- -en 

en 

OXFORDIAN{?)~ ::::> 

...., 

PALEOENVIRONME 

SELECTED NANt\OFOSSIL SF::CIES 

IN THE CRETACEOUS 

AND JURASSIC OF COST G-1 

------, Highest occurence 

___j Lowest occurence 

( 1) International Biostratigraphers, Inc. (1976) 

t 2) Steinkraus (1980) 

10721 E. ex~m~us (l) -----, M. furcatus (l) 

1180 1-----, C. cuneatus 

1300 ~ L. floral~s 

1630 1 ______J M. furca tus 

1859 1 -----, c. achylosulT' t 1) 

19001 ______J E. ex~m~us 

2200 1-----, P. alb~imus 

3477'-----, N. buchen (l) 

5070'-----, P. senaria t1) 

5380 1 -----, p. beckmann 

5760 1------, S. bigotu (2) 

Nannofossils rare to about 9800 1, 

absent below . 

FIGURE 13.-Calcareous nannofossil biostratigraphy and paleoenvironments of the upper 6,500 ft (1,981 m) of the COST 

No. G-1 well. Paleoenvironment curves are qualitative and depict only trends. Depths are relative to the Kelly n~lshing 

(KB), 98ft (30m) above sea level. Water depth is 157ft (48 m). CSG indicates a casing point. In sample column, bla!'!k areas 

indicate a complete sequence of samples studied. Ages are based on findings of this study but incorporate some b~()stratigraphic information from International Biostratigraphers, Inc. (1976). 

35 
SANTONIAN AND CONIACIAN 

(1,072-1,859 n: 327-567 M). 

The 100-ft (30-m) interval between the casing at 

972 ft (296 m) and the top of Santonian and Coniacian strata at 1,072 ft (327 m) contains few 

fossils. Paleocene dinoflagellates and a Cretaceous pollen specimen are present in a sidewall 

core from 1,013 ft (309m), but calcareous nannofossils and foraminifers are absent (International 

Biostratigraphers, Inc., 1976). A cutting sample 

from 1,030 to 1,060 ft (314 to 323 m) contains 

quartz sand and mollusk shell fragments, as well 

as cement chips that are contaminated with both 

Tertiary and Cretaceous nannofossils. The next 

sample down (1,060-1,090 ft; 323-332 m) is also 

predominantly quartz sand and cement, but calcareous glauconitic siltstone clasts are also present; some of these clasts contain nannofossils of 

middle to late Eocene age, and others contain a 

sparse Late Cretaceous flora Maestrichtian and 

Campanian strata were not recovered and are 

apparently missing at the site. Disconformities 

probably exist below the Eocene limestone and 

also between the thin Paleocene strata and the 

underlying Santonian and Coniacian calcareous 

siltstone. 

Undifferentiated Santonian and Coniacian 

strata 787 ft (240 m) thick are present from 1,072 

to 1,859 ft (327 to 567 m). Fossiliferous calcareous siltstone is interbedded with quartz sand and 

mollusk shell fragments that were deposited in a 

marine shelf environment. Marthasterites furcatus, a species that is not known to range above 

the Santonian, and Eiffellithus eximius are present in sidewall cores at 1,072 ft (327m) (International Biostratigraphers, Inc., 1976). Two species 

that also are not known to range above the Santonian, Chiastozygus cuneatus and Lithastrinus 

floralis, are found at 1,180 ft (360m) and 1,300 ft 

(396 m), respectively. 

TURONIAN (1,859-2,200 n: 567-671 M) 

The top of the Turonian is placed at the highest 

occurrence of Corollithion achylosum, in a sidewall core from 1,859 ft (567 m) (International Biostratigraphers, Inc., 1976). Eiffellithus eximus, a 

Turonian (and younger) species, is not present 

below 1,900 ft (579 m). Podorhabdus albianus, a 

renee marks the provisional lower boundary of 

this interval. The Turonian is 341ft (104m) thick 

and consists of calcareous siltstone, coarse quartz 

sand, and mollusk shells that are indicative of a 

marine-shelf environment. 

CENOMANIAN AND ALBIAN (2,200-3,4T." n: 671-1,060 M) 

The 1,277-ft (389-m) section from 2,200 to 

3,477 ft (671 to 1,060 m) is chiefly quartz sand, except for about 200ft (61 m) of calcareous siltstone 

at the top of the interval. At about 2,400 ft 

(732 m), quartz sand and gravel be~ome dominant 

and are associated with mica, lignite, and mollusk 

shell fragments, and the few sedimentary clasts 

that are present do not contain calcareous nannofossils. These strata represent a nonmarine to 

shallow marine environment. Sp<'~es and pollen 

are present, and Albian species arn reported from 

the lower part of the interval; foraminifers are absent and dinoflagellates are rare (International 

Biostratigraphers, Inc., 1976). 

APTIAN TO VALANGINIAN (3,477 -5,070 n: 1,060-1,545 M) 

The top of the Aptian to V alanpnian section is 

provisionally placed at 3,477 ft (1,060 m) based on 

the highest occurrence of Nann':>conus bucheri 

from a sidewall core (lnternati<'"'lal Biostratigraphers, Inc., 1976). This interval is 1,593 ft 

(486 m) thick and is characterized by coarse 

quartz sand and gravel, lignite, 1nica, and sandstone. Calcareous nannofossils and foraminifers 

are rare in the sandstone, although several sidewall cores near 3,500 ft (1,067 m) contain sparse 

assemblages. Dinoflagellates are present in the 

upper part of this section; spores F"'ld pollen occur 

throughout (International Bio~tratigraphers, 

Inc., 1976). Casing was set at 4,( 23 ft (1,226 m) 

and the underlying 700 ft (213 m) of cuttings are 

quartz sand devoid of sedimentary rock fragments. Lower Cretaceous stages cannot be differentiated in the Aptian to V alaiJ ginian interval, 

and hiatuses may be present. These beds were 

deposited in a nonmarine to rl:tallow marine 

environment. 

BERRIASIAN (5,070-5,410 n: 1,~45-1,649 M) 

species that ranges from the Albian into the lower Berriasian calcareous siltstone 340 ft (104 m) 

Turonian, does not occur above 2,200 ft (671 m) in thick is present from 5,070 to 5,410 ft (1,545 to 

the COST No. G-1 well, and its highest occur- 1,649 m). The top of this interval is placed at the 

36 
highest occurrence of the Berriasian nannofossil 

species Polycostella senaria in a sidewall core 

from 5,070 ft (1,545 m) (International Biostratigraphers, Inc., 1976). A small assemblage composed of Cyclagelosphaera margereli~ Micrantholithus obtusus, Polycostella beckmanni~ P. 

senaria, Watznaueria bamesae, and W. communis 

that is indicative of Berriasian Age was observed 

in the sample from 5,380 to 5,410 ft (1,640 to 

1,649 m). The Jurassic-Cretaceous boundary is 

drawn here at the lowest occurrence of Polycostella senaria. Polycostella beckmannii is present 

also somewhat lower in the section, and it has 

been reported from conventional cores and sidewall cores from 5,478.3 ft (1,670 m), 5,531 ft 

(1,686 m), and 5,699 ft (1,737 m) (International 

Biostratigraphers, Inc., 1976). Dinoflagellates are 

rare or absent in overlying strata, but they are 

more abundant in the Berriasian beds (International Biostratigraphers, Inc., 1976), which were 

probably deposited in a marine shelf environment. 

JURASSIC (5,410-15,310 n: 1,649-4,666 M) 

The Jurassic-Cretaceous boundary is drawn at 

the lowest occurrence of Polycostella senaria at 

5,410 ft (1,649 m). International Biostratigraphers, Inc. (1976), reported nannofossil assemblages of Jurassic aspect that included Polycastella beckmanni~ Ethmorhabdus gallicus, 

Cyclagelosphaera margereli~ and Polypodorhabdus escaigii from cores in the interval 

5,475.8-5,767 ft (1,669 to 1,758 m), but sidewall 

cores and conventional cores from 5,839 to 

15,851 ft (1,780 to 4,831 m) contain no nannofossils. The cutting samples from 5,410 to 

6,300 ft (1,649 to 1,920 m) are barren or contain 

few nannofossils, and only the species Cyclagelosphaera margerelii is present. However, one sample from 6,400 to 6,410 ft (1,951 to 1,954 m) contains rare, moderately preserved specimens of 

Stephanolithion bigotii, Polypodorhabdus 

escaigii, Cyclagelosphaera margerelii, and 

Vagalapilla stradneri and is probably Oxfordian 

in age. Steinkraus (1980) reported the CallovianOxfordian species Stephanolithion bigotii in cuttings from 5,760 to 5,770 ft (1,756 to 1,759 m) and 

6,400 to 6,410 ft (1,951 to 1,954 m). Oxfordian 

assemblage containing Cyclagelosphae~~ margereli~ Ethmorhabdus gallicus, Watz.'"".aueria 

bamesae, and W. crucicentralis is prer~nt at 

9,800-9,810 ft (2,987-2,990 m). All cutting 

samples below this level contain no calcareous 

nannofossils. The Jurassic section down to about 

10,000 ft (3,048 m) is interbedded sandstc~e and 

shale that were deposited in a nonmarine environment interrupted by occasional marine incursions. Below about 10,000 ft (3,048 m), interbedded limestone, dolomite, sandstone, ani shale 

contain predominantly terrestrial palynomorphs 

(International Biostratigraphers, Inc., 1976) and 

are indicative of deposition in nonmarine and 

shallow marine carbonate bank environme"lts. 

BIOSTRATIGRAPHY AND PALEOENVIROt~~ENT 

OF THE COST NO. G-2 

The COST No. G-2 well was drilled to a depth 

of 21,874 ft (6.667 m). Rotary cutting sqmples 

from the COST No. G-2 well were collected and 

processed for the study of calcareou~ nannofossils as described for the COST No. G--1 well. 

From 1,100 to 8,800 ft (335 to 2,682 1n), the 

samples studied were generally at intervals of 30 

ft (9 m) or less, but several samples were as much 

as 60 ft ( 18 m) apart. Deeper in the well~ down 

through 21,850 ft (6,660 m), most samples were 

studied at 260-ft (79-m) intervals or less, 

although a few were as much as 360 ft (11 0 m) 

apart. A total of 777 samples from 238 levels in 

the well were analyzed (fig. 14). Sample depths 

are relative to the Kelly Bushing, which wrQ 79 ft 

(24m) above sea level and 351ft (107m) above 

the sea floor. Selected information fro~ the 

reports on the COST No. G-2 well by International Biostratigraphers, Inc. (1977) and Amato 

and Simonis (1980) has been incorporated into the 

present study. The highest and lowest occurrences of stratigraphically important calcareous 

nannofossil species were determined fro1n this 

study and from the study by International 

Biostratigraphers, Inc. (1977) (fig. 14). 

EOCENE(- 1,000-1,310 ft: -305-399 M) 

strata also may exist lower in the section. Four Casing was set at 505 ft (154 m) and also at 

species, Cyclagelosphaera margereli~ Ethmor- 1,061 ft (323m), probably in the Eocene s~ismic 

habdus gallicus, Polypodorhabdus escaigi~ and reflector, and samples were collected starting at 

Watznaueria bamesae, are present sporadically 1,100 ft (335 m). Cuttings from 1,100 to 1,460 ft 

from 6,710 to 7,710 ft (2,045 to 2,350 m), and an (335 to 445 m) are characterized by glauconite, 

37 
DEPTH 

(BELO KB) 

METERS FEET 

a:: 

8 

.....J 

1.&.. 

<t 

UJ 

(/') 

i 

I 

AGE 

1310 I 

SANTONIAN 

and 

CONIACIAN 

2120'---

2300 , TURONI~ 

CENOMANIAN 

ALBIAN en 

3180'-- -5-

w 

u 

APTIAN ~ 

w 

a: 

4184'-- -U 

BARREMIAN 

5345'-- -

HAUTERIVIAN and 

VALANGINIAN 

5680'---

BERRIASIAN 

5900'- --

TITHONIAN S:2 

and ~ KIMMERIDGIAN <( 

6420'- - -0:: 

OXFORDIAN(?) ~ 

PALEOENVIRONME 

LL. LL. LL. LLI LLI .....J LLI .....J LLI .....J Q.. Q.. 

~ LLI LLI g ~ ~ ~ a:: ~ (J) (J) 

<t (J) 

2 LLI a:: a:: 0:: 0:: .....J LLI LLI z LLI 

z 8 ~ Q.. ~ 0 ~ SE :::::> Q.. g z 0 :::::> 

SELECTED NANOOF1SSILSPECIES 

IN THE CRETACEOUS 

AND JURASSIC OF COST G-2 

----, Higest occurence 

__.1 Lowest occurence 

( 1 ) International Biostratigraphers, Inc. (1977) 

1460' -----"1 E. enm.rus 

1490'----, c. cuneatus 

1610' -----"1M. furcatus 

1670'----, L. floral.rs 

2120'__j M. furcatus ~c. 

2150'____j E. ex.rm.rus 

2222'----, P. alb.ranus 

2276' ----, P. as per 

300'~ R. fenestratus 

2390 ,____j C. cuneatus 

2570'____j P. alb.ranJs 

(1) 

(1) 

3110'--,n. lehmann.r.r,F. b.rforam.rnis 

3180' ____j P . ._·retacea ( 1) 

3200'-----, c. ch.rast.rd 

3433'-----, B. afr.rcana (1) 

3530'----, N. bucher.r 

3796'__j F. b.rforam.rms (1) 

3919'----, C. mex.rcan" ( 1) 

3947'----, M. obtusus (1) 

4070' __j C. achylos1m 

4184 ,____J L. Elural.rs (1) 

B. colliyatus, C. cuv.rll.rer.r ( 1) 

5345 '--,c. deflandre.r, N. colomi.r (I) 

5400'----, T. veranae (1) 

5560 1----, M.rcranthol.r thus Sp. 

5680'----, P. senaria 

5710'__j T. verenae 

5740'--, Braciuol.rthus? sp. 

5799'__j B. colligatus, P. asper (1) 

5800' ----, P. hc'<-·kmann.r.r 

58go•____J c. cuv.rll.rer.r 

5895'__j N. colom.r.r, P. senar.ra (1) 

6420'----, s. bigot.r.r (1) 

Nannofossils rare to about 10,000', n bel ow. 

FIGURE 14.-Calcareous nannofossil biostratigraphy and paleoenvironments of the upper 6,500 ft (1,981 m) of the COST 

No. G-2 well. Paleoenvironment curves are qualitative and depict only trends. Depths are relative to tl..P- Kelly Bushing 

(KB), 79 ft (24 m) above sea level. Water depth is 272 ft (83 m). CSG is a casing point. In sample colunm, black areas indicate a complete sequence of samples studied. Ages are based on findings of this study, but incorporate some 

biostratigraphic information from International Biostratigraphers, Inc. (1977), and Steinkraus (1980). 

38 
quartz sand, fragments of bivalves and bryozoans, and abundant cement. Sedimentary clasts 

are not common, and most are barren, although 

glauconitic limestone fragments containing a 

rich, diverse, well-preserved, calcareous nannofossil assemblage were sampled at 1,310 ft 

(399 m). The following species are present, among 

others, and they are indicative of the upper 

Eocene Discoaster barbadiensis zone of Bukry 

(1973, 1975): Chiasmolithus oamaruensis, Cyclococcolithina formosa, Dictyococcites bisectus, 

Discoaster saipanensis, Reticulofenestra reticulata, and R. umbilica. International Biostratigraphers, Inc. (1977), reported a foraminiferal 

fauna of late middle Eocene age from a sidewall 

core at 1,289 ft (393 m). The Eocene cuttings are 

indicative of a marine shelf environment. The cuttings may be mostly cavings, but together with 

the sidewall core they confirm the presence at the 

COST No. G-2 site of a widespread Eocene limestone unit that has been sampled elsewhere 

beneath Georges Bank and in submarine canyons 

on the slope (Weed and others, 1974; Ryan and 

others, 1978; Hathaway and others, 1979; V alentine, 1981). Upper Eocene limestone cavings are 

present in samples down to 4,120 ft (1,256 m). 

SANTONIAN AND CONIACIAN (1,310-2,120 FT: 399-646 M) 

Paleocene, Maestrichtian, and Campanian 

strata were not observed in the COST No. G-2 

well, suggesting that there is a major disconformity at the Cretaceous-Tertiary boundary at about 

1,300 ft (396m). International Biostratigraphers, 

Inc. (1977), reported Inoceramus shell prisms and 

Upper Cretaceous foraminifers in cuttings at 

1,310 ft (399m) and a Santonian foraminiferal assemblage in a sidewall core from 1,324 ft (404 m). 

In the present study, a mixed assemblage of rare, 

poorly preserved Eocene and Upper Cretaceous 

nannofossils was observed at 1,340 ft (408 m); 

and a poorly preserved flora of probable Santonian Age containing Eiffellithus eximius, Tetralithus obscurus, and T. ovalis was found at 

1,460 ft (445 m). 

Santonian and Coniacian nannofloras are present in a 796-ft (243-m) -thick section of glauconitic, silty limestone and gray calcareous siltstone from 1,460 to 2,120 ft (445 to 646 m). The 

nannofossils are abundant and well-preserved. 

The highest occurrence of Chiastozygus cuneatus, a species that is not known to range above 

the Santonian, is at 1,490 ft (454 m). Mar39 

thasterites furcatus (1,610 ft; 491 m) and 

Lithastrinus floralis (1,670 ft; 509 m) are also 

present lower in this interval. The abundant glauconite and mollusk-shell fragments, particularly 

Inoceramus prisms, are indicative of deposition 

in a marine shelf environment. 

TURONIAN (2, 120-2,270 FT: 646-692 M) 

A relatively thin (150-ft; 46-m) section of richly 

fossiliferous, gray, argillaceous limesto,e of 

Turonian Age is present from 2,120 to 2,270 ft 

(646 to 692 m). These beds are litholo[rically 

similar to the overlying Santonian and Coniacian 

strata, and the top of the Turonian is drawn at 

the highest occurrence of Corollithion achylosum. 

Podorhabdus albianus, a species that is restricted 

to Turonian and older rocks, appears in a sidewall 

core from 2,222 ft (667 m) in the COST No. G-2 

well (International Biostratigraphers, Inc., 1977). 

Two species, Marthasterites furcatus and Eiffellithus eximius, which are restricted to Tur-:»nian 

and younger strata, are absent below 2,l20 ft 

(646 m) and 2,150 ft (655 m), respectively. Cuttings from the Turonian interval contain m<'lluskshell fragments that indicate deposition in a 

marine-shelf environment. 

CENOMANIAN (2,270-2,600 FT: 692-792 M) 

Cenomanian gray calcareous siltstone is approximately 330ft (101m) thick and is somewhat 

more siliceous than the overlying strata. N annofossils are common and well preserved. The top of 

the Cenomanian is placed at the highest occurrence of the planktic foraminifer Rotalipora cushmani in a cutting sample from 2,270 ft (6~2 m) 

and in a sidewall core from 2,276 ft (694 m) (International Biostratigraphers, Inc., 1977). Porhabdolithus asper and Reinhardites fenestratus 

are not present in the COST No. G-2 well above 

2,276 ft (694 m) and 2,300 ft (701 m), respectively; 

these nannofossil species become extinct at or 

near the Cenomanian-Turonian boundary. 

The base of the Cenomanian is arbitrarily 

drawn at 2,600 ft (792 m), where the litholCJ qy of 

the section changes from a shelly siltstone to a 

calcareous quartz sandstone containing lignite, 

mica, and mollusk-shell fragments. Sidewall cores 

from about 2,600 to 3,100 ft (792 to 945 m) contain almost no calcareous nannofossils and foraminifers, but cuttings contain benthic foraminifers 
no younger than Albian age at about 2,650 ft 

(808 m) (International Biostratigraphers, Inc., 

1977). Cenomanian strata were deposited in a 

marine-shelf environment, probably shallower 

than that of Turonian, Coniacian, and Santonian 

time. 

ALBIAN (2,600-3, 180 FT: 792-969 M) 

Albian, Aptian, and Barremian strata approximately 2,745 ft (837 m) thick are present from 

2,600 to 5,345 ft (792 to 1,629 m). Most of this 

section contains few fossils and is difficult to 

date; therefore, the stratigraphic boundaries are 

provisional. The upper 580ft (177m), from 2,600 

to 3,180 ft (792 to 969 m), is gray calcareous sandstone and shale with associated mollusk shells, 

glauconite, and lignite, and indicates deposition 

in a marine inner-shelf environment. Sidewall 

cores contain almost no calcareous nannofossils 

and foraminifers, and dinoflagellates are less 

common than in overlying strata (International 

Biostratigraphers, Inc., 1977). These beds are 

assigned to the Albian based on the lowest occurrence of Prediscosphaera cretacea in a sidewall 

core from 3,180 ft (969 m). 

APTIAN (3, 180-4,184 FT: 969-1,275 M) 

The strata from 3,180 to 4;184 ft (969 to 

1,27 5 m) are more fossiliferous than the overlying 

Albian beds. This 1,004-ft (306-m) interval is 

provisionally assigned to the Aptian based on the 

highest occurrences of Nannoconus bucheri, Conusphaera mexicana, and Micrantholithus obtusus, and the lowest occurrences of Flabellites 

biforaminis, Corollithion achylosum, and Lithraphidites floralis. Nannofossils are not abundant, and preservation is only moderate. The 

Aptian beds are chiefly sandstone and shale con 

taining mollusk shell fragments. They are more 

calcareous and contain less lignite than the 

overlying Albian strata, and they were laid down 

in a marine shelf environment. 

BARREMIAN (4, 184-5,345 FT: 1,275-1,629 M) 

Casing was set at 4,120 ft (1,256 m), apparently 

at a lithologic boundary. The 1,161-ft (354-m) 

section from 4,184 to 5,345 ft (1,275 to 1,629 m) is 

calcareous sandstone containing lignite and mica 

40 

and a few fossils. It was deposited in an innershelf environment similar to that of the Albian. 

Sidewall cores from this interval C'lntain almost 

no calcareous nannofossils and foraminifers, but 

palynomorphs are present, and the t.op of the Barremian is based on the highest occurrences of several dinoflagellate species (lnternat:\onal Biostratigraphers, Inc., 1977). 

HAUTERIVIAN AND VALANGINIAN (5,~~5-5,680 FT: 

1,629-1,731 M) 

Hauterivian and Valanginian arg;Uaceous limestone 335 ft (102 m) thick extends from 5,345 to 

5,680 ft (1,629 to 1,731 m). Modera~ely preserved 

calcareous nannofossils are common. Species 

indicative of Hauterivian and olc~r strata are 

present at 5,345 ft (1,629 m). The highest occurrences in sidewall cores of Bipodorhabdus colligatus, Cruciellipsis cuvillieri, and Cyclagelosphaera deflandrei are at 5,345 ft (1,629 m), and 

Tubodiscus verenae is present at 5,400 ft 

(1,646 m). Micrantholithus sp. (V dentine, 1980, 

pl. 2, fig. 13) is present in two cutting samples 

from the interval 5,560 to 5,65C ft (1,695 to 

1,722 m) in the Hauterivian and Vl'langinian and 

in one sample from the underlying Berriasian 

strata. A single occurrence of thi~ species was 

reported from the Hauterivian and Valanginian 

of the COST No. B-3 well on tJ1~ continental 

slope off New Jersey (Valentinn, 1980). The 

Hauterivian-Valanginian argillaceous limestone 

at the COST No. G-2 site was probqbly deposited 

in a marine shelf environment. 

BERRIASIAN (5,680-5,900 FT: 1,731-1,798 M) 

The Berriasian is represented b~r a short interval (210 ft; 64 m) of light-gray lim~stone that extends from 5,680 to 5,900 ft (1,7f1 to 1,798 m). 

The Berriasian-Valanginian boundary is placed at 

the highest occurrence of the Berriasian nannofossil Polycostella senaria The highest occurrence of Polycostella beckmanni~ a species that 

ranges from the Tithonian into tb~ Berriasian, is 

at 5,800 ft (1,768 m). Several stratigraphically important species that are restricted to Berriasian 

and younger rocks and have thei~ lowest occurrences in this interval of the well zre Bipodorhabdus colligatus and Parhabdolithus asper at 

5,799 ft (1,768 m), Cruciellipsir cuvillieri at 
5,890 ft (1, 795 m), and Nannoconus colomii and 

Polycostella senaria at 5,895 ft (1,797 m). 

Brachiolithus? sp. (Valentine, 1980, pl. 2, figs. 1, 

2) is present at 5,800 ft (1,768 m) and in several 

lower samples in the COST No. G-2 well. This 

species is restricted to the Berriasian of the 

COST No. B-3 well (Valentine, 1980) and may 

prove to be a valuable marker for that stage. In 

addition, the Cretaceous dinoflagellate Pseudoceratium pelliferum is not present in sidewall 

cores below 5,856 ft (1,785 m) (International 

Biostratigraphers, Inc., 1977). The Berriasian 

limestone probably was deposited in a marine 

shelf environment similar to that of the overlying 

Hauterivian and Valanginian beds. 

JURASSIC (5,900-21,874? n: 1,798-6,667? M) 

The Jurassic-Cretaceous boundary is provisionally placed at 5,900 ft (1,798 m), near the 

lowest occurrences of the nannofossil species 

Cruciellipsis cuvillieri, Nannoconus colomi~ and 

Polycostella senaria. Below this depth nannofossil diversity is low and the limestone is partly 

recrystallized. International Biostratigraphers, 

Inc. (1977), studied sidewall cores from the 

boundary interval and observed a Late Jurassic 

dinoflagellate assemblage at 5,962 ft (1,817 m); 

the Jurassic dinoflagellate Meiourogonyaulax 

staffensis is present from 6,155 to about 7,500 ft 

(1,876 to about 2,286 m), and the TithonianBerriasian nannofossil species Polycostella 

beckmanni~ is present down to 6,270 ft (1,911 m). 

In this study, cuttings that are almost barren of 

calcareous nannofossils appear at about 5,900 ft 

(1,798 m): Except for Lower Cretaceous cavings, 

most samples down to about 10,000 ft (3,048 m) 

are barren or contain poorly preserved specimens 

of two long-ranging Jurassic-Cretaceous species, 

Cyclagelosphaera margerelii and Watznaueria 

bamesae. 

Samples of the present study from below 

10,000 ft (3,048 m) are barren of nannofossils. 

However, International Biostratigraphers, Inc. 

(1977), reported the presence of the nannofossil 

Stephanolithion bigoti~ of Callovian-Oxfordian 

Age, in five sidewall cores from 6,420 to 6,818 ft 

(1,957 to 2,078 m) and in two sidewall cores from 

10,135 and 10,24 7 ft (3,089 and 3,123 m); the upper five samples are from a part of the section 

dated as Kimmeridgian and Tithonian using 

foraminifers and palynomorphs. At the COST 

41 

No. G-1 well, Stephanolithion bigotii was observed in a cutting sample of the present study 

from 6,400 to 6,410 ft (1,951 to 1,954 n1); and 

Steinkraus (1980) reported the species in c11ttings 

from the same level and also from 5, 760 to 

5,770 ft (1,756 to 1,759 m). Thus, in both wells, 

Stephanolithion bigoti~ a species that d(J ~s not 

normally range above the Oxfordian, is pre;--~nt in 

strata that have been provisionally dated a~ Kimmeridgian and Tithonian on the basis of r~ynomorphs and foraminifers. Below about 9,500 ft 

(2,896 m) in the COST No. G-2 well, rq}ynomorphs and foraminifers indicate that strrta are 

Oxfordian, Callovian, and possibly Late T'iassic 

to Early Jurassic in age (International Biostratigraphers, Inc., 1977). The Jurassic section in the 

COST No. G-2 well is about 16,000 ft (4,r77 m) 

thick. It is predominantly shallow marine limestone, but it also includes dolomite and b<lds of 

anhydrite; halite is present at the bottom of the 

well. 

SUMMARY 

The Jurassic stratigraphy of the COST Nos. 

G-1 and G-2 sites is not well defined. Strata 

dated as Middle and Late Jurassic age using terrestrial and marine palynomorphs are pres·ent in 

both wells, but the stages are difficult to delineate. T'ne deeper, less fossiliferous beds may be as 

old as Early Jurassic or late Triassic. The s<l.ction 

in the COST No. G-1 well from the Ju:"."assicCretaceous boundary at 5,410 ft (1,649 m) down 

to about 10,000 ft (3,048 m) is composed of calcareous and noncalcareous shale, siltstonP., and 

sandstone, all of which contain dinoflagellates, 

terrestrial palynomorphs, and sparse calcareous 

nannofossils. From 10,000 ft (3,048 m) do~'ll to 

the metasedimentary basement rocks at about 

15,600 ft (4,755 m), shale and sandstone are interbedded with limestone, dolomite, and anh~~drite; 

terrestrial palynomorphs are present, but dinoflagellates and calcareous nannofossils are extremely rare. Jurassic strata at the G-1 site were 

deposited in alternating nonmarine and sl· sill. ow 

marine environments. The COST No. G-J well 

was drilled on a basement high (Klitgorcl and 

Behrendt, 1979, fig. 7c; Waetjen, 1980, pl. 4), 

whereas the COST No. G-2 well is in a d~eper 

part of the Georges Bank basin where the ,Jurassic section contains more calcareous sediment 
and is representative of a shallow marine environment. At the G-2 site, calcareous shale and sandstone are interbedded with limestone from 5,900 

to about 10,000 ft (1,798 to about 3,048 m), below 

which ooltic limestone is the principal rock type 

down to about 13,500 ft (4,115 m); below 7,500 ft 

(2,286 m), marine and terrestrial palynomorphs 

are present, but calcareous nannofossils and 

foraminifers are rare or absent. Limestone, 

dolomite, and anhydrite dominate the section 

from about 13,500 ft (4,115 m) down to the salt 

encountered near the bottom of the hole; palynomorphs are rare, and calcareous nannofossils and 

foraminifers are absent in this part of the section. 

Lower Cretaceous and Cenomanian rocks at the 

COST No. G-1 site are present from 2,400 to 

5,410 ft (732 to 1,649 m). They are chiefly coarsegrained quartz sand and lignitic, micaceous sandstone interbedded with calcareous siltstone 

representing deposition in nonmarine and shallow 

marine environments. These strata contain few 

fossils, and neither the Lower Cretaceous stages 

nor the Albian-Cenomanian boundary can be 

delineated accurately. Terrestrial palynomorphs 

are present throughout the section, whereas 

dinoflagellates, calcareous nannofossils, and 

foraminifers are absent except in shallow marine 

beds near 3,500 ft (1,067 m) and in the Berriasian 

strata at the base of the interval. 

At the COST No. G-2 site, the upper part of the 

Lower Cretaceous, from 2,600 to 5,345 ft (792 to 

1,629 m), is mainly calcareous siltstone and shale 

containing mollusk shells, glauconite, and lignite. 

Albian and Barremian strata of this interval are 

notably less fossiliferous than the intervening 

42 

Aptian beds; all were deposited in a marine innershelf environment. At both sires, the Aptian 

strata show more marine influence than Albian or 

Barremian strata The Hauterivia"1, Valanginian, 

and Berriasian strata from 5,3A5 to 5,900 ft 

(1,629 to 1,798 m) are fossiliferouf limestone also 

of marine shelf origin. The Lower Cretaceous at 

the G-2 site is slightly thicker and generally 

more fossiliferous than at the G-1 site. The 

Hauterivian and Valanginian strata in the G-2 

well were deposited in a marine shelf environment; strata of the same age in the G-1 well represent nonmarine to shallow marine conditions. The 

Berriasian is marine in both wells, 

The Upper Cretaceous sections are comparable 

in thickness at both sites. Cenm"1anian beds at 

the COST No. G-2 site are calcar~0us siltstone of 

marine shelf origin. At the COS':':' No. G-1 site, 

the Cenomanian and Albian quartz sand was 

deposited in a nonmarine to shallow marine environment. Santonian, Coniacian. and Turonian 

strata at the two well sites represent different 

sedimentary facies, but they incicate a marine 

shelf environment at both sites; at G-1, calcareous siltstone is interbedded with shelly quartz 

sand, whereas coeval strata at G-2 are glauconitic, argillaceous limestones t':tat represent a 

facies deposited farther offshore. 

Maestrichtian and Campanian beds were not 

observed in either well; there is a hiatus in the 

100- to 200-ft (30- to 61-m) interval of poorly 

fossiliferous, reworked beds bet~·een Santonian 

and Eocene strata The Eocene ir both wells is a 

glauconitic limestone rich in ca ~areous nannofossils that was deposited on a rrarine carbonate 

shelf. 
Foraminiferal and Seismic Stratigraphy, 

Paleoenvironments and Depositional Cycles in tha 

Georges Bank Basin 

C. Wylie Poag 

In this paper geologic information from the 

COST Nos. G-1 and G-2 wells and auxiliary 

shallow coreholes is combined with interpretations of multichannel seismic reflection profiles to 

provide a stratigraphy and depositional history 

of the Georges Bank basin (fig. 15). The biostratigraphic summary is based on the foraminiferal 

assemblages sampled from rotary cuttings taken 

at 10- to 90-ft (3- to 29-m) intervals, except for 

wider spacing in the Oxfordian(?) to 

Hettangian(?) section of the COST No. G-J well. 

Sidewall cores provided by International Biostratigraphiers, Inc., were also examined for 

foraminifers. (See Amato and Bebout, 1980, and 

Amato and Simonis, 1980, for locations o~ sidewall cores.) Age sequences are described fro~ the 

youngest to the oldest. The zonation of the COST 

Nos. G-1 and G-2 wells is based on the fi.IJ al appearances of diagnostic planktic and benthic 

foraminifers. Established planktic foraminiferal 

0 50 100 

KM 

FIGURE 15.-Locations of well and core sites and seismic reflection profiles on North Atlantic Outer Continental Shelf and 

slope. 

43 
<..9 

z 

CSG 

~ 1000 

:::) 

CD 

>-

_j 

_j 

w 

~ 1500 

3 

0 

_j 

w 

CD 

I- 2000 w 

w 

LL 

COST G-1 

SEA LEVEL PALEOENVIRONMENT NON IN MID OUT UP LOW 

\MARINE\ SHELF I SHELF I SHELF I SLOPE\ SLOPE\ 

SEA FLOOR < 

0 

c:; 

I 100 

I 

l::> 

,.-- TOP SAMPLE 

200 

300 

400 

500 

600 

700 

800 

0:.. 

0 

0 

_j 

LL 

<t 

w 

(j) 

3: 

0 

_j 

w 

CD 

(j) 

0::: 

w 

1----

w 

~ 

FIGURE 16.-Stratigraphic column of COST No. G-1 well 

showing chronostratigraphy, biozones, and paleoenvironments. The age terms abbreviated in the left side column 

are spelled out on figure 17. 

zonations are used where possible (Blow, 1969: 

Berggren and Van Couvering, 197 4; Hardenbol 

and Berggren, 1978; Pessagno, 1967; Stainforth 

and others, 1975; van Hinte, 1976a, b). The benthic foraminiferal zonation of Ascoli (1976) was 

used to date Mesozoic assemblages. The biostratigraphic interpretations presented here are 

preliminary and later studies may modify and 

refine them. 

The biostratigraphic analyses are used with interpretations of the seismic sequences to deterCOST G- I 

44 

<..9 

z 

3000 

3500 

4500 

~ 5000 

:J 

CD 

>-

_j 

_j 

w 

~ 5500 

3: 

0 

_j 

w 

CD 

I- 6000 w 

w 

Ll.. 

6500 

7000 

7500 

8000 

z 

<l 

~ 

w 

a:: 

a:: 

<( 

m 

-z_- .... <{ 

~ a: 

w 

1-

::J 

<{ 

:f ..... 

z 

<l 

z 

Cl 

z 

<l 

...J 

<l 

> 

z 

<( 

Vl 

<l 

a:: 

a:: 

w 

m 

I~ "'~ .... 

Zl! 

0::0 

... ~ 

z 

<l 

Cl 

0 

a:: 

w 

~ 

~ :l( 

w 

z 

<( 

0 

a:: 

0 

ll.. 

X 

0 

z 

<l 

> 

0 

...J 

...J 

<l 

u 

PALEOENVIRONMENT 

NON IN MIO OUT UP LOW 

'MARINE' SHELF I SHELF ISHEL F I SLOPE' SLOPE I 

900 

\000 

1\0 0 

1200 

1300 

1400 

1500 

1600 

1700 

1800 

1900 

2000 

2100 

2200 

2300 

0::: 

0 

0 

_j 

LL 

<t 

w 

(j) 

3: 

0 

_j 

w 

CD 

(j) 

0::: 

w 

1----

w 

~ 
COST G-1 

(.9 

z 

8000 

8500 

~ 10000 

::J CSG m 

>-

_j 

_j 

w 

~ 

~ 

0 

_j 

w 

m 

1-

w 

w 

LL 

12000 

12500 

13000 

z 

<( 

> 

0 

...J 

...J 

<( 

l) 

z 

<l: 

z 

0 

I 

~ 

<l: 

Ill 

z 

<( 

u 

0 

"""') 

<( 

0? 

z 

<( 

z 

w 

z 

<( 

u 

a: 

<( 

0 

f-;" 

z 

<( 

;;I 

u 

<( 

al 

(/) 

z 

WI 

-I 

~I 

·r;.: .... 

z 

<( 

:r 

0 

~ fl) 

z 

ILl 

::::i 

n. 

I

ii 

~I 

z 

u; 

PALEOENVIRONMENT 

NON IN MID OUT UP LOW 

!MARINE' SHELF p~~LOPE I SLOP~ 

2400 

2500 

2600 

2700 

2800 

2900 

3000 

3100 

3200 

3300 

3400 

3500 

3600 

3700 

3800 

0:: 

0 

0 

_j 

LL 

<[ 

w 

(f) 

~ 

0 

_j 

w 

m 

(f) 

0:: 

w 

1-

w 

~ 

COST G-1 PALEOENVIRONMENT 

45 

13000 

13500 

(.9 14000 

z 

I 

(f) 

::J 

CD 

>- 14500 _j 

_j 

w 

~ 

~ 

0 d 15000 

CD 

1-

w 

w 

LL 

15500 

16000 

z 

<( 

(!) 

z 

<( 

IIw 

~ 

z 

<( 

1-

,.._ 

z 

... 

"' ... 

... 

<( ~ 

- z 

a: w a! ::E 

::E w 

(f) 

<( <( 

l) a! 

NON IN MID OUT UP LOW 

I MARINE! SHELF I SHELf I SHELF I SLOPE I SLOPE I 

3900 

4000 

4100 

4200 

4300 

4400 

4500 

4600 

4700 

_..___.__.~........~..16071 TD 

0:: 

0 

0 

_j 

LL 

<[ 

w 

(f) 

~ 

0 

_j 

w 

CD 

(f) 

0:: 

w 

1-

w 

~ 

mine the presence of unconformities and to 

establish a chronostratigraphic framework for 

each well. The chronostratigraphic sequencer are 

then used to calculate sediment accumulFt.ion 

rates. The chronostratigraphic and lithost. .. atigraphic units are compared with those of the Scotian basin of Canada, and correlations are 

established between the COST No. G-2 and ~ltell 

Mohican 1-100 wells. The stratigraphic nmnenclature used in this basin is extrapolated from 

that used in wells on the Scotian shelf of Canada 

The paleoenvironmental analysis is based on 

the microfossil record of the COST Nos. G-1 and 

G-2 wells and an interpretation of seismic fF!Oies 

along USGS multichannel line 19. The biost""atigraphic, paleoenvironmental, and seismic sequence data are combined to determine depositional cycles. The lack of microfossils thrc'Igh 

~ 

........ I 

u 

w- .....JUl 

cw 

c<C 

-a: 

~::::> -, 

C'-· 

u 

-(/) 

(/) 

<t 

a: 

:::J 

--:> 

~ a: 

<t 

w 

"-· ('-. 

S2 u 

(/) - (/) (/) 

<t (/) - <t a: ocr 

1-1-:::J --:> 

w ~ I- a: 

<t <t _J w 

EARLY 

CAMBRIAN? 

CALLOVIAN? 

BAJOCIAN?-

AALENIAN? 

TOARCIAN?-

PLIENSBACHIAN? 

PLIENSBACHIAN ?-

SINEMURIAN? 

HETTANGIAN?-

RHAETIAN? 

·~ 

~~ ~<( 

ui 

-o 

~~ 

~ 

0 

::::> 

d 

0 

a: 

I 

z 

<( 

u 

I 

0 

~ 

UNNAMED 

BASEMENT 

~~--.~;;~·-: .. 1 ~ 

·~··~·· 

SAND very coarse, unconsoltdoled;thtck tnterbeds of 

SHALE,red-brown,groy;some COAL, pyrite 

SANDSTONE consolidated ,medium; interbedded SHALE, 

red-brown,green,silly,troces of COAL;Ihtn beds of 

micrite 

LIMESTONE fine to medium crystalline pelletal, fossiliferous;m icrite at bose 

SHALE groy-green;obundont carbonaceous flecks; LIMESTONE ,dense ,fossiliferous; few thin beds of very fine 

SANDSTONE 

SANDSTONE thinly interbedded;very ftne-crystolline 

liQhl DOLOMITE ;SHALE,red-brown and gray, grading to SILTSTONE;thin LIMESTONE of bose 

SHALt, red, brown,groy ,si It y ,m i coceous ,dolomitic;interbedded SANDSTONE, fine to medium,consolidoted, 

trace COAL 

2500 

10000 

3000 

11000 

3500 

12000 

DOLOMITE light groy-buff,cryptocryslolline,in port sandy, 

stlly or pelletal; interbeds of ANHYORITE,scottered H3000 

GYPSUM nodules, few thin beds of red-brown SHALE 

SANDSTONE light gray- ptnk, very fine to fine,DOLOMITE, 

creom-buff,brown,dense,a little red SHALE and 

ANHYDRITE 

SHALE red-brown,streoks and indusions of DOLOMITE 

and ANHYDRITE ;thin interbeds of DOLOMITE;few thin 

beds of tiaht SANDSTONE 

SANDSTONE· fine to medium ,rust-red,argtllaceous; 

interbeds of SHALE,red,brown,micoceous,port dolomil ic; conglomerate zones with interbedded SANDSTONE and SHALE; few thin beds of DOLOMITE, 

gray -ton microcrystoll ine 

QUARTZ CONGLOMERATE, red-ptnk; red do lomtttc 

SHALE matrix; few interbeds of red SHALE, SANDSTONE onJ dense LIMESTONE and DOLOMITE; 

thick,red,sand y, SHALE ;pink-red,medtum to coorseromed SANDSTONE at bose 

SERICITIC METADOLOMITE,tight-groy to while,fine4000 

15000 

4500 

1 dense crystalltne;black SLATE portmgs 

PHYLUTE with wedges and layers of metoquortzite; I 16000 

pyrite cubes and mosses; some schistose foliotton 

and graphite stain 

~0 

~----~--------------~----~----~----~------~----------------------~17000 

FIGURE 17 .-Geologic column of COST No. G-1 well. The formation names in this paper are those of similar rocks on the Scotian shelf of Canada. 
most of the thick Jurassic carbonate sections 

makes identification of older depositional cycles 

difficult, but first-order cycles can be easily 

recognized in the Cretaceous and Cenozoic. 

Finally, comparisons of stratigraphic and depositional sequences between the Georges Bank 

wells, the Scotian basin, and deep-sea sites reveal 

some marked regional similarities in geologic 

history. 

BIOSTRATIGRAPHY AND 

CHRONOSTRATIGRAPHY OF 

THE COST No. G-1 WELL 

QNOZOIC ROCKS (157-1,030 n: 48-314 M) 

The youngest cutting sample from the COST 

No. G-1 well in this study is from 1,030 ft (314m) 

and is considered to be Santonian in age (figs. 16 

and 17). However, it does contain a few middle 

Eocene foraminifers (Acarinina bulbrooki) and 

(/) 

0 51 

u 

w 

(/) 

w 

~ 

f--

2 _j 

w 

> 

~ 

0::: 

f-

~ ~ 3 I 

C\J 

4 

0 

0 IOKM 

COST G-1 

NW9o 

some Paleocene foraminifers (Pseudohastigerina 

wilcoxensis) which indicate the presence, higher 

in the well, of unsampled Cenozc ic strata. 

Seismic correlation with the COST No. G-2 

well indicates that the Santonian strata are unconformably overlain by 120 ft (37 m) of Paleogene rocks (probably mainly middle Eocene), 

475ft (145m) of Neogene rocks (probably chiefly 

Miocene), and 170 ft (57 m) of P'~istocene rocks. 

At the G-1 well site, 161 ft (49 n) of Pleistocene 

rocks was recovered from USGS AMCOR site 

No. 6018 (Hathaway and others, 1979). 

A prominent seismic reflector 650 ft (198 m) 

below the sea floor at the G-1 siw (Hathaway and 

others, 1976) apparently marks l' middle Eocene 

limestone unit (fig. 18). This middle Eocene limestone was penetrated and sampled at AMCOR 

site No. 6019, 60 mi (100 km) to the northwest 

(fig. 15), and at the G-2 well site (figs. 19, 20, 21), 

and its upper surface can be correlated seismically between the three sites. At AMCOR No. 

6019 the middle Eocene limestone is white, 

10M I 

------ -----

;;:..... --

~-~--- -----. ~~ 

FIGURE lB.-Structural and chronostratigraphic interpretation of seismic reflection profile line 77-1, which crosses the G-1 

well site along dip. 

48 
glauconitic, and bioclastic and contains abundant 

foraminifers and bryozoan remains. Small to 

medium fragments of this limestone were present 

in the uppermost G-1 sample. Some fragments 

have been altered and have a dense, light-gray, 

weathered appearance. 

CROACEOUS ROCKS 

SANTONIAN (1,030--1,390 FT; 314-424 M) 

The top cutting sample, collected at 1,030 ft 

(314m), contains a predominantly Cretaceous 

assemblage of Archaeoglobigerina cretacea, 

Hedbergella delrioensis, Heterohelix sp., 

Arenobulimina americana, Kyphopyxa christneri, 

Epistomina supracretacea, Gavelinella sp., 

Vaginulina wade~ Marginulina silicula, and 

Bolivinita eleyi. This assemblage could be as 

young as early Campanian, but seismic correlation with the G-2 well (fig. 21) suggests that the 

strata are probably Santonian (fig. 16; see below). 

This is in agreement with palYilomorph and nannofossil evidence (Steinkraus, 1980; Valentine, 

this volume). The lower Santonian indicator 

foraminifer Marginotruncana sinusoa, appears at 

1,150 ft (351 m) along with Archaeoglobigerina 

blowi and Globotruncana lapparenti. 

CONIACIAN (1,390-1,940 FT; 424-951 M) 

At 1,390 ft (424 m) there is a slight increase in 

the number of specimens and an increase in 

species diversity that coincide with a major unconformable seismic reflector and the appearance 

of gypsum and siderite nodules (figs. 16, 18, 21). 

Whiteinella sp. cf. W. aprica makes its first appearance1 here along with the first specimens of 

Epistomina spinulifera colomi, and a few 

redeposited specimens of Rotalipora cushmani 

and Guembelitria harrisi. 

LOWER TURONIAN (1,940--2,320 FT; 591-707 M) 

At 1,941 ft (593 m) the early Turonian species 

Marginotruncana helvetica and Praeglobotruncana stephani first appear in a sidewall core (fig. 

16). This occurrence coincides with a major un1

In this paper, "first appearance" refers to the point at which a species is first 

encountered in examining the well core from top to bottom. Biostratigraphically, 

this is the last appearance of the species. 

conformable seismic reflector (figs. 18, 21). The 

first occurrence of these species in cuttings is 

slightly lower at 1,960 ft (597 m), where th~y are 

accompanied by H edbergella amabilis, V'hiteinella archaeocretacea, and abundant Epistomina 

spinulifera colomi. 

UPPER CENOMANIAN (2,320-2,380 FT; 707-725 M) 

The first non-redeposited Rotalipora cushmani 

occur in abundance at 2,320 ft (707 m), which 

coincides with a major seismic unconformity 

(figs. 16, 18, 21). This species is accompanied by 

abundant Guembelitria harris~· however, G. harrisi is abundant without R. cushmani sF~htly 

higher in the well at 2,260 ft (689 m). 

APTIAN (2,380-2,750 FT; 725-838 M) 

At 2,380 ft (725 m) a change in the foraminiferal 

assemblage accompanied by lignite and red shale 

corresponds to an unconformable seismic reflector that can be correlated with the top of the 

Aptian interval in the G-2 well (figs. 16, 21); 

Albian rocks appear to be missing. The Aptian 

species Lenticulina nodosa and Vaginuli11a aptiensis are present in G-1, as is a large nurr l:ler of 

Epistomina chapmani. The rest of the Aptian 

rocks at G-1 contain only a sparse, poorl:T preserved assemblage of foraminifera and occzsional 

siderite nodules. Steinkraus (1980) reporte:1 Aptian dinoflagellates as deep as 3,671 ft (1,119 m) 

in a sidewall core. 

BARREMIAN (2,750-3,600 FT; 838-1,097 M). 

The unconformable boundaries of the Barremian Stage at the G-1 site are determined from 

an analysis of seismic sequences (Vail and others, 

1977) on reflection profiles 77-1 and 19, Fnd by 

seismic correlation with the G-2 site. The foraminiferal assemblage in this interval is spar~~e and 

appears to be chiefly derived from cavings. Steinkraus (1980) reported Aptian dinoflagellates in 

the lower part of this section. 

HAUTERIVIAN (3,600-4,000 FT; 1,097-1,219 M) 

The unconformable boundaries of the Hauterivian Stage at the G-1 site are inferred fr<''ll the 

analysis of seismic sequences on lines 77-1 and 

49 
COST G-2 

;;; 

500 -~-

l9 

z 1000 

I 

(f) 

::::> 

(l) 

r 

_j 

_j I 500 w 

~ 

~ 

0 

_j 

w 

(l) 2000 

1--

w 

w 

u... 

2500 

3000 

w 

z 

w 

u 

0 

:::::i 

a.. 

SEA LEVEL PALEOENVIRONMENT 

NON IN MID OUT UP LOW I MARIN~ SHELF I SHELF I SHELF I SLOPE I SLOPE I 

SEA FLOOR 1351'1 0 

100 

200 

TOP SAMPLE 

300 

400 

500 

600 

700 

800 

cr: 

0 

0 

_j 

u... 

<1 

w 

(f) 

~ 

0 

_j 

w 

(l) 

(f) 

cr: 

w 

1--

w 

~ 

FIGURE 19.-Stratigraphic column of COST No. G-2 well 

showing chronostratigraphy, biozones, and paleoenvironments. The age terms abbreviated in the left side column 

are spelled out on figure 22. 

19, and by seismic correlation with the G-2 well. 

The foraminiferal assemblages are sparse. The 

only stratigraphically significant species present 

are Planularia crepidularis (first appearance at 

3,640 ft; 1,110 m), which does not occur above the 

Barremian in Scotian shelf wells, and the ostrocod Protocythere triplicata (first appearance at 

3,730 ft; 1,137 m), which is diagnostic of Hauterivian and Barremian rocks in Scotian shelf wells. 

COST G-2 

50 

l9 

z 

3000 

3500 

4000 

CSG4500 

~ 5000 

:::> 

(l) 

r 

_j 

_j 

w 

~ 5500 

~ 

0 

_j 

w 

(l) 

1-- 6000 w 

w 

LL 

6500 

7000 

7500 

8000 

z 

c( 

z 

PALEOENVIRONMENT 

NON IN MID OUT UP LOW I liAR I~ SHELF I SHELF I SHELF I SUl!'E I $LOPE I 

T 

(!) 

z 

a: 

<[ 

w 

CII..J 

o> '"' -a: 

..Jw 

..JI-

~~ 0 

a: 

..J 

<[ 

1_ 

800 

900 

1000 

II 00 

1200 

1300 

1400 

1500 

1600 

1700 

1800 

1900 

2000 

2100 

2200 

2300 

cr: 

0 

0 

_j 

LL 

<1 

w 

(/) 

~ 

0 

_j 

w 

(l) 

(/) 

cr: 

w 

1--

w 

~ 
51 
COST G-2 

18000 

18500 

CSG- ---=-

19000 

-

-

<..9 

z - - z ~ 19500 ~ 

:J (.!) 

CD z 

<t: 

1-

>- 1-

w _J :I: 

...J 

w 

~ 20000 

3: 

0 

_J 

w 

CD 

t- 20500 ,.._ 

z w <t: 

w i= 

w l.J.. <t: 

:I: 

a: 

21000 

21500 

22000 

PALEOENVIRONMENT 

NON IN MIO OUT UP LOW 

I"ARIN[I SH[bf I SH[bfl SHELF I SLOP(I SLOP(I 

5400 

5500 

5600 

5700 

5800 

5900 

6000 

6100 

6200 

6300 

6400 

6500 

21874 TO 

a:: 

0 

0 

_J 

l.J.. 

<1 

w 

(/) 

3: 

0 

_J 

w 

CD 

(/) 

0:: 

w 

tw 

~ 

FIGURE 19.-Stratigraphic column of the COST No. G-2 

well-Continued. 

VALANGINIAN (4,()()()....4,500 FT; 1,219-1,372 m) 

The unconformable boundaries of the V alanginian Stage at the G-1 site are estimated from 

an analysis of seismic sequences on lines 77-1 

and 19, and by seismic correlation with the G-2 

site. Microfossils are rare and not diagnostic. 

52 

BERRIASIAN (4,500-5,380 FT; 1,372-1,640 M) 

The unconformable upper boundary of the Berriasian Stage at the G-1 site is estimated from an 

analysis of seismic sequences on lines 77-1 and 

19, and by seismic correlation with the G-2 site. 

At 5,080 ft (1,548 m) a major faunRl and lithologic 

change takes place. At the top of a thick sandstone unit, the first specimens of coarse-grained 

Everticyclammina virguliana app<:)ar and are accompanied by a small, fragile Haplaphragmoides 

sp., coal fragments, and red shale. Steinkraus 

(1980) reported Berriasian nannof~''ssils in a sidewall core at 5,070 ft (1,545 m). 

JURASSIC ROCKS 

TITHONIAN AND UPPER KIMMER'')GIAN 

(5,380-5,800 FT; 1,640-1,76S M) 

At 5,380 ft (1,640 m) (fig. 16) Er~stomina uhligi 

first appears in low numbers, Eoguttulina aff. E. 

liassica appears in moderate numbers, a few 

specimens of Cytherella index ap..,ear, and Everticyclammina virguliana specim~ns have finer 

grained tests than younger spe~imens of that 

species. These changes are typical of the top of 

the Tithonian in other U.S. and Canadian shelf 

wells, and the Tithonian Age is in agreement with 

the interpretation of palynomonh and nannofossil assemblages (Steinkraus, 1 fQQ). 

LOWER KIMMERIDGIAN (5,800-6,400 FT; 1,768-1,951 M) 

The unconformable upper and lower boundaries 

of the lower part of the Kimmeridgian Stage at 

the G-1 site are estimated from analysis of seismic sequences on lines 77-1 and 19 and seismic 

correlation with the G-2 well. Tl'a. upper boundary lies within an oxidized zone of foraminifera 

and siderite nodules (5,700 to 6,000 ft; 1,737 to 

1,829 m). Steinkraus reported l<'wer Kimmeridgian dinoflagellates in a sidewall core at 6,543 ft 

(1,994 m). 

OXFORDIAN(?) TO AALENIA"J(?) 

(6,400-10,500 FT; 1,951-3,201 M) 

From 6,400 to 10,000 ft (1,951 m to 3,048 m) is 

a thick sequence of coarse, ligritic sandstones 

interbedded with brown to red s:b ales, which con-
tains few calcareous microfossils (fig. 16). Below 

10,000 ft (3,048 m), the carbonate content is much 

greater (fig. 17). Interbedded pelletal limestones, 

gray-green shale, finely crystalline dolomite, and 

fine-grained sandstones and siltstones are found 

down to 10,500 ft (3,201 m), but free tests of 

foraminifera are absent. The unconformable 

boundaries of stages and groups of stages within 

this interval are estimated from analysis of 

seismic sequences on USGS multichannel lines 

77-1 and 19 (figs. 18, 21) as follows: 

Oxfordian(?), 6,400-7,400 ft (1,951-2,256 m; 

Callovian(?), 7,400-8,500 ft (2,256-2,591 m); 

Bathonian(?), 8,500-9,300 ft (2,591-2,835 m); 

Bajocian(?) to Aalenian(?), 9,300-10,500 ft 

(2,835-3,201 m). 

TOARCIAN(?) TO SINEMURIAN(?) 

(10,500---13,600 FT; 3,201-4,145 M) 

The rocks from 10,500 to 13,600 ft (3,201 to 

4,145 m) are chiefly carbonates (gray, microcrystalline to finely crystalline limestones, gray to 

buff, finely crystalline to cryptocrystalline 

dolomite, and anhydrite) with thin interbeds of 

sandstone and shale, occasional coal beds, and 

scattered gypsum nodules (fig. 1 7). No foraminifera were recovered in this interval, but it can be 

divided into two parts through analysis of seismic 

sequences on lines 77-1 and 19, (figs. 16, 18, 21) as 

follows: Toarcian(?) to upper Pliensbachian(?), 

10,500-12,300 ft (3,201-3,749 m), and Lower Pliensbachian(?) to Sinemurian(?), 12,300-13,600 ft 

(3,749-4,145 m). 

HETTANGIAN(?) TO RHAETIAN(?) 

(13,600--15,630 FT; 4,145-4,764 M) 

The age of these sedimentary rocks is 

estimated from analysis of seismic sequences as 

interpreted from USGS lines 77-1 and 19. The 

upper rocks are chiefly sandstones and shales 

with thin intervals of dolomite and anhydrite 

(13,600-14,970 ft; 4,145-4,563 m). Late Triassic 

dinoflagellates have been recovered from the 

lower part of this unit (anonymous oral commun., 

1980). From 14,970 to 15,630 ft (4,563 to 4,764 m) 

is a quartz conglomerate with a matrix of red 

dolomitic shale and interbeds of red shale, sandstone, and dense limestone and dolomite (fig. 17). 

The conglomerate lies unconformably upon a 

53 

metamorphic basement composed of sericitic 

metadolomite and black slate (15,630-16,000 ft; 

4,764-4,877 m), which overlies graphitic phyllite, 

metaquartzite and gneiss (16,000-16,071 ft; 

4,877-4,899 m). Radiometric dates of 450 to 

5.50 m.y. (K/Ar) indicate that the metamorphism 

took place in the Cambrian or Ordovician (Steinkraus, 1980). 

BIOSTRATIGRAPHY AND 

CHRONOSTRATIGRAPHY OF 

THE COST NO. G-2 WELL 

CENOZOIC ROCKS (351-1,324 FT: 107-404 M) 

The first cutting sample in the COST No. G-2 

well was collected at 1,100 ft (335 m) (fig. 19). 

From there to 1,250 ft (381 m) a sparse benthic 

fauna consisting chiefly of Brizalina brady~ 

Globobulimina auriculata, Bu.limina elongata, 

Lentliculina spinosa, L. americana, Cassidulina 

"carinata ': Florilus pizzarensis, and Cibicidoides 

aff. C. floridanus indicates rocks of Pliocene to 

Miocene age. A few radiolarians and reworked 

Cretaceous planktic foraminifers also are present 

in this interval. Seismic sequence analysis and 

results from AMCOR drilling (Hathaway and 

others, 1979) indicate that Pliocene to Miocene 

rocks are present up to 550 ft (168 m) in the section, and are overlain unconformably by 260 ft 

(61 m) of Quaternary rocks (figs. 19, 21, 22). 

Below 1,250 ft (381 m) the number of 

foraminiferal specimens and the diversity of 

species increases dramatically, and there is an 

abundance of large fragments of cheilostome 

bryozoans. Among the many planktic species 

present, Truncorotaloides rohri and Acarinina 

bullbrooki indicate that this rich assemblage is of 

middle Eocene age. These same planktic species 

are present in a sidewall core from 1,289 ft 

(393m), along with Morozovella spinulosa, 

Truncorotaloides topilensis, Eoglobigerina senn~ 

and Globigerinatheka subconglobata. This middle Eocene assemblage continues to 1,324 ft 

(404 m); and additional middle Eocene species, 

such as Acarinina pentacamerata, appear within 

this interval. The presence of a few specimens of 

Globigerina opima opima at 1,289 ft (393 m) suggest that a thin interval of late Oligocene strata 

may lie unconformably above the middle Eocene 

rocks. 
FIGURE 20.-Uninterpreted portion of seismic reflection profile line 19, which traverses the Georges Bank 

basin along dip approximately 15 km (9.3 mi) northeast of the COST No. G-2 well. 

54 
FIGURE 20.-Uninterpreted portion of seismic reflection profile line 19-Continued. 

55 
FIGURE 20.-Uninterpreted portion of seismic reflection profile line 19-Continued. 

56 
FIGURE 20.-Uninterpreted portion of seismic reflection profile line 19-Continued. 

57 
NW 

0 -------------

ifil 

::::l 

z 

0 

:.> 

~2 

w 

~ ~ 

3 _J 

w 

> 

<[ :=4 

>-

~ 

~5 

6 

NW 

6-

COST G-1 

2000 2200 

IOKM 

COST G-1 

2400 

IOMI 

2600 

-- .:.~-~------ .. ,........_.. 

' ' 

FIGURE 21.-Interpretations of structure, chronostratigraphy, and lithostratigraphy of the portion of seismic line 19 shown in 

figure 20. COST well locations are projected northeastward along strike to line 19. Section at G-1 projection is thicker than 

at the actual well site; chronostratigraphic boundaries are adjusted to accomodate this difference. CM, carbonate mound. 

Many of the age terms shown are uncertain. The formation names in this paper are those of similar rocks on the Scotian shelf 

of Canada 

CRETACEOUS ROCKS 

LOWER SANTONIAN (1,324-1,700 FT; 404-518 M) 

The first non-redeposited Cretaceous 

assemblage occurs in cuttings at 1,400 ft (427 m) 

and is characterized by Marginotruncana 

sinuosa, Globotruncana lapparen~ Heterohelix 

striata and Archaeoglobigerina cretacea, an early 

Santonian association. A sidewall core at 1,324 ft 

(404 m) contains a similar association. The 

presence of well preserved Globorotalites 

pseudomenardii in the 1,400-ft (427-m) sample indicates that a thin interval of Paleocene rock is 

present above the Santonian. No evidence of 

Maestrichtian or Campanian strata was observed. Santonian rocks are present down to 

1,700 ft (518 m) and Sigalia ornatissima, 

Globigerinelloides prairiehillensis, H edbergella 

planispira, Archaeoglobigerina blow~ and Mar58 
COST G-2 

2800 3000 3200 3400 3600 

COST G-2 

2800 3400 3600 

l 

A RENTIAN .·.-. ·. 

-~ ~ .. . ---- ---'"<'DAWSON.·· :~NYQN:. -~ . -. - .·"-: .- · : ..,. . - · 

,·,· :··-~: 14ARK~..,..:. ·.:,L ~'.MISSISAL&_A~>·.-2~.~- ;.-..:.- · ·· ·. .. ': . .-.;~- . . ·.· -.· ._ 

.· ~-.-"""-: ~--+--·. · 

.. · - MOHAWK;_t".'- · ~ ""'iLBACCARO LS ~ • . ·MICMAC .1'.; • ~·. -~ -c· ~ MBR..£~ 

IROCUOIS 

MOHICAN 

MISAINE SH MBR ABENAKI 

AND 

IROQUOIS 

• ' •.' ~~· • '

~;,;" vVV'VV ~ 

1 

V V 1/ V V V 1/ V · • ' ' ·. ' Vv VII V 'I 1/ V y V 1/ ~ V V V lj V 11 V V V v V V V ...; V 1/ II V V V y ~ V - 'Y..J ~ ~ y 'I 'f V V V V ~ 'IV • • 0 ••• v " 1/ 1/1/ v v II v v v "/ 1/ ••••• EuRvoicE? 1/~ v v v v v " v " v 'v v v v 1/ v v IJ II v ~" rJ 'J y ~ \( IJ "v 'I 'IJ " ... '4v v ~ V' "v vi~ r v v r v ~" r '. • • • • v 1/ 1/ v v v "¥ v •••• •. v" v '{ • • • v v 1/ v v • • • " 1/ 

• ,:; v vV "vv vv v 

ACOUSTIC 

~ 

BASEMENT 

D<X...OMITE 

~ LIMESTONE ~ HALITE ~ 1:!:1 

ERODED BLOCKS 

8 

LITHOCLASTS 

[J 

SAND 

8 

SANDSTONE 

[] 

SILT 

8 

SILTSTONE 

~ CLAY 

8 

SHALE 

FIGURE 21.-Interpretations of a portion of seismic line 19-Continued. 

ginotruncana renzi are part of the assemblage in 

this interval. Dinoflagellate and nannofossil 

assemblages also indicate that this interval is of 

Santonian Age (Bebout, 1980; Valentine, this 

volume). 

CONIACIAN (1,700-2, 120FT; 518-046 M) 

At 1,700 ft (518 m) the presence of Whiteinella 

archaeocretacea and Marginotruncana schneegansi marks the top of the Coniacian interval. 

Globotruncana sigali appears at 1,760 ft (536 m), 

and Clavihedbergella simplex and Hedbergella 

59 

amabilis appear in abundance at 1,850 ft (564 m). 

Marginotruncana concavata also was observed at 

1,970 ft (600 m), but this occurrence is clearly 

much older than its known range. 

LOWER TURONIAN (2, 120-2,270 FT; 646-692 M) 

At 2,120 ft (646 m) Praeglobotruncana stephani 

and Marginotruncana cf. M. helvetica appear and 

mark the top of the early Turonian zone UC4. In a 

sidewall core P. stephani occurs at 2,186 ft 

(666 m). Lingulogavelinella turonica appears at 

2,180 ft (664 m). 
COST G-2 

2600 2800 3000 3200 3400 

PLIOCENE-MIOCENE 

IAN 

=--- ~· -~-.::~-- -- ---

TTANGIAN-RHAETIAN 

E. I IENSBICHIAN·SINEM~IAN 

I 

COST G-2 

2600 2900 3000 3200 3400 

. ·. : :_: : .. ·:.: ':. 

~ 

ACOUSTIC 

~ 

BASEMENT 

DOLOMITE 

~ LIMESTONE 

~ HALITE 

~ 1:?:1 

EliiOOED BLOCKS 

8 

LITHOCLASTS 

D 

SAND 

8 

SANDSTONE 

LJ 

SILT 

8 

SILTSTONE 

CLAY 

8 

SHALE 

FIGURE 21.-lnterpretations of a portion of seismic line 19-Continued. 

UPPER TO MIDDLE CENOMANIAN 

(2,270-2,330 FT; 692-710 M) 

At 2,270 ft (692 m), the appearance of 

Rotalipora cushmani marks the Cenomanian. 

(Guembelitria harrisi appears 30 ft (9 m) above 

this in the Turonian interval.) Rotalipora cushmani is accompanied at 2,270 ft (692 m) by 

R. greenhomesis, which indicates that the top 

part of zone UC3 is missing or very thin. This 

rotaliporid association is also found in a sidewall 

core at 2,276 ft (694 m). Whiteinella aprica, Epistomina chapman~ and Gavelinopsis cenomanica 

also first appear at 2,270 ft (692 m), as do numerous specimens (presumably redeposited) of Lenticulina nodosa, an Aptian marker (Ascoli, 1976). 

60 
3600 

CROSSES 

LINE 204 at 17080 

3800 4000 

LINE 19 

SE 

4200 4400 ~ 

--------~--------------~--_L ____________ L_ ______________ _L ______________ ~~Uwl 

-?---

3600 3800 4000 

---

4200 

1000 

SE 

4400 Sto 

~~~;::-__j_____l_----...L._~~:/ 

~BENAK I .,-J AND . IROQUOIS 

--?--- -~ ' ' 

1000 

FIGURE 21.-lnterpretations of a portion of seismic line 19-Continued. 

APTIAN (2,330-2,810 FT; 710-SS? M) 

At 2,330 ft (710 m) seismic, faunal, and 

sedimentological data indicate that a major 

unconformity separates the very thin middle to 

upper Cenomanian strata from the Aptian. Here, 

the lithofacies changes, the fauna is somewhat 

diminished and more poorly preserved, and the 

number of rotaliporids decreases, but the number 

of Lenticulina nodosa remains high. At 2,360 ft 

(719 m) the foraminifer Lenticulina aff. L. 

61 

gaultina and the ostracod Hechticythere derooi 

appear. Lenticulina nodosa is an amphiatlantic 

marker for Aptian rocks (Hartenstein, 1974), and 

Lenticulina aff. L. gaultina ranges no higher than 

the Aptian on the Scotian shelf (Ascoli, 1976). At 

2,360 ft (719 m) the sample contains abundant oxidized, calcareous sandstone and lignite. Below 

this depth the species diversity is further reduced. Similar lithologic and faunal changes 

mark the unconformable Cenomanian-Aptian 

contact in the Shell Mohawk B-93 well, the 
~ 

~ 

AGE .... "-'-

"' 

0~~ 

....... 0 LITHOLOGY I RESISTIVITY 

(ohms) LITHOLOGY 

DEPTH 

I ~~~ 

~6'& ~ ... -

l Datum: Kilty Bushin9(KB) r"' IMitn T su LEVEL 79 FEET BEL W~ 0 --

~--;~-;--t:-:-~'I~"fE.!i]ls_ 'frp"OCJ~E;J, __ Nir~--~IL:i~UiRiEENNTfi AAN.t---+ .. :--•• :;-.. rc .•~;-:.',... ;"';:~ .. ----+-------SEA FLOOR 351 FEET BELOW KB 

~ PLIOCENE- MIOCENE ;:. : .:.::< ~ ~ BANQUEREAU ,: ;· :·: ':.'.'. 

f../ PALEOGENE -(•~. 

....,§ f?ANTONIAN 1 .':':':.:,_;c.,;,:.;;l 

5~ CONIACIAN ~ ~ E. TDifbiiJI N "'""\.... 

t--__:::'-':.._-~..;· SM. CENOMA~IAN f 

(J) 

~ 

0 

L.LI 

u 

<( 

tL.LI 

a:: 

u 

~ a:: 

<( 

L.LI 

APTIAN 

BARREMIAN 

HAUTERIVIAN 

VALANGINIAN? 

BERRIASIAN? 

TITHONIANzz 

00 

U>>-

3::Z 

<(<( 

au 

<[ 

<.!> 

::::> 

<[ 

~ 

(/) 

(/) 

'i 

"o" MARKER 

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::;) 

"' fl) 

(ij 

fl) 

:i'j 

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z 

L.LI 

CD 

<( 

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LATE KIMMERIDGIAN 

f---'-1 

u 

u; 

(J) 

<( 

a:: 

~ 

"J 

L.LI 

~ _J 

"-• u wen 

_J(/) 

0<! 

OQ: 

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~"'? 

EARLY 

KIMMERIDGIAN 

OXFORDIAN? 

CALLOVIAN? 

~ :IE 

~ 

:IE 

I 

::..:: 

3': 

<( 

:I: 

0 

:IE 

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:I 

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·~: :~::: ...... ... 

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.: :·.·::.: 

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.. 

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~ . ·:__.;.:_'-'1 ~ 

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m

. 

:_ 

:.::._~ !.......:. 

~ 

:~·~: · 

··.---::· · .. . 

~ 

l ·~.":-'.:,n

"!:L't:!:i 1 

SAND: unconso~doted,coarse ,rounded 1obundonl glouconi It and shells; interbedded SILTSTONE: oroy, soft, 

clayey. 

CLAYSTONE ond SILTSTONE : liQIYt gray ,wry calcareous, 

ranQinQ to LIMESTONE : org~loceous,cholky;glouconilt, 

fassiliftrous;corbonaceous plan! fraomenls, mico, pyrilt. 

LI~JJ?,Wn;o,~:.~~~ f~~?cTI'e"!'J~"r::rit;:~~ed SANDSAND: 't'llry coorse, rounded; SANDSTONE medium to flne,subo~ulor ,oolcite- cemented;inlerbeds of 1\ ~;;~silty MUDSlONE;streoks of COALishtlls;glouco- ( 

MUOSTONE =groy, silty ,glauconitic,in port calcareous; interbeds of SANDSTONE gray,flne to medium, muddy. 

1000 

500 

2000 

3000 

1000 

LIMESTONE b•oclosllc ,portlyoolitic grainstone,pock - t"-4000 slone CJ'Id wackestone rongi~ to argillaceous rricril1 a~d 

Ugh! gray oalcoreous claystone; SHALE = gray fissle . 

SAND: very coarse fO-nwdTum,subrounded to subongulor; 

SANDSTONE: while to tighl groy, fil'll, cemenled with 

colcltt and silica, angulor-subonoular ,moderately to well sorttdi interbeds of COAL, dark brown UGNITE, brown-CJfOY SHALE,Iighl gray MUDSTONE ;pyrite, 

_i_lauconite. 

MUOSTONE:groy sitly,colcoreou5 1 few btdl of SAND - STONE ond LIIIESTONE. 

LIMESTONE : light groy, micrite, chalky ,orgi lloceous, interbedded wtth SHALE 9f'OY,tllty,colcortout, pyritt, 

glauconitic ; fn btdl of SANDSTONE 

I r5000 

f-J 1500 

6000 

2000 

f----------------------~~ 

sfuN:.~~~~~~ ~ohr'-~irro!~J!~;:r,;~o·:n ~~~:t cemented with col cite ; muscovite,biotlte,chlorite; 

SHALE= oroy, in port very colcoreoua and aNty i red- brown to maroon,sitty, micoctous MUDSTONE ; muddy SILTSTONE . 

LIMESTONE : light gray oolite and algol - clast groin- stone to mudstone, sandy; thin strellks of COAL. 

LIMESTONE: brown-gray oolitic and oncolitic vroln -

S~~~S~~~~!~~ir,ttg~~~f fin e ,well-sorttd 

LltiiESTUN£: biOwn-QI'OY m•critt,orgllloceoos; minor oolite-

~!fZ~~!~~;otL'~~~~~dE ~~:J ~~~~ ~~~~~ ;'f::'SJ~g sTONE beds. 

~sE~?':lo:'"~;,'a;e~rc;~ Lr:E~~o~;~:.~~Pii~': to fine SANDSTONE; pyrite . 

8000 

2500 

9000 

~IOOO£oo 

11000 
f; 

"-· 

~· 

~ 

(/) 

(/) 

~ 

a:: 

::::> 

--_, 

LLJ 

...J 

Cl 

Cl 

~ 

~· 

u 

c;; 

(/) 

~ 

a:: 

::::> 

--_, 

~ a:: 

~ 

LLJ 

~ ~· (/) u (/) - ~ (/) 

a:: (/) ::::>0~ 

-_,I-ii: 

>- 1-- ...J LLJ 

~ ~ LLJ ...J 

CALLOVIAN? 

rvvvvvvvvv 

BATHONIAN? 

l"""vv 

BAJOCIAN?-

AALENIAN? 

TOARCIAN?-

L. PLIENSBACHIAN? 

E. PLIENSBACHIAN?-

SINEMURIAN? 

HETTANGIAN?-

RHAETIAN? 

~ 

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z 

w 

(]J 

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LIMESTONE brown-gray,argillaceous m1crite; few beds 

~Y~:l~w g;~;ra~:~~ea:~:,:~~m!J :~ina:~~~~c lures, interbeds of SHALE, CLAYSTONE; pyrite 

TUFF trace between 11,720 feet ond 12POO feet green and gray vesicular devitrified glass1mineral- filled ves1cules rang1ng ;pale green groundmass, fine elongate phenocrysts, dark gre111 clasts. 

SANDSTONE, MUDSTONE and SHALE• red-brown, w1th 

chlorite and red biotite . 

u:~~~~~~ ~~~~~~~:;~~~!;~~~~~~~ ~~'~!;:e~: ~~ indistinct oolitic- peloidal texture ,In port dolomitic, 

ranging to DOLOMITE, gray,brown-gray, in part 

motlled,micro- to fine-crystalline, in part anhydntic, ranging to ANHYDRITE; wh1te, very fineto micro- crystalline,portly sucroslc,light gray, translucent, medium crystalline; some streaks i1f 

gray shale and dolomite; thin laminae of dark brown gray SHALf, thin layers of black asphaltic material. 

3500-

HIDOO 

1-13000 

4000-

H4000 

I r15000 

w 4500 

1-16000 

5000 

17000 

18000 

5500 

~'hJf:'~ 2 ~~~~':T::::r=:-::=~=:-:-:::-::==------LI9000 

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I riDOOO 

r 6ooo 

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) 6500 

~~~~~~~~~~~--r~ooo 

FIGURE 22.-Geologic column of COST No. G-2 well. The formation names in this paper are those of similar 

rocks on the Scotian shelf of Canada. 
closest drill hole on the Scotian shelf. Analysis of 

seismic sequences shows that this unconformity 

is a strong reflector (figs. 20, 21) that displays irregular physiographic relief and terminates 

underlying reflectors, indicating that it is an erosional surface. Single specimens of Ticinella 

roberti, T. breggiensis, and T. primula between 

2,300 and 2,390 ft (701 and 728 m) suggest that a 

thin remnant of Albian strata may have been 

penetrated at this site, but no other firm evidence 

of Albian rocks in the COST No. G-2 well has 

been observed. (See also Bebout, 1980.) 

BARREMIAN (2,810-3,920 FT; 857-1,195 M) 

The next significant faunal change occurs at 

2,810 ft (857 m), where Conorboides bulgaricus 

becomes a persistent part of the sparse foraminiferal assemblage. This form is diagnostic of 

Barremian rocks in the Scotian basin (P. Ascoli, 

written commun., April 1980) and in Europe (Hartenstein and others, 1971). Other benthic foraminifers and ostracods diagnostic of Barremian 

strata in the Scotian basin occur just below this: 

Conorotalites bartensteini at 2,960 ft (902 m); 

Schuleridea sp. 9 of Ascoli (1976) at 2,990 ft 

(911 m); Epistomina ornata at 3,260 ft (994 m); 

Neocythere aff. N. mertensi at 3,260 ft (994 m) 

and Conorboides hofkeri at 3,290 ft (1,003 m). 

Bebout (1980) placed this interval in the Aptian 

Stage on the basis of a single dinoflagellate 

species believed to be restricted to the Aptian. 

HAUTERIVIAN (3,920-4,510 FT; 1,195--1,375 M) 

At 3,920 ft (1,195 m), there is a increase in 

foraminifers and the species Haplaphragmoides 

concavus, Planularia crepidularis, Lenticulina 

saxonica and Lamarckina lamplughi appear, 

which are typical of Hauterivian intervals in the 

Scotian basin (Ascoli, 1976). The Hauterivian 

species Marssonella kumm~ Hechticythere 

hechti, and Hutsonia sp. 3 of Ascoli (1976) are 

found at 4,010 ft (1,222 m); Dolocytheridea sp. 1 

and Macrodentina sp. 1 of Ascoli (1976) at 

4,130 ft (1,259 m); Eoguttulina spp. and the ostracod Rehacythereis senckenbergi group at 4,300 ft 

(1,311 m). The highest occurrence of Choffatella 

decipiens is at 3,950 ft (1,204 m), but I interpret 

this level to be older than its known time of extention. Bebout (1980) used C. decipiens and several 

64 

dinoflagellates to assign most of this interval to 

the Barremian. 

VALANGINIAN(?) (4,510-5,440 FT; 1,375--1,658 M) 

A major lithological and faunz' change occurs 

at 4,510 ft (1,375 m), where th~re is coarse to 

medium sandstone which contain~ an assemblage 

of small, fragile, loosely cementAd specimens of 

Ammobaculites and Haplophrc.gmoides along 

with gypsum crystals. Although this fauna is not 

age-diagnostic, the sedimentoloil'"cal and faunal 

changes appear to coincide with a strong, unconformable seismic reflector near this depth (figs. 

20, 21). The underlying reflectorr that terminate 

against it indicate an erosional s~lrface, which is 

in accordance with the low sea level postulated 

for Valanginian time by Vail ani others (1977). 

Bebout (1980) reported one pre-Hauterivian dinoflagellate species from 4,450 ft (1,356 m). 

BERRIASIAN(?) (5,440-5,920 FT; 1,658-1,804 M) 

At 5,440 ft (1,658 m) there is ar increase in the 

diversity and number of specimens and a change 

from sandstone to mudstone (fiil~~. 19, 22). This 

level is marked by a strong unconformable seismic reflector which terminates underlying reflectors, indicating erosion (figs. 20, 21). These 

events correlate well with the SE''l-level changes 

postulated for the Berriasian by Vail and others 

(1977). The foraminiferal fauna cannot be assigned a Berriasian Age, but Bebout (1980) identified Berriasian spores in his samples of the 

COST No. G-2 well at 5,020(?) to 5,920 ft 

(1 ,530(?) to 1,804 m). Everticyclammina 

virguliana, a distinctive agglutinzt.ed benthic forminifer, first appears at 5,530 ft. (1,686 m), but 

this is older than its known Valanginian range. 

At 5,650 ft (1,722 m) a tubereulate form of 

Epistomina appears, and it is qu~te abundant in 

deeper samples. P. Ascoli (written commun., 

April1980) has noted this same form in the Scotian basin where it ranges from the late Kimmeridgian to the early V alanginia:t. It may prove 

to be useful for approximating the top of the 

Berriasian. 

P. Ascoli has examined thin sec+ions of cutting 

samples from the COST No. G-2 well for of calpionellids. Calpionellids are planktic microfossils 

that occupy a narrow biostratig·raphic zone of 
Valanginian to Tithonian Age in Europe 

(Alleman and others, 1971) and in Canadian offshore wells (Jansa and others, 1980). Jansa (written commun., 1980) reports that they are absent 

above 5,530 ft (1 ,686 m), but appear in low 

numbers down to 5,710 ft (1,740) and are abundant from 5,710 to 5,950 ft (1,740 to 1,808 m; 

fig. 19). 

JURASSIC ROCKS 

TITHONIAN (5,920-6,700 FT; 1,804-2,042 M) 

The first rare Epistomina uhligi appears in cuttings at 5,920 ft (1,804 m) (fig. 19). It occurs in a 

sidewall core at 5,962 ft (1,817 m) and becomes 

more abundant below 6,040 ft (1,841 m). This 

form is a consistent Tithonian marker in the 

Baltimore Canyon trough and the Scotian basin 

(Poag, 1980b; Ascoli, 1976). Rocks in this depth 

interval also were assigned a Tithonian age on the 

basis of nannofossils and palynomorphs (Bebout, 

1980). Epistomina stellicostata, another Tithonian form in the Scotian basin (Ascoli, 1976), 

appears at 6,610 ft (2,015 m). Calpionellids are absent below 6,300 ft (1,920 m). 

UPPER KIMMERIDGIAN (6,700-7,660 FT; 2,042-2,335 M) 

At 6, 700 ft (2,042 m) the fauna is sparse and 

Cytherella index, a species that last appears in 

upper Kimmeridgian strata in the Scotian basin 

(P. Ascoli, oral commun., April 1980) is present. 

At 6,910 ft (2,106 m) in cuttings and at 7,148 ft 

(2,179 m) in a sidewall core, Eoguttulina liassica 

occurs in great abundance at a lithologic change 

from limestone above to dark shale below (fig. 22). 

In abundance this species is typical of Kimmeridgian strata elsewhere (Lloyd, 1962). Other species 

present in the G-2 well that range no higher than 

Kimmeridgian in the Scotian basin are Lenticulina bruckmanni at 6,970 ft (2,125 m) and L. 

varians at 7,060 ft (2,152 m). A strong seismic 

reflector at 6,700 ft (2,040 m) is interpreted as an 

erosional unconformity because underlying 

reflectors terminate against it (figs. 20, 21). 

lOWER KIMMERIDGIAN (7,660-8,660 FT; 2,335--2,640 M) 

Alveosepta jaccard~ which marks the top of the 

lower Kimmeridgian in the Scotian basin, ap65 

pears and is abundant at 7,660 ft (2,335 m) (fig. 

19). Another Kimmeridgian marker found in the 

Scotian basin, Schuleridea triebel~ occurs at 

7,690 ft (2,344 m). The Kimmeridgian specie:-- Cytherelloides weberi occurs at 8,530 ft (2,600 m), 

and Galliaecytheridea sp. 2 of Ascoli (197f\ occurs at 8,610 ft (2,624 m). 

OXFORDIAN(?) (8,660-10, 100 FT; 2,640-3,079 M) 

The large numbers of Alveosepta jaccardi that 

occur at 8,660 ft (2,640 m) are typical of C ;·fordian assemblages of the Scotian basin (P. Ascoli, 

written commun., April, 1980; fig. 19). This 

faunal increase coincides with a strong u:tconformable reflector on seismic profiles 19 anrl 209 

(figs. 20, 21). Oxidized sediments are also associated with the upper boundary. 

CAllOVIAN(?) TO UPPER PliENSBACHIAN(?) 

(10,100-16,900 FT: 3,079-5,151 M) 

The boundaries of the stages in this interval are 

estimated from the presence of prominent, unconformable reflectors on seismic lines 77-2, 1!', and 

209. The tentative stage determinationf and 

depth intervals are as follows: 

Callovian(?), 10,100-12,100 ft (3,079-3,6rq m); 

Bathonian(?), 12,100-14,100 ft (3,688-

4,298 m); 

Bajocian(?) and Aalenian(?), 14,100-15,000 ft 

(4,298-4,572 m); 

Toarcian(?) and upper Pliensbachian(?), 

15,000-16,900 ft (4,572-5,151 m). 

lOWER PliENSBACHIAN(?) AND SINEMURIAN(?) 

(16,900-18,800 FT; 5,151-5,730 M) 

The boundary between the upper and lower 

parts of the Pliensbachian(?) Stage and the lower 

boundary of the Sinemurian(?) Stage arE: estimated from an analysis of seismic sequences on 

lines 77-2, 19, and 209, where they appnar as 

prominent unconformable reflectors (figs. 2~1, 21). 

A calcareous quartzose sandstone is asso~iated 

with the lower Sinemurian(?) boundary (fig. 19). 

Bebout (1980) tentatively assigned this interval 

to the Middle Jurassic on the basis of a few 

palynomorphs. 
HETIANGIAN(?) AND RHAETIAN(?) 

(18,800--21,874 ft; 5,730-6,667 M) 

The upper boundary of the Hettangian(?) Stage 

is estimated from seismic sequence analysis of 

lines 77-2, 19, and 209 to be the prominent reflector at 18,800 ft (5,730 m) at the G-2 site (figs. 19, 

20, 21, 22). The halite-bearing strata at 21,874 ft 

(6,667 m) appear to be of Rhaetian Age (Late 

Triassic), on the basis of seismic sequence analysis, correlation with the Rhaetian section in the 

COST No. G-1 well, and the presence of Triassic 

dinoflagellates in rocks overlying it (Anonymous, 

oral commun., 1980). If this interpretation is correct, this evaporitic section is equivalent to the 

Argo Formation of the Scotian basin (Eliuk, 

1978; Barss and others, 1979). Seismic lines 77-2 

and 209 indicate that basement lies 1,000 ft 

(305 m) below the bottom of the COST No. G-2 

well. A prominent unconformable reflector just 

below the bottom of the well on line 209 may 

mark the Rhaetian-Norian boundary, and if so, 

the oldest rocks above basement at this site are 

probably of Norian (Late Triassic) age. However, 

Bebout (1980) identified no fossils definitely older 

than Middle Jurassic. 

SEDIMENT ACCUMULATION RATES 

Knowing the detailed chronostratigraphy of 

the COST Nos. G-1 and G-2 wells allows the 

calculation of sediment accumulation rates at 

these sites. These rates can be extrapolated to 

other parts of the Georges Bank basin using 

seismic data 

Figure 23 shows the rates of sediment accumulation the G-1 and G-2 sites and compares them 

with rates at the three other Atlantic COST wells. 

During the Jurassic and Early Cretaceous the 

rates at G-2 exceeded those at G-1, but this pattern was reversed during the Late Cretaceous, 

and rates were nearly equal during the Cenozoic. 

The general trend from high to low rates with 

decreasing age can be seen in all the wells, but 

there are some exceptions, such as the high middle Miocene rates in the COST No. B-3 well 

(Poag, 1980b). The accumulation rates calculated 

for the Callovian and older rocks in the COST 

Nos. G-1 and G-2 wells are minimum rates, 

because there is no way to estimate from the 

seismic stratigraphy how much time each uncon66 

formity represents. The stage thi ~knesses determined from seismic stratigraphy rave been divided by the duration of the stage, a~ given by Vail 

and Mitchum (1979). 

During deposition of the olde<-~t rocks penetrated (Hettangian?-Rhaetian?), the accumulation rates at G-1 and G-2 were 6.8 cm/kyr 

(2.7 in/kyr) (kyr=1,000 years) ani (10.0 cm/kyr) 

(4 in!kyr) respectively. The rater decreased at 

each location in the early Pliensbachian(?)-

Sinemurian(?) and remained near~y the same or 

decreased slightly through the Toarcian(?). In the 

Bajocian(?)-Aalenian(?) the rates c_ropped to half 

or less than half of what they were in the 

Toarcian(?): at G-1 the rate was 3.5 cm/kyr 

(1.4 in/kyr), and at G-2 the rate ~·as 2.7 cm/kyr 

(1.1 in/kyr). These lower rates cortinued at G-1 

through the Bathonian(?), but not at G-2. In the 

Callovian(?) at G-1 and in the P athonian(?) at 

G-2, the rates resumed approximately their preBajocian(?)-Aalenian(?) values. Maximum rates in 

both wells occurred during the Kinmeridgian. At 

G-1 the rate was 8.9 cm/kyr (L6 in/kyr) and 

at G-2 the early Kimmeridgian rate was 

15.0 cm/kyr (6 in/kyr). The rate dropped to 

7.5 cm/kyr (3 in/kyr) in the late Kimmeridgian to 

Tithonian at G-2, but fell even mo:-:-e dramatically 

at G-1 to 2.2 cm/kyr (0.9 in/kyr). FJ~om the Berriasian to the Barremian the rates vru.;ed from 2.2 to 

4.5 cm/kyr (0.9 to 1.8 in!kyr) at G-1 and from 2.0 

to 6.0 cm/kyr (0.8 to 2.4 in/kyr) at G-2. A significant drop occurred at each well sit£ in the Aptian: 

at G-1 the rate was 1.5 cm/kyr (0.6 in/kyr), and at 

G-2 the rate was 2.1 cm/kyr (0.8 in/kyr). During 

the Cenomanian to Santonian interval, rates 

ranged from 2.8 to 6.0 cm/kyr (1.1 t-o 2.4 in/kyr) at 

G-1, but only from 2.0 to 3.0 c.m/kyr (0.8 to 

1.2 in/kyr) at G-2. 

Cenozoic rates ranged from 0.6 to 3.3 cm/kyr 

(0.2 to 1.3 in/kyr) at G-1 and from 0.5 to 

3.8 cm/kyr (0.2 to 1.5 in/kyr) at G-2. The highest 

Cenozoic rates prevailed during the Pleistocene. 

CORRELATION WITH SCOTIAN B'SIN WELLS 

The offshore Canadian well neare::.t the Georges 

Bank wells is the Shell Mohawk B-93, drilled 195 

statute miles (310 km) northeast of the COST No. 

G-2 well on a small basement l:igh (Mohawk 

ridge) on the southwestern margin (western shelf) 

of the broad Lahave platform (fig. J5). Because of 
~ 

·.r-:: ! ,'\UL 

(M.Y.l 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

105 

110 

115 

120 

125 

130 

135 

140 

145 

150 

155 

160 

165 

170 

175 

180 

185 

190 

195 

200 

205 

ii\i fERVAL DEPTH JELO';J SEA f"LOOi1 1:~ 

UJ 

z 

u 

g 

:_:;; 

6UJ 

248 

\.0 LATE 

<.::! z I . ~~ EARLY 2 s··. 

~3 \2.2 

\ 

LATE 

: \'···~:~ ~2 4 \2.0 06: 0.5 ···· .... 1.0 \ 1.4 

--------l I • 3 9 \ EARLY 28'··... ',,3.3 

uJ 

~ u 

8 

MIDDLE 

8 ~ ___ L_A_T_E __ ~ 3.3· ... 

-'UJ 

~ u EARLY 

Ul 

:::J 

8 

u 

<( 

~ a: 

u 

UJ 

fMAESTRICHTIAN 

CAMPANIAN 

SANTONIAN 

CONIACIAN 

TURONIAN 

--~3.0 

3.5'~ 

\13 

2.6~\· .. 1.8 \ 1.4 ·. \ 

··... \19 

46 · .. ?0 ' 6.s· ... .... ... .7_5 

5.5-...:.:~ 9 _1S,)5 

:s CENOMANIAN 

\~20 

4.9'\ 

17 \16 Ul 

:::J 

8 

u 

<( 

~ a: 

u 

>-

-' 

a: 

~ 

ALBIAN 

APTIAN 

BARREMIAN 

HAUTERIVIAN 

VALANGINIAN 

BERRIASIAN 

,_A TITHONIAN 

::=~u KIMMERIDGIAN 

S~Ul OXFORDIAN 

u CALLOVIAN 

UJ(j)~-----~ _j(j'J 

BATHONIAN 0<( 

Da: 

~ ~I BAJOCIAN 

u ~~A~A~L~E~N~IA~N-~ 

>- Ui TOARCIAN AND 

ii! ';}, L PLIENSBACHIAN 

~a: E PLIENSBACHIAN 

~ AND SINEMURIAN 

HETTANGIAN 

~ '=! I RHAETIAN I a: VJ NORIAN f33"''·~4 

29 ~5.5 

45 ---~ 22'\ 

21 

30' ...... , 45' ... , 

2 2'', 

89',,, 

53'', 

35 

...... 

\ 

' ,28 

', 2 5 

' IIJ,.oJec~ '\ 2 I ~o,.,, '\ 

70 

5 ,-- ......... , 

2 7'',,' ... , 

3 5 --... ,, 

... _ 

COST GE-l -- - -- - COST B- 2 

COST B-3 ---------- COST G-1 

COST G-2 

_186 

6 8 --... 

56---, __ 

68 

FIGURE 23.-Sediment accumulation rate curves for the COST Nos. G-1 and G-2 wells compared with those for the COST Nos. GE-l, B-2 

~~rl B-3 '.'.'ells. '!alues ~~e ze~th~et:e~s ?e~ th~us~~rl ye~~s. a~?S b zu~es q~e hiatuses, rlet:ezt:erl by fau~:ll 'l~rllithi::: 'l~alyses. Unconformities inferred entirely from the seismic profiles are not shown because the magnitudes of time gaps are not known. As a result, the accumulation rates in the Triassic, Jurassic, and earliest Cretaceous are minimum rates. The formation names in this paper are those of 

similar rocks on the Scotian shelf of Canada. 
its high structural position, the Mohawk B-93 

well reached granitic basement at 6,930 ft 

(2,112 m) and penetrated sedimentary rocks as 

old as Bathonian (Barss and others, 1979). The 

nearest well in the Scotian basin (Mohican subbasin) is the Shell Mohican 1-100 (313 mi 

(504 km) NE. of COST No. G-2; fig. 15). This well 

is more like the COST G wells (especially G-2) in 

structural setting than the Mohawk B-93, and 

reached salt at 14,322 ft (4,365 m) after penetrating rocks of Early Jurassic age (early 

Sinemurian?-late Hettangian?) (fig. 24; Barrs and 

others, 1979). Both Canadian wells are located 18 

mi (29 km) landward of the Upper Jurassic shelfedge bank, a paleogeographic position similar to 

that of the COST No. G-2 well (Eliuk, 1978). The 

sequence of rocks, paleoenvironments, and faunal 

assemblages in the COST G wells is similar to 

that of the Canadian wells and allows correlation 

of the Scotian shelf formations (Mciver, 1972; 

Given, 1977) with the rocks beneath Georges 

Bank (figs. 17, 21, 22, 24). 

In general, the updip Jurassic formations of the 

Scotian basin and the LaHave platform are chiefly nonmarine sandstones and shales; these grade 

diachronously downdip into the marine shales, 

mudstones, limestones, dolomites, and evaporites 

found in wells nearer the basin. The lateral relationships among these formations are extremely 

complex (Given, 1977, Eliuk, 1978) and the lithostratigraphic terminology presently employed is 

not entirely satisfactory, but it simplifies the 

discussion of the depositional facies involved. 

ARGO FORMATION 

The name Argo Formation has been given to 

salt deposits at or near the base of the Jurassic 

section beneath the Scotian shelf (Mciver, 1972). 

At least 2,500 ft (762 m) of relatively pure, white, 

coarsely crystalline halite with a few shale and 

anhydrite interbeds have been penetrated, and 

seismic evidence indicates that several thousand 

feet of salt occupies the Orpheus, Abenaki, and 

Sable basins. At the Mohican 1-100 well, 92 ft 

(28m) of Argo Formation was penetrated directly 

under rocks of Sinemurian to Hettangian Age 

(Barss and others, 1979). In the COST No. G-2 

well, the 41 ft (12m) of halite and anhydrite that 

lies below rocks of inferred Hettangian to Rhaetian Age (figs. 21, 24) is thought to represent the 

Argo Formation. 

68 

IROQUOIS FORMATIOt• 

Overlying the Argo Formation in the Scotian 

basin is a sequence of dominant} y brown, anhydritic dolomite, red to brown shale interbeds, and 

some limestones in the upper part. Given (1977) 

reported that two types of dolomite have been 

recognized in the Iroquois Fonr'ition: a microcrystalline dolomitic (commonly anhydritic) 

mudstone indicating shallow, rertricted marine, 

often supratidal, deposition; anc1 a dolomitized 

oolitic and pelletal grainstone that represents 

higher energy marine deposition. 

In the Mohican 1-100 well, 1,9")0 ft (579 m) of 

dolomitic Iroquois Formation mas penetrated 

(fig. 24). It ranges in age from E'ijocian to Hettangian (Barss and others, 1979', In the COST 

No. G-2 well an 8,200-ft (2,49f m) section of 

dolomite, limestone, and anhydrite equivalent to 

the Iroquois constitutes the lower Bathonian(?) to 

Rhaetian(?) interval immediately above inferred 

Argo Formation (figs. 21, 24). This section is 

more than four times thicker than that penetrated in the Scotian basin. This sequence in the 

COST No. G-2 well is also sandy near its base as 

in the Mohican 1-100 well. 

MOHICAN FORMATIOI' 

The carbonate regime of the &.otian shelf was 

interrupted in the early Middle J nrassic by deposition of the widespread silicic:lastic Mohican 

Formation. Given (1977) described the Mohican 

as chiefly sandstones, generally immature texturally, poorly sorted, dolomitic, sil .. y, argillaceous, 

kaolinitic, and locally interbedded with varicolored shale. Given (1977) further suggested 

that the Mohican sands may rer~esent the first 

depositional phase of onlapping sands after the 

breakup of North America and Puro-Africa, but 

in the Georges Bank basin availal:lle seismic data 

suggest the continental breakup occurred earlier. 

In the Mohican 1-100 well 55 f:. (17m) of argillaceous sandstone and shale constitutes the type 

section of the Mohican Formatior. It is chiefly of 

Bathonian Age, but the base is upper Bajocian 

(Barss and others, 1979). In the COST No. G-2 

well, a 30-ft (9-m) interval of squdstone, mudstone, and shale separates the lr'lquois from the 

Abenaki Formation and is of early Bathonian(?) 

age; these terrigenous rocks ar~ presumed to 
NE SCOTIAN BASIN GEORGES BANK 

CENOMANIAN 

BATHONIA 

BASIN 

COST G-2 313 Mi; 500 Km,-------...,==.--. 

'\.SEA FLOOR 

.q "" 

~----------~M~I~S~A-IN-E---M-B_R ____________ ~~ 

:------------------~~~ 

f:72l DOLOMITE 

[ITI LIMESTONE 

-ANHYDRITE 

-HALITE 

0 SAND and SANDSTONE 

~ SHALE and CLAYSTONE 

b~~1 CALCAREOUS SHALE 

TO 21,87411 

l'lllEO• 

CENE 

CENOM T0 

1000 

2000 

3000 

4000 

5000 

6000 

7000 

8000 

9000 

10000 ..... 

.... 

~ 

11000 ~ 

:J: 

..... 

CL 

.... 

0 

12000 

13000 

14000 

15000 

16000 

17000 

18000 

19000 

20000 

21000 

22000 

sw 

0 

500 

1000 

1500 

2000 

2500 

3000!Q .... 

t;J 

:::E 

~ 

:J: 

..... 

3500 ~ 0 

4000 

4500 

5000 

5500 

6000 

6500 

FIGURE 24.-Lithologic correlations between the Shell Mohican 1-100 and COST No. G-2 wells. The 

formation names given are those that have been applied to similar rocks on the Scotian sheH of 

Canada The age terms abbreviated in the left and right side columns are spelled out on figure 22. 

69 
represent the equivalent of the Mohican Formation (figs. 21, 24). 

At the G-1 site, the lower 6,000 ft (1,829 m) of 

sedimentary rocks appears to be a repetitious interfingering of Iroquois dolomite and limestone 

with sandstone, shale, and siltstone of the 

Mohican Formation (figs. 17, 24). The age of the 

interval is Bajocian(?) to Rhaetian(?). The lower 

third is quartz conglomerates, fine to mediumgrained sandstones, and red-brown shale; the 

middle third is dolomite and anhydrite; the upper 

third is limestone and sandstone; a thick Mohican 

sandstone tongue constitutes the top of the 

sequence. 

ABENAKI FORMATION 

On the Scotian shelf the Mohican Formation is 

overlain by dominantly oolitic, reef-bearing 

limestones of the Abenaki Formation. The lowest 

or Scatarie Limestone Member of the Abenaki is 

oolitic lime packstone to grainstone; it accumulated in warm, agitated, shallow marine 

waters. The Scatarie reaches a maximum thickness of 600ft (183 m) in the Mohican I-100 well 

and is of Bathonian and Callovian Age. In the 

COST No. G-2 well, a 2,000-ft (610-m) section of 

argillaceous micrite and oolitic grainstone and 

packstone of Bathonian(?) and Callovian(?) age 

constitutes the Scatarie Limestone Member 

equivalent (figs. 21, 24). 

The middle member is the Misaine Shale Member, a dark-olive-gray to gray-brown, somewhat 

calcareous, sparsely fossiliferous shale, which has 

a maximum thickness of 560 ft (171 m) on the 

Scotian shelf. In the Mohican I-100 well, the Misaine Shale Member is 330ft (101 m) thick and is 

late Callovian in age. In the COST No. G-2 well, 

the Misaine Shale Member equivalent is 4 7 5 ft 

(145m) thick and is of middle Callovian(?) age. 

The thickest member of the Abenaki Formation 

on the Scotian shelf is the Baccaro Limestone 

Member. The limestone comprises pelletal, oolitic 

fossiliferous, and ''reefal'' facies, and the member 

includes shale, sandstone, and dolomite. All the 

dolomites analyzed have been diagenetically 

altered limestones (Eliuk, 1978). The Baccaro is 

as much as 3,680 ft (1,122 m) thick and was 

deposited during Middle and Late Jurassic and 

Early Cretaceous time. 

In the Mohican I-100 well the Baccaro 

Limestone Member is a 2, 700-ft (823-m) -thick 

70 

limestone (micritic to oolitic and oncolitic) with 

sandstone, claystone, and shale interbeds of late 

Callovian(?) and early Oxfordian ag~ (figs. 21, 24). 

The upper part of 1,360 ft (396 m) c f micritic limestone of Tithonian or late Kimmer~1gian to early 

Berriasian age. 

MOHAWK AND MICMAC FORMATIONS 

Updip equivalents of the Baccaro Limestone 

Member of the Abenaki Formation are the sandy 

Mohawk Formation and the shaley MicMac Formation. The sandstones of the Mohawk are 

distinguished from the Mohican sandstones by 

their more mature texture, bette:-:- sorting, and 

locally calcareous nature. 

The Mic Mac shales are medium to dark brown 

to olive gray and have fine-grained sandstone and 

limestone interbeds. These finer lithologies are 

not developed at the Mohican I -100 or Mohawk 

B-93 locations (Eliuk, 1978). At the COST No. 

G-2 well, a 2,500-ft (762-m) sequence of coaly 

sandstone, shale, and limestone intertongues 

with the Baccaro equivalent and ar"lears to represent both Mohawk and MicMac lithologies (figs. 

21, 24). The age of the sequence i~ Oxfordian to 

late Kimmeridgian or Tithonian. Updip in the 

G-1 well, the Abenaki carbonates rre not present, 

but the equivalent of the Mohawk and MicMac 

Formations is a 3,900-ft (1,189-nl) sequence of 

coarse- to very coarse-grained coaly sandstones, 

and red, yellow, gray, brown, and variegated 

shales (figs. 17, 21). The age range of this unit is 

Bajocian(?) to Tithonian. 

MISSISAUGA AND VERRILL CANYON FORMATIONS 

Above the Abenaki and its upcip equivalents 

on the Scotian shelf are the sandy Missisauga 

Formation and its downdip shalely equivalent, 

the Verrill Canyon Formation. Massive sandstones (maximum thickness 3,8(]0 ft; 1,158 m) 

grade downdip to thinner sand units. A persistent calcareous seismic marker nrlll' the base of 

the Barremian, named the "0" ma"':'ker, is present 

over most of the Scotian shelf about 1,000 ft 

(305m) below the top of the Missisauga. It consists of about 150ft (46 m) of thin limestone beds 

and calcareous shales that contair a characteristic foraminiferal fauna dominated by Choffatella 

decipiens. Downdip, the Missisauga interfingers 
with medium-gray to brown carbonaceous shale 

of the Verrill Canyon Formation, whose maximum thickness is around 1,200 ft (366 m). The 

Missisauga and Verrill Canyon Formations range 

in age from Tithonian to Barremian. The "0" 

marker persists near the base of the Barremian 

Stage. 

In the Mohican I-100 well, the Missisauga and 

Verrill Canyon Formations overlap, constituting 

a 500-ft (152-m) unit of shale, sandy shale, and 

sandstone of Hauterivan to Barremian Age (fig. 

24). The "0" marker is not developed there. 

At the COST No. G-2 site, massive, lignitic, 

coarse-grained sandstones and mudstones assignable to the Missisauga Formation are 1,100 ft 

(335 m) thick; their age is Berriasian to Hauterivian. These are overlain by a 550-ft (168-m) section 

of calcareous claystones and gray fissile shales, 

topped by a 225-ft (69-m) interval of bioclastic 

limestone and calcareous shale. These upper carbonates are of late Hauterivian age and contain 

the characteristic Choftatella descipiens fauna of 

the "0" marker. 

Updip at G-1, four massive, coaly, medium- to 

very coarse-grained sandstone units and two 

thick, gray shale units (total 3,200 ft (97 5 m) 

thick) constitute the Missisauga Formation 

equivalent of late Kimmeridgian or Tithonian to 

early Aptian age; figs. 17, 21). A thin argillaceous 

dolomite at the top of the Hauterivian Stage 

(1,000 ft (305m) below top of Missisauga) may be 

the equivalent of the "0" marker, but Choftatella 

decipiens was not observed in the sparse faunas 

of this well. 

Commonly overlying the Missisauga Formation on the Scotian shelf is the Naskapi Formation, 500 to 600 ft (152 to 183 m) thick, which is 

gray and olive-gray to dusky-red, fissile, carbonaceous shale of early Aptian age. In the Mohican 

I-100, the Naskapi Formation is 500 ft (152 m) 

thick and represents late Barremian through 

early Aptian deposition. The middle part is sandy 

and calcareous. In the COST Nos. G-1 and G-2 

wells, the Naskapi Formation is not recognized. 

LOGAN CANYON AND DAWSON CANYON FORMATIONS 

rated into two parts by an olive-green midc!le unit 

(Sable shale) 200 to 300ft (61 to 91 m) thic~. The 

Dawson Canyon Formation is the shalier downdip unit consisting of 900 ft (27 4 m) or n1ore of 

calcareous, marly to glauconitic shale, bec0ming 

siltier at the base. The Logan Canyon is lrt.e Aptian to late Cenomanian in age, wherem; the 

Dawson Canyon Formation can be as young as 

late Maestrichtian. The thin Petrel Lim~stone 

Member is a widespread marker in the Turonian 

part of the Dawson Canyon. The Logan Canyon 

Formation underlies the Dawson Canyon Pormation in the Mohican I-100 well; the two formations have a total thickness of 1,700 ft (f18 m). 

and represent the late Aptian and Cenmnanian 

(fig. 24). 

At the COST No. G-2 well the mudston~s and 

sandstones equivalent to the Logan Canyon Formation also underlie the claystone and sil .. stone 

of the Dawson Canyon equivalent, and tl'·~ two 

are separated by a 200-ft (61-m) thick shelly 

limestone of Aptian Age that may represe"lt the 

Petrel Limestone Member, although it is older 

here than on the Canadian shelf (figs. 21, 2~). The 

Logan Canyon equivalent is 1,200 ft (3,~~ m) 

thick, and is of Barremian through early Aptian 

age; the Dawson Canyon equivalent is 1,000 ft 

(305 m) thick and represents the late Aptian to 

Santonian interval. At the COST No. G-1 well, 

1,450 ft (442 m) of unconsolidated, mr~sive, 

coarse-grained, glaucontic, lignitic sandstor~ and 

gravel, and gray, glaucontic shale beds rep~esent 

both the Logan Canyon and Dawson Canyo"l Formations and are Cenomanian to Santonian in age 

(figs. 17, 21). 

BANQUEREAU FORMATION 

The Tertiary strata of the Scotian shelf have 

not yet been subdivided into formationr~ the 

varied siliciclastic sandstones, mudstones, 

shales, siltstones, and claystones are lumped 

together into the Banquereau Formation. In the 

Mohican I-100 well, the Banquereau Fonrl=ltion 

is 7 50 ft (229 m) thick and includes middle 

Miocene, upper Miocene, and Pliocene siltstones. 

In contrast to the siliciclastic Tertiary str."'ta of 

On the Scotian shelf these lateral equivalents the Scotian shelf, the Tertiary of the Georges 

overlie the N askapi and Missisauga Formations. Bank basin contains carbonates of Paleocene, 

The Logan Canyon Formation is the sandier Eocene, and possibly Oligocene age, which s"tauld 

updip unit, consisting of 3,000 ft (914 m) of alter- eventually be designated as a separate forrr.$J.tion 

nating sandstone, mudstone, and shale, sepa- or formations from the terrigenous Miocen~ and 

71 
Pliocene strata. Therefore, Banquereau is not a 

satisfactory term to use for the Paleogene units 

of Georges Bank. White bioclastic limestone 

mostly of Eocene age similar to that found further offshore is present throughout the Coastal 

Plain province of North America and crops out as 

the Ocala, Cooper, Castle Hayne, and other formations. One of these Coastal Plain names could 

probably be appropriately applied to the offshore 

Eocene strata, including those of the Georges 

Bank basin. 

LAURENTIAN FORMATION 

The Laurentian Formation of the Scotian shelf 

consists of Quaternary glacial drift and stratified 

proglacial sediments ranging in thickness from 

100 ft (30 m) to 4,000 ft (1,220 m) (Jansa and 

Wade, 1975a). The rocks are even thicker near the 

shelf edge. The Mohican 1-100 well penetrated 

more than 4,200 ft (1,280 m) of Laurentian sands, 

silts, and clays that represent several glacial 

cycles (fig. 24; G. L. Williams, written commun., 

1974). The thickness of the Laurentian Formation 

is variable on the upper continental slope as a 

result of submarine slumping and erosion, but 

Jansa and Wade (1975a) estimated a maximum 

thickness of more than 6,000 ft (> 1,800 m) on the 

lower slope and rise. 

The Laurentian Formation equivalent appears 

to be no more than 200 ft (61 m) thick in the 

COST Nos. G-1 and G-2 wells and consists of 

glacially derived sands (figs. 17, 22). It thickens 

toward the shelf edge, reaching 800 ft (244 m) on 

line 19 (fig. 21). (See also Lewis and Sylvester, 

1977; Hathaway and others, 1979.) It may be 

somewhat thicker on the lower slope and rise, 

where it constitutes a chaotic olisthostrome. (See 

Comparison with Deep-Sea Sedimentary Sequences, this chapter). 

LITHOLOGIC FACIES AND PALEOENVIRONMENTS 

AT THE 

COST G WELL SITES AND ALONG SEISMIC LINE 19 

The analyses of lithologic facies and paleoenvironments of the COST Nos. G-1 and G-2 wells 

and vicinity are based on foraminiferal and lithologic interpretations of well samples and on 

seismic facies analysis of nearby seismic lines 

72 

(Vail and others, 1977). The discus~ion herein proceeds from oldest to youngest ro~ks. Line 19 is 

the closest long profile to which b<'t,h the G-1 and 

G-2 wells can be projected along strike (figs. 15, 

20, 21). This line is augmented b;T dip line 77-1 

(fig. 18), which nearly crosses th~ G-1 site, and 

strike line 204 (collected by the Bundesanstalt fiir 

Geowissenschaften und RohstoffP.; BG R), which 

crosses line 19 near the shelf edgn (fig. 25). BGR 

line 209 crosses the G-2 well site but is not 

discussed here because the G-1 well cannot be 

projected to it along strike (fig. 1ff~. However, my 

analysis of line 209 and that of Klitgord and 

others (this volume) confirm the f(~atures inferred 

from line 19. 

HmANGIAN(?) AND RHAETIAN~?) ROCKS 

Hettangian(?) or Rhaetian(?) rocks lie on a 

block-faulted basement which is believed to be 

Paleozoic metasedimentary strata. Thick accumulations of Triassic arkosic sandstones and 

marine interbeds (indicated by thn dinoflagellates 

in the G wells) fill the basement wabens (figs. 18, 

21). At G-1 the basal1,600 ft (48r m) of sedimentary rocks are sandstones, shales, and conglomerates. Pink, red, and red-brown cohrs (fig. 17) suggest oxidizing, high-energy environments in an 

alluvial or fluvial depositional r,.~gime. Thin interbeds of anhydrite and dolomit~ indicate occasional flooding by shallow marin£. waters. 

Seismic lines 77-1 (fig. 18) and 19 (figs. 20, 21) 

show that the coarse siliciclastic part of the Hettangian(?)-Rhaetian(?) sequence fqls a basement 

low that extends southeastward from the G-1 

well site. The discontinuous, subparallel, slightly 

chaotic reflectors in these updip siliciclastics are 

characteristic of accumulation un 1er rapidly fluctuating environments in a higl' ~nergy regime 

(Vail and others, 1977). Downdip the beds onlap 

and interfinger . with a sequence of somewhat 

chaotic reflectors near shotpoint 2300 that are interpreted to come from an elongate carbonate 

mound, which overlies a basement high. This high 

may be the southern end of the Yarmouth arch 

(see Klitgord and others, this vol 'lme). Two more 

small carbonate mounds occur b~tween s.p. 2400 

and 2600. 

The uppermost 300 ft (91 m) of Hettangian(?)-

Rhaetian(?) rocks in the G-1 weJl comprises redbrown shale with dolomite and anhydrite inclusions, some thin interbeds of dolomite, and a few 
0 10M I 

0 IOKM LINE 204 

crosses crosses crosses 

LINE I 0 1620 

t 

LINE 209 (() 1306 LINE 19 0 3845 

SW I 6600 16680 11Jso NE Sea 

0 I I 

16760 

I 

I 6~40 ! 16~20 17000 

I 

~Sea Floor 

I Level 

CONIAClAN " PLEISTOCENE .J'OL IGOCENE -PALEOCENE 

-

r- ~ 

- - CAMBRIAN ? BASEMENT - - ~ I 

N 5 -

-

6 -

FIGURE 25.-Structural and chronostratigraphic interpretation of seismic reflection profile line 204 (collected l'v the 

Bundesanstalt flir Geowissenschaften und Rohstoffe, Hanover, West Germany), which traverses the outer part of the 

Georges Bank basin along strike. 

beds of well cemented sandstone (fig. 17). The 

seismic profiles show few reflectors in this interval, indicating either lithologic homogeneity or 

bedding too thin to detect with the seismic frequencies used (figs. 18, 20, 21). Nearshore marine 

to nonmarine paleoenvironments are inferred for 

this interval. The reflection-free interval extends 

from the updip end of line 19 to approximately 

s.p. 2200. At this position a series of highamplitude reflectors appear and lap onto the carbonate mound. 

Downdip from s.p. 2200, a series of continuous, 

parallel, high-amplitude reflectors extend to 

about s.p. 2760. These continuous reflectors are 

typical of uniform, low-energy environments, and 

their high amplitudes, interpreted along with 

rocks recovered from the well, suggest discrete 

strata within carbonate rock sequences (Vail and 

others, 1977). The continuity of these reflectors is 

interrupted at s.p. 2480 and 2580 by the more 

chaotic high-amplitude reflectors of the carbonate mounds. Farther downdip the continuous 

73 

reflectors become intermittent and orJaiJ both 

flanks of a large carbonate mound just updip 

from the projected G-2 well site (figs. 20, 21). 

This carbonate mound (or perhaps another) is also 

visible at a similar paleogeographic position 

on line 209, but is much smaller there. Th~ G-2 

well penetrated mostly carbonates in the H ettangian(?)-Rhaetian(?) interval (fig. 22). A 3,000-ft 

(914-m) sequence of light- and dark-broWIT-gray, 

micritic and oolitic, pelloidallimestone, gray and 

brown-gray, fine to crystalline dolomite, b~ded 

anhydrite, and interbeds of fine- to very finegrained sandstone and dark-brown-gray, calcareous, silty shale overlies 40 ft (12 m) of halite. 

(Acoustic basement appears to be about 1,500 ft 

(457 m) below the top of the halite.) PresuiJ~ably, 

the salt accumulated in restricted shallow n1arine 

waters in an arid climate. The overlying rocks 

probably accumulated chiefly in quiet, nem·~hore 

marine waters and in supratidal sabkhas, ~'It intervals of higher energy marine conditions are indicated by the oolitic strata 
On line 19, downdip from the G-2 projection, 

high-amplitude, intermittent, subparallel carbonate reflectors persist to about s.p. 3340, but 

are interrupted by three zones of more chaotic, 

arched reflectors interpreted here as carbonate 

mounds (figs. 20, 21). Between s.p. 3340 and s.p. 

3680 the reflectors regain some of their updip continuity and parallelism, suggesting quieter, more 

uniform deposition than that near the mounds. 

The somewhat chaotic bedding of another large 

mound is present, however, between s.p. 3680 and 

3750. Downdip from this mound the reflectors 

become indistinct as the strata intersect the 

shelf-edge reefal bank. 

LOWER PLIENSBACHIAN(?) AND SINEMURIAN(?) ROCKS 

At G-1, the early Pliensbachian(?) and 

Sinemurian(?) are represented by 1,200 ft (366 m) 

of light-gray to buff, crypotocrystalline to pelletal 

dolomite with interbeds of anhydrite, thin beds of 

red-brown shale, fine- to very fine-grained sandstone, and gypsum nodules (fig. 17). The seismic 

character on line 77-1, which crosses near the 

G-1 well site, shows nearly reflector-free intervals above and below a single, high-amplitude, 

continuous reflector that occupies the middle of 

the sequence (fig. 18). At the G-1 projection on 

line 19, a zone of faint subparallel reflectors 

crosses the well site and extends updip to the end 

of the profile (figs. 20, 21). These characteristics 

suggest rather uniform shallow marine paleoenvironments much like those of the Hettangian(?)-

Rhaetian(?) interval. 

On line 19, at about s.p. 2120, the parallel 

reflectors become more continuous and their 

amplitude increases as the section thins and 

drapes over the underlying carbonate mound 

(figs. 20, 21). These reflector characteristics suggest more strongly defined bedding and less 

uniform, shallow-water carbonate environments 

than observed updip. Downdip from the carbonate mound, the lower Pliensbachian(?) and 

Sinemurian(?) rocks thicken somewhat, reaching 

a maximum thickness of 0.2 seconds (two-way 

traveltime) in a small trough near s.p. 2520. In 

this interval, the low-amplitude, discontinuous 

reflectors suggest more uniform depositional conditions. From near s.p. 2520 to the G-2 projection 

the lower Pliensbachian(?)-Sinemurian(?) interval 

is nearly reflector-free, suggesting lithologic 

homogeneity or very thin bedding. 

74 

At the G-2 well site the lower Pliensbachian(?) 

and Sinemurian(?) section is tan to brown-gray to 

dark-brown-gray micritic limestone with oolitic 

and pelloidal interbeds, gray to light-gray to 

brown-gray, fine-grained to 1nicrocrystalline 

dolomite and white, very fine-grained to microcrystalline anhydrite (fig. 22). All these characteristics suggest shallow nearsho-:-e marine and 

sabkha-like environments (fig. J 9). Alternating 

zones of low- to high-amplitu~e, continuous 

reflectors (shallow-water carbonates) extend 

downdip from the G-2 projection and onlap the 

arched reflectors of a low carbonate mound between s.p. 3620 and s.p. 3720 (figs. 20, 21). 

Downdip from this mound, the lower Plei.nsbachian(?)-Sinemurian(?) rocks appear to thicken 

considerably as the reflectors lo~~ definition in 

the shelf-edge reefal bank. 

BAJOCIAN(?) TO UPPER PLIENSBAC~~AN(?) ROCKS 

In the G-1 well, the B~iocian(?)-upper 

Pliensbachian(?) rocks are a 4,00f .. ft (1,219-m) sequence of generally thin-bedd~d, alternating 

units of limestone, sandstone, ~"ld shale, with 

some dolomite near the base (fig. 22). The evaporitic rocks common in the underl~ring section are 

not present. The limestones include microcrystalline to medium crystalline, pelletal, and micritic 

textures; sandstones are medimn to very fine 

grained; shales are red-brown, gr?y-green, green, 

and gray. Thin coal beds are sc~ttered throughout the sequence. 

On profile 77-1 the Bajocian(~)-upper Pliensbachian(?) interval displays co,tinuous highamplitude reflectors in the lower two-thirds, but 

the reflectors are discontinuous and of lower 

amplitude in the upper one-third (fig. 18). At the 

G-1 projection on line 19, similar reflector 

characteristics with lower amplitudes mark the 

Bajocian(?)-upper Pliensbachian(!1 section (figs. 

20, 21). These lithologic and seismic characteristics suggest high-energy regimer in fluctuating 

shallow marine and nonmarine coastal environments (fig. 16). The seismic characteristics and 

thickness of the interval are conr~ant on line 19 

from the updip limit to s.p. 274('. At this point 

the unit begins to thin markedly and the reflectors became intermittent, more widely separated 

vertically, and of higher amolitude. These 

changes persist downdip to the G-2 projection. 

In the G-2 well, the 2,800-ft (853 m) section of 
Bajocian(?)-upper Pliensbachian(?) rocks is a continuation of the thick sequence of shallow marine 

limestones, dolomites, and anhydrites that make 

up the underlying lower Pliensbachian(?) and 

Sinemurian(?) rocks. This unit continues downdip 

from the G-2 projection with approximately the 

same thickness and seismic characteristics to 

near s.p. 3040, where it lies unconformably above 

Hettangian(?)-Rhaetian(?) rocks. Where the Bajocian(?)-upper Pliensbachian(?) rocks resume contact with the lower Pleinsbachian(?)-Sinemurian(?) rocks (near s.p. 3180), their seismic 

character changes to include wide nonreflective 

intervals between high-amplitude, moderately 

continuous reflectors, and the unit thins even 

more. The section becomes even thinner where 

the Bajocian(?)-upper Pleinsbachian(?) rocks 

onlap the carbonate mound near s.p. 3600. The 

unit thickens again downdip from the carbonate 

mound, becoming indistinguishable in the shelfedge reefal bank. Rocks as old as Pliensbachian 

may be present in the basal sedimentary sequences on the oceanic side of the reefal bank. 

(See Comparison with Deep Sea Sedimentary Sequences, this chapter.) 

BATHONIAN(?) ROCKS 

At the G-1 well site Bathonian(?) rocks are 

very coarse-grained, unconsolidated sandstones 

with thick interbeds of red-brown and gray shale 

and scattered coal seams and pyrite (fig. 22). The 

seismic reflectors on lines 77-1 and 19 are discontinuous, subparallel, and of moderate to low 

amplitude (figs. 20, 21). These characteristics are 

typical of nonmarine fluvial and shallow-marine 

environments (fig. 16). These discontinuous 

reflectors extend downdip to near s.p. 2230 where 

the lower reflectors become more continuous and 

increase in amplitude, which is indicative of carbonate facies. Near s.p. 2460 the seismic characteristics of carbonates appear throughout the 

entire Bathonian(?) section. They persist to the 

G-2 well, which penetrated brown- gray micritic 

limestones, a few oolitic beds, and layers of 

anhydrite. Interbeds consist of shale, claystone, 

and sandstone; traces of tuff occur between 

11,720 and 12,000 ft (3,572 to 3,658 m). AlterBathonian(?) unit is half its thickness uprlip at 

s.p. 2230; the amplitude and continuity of reflectors increase, suggesting perhaps the absence of 

the nonmarine facies at the downdip site. The 

Bathonian(?) rocks drape over the carb '>nate 

mound near s.p. 3680 and can be traced as indistinct reflectors to about s.p. 3940 where they 

abut the shelf-edge reefal bank. Bathonian rocks 

may be present on the oceanic side of the reefal 

bank. 

CALLOVIAN(?) ROCKS 

At the G-1 well site the Callovian(?) rockf comprise 1,200 ft (366 m) of very coarse-grainei, unconsolidated, slightly arkosic sandstones, some 

pea gravel, and red, yellow, gray, brown, and 

variegated shales with a few coal and pyritic beds 

(fig. 17). The seismic reflectors on lines 77-1 and 

19 are discontinuous, parallel, and of vatiable 

amplitude (figs. 20, 21). These characterrstics 

sugest deposition in fluctuating nonirmne 

fluvial and shallow-marine coastal environ1nents 

(fig. 16). Near s.p. 2480 on line 19 the refl('~tors 

become more continuous and increase in p_mplitude, suggesting more uniform marine cond~tions 

and carbonate deposition. The high-amplitude, 

continuous reflectors extend downdip and cross 

the G-2 projection. 

At G-2 the inferred Callovian unit comprises 

2,000 ft (610 m) of chiefly brown-gray, ooliti~. oncolitic, bioclastic limestones with interbeds of 

well-sorted, fine-grained sandstones, and gray to 

red silty and partly calcareous shales (fig. 22). 

The reflections nearly disappear downdip at s.p. 

3400, which suggests very thin bedding or more 

homogeneous lithology. The continuous, highamplitude reflectors reappear near s.p. 3680 

where they drape over the buried carbnnate 

mound. The reflectors are indistinguishable 

downdip from s.p. 3940 as they enter the shelfedge reefal bank. A series of intermittent highamplitude reflectors above basement on the 

oceanic side of the shelf-edge reefal bank may 

include Callovian rocks. 

OXFORDIAN(?) ROCKS 

nating shallow-marine and nonmarine environ- At the G-1 well site the Oxfordian(?) rocks 

ments are inferred for most of the time interval comprise 900 ft (27 4 m) of alternating coarfl~- to 

represented by this section (fig. 19). very coarse-grained, loosely consolidated, lipritic 

Downdip, near s.p. 3280, the thickness of the and pyritic sandstone and red, yellow, gray, 

75 
brown, silty, micaceous shale (fig. 1 7). The intermittent, variable-amplitude seismic reflectors on 

lines 77-1 and 19 (figs. 20, 21) are typical of nonmarine fluvial and shallow-marine coastal 

deposits (fig. 16). The sparse benthic assemblages 

of this section appear to be entirely cavings and 

the lack of indigenous fauna could indicate nonmarine deposition or diagenetic destruction of the 

original assemblages. Steinkraus (1980) reports 

dinoflagellates in a core at 6,543 ft (1,994 m), indicating that some marine beds are present in the 

upper part of the Oxfordian section. 

Downdip between s.p. 2500 and 2700 are bursts 

of discontinuous, parallel, very high amplitude 

reflectors, which indicate high-energy nonmarine 

deposition. Between s.p. 2700 and the G-2 projection the loss of internal reflectors suggests either 

uniform lithology or very thin bedding. The G-2 

well encountered 1,400 ft (427 m) of alternating 

sandstone, shale, mudstone, and limestone (fig. 

22). The sandstone is white, gray, and red, fine to 

medium grained, poorly to well sorted, coaly, and 

micaceous; the shales and mudstones are gray, 

dark gray, red brown, and maroon; limestones, 

which are concentrated in the lower part of the 

section, are tan to light gray, oolitic, and oncolitic. These characteristics indicate fluctuating, 

mostly nonmarine fluvial environments for the 

upper parts of the unit and chiefly shallow-marine 

conditions for the lower part (fig. 19). The 

foraminiferal assemblages are typical of shallow 

marine Tethyan faunas of western Europe and 

the Scotian basin. Agglutinated species predominate, chiefly Alveosepta jaccard~ accompanied 

by Everticyclammina virguliana, Epistomina 

spp., and Trocholina spp. High-spired microgastropods, ostracods, fish teeth, and charophytes 

are also present. 

Just downdip from the G-2 projection, the 

greater continuiuty and higher amplitude of the 

reflectors suggests a change to widespread 

shallow-water carbonate deposition (figs. 20, 21). 

The Oxfordian rocks drape over the buried carbonate mound at s.p. 3680 and become indistinguishable downdip in the shelf-edge reefal bank. 

A series of intermittent high-amplitude reflectors 

above basement on the oceanic side of the reefal 

bank may include Oxfordian rocks. 

LOWER KIMMERIDGIAN ROCKS 

The lower Kimmeridgian rocks at G-1 are 

chiefly sandstones and shales similar to the 

underlying Oxfordian rocks, e:r.cept for some 

oolitic limestones in the upper p~tt of the interval. Siderite nodules are scattered throughout the 

section (fig. 17). The faunas co:"lsist mainly of 

sparse, poorly preserved, and often oxidized 

foraminifers and ostracods. Everticyclammina 

virguliana is the predominant foraminifer, accompanied by a few lenticulinids. &~ smic reflectors 

on lines 77-1 and 19 are discontinuous, parallel, 

and of variable amplitude (figs. 21, 21). All these 

characteristics indicate depositio:"l in alternating 

nonmarine fluvial and shallow marine coastal environments, perhaps including some "middle 

shelf" deposits (fig. 16). 

On line 19, the intermittent sEC;smic reflectors 

persist downdip to the G-2 projection. The G-2 

well penetrated sandstones and shales (comparable to the Oxfordian(?) sandstonP-s and shales) in 

the lower part of the lower Kimm~tidgian section 

(fig. 22). Gray oolitic limestones are present near 

the middle and at the top of the P~ction. 

The foraminiferal assemblagE:~ at G-2 are 

somewhat more abundant and more diverse than 

at G-1. Tethyan shallow-marir~ agglutinated 

forms still predominate, chiefly Everticyclammina virguliana and various sp~ies of Haplaphragmoides and Ammobaculites. Among the 

calcareous forms Eoguttulina is prominent. 

Ostracods and high-spired microgastropods are 

sparse. Oolites, lignite, and oxidized shale and 

sandstone fragments are common in the washed 

rotary cuttings. 

These characteristics suggest greater marine 

influence at G-2 than at G-1 (fi.fit. 19). The continuity and amplitude of seismic reflectors increase downdip from the G-2 projection, with the 

exception of a nearly reflector-fr·ee interval between s.p. 3100 and 3560 (figs. 20, 21). The highamplitude reflectors are especially prominent 

downdip from s.p. 3680 but becorr~ indistinguishable in the shelf-edge reefal bank. A series of intermittent high-amplitude reflectors on the 

oceanic side of the reefal bank mr-y include lower 

Kimmeridgian rocks. 

UPPER KIMMERIDGIAN TO BERRIASIAN ROCKS 

In the G-1 well, the 1,300-ft (396-m) upper 

Kimmeridgian-Berriasian interval is divided into 

two sandstone sections separated by interbedded 

shale and dolomite (fig. 17). The sandstones are 

chiefly medium to very coarse grained, lignitic, 

76 
micaceous, and pebbly; the shale and dolomite are 

light gray. In the shales and lower sandstones 

foraminifers are common and ostracods and highspired microgastropods are present. Dominant 

foraminifers are Everticyclammina virguliana, 

small, fragile Haplaphragmoides, Eoguttulina 

sp., Trocholina sp., Epistomina spp. and Lenticulina spp. The seismic reflectors at the G-1 projection on lines 77-1 and 19 are parallel and of 

variable continuity and amplitude (figs. 23, 24). A 

single high-amplitude reflector appears to represent the dolomitic zone. 

All these characteristics suggest deposition in 

fluctuating nonmarine fluvial to shallow marine 

inner-shelf environments (figs. 16). The intermittent variable-amplitude reflectors and the dolomite reflector can be traced downdip on line 19 to 

near s.p. 2520, where the strata just above the inferred dolomite begin to display closely spaced, 

continuous, parallel, high-amplitude reflectors 

(figs. 20, 21). This pattern suggests a basinward 

change to more carbonate-rich facies. The inferred carbonate interval thickens toward the basin 

from s.p. 2520 until it makes up the entire Berriasian to upper Kimmeridgian interval at the G-2 

projection. The G-2 well encountered a 1,300-ft 

(417-m) interval of light-gray to tan, micritic to 

chalky limestone bounded above by 200ft (61 m) 

of mudstone and below by 600 ft (183 m) of sandstone (fig. 22). 

to the shelf-edge reefal bank near s.p. 395(" but 

the thin Berriasian unit can be traced no fzrther 

than s.p. 3930. 

Reefal rocks of Berriasian and Neoc(J'fllian 

(Hauterivian to Barremian) Age have beer collected from Heezen Canyon, northeast of line 19 

(fig. 15; Ryan and others, 1978). The Berriasian 

limestone sample was identified on the ba."is of 

pelagic calpionellids, and it also containei remains of the pelagic crinoid Saccocoma, abur1ant 

corals, hydrozoa, calcareous algae, and large 

foraminifers. This unit is interpreted to have 

accumulated in an ocean-facing reef envirom'1ent. 

Neocomian samples contained rudistids, echinoids, bivalves, bryozoans, ostracods, be,thic 

foraminifera, and calcareous algae, but lacked the 

corals and other colonial organisms. These aCJsociations probably accumulated in non-reefal parts 

of the carbonate platform. Equivalent faci~s on 

line 19 would be expected between s.p. 400f and 

4100 (figs. 20, 21). 

A series of high-amplitude, discontinuous 

reflectors on the seaward side of the shelf-edge 

reefal bank may include upper Kimmeridgian to 

Berriasian carbonate rocks of hemipelagic and 

pelagic origin. 

VALANGINIAN ROCKS 

Rich, diversified foraminiferal assemblages oc- In the G-1 well, Valanginian rocks consi ~t of 

cur throughout this section. Everticyclammina very coarse-grained pebbly sandstones, inter"'>eds 

virguliana, Choffatella decipiens, Lenticulina of gray shale, and coal and lignite at the basE: (fig. 

spp., and Epistomina spp. predominate, accom- 17). These sandstones may be a continuation of 

panied by Trocholina, Conorboides, Ophthal- the sandstones of the underlying BerriasiaiJ secmidium, and Eoguttulina. Ostracods and high- tion. The Valanginian microfossils are sparse and 

spired microgastropods also are abundant in may be entirely cavings. 

some intervals. The presence of common to abun- On seismic line 77-1 the reflectors in the 

dant calpionellids in the upper, more calcareous Valanginian interval are intermittent and of low 

part of this unit suggests moderately deep, open amplitude. At the G-1 projection on line 19, a 

marine conditions (300 ft; 100 m) (fig. 19). Inter- single ilttermittent reflector with var..stble 

vals containing well-developed assemblages alter- amplitude occupies the middle of an othe1"'1Tise 

nate with more sparsely populated intervals in reflector-free Valanginian section (figs. 20, 21). 

which leached specimens, lignite, gypsum, and These characteristics indicate dominantly nonoxidized clays all suggest shoaling and perhaps marine fluvial deposits that accumulated under 

subaerial exposure. uniform conditions (fig. 16). The same sei~mic 

Downdip from the G-2 projection (figs. 20, 21) characteristics extend downdip on line 19 to the 

the vertical spacing of reflectors is variable, few G-2 projection (figs. 23, 24). The G-2 well als'l enreflectors are continuous, and many have high countered a thick sandstone unit of V alangjnian 

amplitudes and are parallel. These characteristics Age. The sandstone is very coarse to fine grF;ned 

suggest continued carbonate deposition in a vari- and white to gray and has interbeds of coal, 

able shallow-marine environment. Upper Kim- lignite, dark-gray shale, light-gray mudst.one, 

"lleridgian and Tithonian reflectors can be traced pyrite, and glauconite (fig. 22). 

n 
A sparse to moderately well developed microfauna is scattered throughout the Valanginian 

rocks at G-2. The large shallow-marine Tethyan 

agglutinated foraminifer Choffatella decipiens is 

prominent, as are large Ammobaculites sp., small 

fragile Ammobaculites sp., and Trochammina sp. 

In the lower 350 ft (107 m) of the Valanginian section, calcareous microfossils are more abundant 

and include Epistomina spp., Lenticuluina spp., 

Planularia sp., and Conorboides sp. These 

lithologic, seismic, and faunal characteristics are 

typical of deposits that accumulated in fluctuating nonmarine fluvial and shallow-marine 

coastal environments (fig. 19). 

Downdip from the G-2 projection the Valanginian section nearly doubles in thickness, reaching a maximum near s.p. 3860. As the section 

thickens, more reflectors are present, but they are 

intermittent and of variable amplitude (figs. 20, 

21). Near s.p. 3860, a delta-like wedge of intermittent, variable-amplitude, sigmoid clinoform 

reflectors fills a faulted depression landward of 

the shelf-edge reefal bank. Oceanward of the 

reefal bank, Valanginian rocks may be present as 

a thin, rather reflector-free unit lying above the 

high-amplitude Berriasian(?) to Callovian(?) 

reflectors. 

HAUTERIVIAN ROCKS 

At G-1 the upper part of the 400-ft (122-m) 

Hauterivian section is a thin argillaceous dolomite. A thin, unconsolidated, very coarse-grained 

sandstone separates the dolomite from a thick, 

reflectors cross the G-2 projectif)n site. The G-2 

well penetrated 600ft (183m) of bioclastic, partly 

oolitic limestone, argillaceous rricrite, light-gray 

calcareous claystone, and gray, fissile, silty shale 

in the Hauterivian interval (fig. 22). 

A moderately rich foraminiferal assemblage is 

present in the G-2 Hauterivian r0eks. Choffatella 

decipiens is prominent, along with Lenticulina 

spp., Planularia sp., Marssonelj'a sp., and occasional floods of Eoguttulina sp., and Trocholina 

sp. High-spired microgastropods, ostracods, echinoid spines, free ooids, and C'~casional charophytes also are typical. These ~~ements suggest 

that here Hauterivian rocks accumulated in 

shallow marine to coastal nor.marine environments (fig. 19). 

Downdip from the G-2 projection the seismic 

reflectors are widely separated, intermittent, and 

of variable amplitude, sugge;;-ting continued 

shallow-marine and coastal nor.marine environments. Hauterivian rocks appec ... to be severely 

eroded near s.p. 3860, but the section thickens 

again in the structural low behind the shelf-edge 

reefal bank. This unit is the f~Tst that can be 

traced with some confidence across the top of the 

reefal bank. The crossing reflectors are discontinuous, have variable amplitudes, and appear to 

pinch out or to be truncated near s.p. 4100. 

Hauterivian rocks are inferred to reappear near 

s.p. 4140 on the seaward flank of the shelf-edge 

reefal bank. 

BARREMIAN ROCKS 

gray shale unit that contains a coal bed near the At G-1 the Barremian rocks a ... e 825ft (251m) 

top. The microfossil assemblages in the Hauteriv- of unconsolidated, coarse- to ve1~' coarse-grained 

ian rocks are sparse and are probably all cavings partly calcareous sandstones with interbeds of 

from overlying fossiliferous beds. On seismic line red and gray sticky shale, lignite, and pyrite (fig. 

77-1 the Hauterivian interval contains character- 17). The microfauna are sparse and are probably 

istic discontinuous reflectors of variable cavings from overlying fossilife~ous beds. Howamplitude. On seismic line 19 at the G-1 projec- ever, a sidewall core from 3,274 ft (998 m) contion, a single, central, nearly continuous reflector tained TrociJ,ammina sp. and Lenticulina spp., 

of variable amplitude characterizes the Hauteri- and a few of the lenticulinids and epistominids in 

vian interval; the reflector can be traced downdip the cuttings may be indigenouf', On lines 77-1 

to near s.p. 2580 (figs. 20, 21). These characteris- and 19 the Barremian interval contains parallel, 

tics indicate early deposition in chiefly nonmarine discontinuous, variable-amplitude reflectors at 

fluvial environments followed by a shallow the G-1 location and its project~~n (figs. 20, 21). 

marine incursion in the late Hauterivian (fig. 16). These characteristics suggest deposition in nonOn line 19 from s.p. 2580 to near s.p. 2880 the marine fluvial and shallow-marine environments 

central Hauterivian reflector becomes more inter- with variable energy regimes (fi~. 16). 

mittent than at updip positions. At s.p. 2880 a On seismic line 19, the Barremian reflectors 

second low-amplitude reflector appears and both maintain constant characteristicr downdip to the 

78 
G-2 projection, although the unit thickens. At 

G-2, the top one-quarter of the 1,100-ft (335-m) 

section is very coarse, rounded sand and mediumto fine-grained, subangular, calcareous sandstone 

with interbeds of gray silty mudstone and some 

coal and glauconite (fig. 22). The lower threequarters are gray, silty, glauconitic, partly 

calcareous mudstone with interbeds of mediumto fine-grained sandstone. 

Microfossils at G-2 are not abundant in the 

Barremian interval. The fauna consists of the 

foraminifers Epistomina spp., Lenticulina spp., 

Gavelinopsis sp., Trochammina sp., and highspired microgastropods and ostracods. These 

characteristics indicate greater marine influence 

than at G-1, but nearshore marine environments 

may have been replaced occasionally at G-2 by 

nonmarine fluvial environments (fig. 19). 

On line 1 downdip from the G""-2 projection, the 

~eismic characteristics of the Barremian section 

·~hange very little (figs. 23, 24). Between s.p. 3620 

.:md 3940, a series of low- to high-angle, sigmoid 

·~linoform reflectors indicate progradation of fine-

·?,I"ained hemipelagic deposits as low-energy turbi-

·iites. This unit thins in front of and across the 

,."uried shelf-edge reefal bank and pinches out or is 

·~runcated near s.p. 4080. A slope-front fill facies 

·1f Barremian Age appears to lie above the infer-

·~~d Hauterivian and Valanginian units seaward 

·1f the shelf-edge reefal bank. 

APTIAN ROCKS 

the Aptian than during deposition of older rocks 

at this site. 

Near s.p. 2380 (line 19) the reflectors are more 

continuous and parallel, suggesting lower er~rgy 

regimes and more uniform environmental C'lnditions; these persist to the G-2 projectior .. At 

G-2, the upper part of the 475-ft (145-m) Aptian 

sequence comprises coarse, shelly limestones interbedded with fine- to medium-grained, ca ~itecemented quartz sandstones. Sandstone is more 

abundant in the lower part of the section. 

Microfossils are rare in the sandy lower pr~ of 

the Aptian sequence, but in the calcareous upper 

part, abundant Epistomina chapmani and Lenticulina nodos~ plus a few Lenticulina sp., 

Vaginulina procer~ Gavelinella sp. and ostracods 

appear to be indigenous. 

All these characteristics suggest that the I 'lwer 

part of the Aptian section at G-2 is of nonmarine 

fluvial origin, but the upper part accumulared in 

shallow marine shelf environments (fig. 19). 

Downdip from the G-2 projection, intermittent, parallel, variable-amplitude reflectors extend to near s.p. 3700. The distal portion o~ the 

Aptian section is completely truncated by aiJ erosional unconformity and can be traced no fru-ther 

than s.p. 3850. Aptian rocks appear to be part of 

a slightly chaotic, slope-front fill sequence that 

onlaps the seaward side of the shelf-edge r,.)~fal 

bank. 

CENOMANIAN ROCKS 

Erosion during the mid-Cenomanian low seaIn the G-1 well the Aptian rocks are 400 ft level stand has eliminated most or all of the 

(122m) thick and are similar in lithology to the Albian rocks from both G wells, and the seismic 

underlying Barremian sandstones and mudstones interpretations of lines 19 and 209 suggest that 

(fig. 18). Fossils are rare or absent except in the Albian rocks are missing over most of the 

upper samples where there are abundant Epis- Georges Bank basin (figs. 20, 21). At G-1, A:r~ian 

tomina chapmani. Lenticulina nodosa and rocks are overlain by a thin, glauconitic, gray 

Vaginulina aptiensis are also probably indig- shale and claystone unit of Cenomanian Age (fig. 

enous. There are also abundant specimens from 19). The microfauna at G-1 is moderately rich 

cavings of the overlying, richly fossiliferous and diverse and contains an abundance of plankCenomanian and Turonian strata. tic foraminifers. The predominant benthic ge"lera 

On seismic lines 77-1 and 19, the G-1location are Lingulogavelinell~ Vaginulin~ Bolivinit~ 

and its projection are characterized by intermit- Lenticulin~ Gavelinopsis, and Epistomina. The 

tent, parallel to subparallel, variable-amplitude Cenomanian interval is so thin (7 5 ft; 23 m) that 

reflectors indicative of nonmarine fluvial to it cannot be distinguished on seismic line 77-1, 

shallow marine deposits (figs. 16, 20, 21). The but on line 19, it appears as a narrow refle~torfauna at the top of the section indicates a shallow free zone at the G-1 projection. Downdip the 

'llarine origin. The subparallel reflectors may in- Cenomanian interval thins and thickens over the 

iicate somewhat higher energy regimes during eroded Aptian surface (fig. 24). All these seismic, 

79 
lithologic and faunal characteristics suggest that 

deposition took place in a moderately deep middle 

to outer shelf marine environment under a lowenergy regime (fig. 16). 

At the G-2 projection on line 19, the Cenomanian interval is still thin (60 ft; 18 m) and 

reflector-free. The claystones here contain a very 

rich and diverse microfauna, including abundant 

planktic foraminifers. The predominant benthic 

genera are Epistomina, Gavelinopsis, Lingulogavelinella, Lenticulina, Vaginulina, Bolivinita, 

Praebulimina, and Frondicularia. Pyritized microgastropods are also common. The faunal, lithologic, and seismic characteristics suggest that 

deposition took place in an outer shelf marine environment under a low-energy regime (fig. 19). 

The seismic character and thickness change little 

downdip from the G-2 projection. The Cenomanian section may be entirely truncated by erosion 

near s.p. 3800, or it me.y be too thin to identify on 

line 19. A prominent slope-front fill sequence, 

which onlaps the seaward edge of the shelf-edge 

reefal bank, appears to include Cenomanian 

rocks. 

LOWER TURONIAN ROCKS 

At G-1, the lower Turonian rocks are 350 ft 

(107 m) of gray, sticky, glauconitic shales 

bounded by coarse-grained sand and gravel with 

lignite at the top and base (fig. 1 7). Pyrite is 

common throughout the section. On seismic line 

77-1, the entire interval contains parallel, intermittent, variable-amplitude reflectors. The lower 

Turonian interval is very thin on line 19 and 

shows up as a reflectorless zone bounded by 

strong unconformable reflectors (figs. 20, 21). The 

microfauna at the COST No. G-1 well is abundant and diverse and includes abundant planktic 

foraminifers in most samples. The predominant 

benthic genera are Epistomina, Lingulogavelinella, Gavelinella, Lenticulina, and Marssonella. 

High-spired microgastropods are common. 

These faunal, lithologic, and seismic characteristics suggest that most lower Turonian deposition occurred in low energy middle shelf marine 

environments (fig. 16). Shallower marine conditions and perhaps nonmarine fluvial conditions 

prevailed during the two sandy intervals. 

Seismic characteristics on line 19 do not change 

downdip to the G-2 projection (figs. 20, 21). At 

G-2 the lower Turonian rocks are 150ft (46 m) of 

80 

calcareous, glauconitic claystone (fig. 22). The 

abundant, diverse microfauna contains abundant 

planktic foraminifers. Predominant benthic 

genera include Epistomina, Gav 'Jlinella, Lingulogavelinella, Lenticulina, Neof'1.bellina, Gaudryina, Bolivinita, and Praebulimina. These characteristics suggest that depositior took place in a 

low-energy regime on an open ma;ne outer shelf 

(fig. 19). On line 19 the lower Tur'lnian rocks are 

uniform in thickness and seismic character from 

the G-2 projection downdip to an apparent pinchout or erosional truncation near f"P· 37 40. Turonian rocks may be included in a sequence of 

horizontal basin-fill reflectors that onlap the inferred early Cenomanian to Aptian sequence on 

the seaward side of the shelf-edge reefal bank. 

CONIACIAN ROCKS 

At the COST G-1 well the lower part of the 

550-ft (168-m) section of Coniacian rocks consists 

of unconsolidated coarse-grained sandstone and 

gravel overlain by a thin shale unit (fig. 1 7). On 

seismic line 77-1, the Coniacian r1~flectors at G-1 

are intermittent, subparallel, a"ld of variable 

amplitude. At the G-1 projection on line 19, the 

reflectors are discontinuous, of low amplitude, 

and parallel (figs. 20, 21). A single, more continuous, higher amplitude reflector can be seen 

near the top of the interval. The microfauna in the 

sandy lower part of the Coniacian interval is 

sparse. Benthic forms include a f~w Epistomina, 

Ceratobulimina, and Neobulimina. A slightly 

richer fauna occurs in the shale a+ the top of the 

section, including a moderate assemblage of 

planktic foraminifera. Predorrinant benthic 

forms are Epistomina, Vaginulina, and 

Gavelinella. 

These faunal, lithologic, and sersmic characteristics suggest that deposition at G-1 during the 

early part of the Coniacian occurrf'd in nonmarine 

fluvial to shallow marine coastal Ptvironments in 

a relatively high-energy regime (fig. 16). Water 

depth increased and the energy level dropped during deposition of the shale layer. 

Downdip from the G-1 projec+-ion on line 19 

high-amplitude reflectors several miles long appear (fig. 20, 21). At the G-2 projection a single 

high-amplitude reflector occupies- the middle of 

the Coniacian interval. In the G-2 well the Coniacian rocks are 425 ft (130 m) of cl'iefly light-gray 

calcareous claystones and siltstones with one 
thin argillaceous limestone in the middle of the 

interval (fig. 22). 

The microfauna in the G-2 well is abundant 

and includes a varied planktic foraminiferal assemblage. Benthic forms include Gavelinella 

spp., Stensioina, Allomorphina, Valvulineria, 

Nodosaria, Lingulina, Eouvigerina, Epistomina, 

and Neoflabellina. These faunal characteristics 

suggest that deposition took place in a lowenergy, open marine, outer shelf environment (fig. 

19). 

Downdip from the G-2 projection the central 

high-amplitude reflector disappears near s. p. 

3460 (fig. 23, 24). The Coniacian interval may be 

truncated near s.p. 3900, beyond which it cannot 

be indentified. Coniacian rocks may be included 

in the sequence of horizontal basin-fill reflectors 

that onlap the early Cenomanian(?)-Aptian(?) sequence seaward of the shelf-edge reefal bank. 

SANTONIAN ROCKS 

At the COST No. G-1 site Santonian rocks consist of 380 ft (116 m) of unconsolidated coarsegrained sandstone and gravel containing some 

glauconite and lignite (fig. 17). The microfaunas 

are moderately rich and planktic foraminifers are 

common. The predominant benthic forms are 

Epistomina, Gavelinella, Lenticulina, Frondicularia, and Vaginulinopsis. On seismic line 77-1 

the Santonian interval at the G-1 projection is 

reflector-free, but at the G-1 projection on 

seismic line 19, a very high amplitude, continuous 

reflector occurs in the middle of the Santonian interval; this appears to be a "follow" cycle beneath 

the principal unconformable reflector that separates the Santonian rocks from overlying Tertiary strata (figs. 23, 24). These lithologic, faunal, 

and seismic characteristics indicate that Santonian rocks accumulated under uniform highenergy conditions in near-shore, inner to middle 

shelf marine environments (fig. 16). 

The seismic character of the Santonian interval 

does not change appreciably on line 19 between 

and Gaudryina. Caved Eocene specimens are 

abundant in these samples. These faunal, lithologic, and seismic characteristics suggest that 

Santonian deposits at G-2 accumulated in open 

marine, middle to outer shelf depths in a 

moderate- to low-energy regime (fig. 19). 

The high-amplitude central reflector in th~ Santonian interval continues downdip from the G-2 

projection, and as the section thickens, the reflector moves closer to the top of the section (figs. 20, 

21). Occasional downlapping high-amp1itude 

reflectors appear at the base of the othE'~se 

reflector-free Santonian sequence. The section 

becomes thicker near s.p. 3640, and prograding, 

chaotic reflectors are present from s.p. 37 40 to 

3960, where the sequence is nearly four tirro.s as 

thick as it was at the G-2 well. This thicken~d sequence may also include Campanian and Maestrichtian rocks. Maestrichtian rocks have been 

collected from Veatch, Oceanographer, and 

Heezen Canyons, which border Georges Bank 

(fig. 15); Campanian rocks have been cor~d in 

Veatch Canyon (Ryan and others, 1979; V alE'"ttine 

and others, 1980). Santonian rocks crop c,1t in 

Veatch and Oceanographer Canyons and have 

been cored at Atlantic Slope Project (ASP) s~te 18 

in Veatch Canyon (figs. 15, 26). At these locrt:.ions 

the rocks are chiefly indurated mudstoner and 

siltstones at least 400 ft (128 m) thick. Moderately well developed planktic and benthic fc,..aminiferal assemblages include Bolivinoides, Epistomina, Stensionina, Lenticulina, Gavelinella, 

Globorotalites, Gaudryina, Brizalina, Nodc~aria, 

Gyroidina, and miliolids. All these faunal, 

lithologic, and seismic characteristics suggest 

that deposition took place in outer shelf to upper 

slope environments. 

Santonian rocks may be part of a sequer~e of 

horizontal basin-fill reflectors that onlap the early 

Cenomanian to Aptian sequences seaward of the 

shelf-edge reefal bank. 

CAMPANIAN ROCKS 

the G-1 and G-2 projections. At G-2 the rocks Though Campanian rocks have not been idenare 420 ft (128 m) of unconsolidated, coarse- tified in either of the COST G wells, the;T are 

grained sand and gray, soft, clayey siltstone (fig. known from one corehole drilled for the At~.mtic 

22). The Santonian microfossil assemblage in the Slope Project (ASP 18) in the lower part of 

G-2 well is diverse and contains an abundance of Veatch Canyon (figs. 15, 26). Dark-olive-gr~y to 

planktic foraminifers. The predominant benthic brownish-gray laminated and massive siltstone 

forms are Eouvigerina, Epistomina, Planulina, with minor amounts of dark-olive-gray sanrl and 

Gavelinella, Nodosaria, Marginulina, Stensioina, medium-gray clay was penetrated between 

81 
3,975 ft and 4,095 ft (1,212 to 1,248 m) below sea 

level. The abundance of Bolivinoides, Gavelinella, 

Lenticulina, Gaudryina, Marssonella, Praebulimina, and Arenobulimina and the presence of 

fewer Nodosaria, Pleurostomella, and Valvulineria suggest outer shelf to upper slope 

deposition. 

Campanian rocks also may be part of the basinfill sequence indicated by horizontal, variableamplitude, intermittent reflectors that onlap the 

inferred early Cenomanian to Aptian reflectors 

seaward of the shelf-edge reefal bank. 

MAESTRICHTIAN ROCKS 

Maestrichtian rocks have also not been identified in the two G wells, but they have been 

sampled in ASP corehole 18 (figs. 15, 26). There, 

190 ft (58 m) of early Maestrichtian, dark-olivegray to brownish-gray, laminated and massive 

siltstone with minor amounts of dark-olive-gray 

sand and medium-gray clay are present between 

3,785 and 3,975 ft (1,154 to 1,212 m) below sea 

level. The abundance of Osangularia, Eouvigerina, Bolivinoides, Brizalina, Nodosaria, 

Praebulimina, Gyroidina, Robertina, and Pseudouvigerina suggests an upper slope paleoenvironment. In addition, lower Maestrichtian hemipelagic deposits have been collected from 

outcrops at depths of 4,659 to 5,134 ft (1,452 to 

1,565 m) in Oceanographer and Corsair Canyons 

(fig. 15; Ryan and others, 1978; Gibson and 

others, 1968; Valentine and others, 1980). 

Maestrichtian rocks may be included in the 

basin-fill facies represented by the horizontal, 

variable-amplitude, intermittent reflectors that 

onlap the inferred early Cenomanian to Aptian 

reflectors seaward of the shelf-edge reefal bank. 

PALEOCENE ROCKS 

A few specimens of Paleocene planktic 

foraminifers were found in the uppermost 

samples of both the G-1 and G-2 wells, indicating the presence of some Paleocene strata 

above the Santonian section. Steinkraus (1980) 

also reported Paleocene dinoflagellates in the G-1 

well. These samples, along with planktic Paleocene assemblages recovered from silty claystones 

in Oceanographer Canyon and Veatch Canyon 

(fig. 15, ASP 17; Poag, 1978) indicate open marine 

82 

conditions as far updip as G-1 during the 

Paleocene and bathyal conditions at the canyon 

localities. The Paleocene interval ir either missing 

or too thin to be observed on mos~ of the seismic 

profiles over the shelf. However, a thickened 

wedge of inferred Paleogene ag~ between s.p. 

3860 and 4020 on line 19 may include Paleocene 

strata (figs. 20, 21). Paleocene strrt.a also may be 

present in a thin zone of very high-amplitude, 

nearly continuous reflectors that form a basin-fill 

facies overlying the inferred Maestrichtian to late 

Cenomanian basin fill between s.r. 4200 and the 

seaward end of line 19. The high-amplitude reflectors and lithologic extrapolation from DSDP 

coreholes (such as site 108) suggnst these rocks 

may be cherty carbonates. 

EOCENE ROCKS 

The bulk of Paleogene strata in both the G-1 

and G-2 wells appears to be of middle Eocene 

age. Even so, the middle Eocene interval is thin 

and cannot be recognized with corfidence on seismic line 19 between the G-1 and G-2 well projections (figs. 23, 24). At G-1 the few planktic 

specimens of middle Eocene age indicate open 

marine conditions (fig. 16). Farther updip, at 

AMCOR 6019, 49ft (15m) of light- to dark-green, 

glauconitic clay and hard, gray to white bioclastic 

limestone contains outer shelf to upper slope middle Eocene foraminiferal faunas (fig. 15; Poag, 

1978; Hathaway and others, 1979). Chunks of 

this white bioclastic limestone are present in the 

upper cutting samples at G-1. 

At G-2, where a strong reflector is inferred to 

mark the top of the middle Eocene (figs. 20, 21), 

the dominant benthic forms are Gyroidina, 

Nodosaria, Dentalina, Bulimina_, Cibicidoides, 

Globocassidulina, Anomalinoides, Brizalina, Turrilina, Uvigerina, and Siphonina. Large 

fragments of cheilostome bryozoans and echinoid 

spines are common. The lithology is dark-green, 

coarse-grained, glauconitic sand and leached, 

white, glauconitic, quartzose, ~~~oclastic limestone. These fauna and lithologies indicate outer 

shelf to upper slope environments in a low-energy 

regime. On the shelf, downdip frc"ll s.p. 3000 on 

line 19, the Eocene is very thin aiJd may be missing in places. Eocene strata frcm outcrops in 

Oceanographer and Corsair Canyons (fig. 15; Gibson and others, 1968; Ryan and o~hers, 1978) are 

brown, silty mudstones, glauconitic calcarenites, 
ASP 18 ? 

VEATCH CANYON z 

WATER DEPTH 3510ft ( 1070m) <t 150 500 

CORE z 

ZONE AGE LITH <( 

0 NO 0 (Sea Q_ 

0 N 23 

Floor) ~ 

<( 

u 

0 

0 

? 

600 

100 w a: 

z 0 

w 0 

u .....J 

0 a: u... 

~ 0 200 <{ (f) 0 - w w .....J CJ) 

_j 50 a: u... 

Q_ 0 

a: 0 <{ 700 ~ 0 .....J w 0 

0 200 u... CJ) .....J 

w .....J <{ 

~ u... co w 

<{ CJ) 0 CJ) 

w ~ .....J z a: CJ) w <( w 

0 co 1- ~ .....J z w 

0 w 1-

co w 0 ~ .....J w Iw CJ) u... 800 z 

co a: <( 

I- 300 w (f) 

w 1- 250 

w w w 

u... ~ 100 

900 

400 

300 

1000 

FIGURE 26.-Geologic column of Atlantic Slope Project (ASP) core 18 (taken in 1967 by Exxon, Chevron, Gulf, and M(Jbil oil 

companies as part of their Atlantic Slope Project), near the mouth of Veatch Canyon. See figure 15 for location. 

83 
and white pelagic chalks, representing hemipelagic channel deposition to pelagic basin 

deposition. A few early Eocene planktic specimens are also present in ASP 17 in Veatch Canyon (Poag, 1978). 

Similar Eocene strata may be present beneath 

the upper slope as seen on line 19 (figs. 20, 21). A 

discrete wedge of high-amplitude, nearly continuous reflectors between s.p. 3860 and 4020 is 

interpreted to be chiefly Eocene limestones and 

mudstones of presumably bathyal origin. Between s.p. 4200 and the seaward end of line 19, a 

series of high-amplitude, intermittent, basin-fill 

reflectors is interpreted to include calcareous, 

cherty strata of Eocene age. 

OLIGOCENE ROCKS 

Oligocene strata have not been identified in the 

G wells, but a few Oligocene planktic specimens 

in G-2 suggest that a thin Oligocene unit may lie 

above the highest sampled interval. The only 

other Oligocene strata known from the Georges 

Bank basin were dredged from Oceanographer 

Canyon (Gibson and others, 1968). The rocks are 

buff, calcareous clay and brown, glauconitic, 

sandy clay, both containing abundant planktic 

foraminifers indicating open marine depositional 

environments in low-energy regimes. The wedge 

of high-amplitude reflectors between s.p. 3860 

and 4020 on line 19 may also include bathyal 

Oligocene strata (figs. 20, 21). 

Beneath the lower continental slope and rise, 

between s.p. 4100 and the seaward end of line 19, 

is a thick sequence of chaotic, steeply dipping to 

subhorizontal, discontinuous reflectors of variable amplitude representing slope-front and 

basin-fill facies presumably deposited by highenergy debris flows and turbidity currents (Vail 

and others, 1977). Oligocene strata may be included in this sequence. 

PLIOCENE-MIOCENE ROCKS 

The only Neogene strata recovered on Georges 

Bank occur at the G-2 well site. Here, tan to 

yellow-brown, micaceous, clayey siltstone contains a sparse Miocene to Pliocene benthic fauna. 

The dominant benthic forms are Bulimina elongata, Lenticulina spinosa, Florilus pizzarensis, 

84 

and Cassidulina sp. A series of co:"tinuous, parallel, variable-amplitude reflectors are present at 

the G-2 projection on seismic lin~~ 77-2. On line 

19 the reflectors are less continuous across the 

G-2 projection, but become mf)re continuous 

downdip. The thick sequence of cl' aotic reflectors 

overlying presumed Paleocene and Eocene strata 

between s.p. 4140 and the seaward end of line 

19 probably contains Pliocene and Miocene 

sediments. 

Updip from the B-2 projection the parallel 

reflectors can be traced to about s.p. 2480, but 

most of them are faint between thore and the G-1 

projection. Discontinuous, parallel reflectors with 

highly variable amplitudes devek"'l in the upper 

part of the Pliocene-Miocene section at the G-1 

projection and extend updip from it to the end of 

line 19. 

These characteristics suggest thtt at G-2 and 

downdip from the site, shallow i"lner to middle 

shelf marine environments were present during 

the Pliocene-Miocene deposition (fig. 19). Updip, 

shallow marine to nonmarine f 'tvial environments prevailed (fig. 16). 

PLIESTOCENE ROCKS 

Pleistocene strata were sampled at the G-1 well 

site by AMCOR corehole 6018. A 161-ft (49-m) 

section of coarse, shelly sand that was recovered 

contained a few organic-rich layer;;- and scattered 

specimens of benthic foraminifers, such as Elphidium spp. and Buccella sp. (Po<:"~.~, 1978; Hathaway and others, 1979). At lea~t one interval 

contains Epistominellti and Buliminella with 

pyritized diatoms and radiolarianf., These characteristics indicate that shallow-wa+er, inner shelf 

to coastal lagoon and perhaps nonmarine fluvial 

environments prevailed during th~ Pleistocene at 

this site when it was not covered vrith ice (fig. 16). 

The Pleistocene unit can be tra~ed downdip as 

it thickens to 200ft (61 m) at the G-2 projection 

(figs. 20, 21). The unit is nearly r~flector-free between the two G-well projectior~ except for a 

strong "follow cycle" beneath the sediment-water 

interface. Downdip from the G-2 projection, the 

Pleistocene unit becomes thicker, until it is approximately 0.27 seconds (two-vray traveltime) 

thick at s.p. 3760, where it develops into two 

separate prograding wedges anrl continues to 

thicken downdip. An erosional channel cuts 
through the Pleistocene strata into presumed 

Paleocene to Oligocene strata between s.p. 3940 

and 3965, but from s.p. 3965 to 4015 the Pleistocene cover forms a topographic mound. On the 

middle and lower continental slope, a thick unit of 

divergent, discontinuous, variable-amplitude 

reflectors make up a slope-front fill deposit that is 

probably a Pleistocene submarine fan. This unit 

also undoubtedly includes talus from eroded Tertiary and Cretaceous strata that crop out along 

the bank margin and in submarine canyons. (See 

Ryan and others, 1978.) On the continental rise 

(s.p. 4200 to the end of line 19), the Pleistocene sequence contains a few scattered high-amplitude 

reflectors. This sequence presumably represents 

homogeneous, silty, hemipelagic, distal turbidite 

deposits. 

COMPARATIVE GEOLOGIC HISTORY OF 

THE GEORGES BANK AND SCOTIAN BASINS 

During the block faulting phase of early rifting, 

coarse continental and evaporitic rocks accumulated in the Scotian shelf area in narrow 

basement grabens under arid climatic conditions 

(Mciver, 1972; Given, 1977). After these rift 

valleys were filled by the terrigenous and evaporitic Eurydice, Argo, Iroquois, and Mohican Formations, the resulting broad basin floor became 

the site of restricted marine deposition during 

late Iroquois time. A similar history has been inferred for the Georges Bank basin (Schlee and 

others, 1976) and is confirmed by the record in the 

COST Nos. G-1 and G-2 wells, although the 

Eurydice Formation equivalent was not 

recovered. There are differences in detail between 

the two regions, however. The Georges Bank 

basin grabens in the area of the COST Nos. G-1 

and G-2 wells seem to have been filled by the end 

of Hettangian(?)-Rhaetian(?) time (figs. 20, 21), 

and the presence of Triassic dinoflagellates at 

G-1 and G-2 is a sign of occasional marine incursions. These characteristics, the persistent influx 

of micritic and oolitic normal marine limestones 

throughout the 8,200-ft (2,499-m) Iroquois sequence at G-2 (fig. 22), and the widespread 

development of carbonate mounds (figs. 20, 21), 

are evidence of more frequent and earlier connection to open marine Tethyan waters at Georges 

Bank than on the Scotian shelf. 

Given (1977) has postulated that continental 

85 

drift began near the end of Iroquois depc ~ition 

(end of Aalenian Stage) and that the upper 

Mohican (Bajocian) detrital rocks represert the 

first deposits above a breakup unconformity. On 

the Scotian shelf, widespread marine depc ~ition 

began with the Scatarie Limestone Member of 

the Abenaki Formation, and the maximum Jurassic marine transgression took place curing 

depositon of the Misaine Shale Member (Callovian; Given, 1977). But in the part of the Gf'qrges 

Bank basin considered here, the Misaine equivalent is not traceable seismically very far upiip or 

downdip from the G-2 well (figs. 20, 21). Major 

Late Jurassic transgressions may have occurred 

here during deposition of the lower and upper 

parts of the Baccaro Limestone Member (Callovian(?) to Bathonian(?) and Tithonian to Kimmeridgian, respectively), but marine cond~tions 

were even more widespread earlier (Aalenian(?) to 

Sinemurian(?)), during deposition of the lrMuois 

Formation. 

During the Late Jurassic on the Scotian shelf, 

carbonate deposition was concentrated alor~ the 

stable shelf edge in a discontinuous series of 

banks of the Baccaro Limestone Member. The 

shelf-edge facies is a skeletal-reef association, 

while the bank interior is a nonskeletal, l'.ighly 

terrigenous, oolitic, muddy limestone as soc~ ation 

(Eliuk, 1978). A broad "moat" of calczreous 

shales developed in a depression behind the shelfedge banks, and farther updip the siliciclastic 

Mohawk sands and Mic Mac shales wer~ deposited as fluvial and nearshore facies (Eliuk, 

1978). Periodic subaerial exposure and development of a freshwater lens on the emergent 1, anks 

altered much of the Baccaro from limestcne to 

dolomite. 

The same general facies patterns develor~ in 

the Georges Bank basin. The equivalent of the 

Baccaro Limestone Member accumulate! in 

shelf-edge banks (presumably including reef 

facies), and a· broad back-bank platform of O'llitic, 

pelletal, and micritic limestones extended to the 

G-2 well site (figs. 20, 21). From there, the: Baccaro was split into two parts by a thick siliciclastic tongue of Mohawk-Mic Mac facies- The 

lower Baccaro unit extended only a few te:ns of 

kilometers updip from G-2, but the upper Baccaro unit extended shoreward of the strike position of the G-1. 

On the Scotian shelf, the widespread Late 

Jurassic carbonate deposition ended abr1ptly 
during the Hauterivian, and the sediments were 

buried under the siliciclastic deltaic deposits of 

the Missisauga Formation near the Sable Island 

delta A rapid sea-level rise influenced deposition 

of the marine shales of the Verrill Canyon Formation in locations away from the Sable Island 

delta, such as at the Mohican I-100 site (Eliuk, 

1978). 

Slightly earlier in the Georges Bank basin, 

during the Berriasian, the coarse siliciclastics of 

the Missisauga Formation began to cover the 

Baccaro shelf carbonates at G-2 (figs. 20, 21). 

During the early Valanginian to early Hauterivian, siliciclastic deposition progressed seaward 

to the shelf-edge reefs and began to spill onto the 

ancient slope. 

The Missisauga siliciclastic deposition was interrupted briefly in both regions by carbonate 

deposition of the "0" limestone marker. The interruption occurred in the early Barremian on the 

Scotian shelf, and in the late Hauterivian to early 

Barremian in the Georges Bank basin; however, 

the resolution of faunal zones and stage boundaries in this time interval is not precise, and deposition of the "0" marker may have been essentially isochronous over the entire region. 

Progressively deeper marine paleoenvironments encroached upon both the Nova Scotian 

and New England shelves during the Late Cretaceous, depositing sandstones, shales, and mudstones (figs. 20, 21). On the Scotian shelf, the 

Upper Cretaceous deep-water deposits culminated in the chalks of the Wyandot Formation, 

but contemporaneous deposits appear to have 

been eroded from the old shelf of the Georges 

Bank basin. However, a thick, slope-fill unit of 

Wyandot age (Campanian-Maestrichtian) appears to be present on the continental slope. 

Deep-water carbonate deposition continued 

into the Paleogene in both regions as bioclastic, 

middle Eocene chalky limestones accumulated in 

the Georges Bank basin. The Neogene sedimentation returned to a shallower water siliciclastic 

depositional mode, which continued into and 

through the Pleistocene. 

SEA-LEVEL FLUCTUATIONS AND 

DEPOSITIONAL CYCLES 

Relative changes in sea level have a direct effect on the lithology and fauna and flora of rock 

86 

sequences and on their vertical and lateral facies 

relationships. Conversely, the interpretations of 

microfaunas and seismic facies leads to the recognition of ancient sea-level fluctuatjons. 

A curve illustrating changing paleobathymetry 

in the G-1 and G-2 wells is shown in figure 27. In 

both wells the Lower to Middle tl urassic carbonate rocks are highly indurated, and microfossils 

were rare or absent in the cuttingf., Several shale 

samples from conventional cores mere also processed, but they yielded no calcareo·1s microfossils 

or palynomorphs. Only broad depositional cycles 

could be inferred from lithologic an~ seismic data. 

These suggest nonmarine fluvial to shallow, nearshore marine conditions in the Early to Middle 

Jurassic. 

Inner shelf marine foraminiferal faunas begin 

to appear in the upper Callovian-kwer Oxfordian 

rocks. The first sustained J urassi ~ middle shelf 

faunas occur in the Tithonian. 

The early parts of supercycle Ka (Valanginian 

through Albian) are represented by inner shelf to 

nonmarine paleoenvironments, but the Albian is 

poorly represented in the two G wells. The 

earliest part of cycle Kb is not represented, but 

deep waters (outer shelf conditionr\ were present 

throughout the late Cenomanian to Santonian interval at G-2. G-1 shows a peak transgression 

during the late Cenomanian, a regression during 

the Coniacian, and a minor transgression during 

the Santonian. The peak of cycle Yb (Campanian 

and Maestrichtian) is not repres~nted in either 

well. 

Tertiary supercycles are poorl~r represented. 

However, the outer shelf and slope. environments 

of the late middle Eocene reflect tl'~ major transgression postulated by Vail and otl'~rs (1977) and 

shown in the other Atlantic COST wells (GE-l, 

Poag and Hall, 1979; B-2 and B-3, Poag, 1980b). 

Miocene, Pliocene, and Pleistocene intervals contain outer, middle, and inner shelf deposits. 

In general, the pattern of transg-ession and regression coincides with the patterts seen in the 

other Atlantic COST wells and tl''lse published 

by Vail and others (1977; fig. 27). 

COMPARISON WITH DEEr,SEA 

SEDIMENTARY SEQUEN ~ES 

The western part of the North American Basin, 

which borders the Georges Banlr basin to the 
south and east, has now been penetrated by 25 

Deep Sea Drilling Project (DSDP) coreholes from 

Legs 1, 2, 11, 43, and 44 and has been crisscrossed 

with thousands of kilometers of seismic reflection 

profiles. Tucholke (1979), Tucholke and Vogt 

(1979), Tucholke and Mountain (1979) and Jansa 

and others (1979) have summarized the sedimentary evolution and stratigraphy of this vast 

deep-sea region. Six widespread formations of 

Mesozoic and Cenozoic age have been formally 

recognized at the core sites, and a series of eight 

major seismic reflectors have made possible extrapolation of the core data across the abyssal 

plain and under the lower continental rise of 

North America (fig. 28). Some of these reflectors 

have been traced beneath the continental rise adjoining Georges Bank (see Schlee and others, 

1979; Klitgord and Grow, 1980) and provide a few 

tie points through which slope and upper rise sequences can be correlated with those of the deep 

sea 

The seismic sequences and inferred lithologic 

facies are more complex beneath the slope and upper rise than at those deep-sea basin localities 

that serve as stratotypes for the oceanic formations. For this reason, and because we have very 

little direct evidence of their composition, the 

slope and rise strata are referred to as "updip 

equivalents'' of the oceanic formations. 

Line 19 provides a typical example of the seismic sequences beneath the slope and upper rise 

off Georges Bank. Six high-amplitude, uncon~ 

formable reflectors or series of reflectors and 

several of lesser amplitude permit tentative subdivision of the slope-rise wedge into the chronostratigraphic section shown in figure 21. The 

oldest seismic sequence overlying the oceanic 

basement comprises a series of steeply dipping, 

nonparallel, discontinuous, variable-amplitude 

reflectors that form a slope-front fill facies and 

onlap the seaward base of the shelf-edge reefal 

bank between s.p. 4140 and 4280. At s.p. 4280, 

the reflectors become flatter, parallel, and continuous and remain so to the end of line 19. The 

very high amplitudes of these reflections suggest 

that they represent carbonate strata. The slopefront fill facies can probably be classified as an 

olistostrome, formed by debris flows that incorporated eroded fragments of the shelf-edge reefal 

bank, whereas the more flat-lying, basin-fill facies 

probably contains finer-grained strata deposited 

by turbidity currents. Some terrigenous detritus 

87 

may have reached the reef front as well, tl'rough 

breaks in the barrier (indicated by the lac~ of a 

reefal bank on some dip lines). These strata constitute the second major seismic sequence below 

the {3 horizon (fig. 28), and as such are belie:ved to 

represent Middle and Upper Jurassic and lowest 

Cretaceous rocks. The presence of car'lonate 

strata of this age behind the reefal bank and in 

the DSDP sites (site 105, for example) suoports 

the conclusion that carbonate rocks shonld be 

abundant on the ancient slope too. Lithostratigraphically, this unit appears to incluie an 

equivalent of the Cat Gap Formation (fig. 28); its 

equivalents farther updip beneath the sh~lf are 

the Abenaki, Mohawk, and Mic Mac Formct.ions. 

The old slope sequence may, however, include 

older formations not yet sampled in the North 

Atlantic Basin, because Tucholke and Mountain 

(1979) have recognized a thick (10,469-ft; 3,200-m) 

series of reflectors older than the {3 se~·~1ence, 

which they estimated may be as old as Pliensbachian. They interpreted these strata to be 

coarse terrigenous and calcareous debris. 

The next seismic sequence is bounded at the 

top by what is believed to be reflector {3 (figs. 20, 

21, 28). At least two facies (slope-front Fll and 

basin fill) can be recognized in this unit, an~. they 

appear to be similar in origin and composi ~.ion to 

the underlying sequence. However, the amplitudes of the reflectors are not as high as th 'lse of 

the underlying unit suggesting, perhr11s, a 

greater proportion of siliciclastic turbidites and 

fewer carbonates. These strata appear to be of 

Valanginian to Barremian Age and are updip 

equivalents of the Blake-Bahama Formae~ns, a 

pelagic limestone known from the basin. Shelf 

equivalents are the upper part of the Abenaki 

Formation, the "0" marker limestone, and the 

Missisauga Formation. 

The seismic sequence immediately above {3 also 

consists of a slope-front fill facies and a bc~in-fill 

facies (figs. 20, 21). The slope-front fill facies has 

the same intermittent, variable-amplitude, divergent reflectors as the underlying slope-front fill 

facies, but the amplitudes are not as high, which 

suggests a change to predominantly silici dastic 

debris flows. The basin-fill facies also ccntains 

lower amplitude reflectors than the und~rlying 

facies, and its reflectors are fairly continuous. 

These basin-fill rocks are interpreted to 1'~ siltstones and clays that are updip equivalent~· of the 

organic-rich black clays of the Hatteras Porma-
RELATIVE CHANGE OF PALEOENVIRONMENT PALEOENVIrONMENT 

TIME w 

(M.Y.) ~ GLOBAL SEA LEVEL 

Tc 

'-._PRESENT 

SEA LEVEL Kb 

Ka 

Jb 

I 

I 

--- --~ 

I 

I 

~·4.::-.. l 

:·.: .... I 

GE~-~~: __ _) 

B-3 --1 

B-2 

FIGURE 27.-Paleoenvironments of the COST Nos. G-1 and G-2 wells, compared with those of previou~ COST wells, the 

relative sea-level curve of Vail and others (1977), and global supercycles. Gaps in paleoenvironmental C"~rves are hiatuses. 

The age terms abbreviated in the left side column are spelled out on figures 17 and 22. 

tion. The inferred coarseness of the slope-front fill 

facies, however, probably makes it similar to the 

equivalent lower siltstones of the Dawson Canyon Formation. 

The next seismic sequence is a basin-fill facies 

bounded above by high-amplitude reflectors that 

are believed to represent reflector A* of the deep 

sea (approximately the Cretaceous-Tertiary contact) (figs. 20, 21, 28). The reflectors are subparallel in the upper and outer parts of the se88 

quence, but divergent and intermittent in the 

basal part beneath s.p. 4300. This sequence is interpreted to be terrigenous turl~~~tes of Late 

Cretaceous age. It is the updip e~~rivalent of the 

Plantagenet Formation, and its sl,~lf equivalents 

are the upper parts of the Dawson Canyon and 

Logan Canyon Formations. 

Above the Plantagenet Formation equivalent 

and onlapping the Dawson Cany<'"'l(?) equivalent 

are a series of intermittent, very high amplitude 
~ 

G- I 

GEORGES BANK 

(Conti nenta I Shelf and 

BASIN 

Slope) 

FORMATION 

(DOMINANT LITHOLOGY) 

G-2 SHELF 

EDGE 

SLOPEUPPER RISE 

. · TAJlREN'"TTAN- · . · · · · · · - · -·. · .. _ . _. _ 

>-

::::!!: 

LLJ 

::E 

1-

AGE 

::·s~~a·u~~~~~-:~ lz~.?-:~~-BL.AKE. RI~GE-~ :_. ... -... :' ·.· ..... _ ............. ·.-·l:f""--:-·---:-. ~. --:-__:___-=- ?_ ~ =-:-· 225 ~----- r·-· --· · · · · . OLIGOCENE 

MIOCENE 

-·-·-·---·-·-·-

NORTH 

(Continenta I 

AMERICAN BASIN 

Rise and Abyssal Plain) 

FORMAT ION 

(DOMINANT LITHOLOGY) 

COLOR 

greenish- grey, 

grey- green, brown 

AVERAGE 

CaC0 3 

0 50 100 

>- a:: (..!) uo 0 

__J 

_I0 t-U 

(/) LLJ 

:I: ;::::>__J 

1- OLL - u LLJ _J <( a:: 

~·-~M­

~-- Ji:..:?C....rc 

...r......r... 

....1'"\.....f\.......A... 

• ~ .1? M EOCENE 

tr---r=UNN AMED l-""1. · 1 1 1 1 M EOCENE BERMUDA RISE (Siliceous 1 .1 .1 I l l JIS. l .1 I I l l claystone chert ) 

J I I l BERMUDA RISE~ E EOCENE Type section Site 387 

dark greeniSh-grey, olive- qrey, yellowiSh brown 

~~..!...\_ ~Ac- ....1'"\... ...L... _,..._A 

L 

-------- A.../"\... A 

f..=- -- -z-_-:- I I I I I I 1 l} I I 1 l PALEOCENE coco - - - II I ? I I I l I 1 I I l 3 t::.._-::1..-=..j * 

D:I_. 65 t------ <...._CRESCENT PEAKS MEMBER : l;IJR--_j-A - ·-· -· -r-- ·-· -·-· -· MAESTRICHTIAN ~ lcarbonote'i' white, light grey 1 ~~.:. 

- · -·-·-·-·-·-·- -CAMPANIAN reddish-brown, yellow, __ _ 

· - · - ·-r- · - ·-· - · - · orange, blue-green - ---::._ -_: 

_ _ _ _ . . . ... - .. ? · ·- -·PLANTAGE~ET_·- PLANTAGENET (variegated cloy) ~ -z....:. 

: _. _ ..... -~ ~- -:-:-. -:-_ ~---:-_:_-:- · -~ _:__---:-_:_--:- ? .. _ . -~ Type section Site 386 : Corg. '- = ·LOGAN·.~DAWSONr--·-·-r-:-·-·-·-·-· 92LCENOMANIAN ·~_(-:.= ~ z_:, 

CANYON ·!:~CANYON: 7-'-:-:-:--:- ·. ·-:-::.:~- -_-_ -_ _ CE NOM AN IAN HATTERAS (carbonaceous block, dark grey, : 14.8 ~ Z --: 

:: ·. ·. ·. --~~·-:--::·:-::- ·-:-:-·---:-·-~-HATTERAS_ cloystone,shole.) olive~block,dark : F----= · · · · · · · . · . · . ·'"'- · · · ? _ _ E APT IAN Type section Site 105 green1sh grey 1 - - -

.MISSISAUGA = -:-_: .. :1~--:-__:__ ~-:-r- _- _-_. _ _ _ BARREMIAN 91 t- --=---~ (3- .· : ·. ·. · .. · · - · · · - · · · · 115 BARREMIAN l 

..•.... - BLAKE- BAHAMA (limestone, light to greenish grey, : 

·MISS I SA UGA : : : : ~ __t BLAKr- _BAHAMA- chalk, mar !• che~t l wh1te 1 pale yellowish : . . . . . . . . . .... ~ 't:. Type sect1on S1te 391C brown 1 · · · · ._.~ 1 1 1 1 _l_l :II I I I I J J} I I 1 L TITHONIAN : -C-

~: .' .' .'.~ ~~~11 11 1 I 1 1 1 l 138 E TITHONIAN CAT GAP (argillaceous limestone, redd1Sh-brown,dus_ky, : - --- -- ''MQHII.\lJK >'MIC MAC L L....::. KIMMERIDGIAN marl l p1nk1Sh red, greeniSb- : - - - 1-'t.YY ·2l -~ l .l l 1CAT GAP I I 1" ...ox.E.OB..olA Type section S1te 105 Qrty _t_ -- --

•••••• •LL_ "" ~ 14 0 4 8 ~~~ •. · . · _-:,. ~~I I 1 _1 1 I 1? I _l l _l '"' %ORGANIC ?

1 

\\1 · r--B- -~ll 1 l l l lll_f!l _l rtl _l I I I I I 1 CARBON ••••• 

o::::!!: 

w:::r:::: 

~I 

_J 1- <(a_ 

a::w 

LLJ 0 :zo 

LLJ LLJ (..!) __J 

<( 

2 0..5 

FIGURE 28.-Comparison of stratigraphy of Georges Bank basin with that of the adjacent North American Basin. Data for North American Basin 

after Jansa and others (1979). 

:z>-

Q::::ii: 

I--... 

~::::!!: 

Zw 

WI-

~<( 

0 a:: LLJ 

(/) 

10 30 50 

4-200 

1-8 

~15 

4.6 

1-3 

3-16 

7-10 

8-10 
reflectors thought to represent the cherty Paleocene and Eocene carbonate strata equivalent to 

the Bermuda Rise Formation (figs. 20, 21). The 

shelf equivalents are unnamed Paleocene and 

Eocene limestones. Some of the high amplitudes 

may be caused by cherty horizons known from 

deep-sea sites to cause the well-known reflector 

AC (fig. 28). 

Above the Bermuda Rise equivalent is a thick 

sequence of slope-front fill and basin-fill facies. 

The slope-front fill extends from s.p. 4080 to 4300 

and contains steeply dipping, divergent, variableamplitude, intermittent reflectors, indicative of 

an olistostrome. The basin-fill facies contains 

horizontal, chaotic refle_ctors with some arcuate, 

high-amplitude reflectors in the middle of the 

sequence. These probably represent siliciclastic 

turbidites deposited during the Miocene and 

Oligocene and constitute part of the updip equivalent of the Blake Ridge Formation. Under the 

shelf, equivalent beds belong to the Banquereau 

Formation. 

The next younger sequence is a narrow band of 

faint reflectors below a moderately highamplitude, discontinuous reflector, believed to be 

a turbidite sequence of Pliocene age (figs. 20, 21). 

Above the Pliocene is another seismic facies 

representing slope-front fill and basin fill. The 

dipping, divergent, high-amplitude, slope-front 

facies is believed to be an olistostrome of Pleistocene age that includes older clastic fragments and 

blocks derived from outcropping Tertiary and 

Upper Cretaceous beds, such as were observed by 

Ryan and others (1978) in Heezen Canyon. The 

basin-fill facies probably is composed of finer 

grained Pleistocene turbidite sequences, but older 

(Eocene, Cretaceous) debris is also present much 

farther seaward (for example DSDP Site 107; 

f!ollister, Ewing and others, 1972). The slopefront fill facies can be correlated with the Laurentian Formation of the shelf, and the basin-fill 

facies and the underlying Pliocene beds form the 

upper part of the updip equivalent of the Blake 

Ridge Formation (figs. 20, 21, 28). 

These sequences show that depositional cycles 

on the shelf have been coupled with and have affected depositional cycles in the deep sea. Carbonate deposition was predominant on the shelf 

and in the deep sea in the Jurassic and Early Cretaceous. The shelf-edge reefal bank and the broad 

carbonate platform behind it served as barriers 

that prevented terrigenous sediments from reach90 

ing the deep basin in significant quantities, except in a few areas where the ree:fal bank system 

was breached or absent. Carbona+e olistostromes 

and turbidites buried the basinward flank of the 

reefal bank and built the protocontinental slope 

and rise, while pelagic limestones accumulated on 

the oceanic basement. 

Sometime during Hauterivian to Barremian 

time the terrigenous constituents of the Missisauga Formation began to cover the reefal 

bank, spilling down the seaward flank and 

extending the terrigenous depositional regime to 

the deep sea At the same timer the rising carbonate compensation depth (O'jD) and widespread oxygen-deficient conditions over the 

abyssal plain allowed preservation of layers enriched in terrestrial organic matter, which 

became the distinctive black drys of the Hatteras Formation (Tucholke and 11ountain, 1979; 

Tissot and others, 1979, 1980). 

Hemipelagic deposition prevf'iled until the 

Paleocene and Eocene, when Ccl"'bonates again 

dominated both the shelf and pcrts of the deep 

sea Then the rapidly deposited siliciclastics of 

the Oligocene and Miocene began to build a thick 

slope-rise wedge that included eroded blocks and 

fragments of the Upper Cretacf'flUS to Eocene 

beds that cropped out along the f'dge of Georges 

Bank. 

During the Pleistocene, glc~iofluvial and 

glaciomarine deposition took place on the bank, 

and during glacial intervals the Laurentian ice 

sheets scoured large volumes of s~diment off the 

bank, forming a thick slope-front fill and basin fill 

beneath the upper continental rise. Even now, 

bank-edge erosion continues to contribute Cretaceous and lower Tertiary debris to the slope-rise 

wedge. 

SUMMARY 

The COST Nos. G-1 and G-2 wells in the 

Georges Bank basin penetrated 15,257 ft 

(4,650 m) and 21,490 ft (6,550 m), respectively, of 

marine and nonmarine sedimentm-y rocks ranging in age from Late Triassic to Pleistocene and 

Holocene(?). The lithologic, fau'"lal, and floral 

records from these wells and from auxiliary short 

cores and dredgings, and the ana1

yses of seismic 

sequences and facies show thzt the geologic 

development of the Georges Bank basin generally 
paralleled that of the neighboring Scotian basin. 

The initial rifting of the Triassic was characterized by terrigenous graben-fill deposits (Eurydice(?) Formation) interspersed with occasional 

marine beds and followed by accumulation of 

thick evaporitic strata (Argo Formation). In the 

Late Triassic and Early Jurassic, as much as 

8,200 ft (2,500 m) of shallow-marine limestones, 

dolomites and evaporites (Iroquois Formation) 

accumulated in the outer part of the basin as 

elongate carbonate mounds and widespread platform facies behind a bordering shelf-edge complex of reefal banks. Concurrently, the inner part 

of the basin was the site of coarse terrigenous 

deposition (Mohican Formation). The Mohican 

sandstones and mudstones prograded far out 

onto the carbonate platform during the early 

Middle Jurassic(?) (early Bathonian(?)), but did 

not reach the shelf edge. 

A major marine transgression during the late 

Bathonian(?) reestablished a carbonate regime 

nearly as far updip as the G-1 well site, 

depositing the oolitic and pelletal strata of the 

Abenaki Formation. Another pulse of terrigenous 

deposition spread thick sandstones and shales of 

the Mohawk and Mic Mac Formations as far 

downdip as the G-2 well site during the Oxfordian(?) to late Kimmeridgian interval. Carbonates 

were dominant for the last time in the late Kimmeridgian to early Berriasian as Abenaki facies 

once more nearly reached as far updip as the G-1 

well site. 

During the Early Cretaceous (Berriasian and 

Valanginian) a sustained influx of coarse-grained, 

lignitic terrestrial sediments (Missisauga Formation) replaced the carbonate regime over the entire shelf, and during the early Hauterivian the 

terrigenous sediment spilled over the shelf edge 

into the North American Basin. A short-liverl but 

widespread interruption of this influx by the thin, 

calcareous "0" marker took place in the late 

Hauterivian. 

During the rest of the Cretaceous, sandstnnes, 

claystones, and mudstones of the Missisaugr. and 

Dawson Canyon Formations spread acros~ the 

shelf and down onto the shelf and rise. 

The sparsely sampled record of Tertiary deposition shows that during the Paleogene, ar unnamed, white chalk, carbonate unit, prominent as 

far south as the southeast Georgia embaytnent, 

extended across the Georges Bank basin as well. 

Terrigenous marine deposition resumed during 

the Neogene (Banquereau Formation) and wrs replaced by glaciofluvial and glaciomarine dE'ryosition in the Pleistocene (Laurentian Formaticn). 

91 

The depositional sequences, hiatuses, sedi"llent 

accumulation rates, and paleoenvironm~ntal 

changes at the COST Nos. G-1 and G-2 well sites 

suggest that the continental shelf of the Georges 

Bank area was created by changing sea level, 

changing volumes of terrigenous and carbonate 

sediments, and episodic subsidence of the bRsin. 

Deposition on the adjacent slope and rise was 

affected by sedimentation on the shelf, and 

throughout the Jurassic and Early Cretaceors by 

the intervening shelf-edge reefal banks. e~~lf, 

slope, and rise deposition was significantly 

altered in the middle Cretaceous (HauterivianBarremian), when the carbonate platform ani its 

bordering reefal bank were buried, allowin~r terrestrial debris to reach the deep sea. 

Terrestrial organic matter was preserved in the 

black shales of the Hatteras Formation or the 

oxygen-deficient, carbonate-free abyssal plain. 

Significance of the Mesozoic 

Carbonate Bank-Reef Sequence for the 

Petroleum Geology of the Georges Bank Basin 

Robert E. Mattick 

Analyses of rock cuttings and cores from the 

Jurassic section in the COST No. G-2 well indicate the following: above 10,500 ft (3,200 m) the 

predominantly clastic rocks have high porosities 

and permeabilities and are too thermally immature for the generation of liquid petroleum 

(Smith, 1980, p. 98). Between 10,500 ft (3,200 m) 

and 14,000 ft (4,300 m) there are moderately 

porous (10-15 percent) limestones which contain 

little organic material. Below 14,000 ft (4,300 m), 

the carbonate rocks show minimal to moderate 

amounts of organic matter, and many rock 

samples near the bottom of the well contain 

"amorphous-sapropelic" organic matter (Smith, 

1980, p. 98). These deeper rocks, however, have 

porosities below 10 percent and permeabilities of 

about 0.1 millidarcy (Malinowski, 1980, figs. 12 

and 13). 

These results suggest that on the North Atlan-

.. ic Outer Continental Shelf potential source rocks 

are generally not in close contact with potential 

~servoir rocks. High-porosity sandstones occur 

at shallow depths where the potential source 

"'ocks are immature; at greater depths where 

'nature potential source rocks occur, porosities 

~nd permeabilities of potential reservoir beds are 

"·'>w. Without proximity of source and reservoir 

"·,eds, petroleum can accumulate in significant 

.,.mounts only through long distance lateral 

""•ligration or through vertical migration along 

~aults. There is little possibility that significant 

·:lmounts of petroleum have accumulated on the 

~J.S. Atlantic shelf by long distance migration, 

"·,ecause of the probable absence of laterally con-

·~inuous, porous Jurassic sandstone beds and the 

11bsence of major post-Triassic tectonic events 

·~hat might have provided major fluid migration 

·"'aths along fault and fracture systems. However, 

there may have been some migration at the shelf 

margin along faults related to mass movemf'ut of 

sediment rather than tectonic events (Mrt.tick 

and others, 1981 ). 

Preliminary analyses of seismic data recorded 

farther seaward on the continental slope tha"l the 

COST No. G-2 well suggest that potential source 

rocks may be in close contact with potential reservoir rocks. According to Mattick and o .. hers 

(1978), Jurassic forereef and reef facies could 

interfinger with basinal facies on the contin~ntal 

slope. Although the seismic evidence for tl·~ interfingering of these facies is strong, neither the 

source-rock potential of the basinal facies n<J,.. the 

porosity and permeability potential of the possible reef and associated facies has been e~tablished. Evidence from the COST No. G-2 w~ll in 

the Georges Bank basin indicates that the sedimentary rocks of Jurassic age at this site were 

deposited at or near sea level; thus, reef and associated carbonate facies deposited at the edge of 

the ancient shelf margin possibly were inte-,nittently exposed to subaerial weathering and, as a 

result of leaching by freshwater and perhaps dolomitization, secondary porosity may have d ~veloped. The basinal facies of the ancient slope environment may have been deposited in a zone o~ low 

oxygen concentration (comparable to the ox:"gen 

minimum zone that intersects the present continental slope), enhancing the preservatio""l of 

organic matter and making these sedimert:ary 

rocks a potential source for petroleum if subjected to deep burial. Under these conditions the 

organic content of the basinal shales is like~y to 

contain a higher percentage of marine-derive-i organic matter than shales formed on the shelf and 

hence should have a greater capacity for g1~nerating liquid instead of gaseous hydrocarbonf .. 

93 
The purpose of this paper is to analyze the 

development of the shelf margin during Jurassic 

time and to show the relationship between carbonate facies, which may or may not be significantly porous, and basinal facies, which may 

contain large amounts of marine-derived organic 

carbon. Areas in which these facies are in proximity may prove to be areas where significant 

amounts of petroleum have accumulated in stratigraphic traps. Although this work is based 

chiefly on the interpretation of seismic data and 

is therefore speculative, a proposed well to test 

these interpretations (COST No. B-4) may be 

drilled in about 4,300 ft (1,300 m) of water in the 

Baltimore Canyon trough area. It should penetrate an area where, based on the interpretation 

of seismic data, Jurassic forereef facies interfinger with basinal facies of the same age. 

SEISMIC DATA 

Figure 29 shows the U.S. Geological Survey 

common depth point (CDP) seismic profiles reEXPLANATION 

G-2 ® SELECTED WELL 

SEISMIC REFLECTION 

PROFILE 

PART OF PROFILE 

DISCUSSED IN REPORT 

0 SO statute miles L--.....1 

0 50 kilometers L...__j 

corded on the northern and central U.S. Atlantic 

margin. The parts of the record discussed in this 

paper are marked, and each is about 30 mi (50 km) 

long. 

In order to correlate reflectjon events with 

stratigraphy and lithology, the seismic grid was 

tied to the COST No. G-2 well. In figure 30 the 

data from the well (Judkins and others, 1980) is 

plotted alongside a segment of s'1ismic profile 15 

that crosses over the well site. Tl'~ well bottomed 

in salt at 21,851 ft (6,660 m). Between 13,571 ft 

(4,136 m) and the top of the sa1t., the dominant 

lithology is dolomite, anhydrite, and limestone of 

Early and Middle Jurassic(?) agE:. Because of the 

similarity in age and litholog';'', Judkins and 

others (1980) correlated this part. of the Jurassic 

section with the upper part of t'le Iroquois Formation of the Scotian shelf. If the correlation is 

correct, these rocks represent derflsition during a 

rift valley stage in the development of the Atlantic Ocean basin (Given, 1977). From 13,306 ft 

(4,056 m) to the top of the Jura-:osic section, the 

rocks are chiefly limestone and sandstone. 

Judkins and others (1980) corr~lated the thick 

FIGURE 29.-U.S. Geological Survey common depth point (CDP) seismic reflection profiles recorded on the northern and central U.S. Atlantic margin. The parts of the profiles displayed in other figures are shown by heavy lines and those discussed 

in the text are numbered. 94 
0 

I/) 

0 

z 

0 

u 

UJ 

I/) ·c 

z 

UJ 

:E 

i= 2 

.....J 

UJ 

> B 

<( 

c.:: 

I-

> 

<( A 3 

0 

3 3 

ICOST NO. G-2 WELL ON GEORGES BANK 

H±±) SALT 

10,000 

15,000 

20,000 

25,000 

LATE 

CRETACEOUS 

EARLY 

CRETACEOUS 

LATE 

JURASSIC 

MIDDLE JURASSIC 

EARLY JURASSIC 

TO LATE 

TRIASSIC (?) 

TERTIARY 

LATE CAMBRIAN (?) CAMBRIAN 

f:':Z:3 DOLOMITE & ANHYDRITE t--=t SHALE 

@ liMESTONE ~:.:::··1 SANDSTONE l/'11 BASEMENT ROCKS 

UNCONFORMITY 

FIGURE 30.-Data from the COST No. G-2 well plotted alongside a part of seismic reflection profile 15 that crosses tht~ well 

site. The vertical scale is two-way reflection time, and depths (not to scale) are annotated on the right. Three proir;nent 

reflectors (A, B, and C) can be mapped throughout much of the Georges Bank basin. The top of basement rocks is 

estimated from interpretation of seismic data Evidence from the COST No. G-1 well indicates that the basement consists 

of highly metamorphosed rocks of Cambrian(?) age. 

limestone unit with the Abenaki Formation of the 

Scotian Shelf and the thick sandstone unit with a 

tongue of the Mohawk and MicMac Formations. 

On the Scotian shelf these formations represent 

deposition during the post-breakup transgression 

of the early Atlantic (Given, 1977). 

Three prominent reflectors were noted and labeled from deep to shallow as A, B, and C. The 

deepest reflector (A) can be correlated with the 

contact between the dolomite-anhydrite unit of 

Early-Middle Jurassic(?) age and the overlying 

limestone unit, and marks the continental 

breakup. Reflector A can be mapped throughout 

the Georges Bank basin except in areas where it 

terminates against basement in a shoreward 

95 

direction and in the vicinity of the Long Island 

platform. Reflector B was picked at a dep .. h of 

about 10,000 ft (3,000 m), near the contact between a thick Upper Jurassic sandstone unit and 

an underlying Upper Jurassic limestone unit. 

Reflector C, at a depth of about 5,300 ft (1,60f) m), 

correlates with Lower Cretaceous strata located 

near the top of the Jurassic section. Throu~~'lout 

this paper, these reflectors are assumed to be 

time correlative rather than lithologic markers. 

This assumption, although probably not completely valid, results in good correlation bet~reen 

seismic events recorded on the shelf margir and 

slope. 

Reflector A at the G-2 site is correlated with 
the "breakup unconformity," which refers to the 

erosional surface developed between the rift 

valley stage of development and the onset of 

seafloor spreading. According to Falvey (197 4), 

the rift valley stage of development is a protracted event that involves hogback uplift due to 

extensive thermal expansion and later, as a result 

of block collapse, results in the accumulation of 

considerable volumes of clastic sediments in the 

rift valley. However, the process of continental 

breakup and the onset of seafloor spreading was 

not instantaneous. Following block collapse and 

accumulation of clastic rocks in grabens, a 

shallow sea apparently occupied the site of the 

present Atlantic Continental Shelf. This event is 

reflected by the salt layer and the dolomiteanhydrite sequence penetrated in the bottom of 

the COST No. G-2 well. Klitgord and others (this 

volume) seem to suggest, by their placement of 

the breakup unconformity between the salt interval and the dolomite-anhydrite sequence, that the 

onset of seafloor spreading immediately followed 

deposition of the salt unit. This author infers that 

seafloor spreading coincided with a deepening of 

the early Atlantic and places the breakup unconformity between the dolomite-anhydrite sequence 

and the overlying limestone unit. According to 

Falvey (197 4), the onset of seafloor spreading 

should involve a secondary heating event that 

leads to a short period of emergence just prior to 

breakup. This short period of uplift, resulting in a 

regression of the sea, may be reflected by the thin 

sandstone interval that separates the dolomiteanhydrite sequence from the overlying limestone 

unit at a depth of about 13,450 ft (4,100 m) in the 

COST No. G-2 well. Accurate placement of the 

breakup unconformity requires better time correlation between the Jurassic sedimentary rock 

units deposited on the continental rise and those 

deposited on the continental shelf. 

Figure 31 shows the part of seismic profile 1 

that crosses the shelf margin in the central 

Georges Bank area. The profile is typical of those 

recorded across the northeastern end of the 

Georges Bank basin. Reflectors can be traced 

from the central basinal area to the outer part of 

the shelf, where they become faint and disappear 

in a poorly defined structureless mass, which 

Mattick and others (1978) and Schlee and others 

(1979) have interpreted to be a Jurassic-Lower 

Cretaceous limestone platform. On seismic lines 

to the southwest, details of the platform complex 

become distinguishable. 

96 

Figure 32 shows part of seismic reflection profile 20 located about 25 mi (40 km) southwest of 

the previously discussed seismi ~ section. On a 

shelf margin of Late Jurassic age, represented by 

reflections between reflectors B and C, Mattick 

and others (1978) and Schlee ar1 others (1979) 

mapped a possible reef sequence. The sequence is 

not well developed on this profilE\ and it appears 

on other sections as a loss of reflections. Two 

distinct facies can be mappE:<i: an obliqueprogradational seismic facies be+ween reflectors 

as A and B, and a sigmoid-progra1ational seismic 

facies between reflectors B and C. According 

to Vail and others (1977) the distinction between 

the two facies is as follows: in the obliqueprogradational seismic facies, reflections terminate by toplap truncation at o:-- near the upper 

surface and by downlap at the ba~~. The sigmoidprogradational seismic units are characterized by 

gentle 8-shaped reflections alo'lg depositional 

dip. On seismic lines parallel to depositional 

strike, the sigmoid-progradationc1 reflections are 

usually parallel and concordant vrith unit boundaries. In figure 32 only the upr~r parts of the 

sigmoid reflections are seen: the: lower parts of 

the reflections are lost under the slope where 

reflections become faint and cha<Jtic. 

As can be seen on figure 32, the obliqueprogradational seismic facies app1ar to be associated primarily with shelf outbuilding; the 

sigmoid-progradational seismic f "'des appear to 

be associated primarily with up building of the 

shelf and a lesser amount of secward progradation. These two types of progradational seismic 

facies can be mapped throughout much of the 

Georges Bank basin. 

Oblique-progradational seismic facies on shelf 

margins are characteristic of fluvial deltas and 

associated coastal-plain sediments and contain 

high-energy deposits (Vail and ot\ers, 1977). The 

undaform zone, corresponding to a delta-plain environment, and the upper part c.f the clinoform 

zone, corresponding to a delta-fro:"lt environment, 

are likely to contain sand. The lower clinoform 

and fondoform zones, corresponding to a prodelta 

environment, are typically shale prone. In addition, the fondoform part of the oblique seismic 

facies may contain turbidite derosits of sands 

interbedded with marine shales. 

In their discussion of sigmoicl·progradational 

facies, Vail and others (1977) sugg~st that the corresponding sedimentary rocks are usually deposited on the slope along continental margins 
V) 

0 

z 

0 

u 

w 

V) 

w 

::E 

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-' 

w 

> 

<t 

~ 

1-

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<t 

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0 

~ 1-

V) 

0 

z 

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u 

w 

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0 

2 

3 

4 

5 

6 

7 

0 

2 

3 

4 

5 

6 

7 

REFLECTOR C 

LINE 1 

AREA OF MASSIVE 

0 

0 

I 

5 km 

I 

5mi 

FIGURE 31.-Part of seismic reflection profile I recorded across the outer shelf and slope in the central part of the Georges 

Bank basin. Location of profile is shown in figure 29. Uninterpreted section is shown above and interpretive lines have 

been added below. 

and that the undaform part of the reflection event wave or fluvial transport, hence there is some 

extends into shelf margin facies. Shelf upbuilding possibility of coarse reservoir clastics in the undaproduces thick deposits corresponding to the un- form environment. 

daform parts of the reflections. Clinoform facies These interpretations suggest that the oblique 

represent dominantly fine-grained clastics that facies between reflectors A and B represent more 

were most likely deposited from low-energy tur- sand-prone sedimentary rocks than do the sigbidity currents and from low-velocity currents as moid facies between reflectors B and C. At the 

hemipelagic deposits. Sedimentary rocks repre- COST No. G-2 well there are predominantly limesented by the undaform facies may result from stone facies below reflector B and predominantly 

97 
V) 

0 

z 

0 

u 

w 

V) 

w 

:E 

f-

-' 

w 

> 

<1: 

er::: 

f-

>-

<1: 

3 

0 

3 

fV) 

0 

z 

0 

u 

w 

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o2 

3 

4 

5 

6 

7 

3 

4 

5 

6 

7 

S 30 E 

OBLIQUE- PROGRADATIONAL 

SEISMIC FACIES 

LINE 20 

SIGMOID- PROGRADATIONAL 

SEISMIC FACIES 

- - L 

0 

I 

5 km 

I 

0 5 mi 

FIGURE 32.-Part of seismic reflection profile 20 recorded across the outer shelf and slope in the central part of the Georges 

Bank basin. Location of profile is shown in figure 29. Uninterpreted section is shown above and interpretive lines have 

been added below. The reflections between reflectors A and B are classified as oblique-progradational seismic facies and 

those between reflectors B and C are classified as sigmoid-progradational seismic facies. 

98 
sandstone facies above. This pattern suggests 

that the oblique seismic facies represent limestone beds deposited in a high-energy environment, perhaps an oolitic limestone. In this case, 

termination of reflections by toplap near the upper surface suggests that the limestone was 

derived at or near a shelf edge and deposited on 

the slope by wave action. Upbuilding of the shelf 

did not occur during this time because there was 

little influx of clastics to the shelf. As the influx 

of clastic material increased after the time 

0 

<./) 

0 

z 

0 

u 

UJ 

':]_ 

LLJ 

::'E 

,_ 

--' 

LLJ 

> 

<t: 

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>-

<t: 

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0 

~ 6 ,_ 

RE FLECTOR C 

<./) 

0 

z 

0 

u 

LLJ 

<./) 

LLJ 

~ 

Iu:::: 

> 

<t: 

;= 

>-

<t: 

<: 

() 

<: 6 

7 

represented by reflector B, the shelf began to 

build upwards. 

Seismic profiles 8, 5, and 22 are shown in 

figures 33, 34, and 35 respectively. The reflecting 

horizons noted in these figures were carried from 

profile to profile by additional mapping on seismic profile 12 (fig. 29), which intersected all of the 

seismic lines discussed in this paper. Although 

they differ in detail, all of the profiles reveal the 

same overall structure of the shelf margin during 

the Jurassic: oblique-progradational seismic 

TERMINATED REFLE CTO RS 

0 ~ S35 E LINE 8 0 

5 km 

L_ _ _ _j 

5 mi 

FIGURE 33.-Part of seismic reflection profile 8 recorded across the outer shelf and slope in the southwestern part of the 

Georges Bank basin. Location of profile is shown in figure 29. Uninterpreted section is shown above and interpretive lines 

have been added below. 

99 
0 

V) 

0 

z 

0 

u 

w 

V) 

w 

:E 

>= 

~ 

w 

> 

<{ 

CL 

1-

>-

<{ 

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0 6 

~ 

1-

7 

REFLECTOR C 

OBLIQUE- PROGRADATIONAL 

oVi 

0 

z 

0 

u 

w 

V) 

w 

:E 

>= 

~ 

w 

> 

<{ 

CL 

1-

>-

<{ 

~ 

0 6 

~ 1-

7 

S 20°E 0 5 km 

LINE 5 0 5 mi 

FIGURE 34.-Part of seismic reflection profile 5 recorded across the outer shelf and slope in the southwestern part of the 

Georges Bank basin. Location of profile is shown in figure 29. Uninterpreted section is shown above and interpretive lines 

have been added below. 

facies, which represent outbuilding of the shelf 

margin during Middle and Late Jurassic time, 

and sigmoid-progradational seismic facies, which 

represent upbuilding of shelf margin during Late 

Jurassic time. On profile 8 (fig. 33) the reflectors 

immediately above reflector A suggest that a carbonate ramp began to build seaward following 

continental breakup. Later, during the Cretaceous, the shelf margin apparently prograded seaward over the Upper Jurassic shelf edge for some 

undetermined distance. The truncation of reflectors that represent Cretaceous strata suggests 

100 

that the Cretaceous shelf edge has retreated 

shoreward because of erosion. 

Profile 5 (fig. 34) is located just northeast of the 

Long Island platform and profile 22 (fig. 35) 

crosses the platform. On the shoreward ends of 

these profiles reflector A, which terminates 

against the basement surface in the shallower 

parts of Georges Bank basin, was absent. Oblique 

seismic facies can be seen at a depth of about 3.4 

seconds (two-way traveltime) on profile 5; the 

base of this seismic facies probably correlates 

with reflector A. Near the southeast end of profile 
(i 

Q 

z 

0 

~ 

!!! 

w 

:::E 

i= 

_, 

w 

> 

c 

a: 

1-

> 

c 

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Ui 

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w 

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REFLECTOR C 

LINE 22 0 5 mi 

FIGURE 35.-Part of seismic reflection profile 22 recorded across the Long Island platform immediately south of the Georges 

Bank basin. The location of profile is shown in figure 29. Uninterpreted section is shown above and interpretive lines have 

been added below. 

5, a zone of weak reflections is interpreted as a 

reef facies of Late Jurassic to Early Cretaceous 

age that grew along the shelf margin during that 

time. Along profile 22 (fig. 35), the sedimentary 

section is substantially thinner than that shown 

on previous profiles. On the Long Island platform 

this thinness results from the absence of the 

rocks correlating to the basal part of the obliqueprogradational seismic facies below reflector B. 

In this area the location of the Middle Jurassic 

shelf edge probably coincides with that of the 

101 

Upper Jurassic-Lower Cretaceous shelf edge. Terminated reflectors appear to mark that location. 

GEOLOGIC IMPLICATIONS 

The interpretation of seismic data recorded 

along the central and northern part of the U.S. 

Atlantic margin indicates two styles of shelf 

construction during the Jurassic and Early Cretaceous (fig. 36). Middle Jurassic time, following 
EARLY 

CRETACEOUS 

LATE 

JURASSIC 

MIDDLE 

JURASSIC 

rJ MOSTLY 

L.J SANDSTONE 

BREAKUP UNCONFORMITY 

p:j MOSTLY 

t:rJ LIMESTONE 

REEF FACIES 

f""') MOSTLY 

t;j SHALE 

FIGURE 36.-Construction of continental shelf during 

Jurassic time. In this period, the shelf margin was marked 

by two primary styles of shelf construction-outbuilding 

during Middle Jurassic time and upbuilding during Late 

Jurassic-Early Cretacous time. 

continental breakup, was marked primarily by 

out-building of the shelf. Late Jurassic-Early Cretaceous time was a period of shelf upbuilding 

with reef growth along the shelf margin. Correlation with the COST No. G-2 well on Georges 

Bank suggests that the change from outbuilding 

"\~· 

G-2 ® SELECTED WELL 

SEISMIC REFLECTION 

PROFILE 

----- PRESENT SHELF EDGE 

-- LOWER CRETACEOUS-UPPER 

JURASSIC SHELF EDGE 

"'f --- MIDDLE JURASSIC SHELF EDGE 

0 50 statute miles 

<?. '--------' 

~Okilameters 

~. "\<:f ~. 

to upbuilding correlates with a Late Jurassic influx of clastic material. 

The locations of the Middle Jurassic and Late 

Jurassic-Early Cretaceous shelf margins can be 

mapped using differing seismic facies. These locations and the location of the present shelf margin 

are shown in figure 37. The present shelf margin 

follows the 600-ft (200-m) bathymetric contour. 

The Late Jurassic-Early Cretaceous shelf margin 

was mapped by following the main mass of suspected reef trend on seismic records. The Middle 

Jurassic shelf margin was delineated by following 

the onset of oblique seismic facies nearest the 

shore. 

In the Baltimore Canyon trough area southeast 

of line 2, the age correlations of the shelf margin 

are tentative because the oldest strata penetrated 

in that area is of Late Jurassic age (Poag, 1980b). 

It was assumed, for purposes of interpretation 

in the Baltimore Canyon trough area, that the 

change from oblique to sigmoid seismic facies is 

~ ~. 

FIGURE 37.-Locations of the continental shelf margin during Middle Jurassic, Late Jurassic-Early Cretaceous, and present 

times. This mapping suggests that basinal shales (possibly containing oil-prone source rocks) underlie the present continental shelf in two areas-one in the vicinity of the Tenneco 642-2 well (the only well on the U.S. Atlantic margin reported 

to have flowed significant amounts of oil) and the other in the vicinity of Oceanographer Canyon on Georges Bank. The 

numbered seismic profiles are those that are discussed in the report. 

102 
the same age as Reflector B mapped in the 

Georges Bank area As in the Georges Bank area, 

the top of the Jurassic section occurs slightly 

below the top of the sigmoid facies representing 

the Upper Jurassic-Lower Cretaceous shelf edge. 

In the Georges Bank basin, the Late JurassicEarly Cretaceous shelf margin lies just seaward 

of the present shelf margin except in vicinity of 

line 20 (fig. 37). In the Baltimore Canyon trough 

area, the Late Jurassic-Early Cretaceous shelf 

margin lies almost 30 mi (50 km) seaward of the 

present shelf-slope break. At the southern end of 

the Baltimore Canyon trough, along line 3, deepwater multiple reflections obscured most of the 

seismic data and prevented interpretation. The 

Middle Jurassic shelf margin lies shoreward of 

the present shelf-slope break except in the vicinity of the Long Island platfo~, where it is assumed to coincide with the Late Jurassic margin. 

SUMMARY 

Several generalizations about the petroleum 

geology of the shelf margin can be made from the 

foregoing discussion. Promising areas for petroleum accumulation occur on the continental shelf 

and especially on the continental slope. On the 

present continental shelf, petroleum may have accumulated in porous limestone or sandstone beds 

of Late Jurassic and Early Cretaceous age by upward migration along faults from possible 

organic-rich sinal shales of Middle Jurassic age. 

The most likely areas for such accumulations 

would be where Jurassic shales extend under the 

present shelf. As shown in figure 36, the maximum shoreward deposition of basinal shales occurred in Middle Jurassic time after continental 

breakup. The shoreward extent of these shales is 

represented by the Middle Jurassic shelf edge 

shown in figure 37. The maximum displacements 

between the Middle Jurassic and present shelf 

margins occur in the vicinity of line 2 in the 

Baltimore Canyon trough and in the vicinity of 

line 20 in the Georges Bank basin (fig. 37). These 

two areas are especially attractive for petroleum 

exploration because the only wildcat well on the 

U.S. Atlantic margin reported to date to have 

flowed significant amounts of oil is Tenneco 

642-2, located at the shelf margin in the vicinity 

of line 2. 

The oil (48.4 API gravity) from the Tenneco 

642-2 well flowed at a rate of 630 barrels p3r day 

from a thin Lower Cretaceous sandstone b('q at a 

depth of 8,315 ft (2,535 m) (Mattick and Bayer, 

1980). According to these authors, the shallow 

depth of the discovery, together with geochemical 

and temperature data from the COST No~, B-2 

and B-3 wells (Scholle, 1977a, 1980), preclu-ie the 

possibility that the oil was generated in proximate strata Whether the 642-2 reservoir was 

charged with liquid hydrocarbons genera~ed in 

more deeply buried basin facies is not known, but 

normal faults mapped in the vicinity of the Tenneco 642-2 well (Mattick and others, 1981) could 

have provided the necessary avenues for u:oward 

migration to Lower Cretaceous beds. 

On the Atlantic continental slope of the l Jnited 

States, a primary task of petroleum exploration 

will be to locate possible hydrocarbon traps i'l forereef, reef, and backreef facies (fig. 38). Alt'lough 

not yet tested, the basinal shales that interfinger 

with carbonate rocks of the forereef facies Ir~Y be 

some of the best potential source rocks on tlTe continental slope in this area Data from the COST 

wells drilled on the continental shelf (Scholle, 

1977b, 1979, 1980; Amato and Bebout, 1980; 

Amato and Simonis, 1980) indicate that rocks 

deposited in the backreef environment havn poor 

potential to generate liquid hydrocarbons. 

If these basinal shales prove to have h~ d the 

capacity to generate large amounts of petroleum, 

the key to hydroca..rbon production wiJl be. locating strata with high porosity and permeability, 

103 

BACKREEF REEF 

~REEFAL • SHALE 

CJ SANDSTONE ~REEF TAWS 

FIGURE 38.-Forereef, reef, and backreef facies of a crrbonate 

bank. Basinal shales deposited in the forereef area could 

prove to be good source rocks for the generation of liquid 

hydrocarbons. 
which formed as a result of subaerial exposure 

during periods of relatively low sea level. According to Benson and others (1976), Lower Cretaceous reef, bank, and backreef facies in DSDP holes 

390, 392, and 392A all showed "evidence of subaerial weathering and leaching by fresh water.'' 

Although Mattick and others (1978) considered 

the Mesozoic shelf margin complex of the U.S. 

Atlantic comparable to the reef and forereef trend 

of the El Abra-Tamaulipas Formation of the 

Golden Lane and Poza Rica trends of Mexico, 

Simonis (1979, p. 105) points out that there have 

been no discoveries of hydrocarbons in the Upper 

and Middle Jurassic Abenaki Formation (carbonate unit) of the Scotian shelf, offshore eastern 

Canada, and that oolitic limestone penetrated in 

the COST No. B-3 well had porosities of less than 

8 percent and permeabilities of less than 0.1 mD. 

Although comparison with the Abenaki Formation (Middle to Late Jurassic age) of the Scotian 

shelf would suggest that carbonate units of the 

same age on the U.S. Atlantic margin are usually 

tight, the Shell Demascota G-32 well, drilled as a 

shelf edge test on the Scotian shelf, penetrated 

104 

551 ft (168m) of porous dolomite and limestone 

(including reef carbonates) that have porosities as 

high as 14 percent in the limesto:"le and fracture 

porosities of unknown magnitude in the dolomite 

(Given, 1977, p. 74). The dolomite in the Iroquois 

Formation (Upper Triassic, Ea~ly to Middle 

Jurassic) on the Scotian shelf hF~ porosities as 

high as 15 percent and oil staining has been 

reported in several wells (Given, 1977, p. 71). It is 

not known whether such potentizl reservoirs exist on the old shelf margin (the pr~sent continental slope) in the Georges Bank a":"ea, or whether 

these reservoirs have been charrred with sufficient amounts of liquid hydrocar':lons generated 

in the nearby basin facies. 

As can be seen from figure 37, in the Georges 

Bank area the Upper Jurassic-Lo~er Cretaceous 

reef trend underlies relatively shallow waters of 

the upper slope. In other areas of the U.S. Atlantic margin, this feature is under C'~eper water on 

the lower slope. Therefore, the Georges Bank 

should be one of the first areas targeted for the 

exploration of potential reservoirs in Mesozoic 

reef trends on the Atlantic margir. 
Organic Geochemistry of the Georges Bank Basir 

COST Nos. G-1 and G-2 Wells 

R. E. Miller, H. E. Lerch, G. E. Claypool, M. A. Smith, 

D. K. Owings, D. T. Ligon, and S. B. Eisner 

PURPOSE AND SCOPE 

The objectives of this petroleum geochemistry 

study were to (1) compare the source-rock characteristics of the stratigraphic intervals that may 

be considered prospects for the generation of oil 

or natural gas in the COST Nos. G-1 and G-2 

wells from the Georges Bank basin; (2) assess the 

depth of burial required for the onset of thermal 

maturation processes; and (3) evaluate the geochemical effects that mud additives may have on 

the source-rock interpretations. 

CONCEPTS AND TERMS 

The basic concepts of petroleum generation and 

source rock geochemistry used in this study are 

those established by V assoyevich and others 

(1970), Dow (1977), Tissot and Welte (1978), and 

Hunt (1974, 1978, 1979). The terms used to 

describe source-rock richness, maturity, and 

potential are consistent with the definitions and 

concepts reported by Claypool and others (1977) 

and Miller and others (1979, 1980). 

The quality or organic richness of a source 

shale and the source potential of such a bed to 

provide petroleum hydrocarbons may be indicated by (1) a minimum amount of total organic 

carbon (0.7 to 1.0 weight percent for argillaceous 

rocks); (2) pyrolytic oil yields greater than 0.2 to 

0.3 percent, and (3) solvent extractable hydrocarbon concentrations in excess of 100 to 500 ppm. 

It is important to note that the weight percent of 

total organic carbon necessary to constitute an 

excellent, good, or poor source rock is not as well 

defined for fine-grained, medium- to dark-gray 

limestones and dolomites. Hunt (1979) points out 

that because of the amorphous nature of the 

organic matter derived from hydrog~n-rich 

marine algae, dark-gray carbonates may have the 

potential to generate more hydrocarbonr than 

shales with equivalent amounts of total o ... ganic 

matter. Thus, medium- to fine-grained, dar1 

... ·gray 

to dull-brown limestones and dolomites ~ith a 

total organic carbon content as low as 0.3 ~~eight 

percent may have sufficient richness to be classified as source rocks (Hunt, 1967). 

The definitions of the terms thermally immature and thermally mature are those estab Hshed 

by Claypool and others (1977) and Mill~r and 

others (1979, 1980). If sedimentary rocks that 

contain an abundance of organic matter are subjected to thermal pyrolysis and are sh.own to be 

capable of generating petroleum hydroca··bons, 

and yet these organic-rich sedimentary rocks 

have not been altered by thermochomical 

petroleum-generating reactions to the degrM that 

a minimum amount of petroleum has been generated and physically expelled, then the sourr~ rock 

is defined as "immature." A source rock is 

''mature'' when thermochemical processer have 

converted the indigenous extractable hydrocarbons to a molecular composition and c~ncentration that is identical to that of petrolemn, and 

the extractable hydrocarbons are present in quantities of about 1 to 2 percent of the total o•ganic 

carbon. 

"Possible" or "potential" source rock refers to 

the degree of thermal maturity of the organic-rich 

rock. An immature organic-rich rock is defi~ed as 

a "potential source rock," whereas a the:-:-mally 

mature organic-rich rock is designated a "possible source rock" (Claypool and others, 1977; 

Miller and others, 1979, 1980). 

105 
ANALYTICAL METHODS AND PROCEDURES 

The USGS analyzed 23 well-cutting samples 

from the COST No. G-1 well from 1,090 to 

16,070 ft (332 to 4,898 m) and 26 well-cutting 

samples from the COST No. G-2 (1,190 to 

21,540 ft; 363 to 6,565 m). The unwashed well cuttings were removed from their plastic storage 

bags, and the drilling mud was carefully removed 

from each rock chip by thoroughly washing each 

chip under running water on a Tyler 100-mesh 

(150-~tm) screen. The washed rock chips were 

oven dried at 95° to 104° F (35° to 40° C). Each 

sample was examined under a binocular microscope, the lithology was described, and all of the 

foreign substances were removed, including 

string, plastic, rubber, and mica The lithologic 

descriptions of the samples analyzed for the 

COST Nos. G-1 and G-2 wells are shown in 

tables 1 and 2, respectively. Only those rock chips 

larger than 10 to 20 mesh (2.0 to 0.85 mm) were 

used for the C15+ hydrocarbon analyses. Each 

sample was ground, using mortar and pestle, to 

smaller than 60 mesh (250 ~tm) and weighed. Aliquots of the ground sample were taken for totalorganic-carbon determinations. Thermal pyrolysis analyses were determined on a separate set of 

washed and ground samples from depths of burial 

that were similar to those used for the extractable 

c15+ hydrocarbon studies. 

The details of the solvent-extraction methods, 

liquid-column chromatography, and gas chromatography procedures employed for the cl5+ 

liquid-hydrocarbon analyses have been described 

previously (Miller and others, 1979, 1980). The 

major steps involved are Soxhlet-solvent extraction in chloroform, followed by removal of sulfur 

by passing the sample over activated copper, 

then elution-column chromatography (gravimetries) on silica gel. The saturated paraffinnaphthene fractions were analyzed both qualitatively and quantitatively on Perkin-Elmer Sigma 

2-B and 3920 gas chromatographs, respectively. 

Both systems were supported by Sigma 10 data 

microprocessors. The qualitative gas chromatographic analyses were performed on 8 ft 

X 0.125 in. (2.4 m X 0.318 em) stainless steel columns packed with 3 percent OV -101, 100- to 

200-mesh (150- to 75-~tm) GCQ. The column temperature was 176° F (80° C) at injection and was 

programmed to increase initially at a rate of 

29° F/min (16° C/min) for 8 minut')s and then at a 

rate of 14° F/min (8° C/min) to a final temperature of 572° F (300° C). Quantitative analyses 

were performed on an OV -1 50-ft (15-m) SCOT 

column. 'rhe column was held for one minute at 

an injection temperature of 212c F (100° C); it 

was then programmed to increa~e at 7 o F/min 

(4 o C/min) to a final temperature of 4 73 o F 

(245 o C) and held at the final tenperature until 

n-C32 eluted. The following expre~sion, modified 

from Hunt (1974), was used to ca ~ulate the Carbon Preference Index (CPI): 

(%nC25 + %nC27 + %nC29 + %nCa1l (%nC25 + %nC21 + %nC29 + %nCa1l 

(%nC24 + %nC2s + %nC28 + %nCaol + (%nC26 + %nC28 + %nCao + %nC32) CPI=--~--~--~--~----~--~---=---= 

Total organic carbon is a mea ~ure of the organic richness of a source rock. Triplicate total 

organic carbon analyses were performed by the 

USGS on dried, weighed ali ~uots of the 

carbonate-free residue produced by leaching with 

hot, 6-normal hydrochloric acid of approximately 

0.07 oz avdp (0.2 g) of ground sample smaller 

than 60 mesh (250 ~tm). The samples were combusted in a Perkin-Elmer model 240 Carbon, 

Hydrogen, Nitrogen Analyzer. T.'.,a. organic carbon analyses for the thermal pyrolysis studies 

were performed by Rhinehart Laboratories, Arvada, Colo., on sample aliquots us:~ng the chromic 

oxidation method outlined by Burlt (1970). 

The thermal pyrolysis analyse~ performed in 

this study were carried out by the USGS on a 

Rock-Eval system following the basic principles 

of source-ock characterization of Espitalie and 

others (1977). The terms used to describe the thermal pyrolysis measurements are those of Claypool and Reed (1976), Claypool an-i others (1977), 

Tissot and Welte (1978), and Miller and others 

(1979, 1980). The free or indigeno·ts hydrocarbon 

component (expressed as mg HC/gC (ppt)) already present in the rock and vola~ilized when the 

rock is heated at 481 o F (250° C) for five minutes 

is the original generation potential of the source 

rock, S1• Those hydrocarbons arq related compounds generated by pyrolysis f~ temperatures 

from about 480° to 1,020° F (250° to 550° C) from 

the nonvolatile organic matter are referred to as 

the residual generation potentia 1

, expressed by 

106 
the term s2. sl and s2 are expressed in units of 

mgHC/gC (ppt). The sum (S1 + S2) is expressed on 

a weight percent basis and is a measure of the 

generation potential of the rock when expressed 

in kgHC/ton rock (Tissot and Welte, 1978). The 

carbon dioxide generated from the kerogen, S3, 

was not determined . for the kerogens in this 

study. 

The ratio of pyrolytic hydrocarbon yield (S1 

+ S2) to percent total organic carbon is a measure 

of the thermal maturation of the organic matter. 

The maximum temperature at which the yield of 

volatile organic components is produced by pyrolysis of the solid organic matter (Ts2 °C) is also 

used as an indicator of thermal maturation 

(Tissot and Welte, 1978). The ratio S2/0rg. C is 

the hydrogen index, whereas SJOrg. C (not determined) is a measure of the oxygen content of a 

kerogen (Tissot and Welte, 1978). Atomic (hydrogen/carbon) ratios, carbon isotopic compositions 

(o1SC PDB), and classes of relative percent of 

kerogen are also used to evaluate the kerogen 

types. 

RESULTS AND DISCUSSION 

This study compares the source-rock potential 

of the sedimentary rocks in the Georges Bank 

COST wells No. 1 and No.2. The interpretations 

of source-rock richness, maturity, and type based 

on the results of different geochemical techniques 

have been assessed and evaluated. 

The amount and molecular composition of the 

solvent-extractable organic matter in shales is 

considered to be indicative of the quality (richness), degree of thermal maturation, and type of 

original organic matter, assuming that the extractable organic matter is indigenous to the 

sedimentary rocks (Tissot and Welte, 1978; 

Miller and others, 1979, 1980). Lithologic descriptions, extractable organic matter data, and 

paraffin-naphthene hydrocarbon gas chromatograms for the Georges Bank COST Nos. 1 and 2 

wells are given in tables 1-4 and figures 39-51. 

Thermal pyrolysis-FID analyses of selected well 

cuttings for determination of the original genetic 

(Sl) and residual (S2) source-rock potential were 

carried out on sample suites different from those 

used for the extractable-organic-matter analyses. 

The whole-rock thermal evolution (pyrolysis) data 

are reported in tables 5 and 6. 

Geochemical analyses on different sampl,~ sets 

collected from the COST Nos. G-1 and G-2 wells 

were performed for the drilling participants by 

several commercial laboratories. These date have 

been summarized by Smith (1980) and Smith and 

Shaw (1980). Measurements of relative kerogen 

types and abundances (percent) and th~rmal 

alteration indices (T AI) determined by optical 

methods were made by GeoChem Laborat.Qries, 

Inc., for both wells; vitrinite reflec+.ance 

measurements were conducted by Superior Oil 

Company for the COST No. G-1 well and by Core 

Laboratories, Inc., for the G-2 well; hydPJgencarbon ratios were provided by Amoco Pr"Xiuction Company for the COST No. G-1 and by Core 

Laboratories, Inc., for the COST No. G-2; stable 

carbon isotope ratios of the saturated paraffinnaphthene and aromatic hydrocarbons, as w~ll as 

the total extractables and kerogens were determined by Phillips Petroleum Company for both 

COST wells (J. G. Erdman, written commun., 

1978). The concentrations and distributio'ls of 

the light hydrocarbons (C1 to C4) and gas·olinerange hydrocarbons (C5 to C7) were determin<:\d by 

GeoChem Laboratories, Inc., for both wells. 

These data are shown in summary depth pr~files 

in figures 53-56. 

Drilling mud additives may influence th ~ molecular composition and distribution of the cl5+ 

saturated paraffin-naphthene hydrocarbons and 

as a consequence can affect interpretations of the 

maturity and type of the indigenous, extrar.table 

organic matter (K. F. Thompson, Atlantic Richfield, written commun., 1977; Miller and o~-hers, 

1979, 1980). Mud additive effects are belieY~d to 

be of particular importance in limestones that 

have less than 0.3 percent organic matter, especially if the organic matter is not all lipt.initic 

(J. M. Hunt, written commun., 1981). Aliqu'lts of 

the major mud additive components used iiJ drilling the COST G-1 and G-2 wells were not made 

available to the USGS for direct comparative 

analysis. However, previously analyzed mud additives ·similar in type and composition to those 

used in drilling both wells were compared to make 

a first-order assessment of the possible influence 

such additives may have had on the distrib 'ltion 

and composition of the extractable hydroca"":"bons 

(Miller and others, 1979, 1980). The cutting samples used in this study were thoroughly washed, 

107 
TABLE !.-Lithologic descriptions of COST No. G-1 well cuttings used for organic geochemical analyses 

[Lithologic descriptions by F. Adinolfi and D. Shaw] 

Depth 

Feet Meters 

1,090- 1,130 332- 344 

2,080- 2,110 634- 643 

3,190- 3,220 972- 981 

4,000- 4,030 1,219-1,228 

5,140- 5,170 1,567-1,576 

5,940- 5,950 1,811-1,814 

7,020- 7,060 2,140-2,152 

8,040- 8,080 2,451-2,463 

9,030- 9,070 2,752-2,765 

9,540- 9,580 2,908-2,920 

10,020-10,060 3,054-3,066 

10,440-10,480 3,182-3,194 

10,950-10,970 3,338-3,344 

Lithology 

95% coarse- to very coarse-grained quartz sand; 3% coarse, golden-brown feldspar fr~ents; 1% fossil fragments, mostly pelecypods; 1% coarse muscovite flakes, green chlorite, traces of medium- to fine-grained glauconite pellets, lignite, chert, igneous rock 

fragments, coarse-grained feldspathic sandstone, brown glauconitic siltstone, hematite, ph~sphate, mica schist, fine-grained quartz fragments and quartz pebbles, and aragonite. 

80% white, very coarse- to coarse-grained quartz sand; 10% gray to buff quartz and feldspar 

gravel, subrounded to well rounded; 6% light-gray/ sandy, silty, micacE:~us, and calcareous 

mudstone; 3% tan mud and claystone; 1% mica flaKes, lignite, pyrite, chy, and fine-grained 

quartz sand and sandstone. 

97% white to clear, very coarse- to medium-grained quartz sand with mi"'or pebbles; 3% tan 

to brownish-red sandy mudstone; traces of lignite, chert, large feldspa~ fragments, pyrite, 

muscovite, hematite, and glauconite. 

95% coarse- to very coarse-grained quartz sand; 2% white to buff feldspar sand and gravel; 2% 

gray coarse-grained quartz sandstone with buff mud matrix; 1% tan, hard mudstone; traces of 

lignite, glauconite, calcite, pyrite, and very fine-grained silica-cemented qu "'rtz sandstone. 

96% white, coarse- to medium-grained quartz sand; 3% black to dark-gray lignite; 1% lightbrown mudstone; traces of feldspar, hematite, muscovite, pyrite, calca~ous siltstone, and 

peat. 

30% white medium- to very fine-grained calcite-cemented sandstone; 30% medium-gray, 

calcareous fissile shale; 25% hard tan mudstone with minor sandy mudstone; 5% mediumto fine- grained angular quartz fragments; 5% light-gray siltstone; 1% black to dark-gray 

lignite; traces of calcite, aragonite, pyrite, and muscovite. 

60% very coarse- to medium-grained sub-arkosic sand (15% feldspar); 10% red calcareous 

mudstone; 5% feldspar gravels; 5% white calcite-cemented sandstone; 5% red siltstone; 5% 

green siltstone; 4% quartz gravel; 3% medium-grained arkosic sandston1 with red hematite 

cement; 3% light- to medium-gray, slightly calcareous siltstone; tracr.q of calcite, chalk, 

black coal, and mica 

45% very coarse- to medium-grained feldspathic sand; 30% reddish-brown sandstone; 10% 

red calcareous siltstone; 5% feldspar gravel; 4% quartz gravel; 2% whi+~ calcite-cemented, 

medium-grained quartz sandstone; 2% light-gray calcareous shale; 2% m~um- to very finegrained, green, purple, and red arkosic sandstone; traces of coal, calcite, and mica 

35% reddish-brown mudstone; 30% medium- to dark-gray shale; ~0% white, calcitecemented sandstone; 5% brown siltstone; 5% light-brown, very fine-grl1'ined arkosic sandstone; 5% medium- to coarse-grained quartz sand; traces of coal, feldspar, buff mudstone, 

and mica 

40% white, coarse- to fine-grained quartzarenite; 40% red to reddish-brown mudstone; 8% coarse- to medium-grained quartz sand having angular grains, generally white; 5% arkosic, red, very fine grained sandstone and siltstone; 5% gray siltstone; 2% C('!'l.rse to very coarse feldspar fragments; traces of feldspar and quartz pebbles. 

25% oolitic quartz sandstone (medium-gray oolites in a very fine-grainei quartz sandstone 

matrix); 25% dark-brown to reddish-brown mudstone; 25% gray, soft, fi~sile, somewhat silty shale; 10% slightly oolitic quartzarenite, oolitic sandstone, sandy oolite, and oolitic 

limestone; 10% wliite, calcite-cemented, very fine-grained sandstone; 5% brown dolomitic 

limestone; traces of coal, mica, medium- to fine-grained quartz fragment:'~. and feldspar pebbles. 

40% buff limestone with micritic matrix; 20% medium-gray shale; 10% oolitic limestone; 

10% brownish-gray, slightly dolomitic limestone; 10% light-gray caJcareous shale; 5% 

white, medium- to fine-grained, calcite-cemented sandstone (quartzarenit~); 2% white to tan, 

slightly calcareous anhydrite; 1% brownish-red mudstone; 1% red shale; 1% brown, arkosic, 

medium-grained sandstone; traces of sandy anhydrite, quartz grains, pyrite, and green 

shale. 

38% buff to white anhydritic sandstone, very fine-grained to fine-grai.,ed; 30% ~nishgray to medium-gray fissile shale; 10% brown to bufflimestone; 10% lig'"-t to reddisn-brown 

shale; 5% white to buff anhydrite; 5% buff siltstone and sandy anhyrlrite; 2% very finegrained quartzarenite; traces of calcite, coarse quartz grains, and oolitic fur~stone. 

108 
TABLE !.-Lithologic descriptions of COST No. G-1 weU cuttings used for organic geochemical analyses-Continu~~ 

[Lithologic descriptions by F. Adinolfi and D. Shaw] 

Depth 

Feet Meters 

11,220-11,260 3,420-3,432 

11,850-11,890 3,612-3,624 

12,360-12,400 3,767-3,780 

12,960-13,000 3,950-3,962 

13,530-13,570 4,124-4,136 

14,040-14,080 4,279-4,292 

14,550-14,590 4,435-4,446 

15,040-15,080 4,584-4,596 

15,640-15,670 4,767-4,776 

16,030-16,070 4,886-4,898 

Lithology 

45% brown micritic limestone; 30% slightly siliceous, light- to medium-gray hard shale; 10% 

buff, slightly sandy siltstone; 5% white to buff, finely crystalline liniestone; 5% reddishbrown shale; 2% green shale; 2% dark-gray laminated micaceous shale; 1% red siltstone and 

fine-grained white slightly micaceous sandstone with subangular to angular grains; traces 

of orange hematite staining, anhydrite, and coal. 

40% medium- to very fine-grained, white to light-pink quartz sandstone; 20% medium- to 

dark-gray shale, somewhat fissile; 15% reddish-brown shale with minor silty shale; 10% 

medium-grained, tan arkosic sandstone, tightly cemented; 5% medium to coarse quartz 

fragments; 5% red and gray siltstone; 5% brown micritic limestone; traces of blacl· coal, 

biotite, and white anhydrite. 

25% white, ,P-ink, and light-gray, fine-grained feldspathic sandstone, silica-cemented~ 18% 

red silty muastone; 18% gray and buff dolomite, some coated with white anhydrite; 15% 

pink to white, transparent anhydrite, some sucrosic; 7% medium- to dark-gray, fissfe and 

carbonaceous shale; 5% hard, red shale; 5% brown, micritic, dolomitic limestone; 5% white 

to buff sparry limestone; 2% red, micaceous siltstone; traces of coal, biotite, c:alcite, 

hematite, purple sandstone, green siltstone, and laminated gray siltstone. 

55% anhydrite; 25% reddish-brown mudstone (coated with yellow anhydrite); 10% drrk- to 

medium-gray, slightly carbonaceous shale (coated with anhydrite) and minor light-green 

shale; 10% medium- and light-gray dolomite; trace of very fine-grained sandstone. 

40% light- to medium-gray and brown, micritic to vuggy dolomite, some porous: 17% 

anhydrite, some yellowish brown and microcrystalline, some white, sucrosic, and cryp- tocrystalline; 15% sandstone, some quartzitic (white with anhydrite and silica cement. very 

fine-grained to fine-grained); 10% medium- to dark-gray shale, 8% reddish-brown mu~~tone 

and minor muddy siltstone; 5% light-gray dolomite with clear anhydrite nodules; 3% white 

crystalline limestone with sparry calcite cement; 2% pelletal dolomite; traces of coal, ryrite, 

hematite, and large quartz grains. 

30% light-gray to buff micritic dolomite; 20% tan, white, buff and light-gray anhydrite; 15% 

red mudstone; 10% buff to white anhydritic dolomite; 10% red micaceous siltstone.: 10% 

dark-gray carbonaceous shale and medium-gray, slightly micaceous shale; 5% very finegrained, pink and reddish-brown sandstone; traces of coal, and calcite. 

35% red medium- to very fine-g_.:ained sandstone, some with anhydrite cement; 20% 

medium-hard, red shale, some With anhydrite streaks; 20% white, tan, pink, and buff 

anhydrite; 5% white anhydritic sandstone with red hematite cement; 5% large <'~lartz 

fragments; 5% sandy anhydrite; 5% very fine- grained white and gray sandstone; 4% 

micaceous dark- and medium-gray shale; 1% angular feldspar fragments; traces of mica, and 

hematite. 

35% white, coarse- to very coarse-grained quartz sandstone, some coated with red heirR.tite; 

25% white anhydrite coated with red hematite; 25% red, slightly micaceous mudston~; 8% 

red to tan dolomite; 5% very fine-grained to medium-grained red quartzitic sandston~; 2% 

light-gray to buff feldspar pebbles; traces of gray shale and hematite. 

65% red tan, white, and light-gray anhydrite, some sucrosic, some transparent, some slightly dolomitic; 23% tan, light-gray, and buff dolomite; 7% brownish-red mudston,1; 5% 

angular, white, coarse quartz grains; traces of gray shale, coal, brown and green p~bbly 

mudstone (green feldspar in brown clay matrix), light-green feldspar pebbles, fine-grained 

anhydrite, and light-green lithic sandstone. 

69% dark-gray to black, schistose, slaty, shiny', micaceous shale; 12% red to brownish-red 

silty mudstone; 8% brown to light-gray, very fine-grained sandstone; 7% bro~"'l to 

brownish-gray micritic dolomite; 2% buff to light-gray anhydrite; 2% brown and buff 

siltstone; traces of angular quartz pebbles, microbreccia of green sanidine in red mud 

matrix, coal, and white calcareous mudstone. 

sieved, and picked to eliminate the effects of mud 

additives, but very low levels of drilling mud 

contamination may have occurred in several intervals in the Jurassic section. Results for those 

intervals that are thought to be influenceq by 

mud additives have been marked on tatle 4. 

Figure 39 is the saturated paraffin-naphthene 

hydrocarbon gas chromatogram of leonr..Wte 

109 
TABLE 2.-Lithologic descriptions of COST No. G-2 well cuttings used for organic geochemical analyses 

[Descriptions by F. Adinolfi and D. Shaw] 

Depth 

Feet Meters 

1,190-12,220 363- 372 

2,180- 2,210 664- 674 

3,020- 3,050 920- 930 

4,130- 4,160 1,259-1,268 

6,070- 6,100 1,850-1,859 

7,000- 7,030 2,134-2,143 

7,990- 8,020 2,435-2,444 

9,010- 9,040 2,746-2,755 

10,490-10,510 3,197-3,203 

11,500-11,510 3,505-3,508 

12,520-12,540 3,816-3,822 

13,500-13,520 4,115-4,121 

14,480-14,500 4,414-4,420 

15,490-15,510 4,721-4,727 

15,900-15,920 4,846-4,852 

16,450-16,470 5,014-5,020 

17,020-17,540 5,188-5,346 

Lithology 

90% buff to light-yellow calcareous mud, slightly micaceous, with about 1% limonitic 

siltstone; 9% white to buff mud; traces of hematite and calcite. 

95% light-gray mud, slightly micaceous, moderately calcareous; 5% wh~te mud; trace white 

calcite, angular to round quartz grains, glauconite, chert, and hematite. 

90% grayish-brown calcareous mud; 4% fossil fragments; 5% white, ror'lded, coarse quartz 

grains; 1% drilling mud (buff); trace hematite, mica, calcite, coal, and possible pipe dope. 

90% gray, soft to firm, .eartly silty and sandy mudstone, contains spots of white, chalky 

limestone, abundant fossils, and shell fragments; 10% loose, very coarsfl quartz sand grains 

and tan, medium-grained, medium to well sorted sandstone with calcite cement and 

subangular glauconite. 

80% tan to tan-griD', argjllaceous, firm (some hard) micrite limestone; 20% gray, partly fissile, calcareous, silty shrue. 

70% medium-gray shaley limestone; 25% gray to buff limestone; 2% tan, silty mudstone, 

1% quartz grains, 2% gray shale; trace pipe dope, drilling mud, threads, gastropod fragments, and mica. 

80% white, very fine-grained, calcite-cemented quartz sandstone; 14% r~edium-gray, slightly calcareous shale; 4% red mudstone; 1% muscovite flakes; 1% oolit:~ limestone (brown 

pellets in gray matrix); trace brown lignite, and asphalt. 

40% silty, reddish-brown, micaceous shale with streaks of yellow-brown and gray mottling; 

25% micaceous quartz sandstone with detrital coal and calcite cement; 20% dark-brown, 

fissile, waxy, noncalcareous shale; 10% dark-gray, micaceous, noncal~areous shale; 2% 

light-pink to reddish sandstone and buff-white and brown pelletal limestone; 1% rounded 

coal grains; trace glauconite and foraminifers. 

30% microcrystalline, tan to light-brownish-gray limestone; 20% ooli~ic, buff-white, tan, 

and dark-brown limestone; 30% gray, silty shale with detrital coal; 15% yellow-brown to 

dark-reddish-brown micaceous, silty, shale; 5% fine-grained, sub-roun-ied white to light 

reddish-brown sandstone, well-cemented with calcite cements and containing detrital coal; 

traces of coal and yellow mudstone. 

90% microcrystalline, brown, gray, and buff-tan pelletal limestone; 8% <',~k-gray shale with 

traces of coal; 2% very fine-grained, green and white glauconitic quartzite sandstone. 

75% microcrystalline, blocky, light grayish-brown and buff-white limestone; 15% white and 

grayish-brown pelletal limestone; 3-5% light-gray, slightly micaceous, noncalcareous shale 

with disseminated organic material; 2% very fine-grained, light- to dark-green, hard 

glauconitic sandstone; 3% silty, micaceous, reddish-brown shale; 2% fine-grained, calcitecemented, glauconitic, light-green, clear, and white sandstone; trace ql'IU'tz grains, coarse- grained pyrite, coal, and orange rust staining. 

80% fine-grained to medium-grained, well-sorted, subrounded, pink to r~d. clear, and white 

sandstone containing quartz, feldspar, biotite, and glauconite; 15% grFv to grayish-brown limestone; 3% dark-gray, fissile, carbonaceous shale; 2% silty, micac('nus, reddish-brown 

shale; trace pelletal limestone, green, hard shale, and coal. 

40% yellow-brown, translucent dolomite; 40% white, light-gray and grayish-brown limestone with larger grains than the dolomite; 20% conglomeratic, well-cemented rock 

fragments of grayish-brown limestone and dark-brown, medium-crystalline dolomite in a matrix of yellow-brown, clear, to white anhydrite and calcite cement; trace gray shale, 

reddish-brown silty shale, and coal. 

45% light-gray, tan to brownish-gray micritic, partly dolomitized limestone; 45% browngray, dark-brownish-gray, and gray, very finely crystalline, partly arrpllaceous dolomite; 

10% dark-reddish hard shale and coal. 

40% buff micritic limestone; 29% medium-gray micrite limestone; 20% dark-gray, slightly 

shaley limestone; 9% sparry white limestone; 2% buff mudstone and grl;'y-white mud; trace 

pyrite, red mudstone, and hematite staining. 

40% light-gray to brownish-gray, partly pelletal, partly recrystallized micrite limestone; 

30% soft, white, chalky, limestone with sugary texture; 30% dark gray, argillaceous, 

dolomitic limestone. 

Composite.1 

110 
TABLE 2.-Lithologic descriptions of COST No. G-2 well cuttings used for organic geochemical analyses-Continued. 

[Descriptions by F. Adinolfi and D. Shaw] 

Depth 

Feet Meters 

17,020-17,040 5,188-5,194 

17,520-17,540 5,340-5,346 

17,4 70-17,520 5,325-5,340 

17,980-18,000 5,480-5,486 

18,4 70-18,500 5,630-5,639 

18,980-19,030 5,785-5,800 

19,500-19,530 5,944-5,953 

19,950-20,010 6,081-6,099 

20,480-20,520 6,242-6,254 

20,970-21,030 6,392-6,410 

21,460-21,540 6,541-6,565 

Lithology 

70% buff to cream, loosely consolidated limestone, mostly sparry calcite, sugary tex~red; 

25% medium- to dark-gray limey dolomite; 5% buff, cryst8llfue, sparry limestone; trac.e tan 

mudstone, black bituniinous limestone, and coal. 

40% buff limestone, micritic; 30% medium-gray shaley limestone; 10% light-gray calcrreous 

mudstone; 10% limey, dark dolomite, slightly shaley; 5% black, fibrous soft coal, m')st in 

fine fragments; 5% white, sparry limestone, sugary textured; traces of hematitA and 

asphaltite. 

60% tan, grayish-brown, and brown, micritic, blocky, dense, slightly dolomitic lime:3t.one; 

10% white, chalky micrite limestone; 20% white, clear, coarsely crystalline anhydrit£. with 

layers of dark-brown dolomite; 10% dark-gray and black, carbonaceous, slightly calcrreous 

shale; trace of a white, soft substance. 

55% buff micritic limestone; 15% white sucrosic, crystalline, sparry limestone; 30% shaley, 

dark- to medium-gray micritic limestone; trace dolomite, coal, hematite, limonite, and oolitic 

limestone. 

35% brownish-gray, micritic, sparry limestone; 35% buff sparry limestone, slightly 

anhydritic; 15% medium-gray micritic, argillaceous limestone; 12% dark-gray, shale~r and 

calcareous dolomite; 3% buff anhydrite; trace coal, tan limonite, bituminous limeston~, and 

oolitic limestone. 

95% dark-gray to black bituminous limestone, micritic; 2% white to buff po~·dery 

anhydrite; 2% dark-gray calcareous sandstone containing fine-grained angular fragments; 

1% medium- to light-gray limestone (micrite with sparry calcite cement). 

65% brownish-gray to medium-gray micrite limestone with minor sparry calcite ce"'lent; 

10% buff to light-gray anhydritic dolomite with sucrosic texture; 15% buff to white 

calcareous anhydrite, some chalky, some clear and microcrystalline; 10% dark-gray, 

micritic, bituminous limestone. 

25% light-gray micritic dolomite; 25% brownish-gray micritic dolomite· 25% darl·-gray shaley dolomite; 8% brown micritic limestone; 8% dark-gray dolomitic shale; 8% whit~ and 

buff anhydrite, some powdery and cryptocrystalline, some sucrosic and microcrystalline; 

1% brownish-gray calcareous dolomite; trace quartz grains and gypsum. 

75% brownish-gray to medium-gray micritic limestone; 10% dark-gray, shaly bituminous 

limestone; 10% powdery white anhydrite; 5% light-grayt sucrosic, calcareous dolomit£. with 

sparry calcite cement; trace white rmcrocrystalline anhydrite and quartz fragments. 

50% brownish-gray to medium-gray anhydritic micrite dolomite with sucrosic dol "'mite 

rhombs; 10% buff to white, anhydritic, powdery, chalky limestone; 40% tan, light- to 

medium-brown clear, and white anhydrite with greasy luster; trace dark-gray shale, cnartz 

sandstone, red mudstone, hematite, and calcite. 

35% light brown to brownish-gray dolomite, micritic greasy texture; 20% dark- to mediumgray dolomitic shale; 20% buff to light-brown micritic limestone; 20% buff, tan, and white 

anhydrite; 5% light- to medium-gray anhydritic dolomite; trace coal, red mudstone, 

micaceous siltstone, and white sandstone. 

1

The 17,020- to 17 ,540-ft sample is a composite of two samples from 17,020-17,040 and 17,520-17,540 ft. 

used in the commercial preparation of the mud from 17,500 to 18,000 ft (5,330 to 5,480 m), traces 

additive lignosulfonate. Except for the specific in- of an asphalt-like substance were found. Th~ gas 

tervals designated, the influence of this compo- chromatogram revealed only an unresolved envenent on the saturated hydrocarbon fraction ap- lope and had no resolved normal aliphatics. 

pears to be minimal because of the dissimilarity GeoChem Laboratories, Inc., observed a similar 

in the molecular distribution and concentration. substance below 14,000 ft (4,267 m), and a gas 

The effects of drilling mud additives on the chromatogram of their paraffin- naphthene fracdeeper stratigraphic samples are believed to be tion is shown in figure 39. This asphal~-1ike 

restricted to specific zones, because there is no substance was not found in the matrix of the. rock 

constant, pervasive mud-additive fingerprint on fragments but appeared to be coating only z part 

the entire suite of C15+ extractable hydrocarbons. of the individual rock chips and thus acted as a 

In USGS samples from the COST No. G-2 well, cement to hold several rock fragments tog~ther. 

111 
TABLE 3.-0rganic carbon and extractable organic matter, COST No. G-1 well 

Ratio of 

Ratio of total Ratio of total saturated Carbon 

Organic Total hydrocarbon to total hydrocarbon hydrocarbon Preference 

Depth carbon hydrocarbon organic carbon to extractable to aromatic Index 

Feet Meters (percentl (ppml (percentl organic matter hydrocarbon (CPI) 

Upper Cretaceous 

1,090- 1,130 332- 344 0.05 5.9 1.18 0.57 0.42 1.29 

2,080- 2,110 634- 643 .12 9.2 0.76 .98 .65 1.10 

Lower Cretaceous 

3,190- 3,220 972- 981 0.04 8.0 2.00 0.53 1.85 1.38 

4,000- 4,030 1,219-1,228 0.12 6.6 0.55 0.38 1.39 1.69 

5,140- 5,170 1,567-1,576 1.97 133.0 0.68 0.63 1.55 5.56 

Upper Jur888ic 

5,940- 5,950 1,811-1,814 2.70 110.7 0.41 0.31 0.52 2.55 

7,020- 7,060 2,140-2,152 0.12 8.8 .73 .19 .98 2.59 

8,040- 8,080 2,451-2,463 .21 70.9 3.37 .64 1.97 1.57 

9,030- 9,070 2,752-2,765 .69 26.3 .38 .34 1.55 2.17 

9,540- 9,580 2,908-2,920 .28 4.0 .14 .16 15.03 0.88 

10,020-10,060 3,054-3,066 .37 10.2 .28 .19 1.79 1.54 

Middle Jurassic 

10,440-10,480 3,182-3,194 0.30 19.1 0.63 0.69 1.58 0.94 

10,950-10,970 3,338-3,344 .28 62.1 2.21 .77 1.92 1.22 

11,220-11,260 3,420-3,432 .22 40.5 1.84 .65 2.50 1.11 

11,850-11,890 3,612-3,624 .53 21.6 .40 .32 1.42 1.31 

12,360-12,400 3,767-3,780 .18 25.21 1.40 .33 .86 1.42 

12,960-13,000 3,950-3,962 .14 47.9 3.42 .61 3.21 1.16 

13,530-13,570 4,124-4,136 .11 37.4 3.40 .69 1.36 1.20 

Lower Jurassic 

14,040-14,080 4,279-4,292 0.18 12.3 0.68 0.29 1.16 1.02 

14,550-14,590 4,435-4,447 .12 87.3 7.27 .59 4.21 .95 

15,040-15,080 4,584-4,596 .02 16.3 8.15 .40 2.08 .68 

Cambrian 

15,640-15,670 4,767-4,776 0.05 36.3 

16,030-16,070 4,886-4,898 .23 40.9 

The origin of this heavy hydrocarbon substance is 

unknown; it may be a well-cutting contaminant, 

but an indigenous source cannot be discounted. 

COMPARISON AND EVALUATION OF SOURCE-ROCK 

RICHNESS AND OF THE TYPE AND MATURITY 

CHARACTERISTICS OF THE ORGANIC MAnER IN THE 

COST NOS. G-1 AND G-2 WELLS 

TERTIARY 

The thin Tertiary strata recovered in the G-1 

and G-2 wells ranged in depth from 1,013 to 

1,030 ft (309 to 314m) and from 1,100 to 1,310 ft 

(33~ to 399 m), respectively. The Tertiary sediments in G-1 consisted of unconsolidated, coarseto very coarse-grained quartz sand with traces of 

glauconite, lignite, chert, mica schists, and 

phosphate. The G·-2 Tertiary sediments are calcareous muds with subordinate limonitic silt7.26 0.52 2.36 1.30 

1.77 .70 l.{\4 .91 

stone. Because of the lack of available Tertiary 

cuttings, only one interval reprer~nting the Tertiary in the COST G-2 (1,190 to 1,220 ft; 363 to 

372 m) underwent solvent extra~tion for determination of the total extractabl~~ hydrocarbons 

(153 ppm) and analysis for total organic carbon 

(0.95 percent by weight) (tables 3 and 4). The 

saturated paraffin-naphthene hydrocarbon gas 

chromatogram (fig. 43) shows an unresolved, 

bimodal complex mixture that is equal to or that 

predominates over the resolved aliphatics, a 

characteristic signature that suggests thermal 

immaturity. 

UPPER CRETACEOUS 

The Upper Cretaceous strata rr1'lge from 1,030 

to 2,680 ft (314 to 817 m) and 1,310 to 2,600 ft 

(399 to 792 m) in the COST Nos. G-1 and G-2 

wells, respectively. The G-1 Up per Cretaceous 

112 
TABLE 4.-0rganic carbon and extractable organic matter, COST No. G-2 well 

Ratio of 

Ratio of total Ratio of total saturated Ca"hon 

Organic Total hydrocarbon to total hydrocarbon hydrocarbon Pref4'l'ellce 

Depth carbon hydrocarbon organic carbon to extractable to aromatic In1ex 

Feet Meters (percent) (ppm) (percent) organic matter hydrocarbon (CPI) 

Tertiary 

1,190- 1,220 363- 372 0.95 153.1 16.61 0.51 4.01 1.75 

Upper Cretaceous 

2,180- 2,210 664- 674 1.06 74.0 0.69 0.34 2.94 2.36 

Lower Cretaceous 

3,020- 3,050 920- 930 1.06 162.7 1.53 0.69 4.10 2.17 

4,130- 4,160 1,259-1,268 0.42 42.9 1.02 0.42 2.09 1.79 

Upper Jurassic 

6,070- 6,100 1,850-1,859 0.55 154.3 2.80 0.54 4.35 1.73 

7,000- 7,030 2,134-2,143 0.86 74.5 .87 .58 1.73 1.23 

7,990- 8,020 2,435-2,444 .66 60.2 .91 .43 2.73 1.32 

9,010- 9,040 2,746-2,755 .72 344.7 4.65 .67 2.91 1.76 

10,490-10,510 3,197-3,203 .62 186.8 3.01 .83 3.44 1.44 

11,500-11,510 3,505-3,508 .31 109.4 3.51 .55 2.29 1.81 

Middle Jurassic 

'12,520-12,540 3,816-3,822 0.33 74.6 

13,500-13,520 4,115-4,121 .05 31.5 

14,480-14,500 4,414-4,420 .19 225.6 

'15,490-15,510 4,721-4,727 .29 792.3 

15,900-15,920 4,846-4,852 .14 65.2 

'16,450-16,470 5,014-5,020 .15 363.8 117,020-17,540 5,188-5,346 .24 179.0 

17,470-17,520 5,325-5,340 0.14 131.9 

'17 ,980-18,000 5,480-5,486 .17 93.9 

18,470-18,500 5,630-5,639 .12 32.0 

18,980-19,030 5, 785-5,800 0.29 117.9 

19,500-19,530 5,944-5,953 .18 125.4 

19,950-20,010 6,081-6,099 .15 75.8 

20,480-20,520 6,242-6,254 .10 42.0 

'20,970-21,030 6,392-6,410 .18 152.4 

21,460-21,540 6,541-6,565 .42 210.0 

1 Possible mud additive contamination. 2

17,020-17,540 is a composite interval of 17,020-17,040 and 17,520-17,540. 

strata are characterized by calcareous shales, 

coarse quartz sands, and gray sticky shales that 

contain trace amounts of glauconite, biotite, 

pyrite, lignite, feldspar, and calcite. In comparison, the Upper Cretaceous rocks of the G-2 

well are represented by light-gray calcareous 

shales, claystones, and chalky limestones with 

varying quantities of glauconite, fossil fragments, plant fragments, ostracods, foraminifers, 

mica, and pyrite (Lachance, 1980; Simonis, 1980). 

The Upper Cretaceous strata of the COST No. 

G-1 well contain significantly less total organic 

carbon than the Upper Cretaceous calcareous 

shales and fine to medium sands present in G-2. 

The total extractable hydrocarbons in the Upper 

Cretaceous of the G-1 are very low, averaging 

8.0 ppm, whereas the single Upper Cretaceous 

2.27 0.58 1.71 1.44 

6.30 .58 1.84 1.27 

11.89 .43 3.52 1.07 

27.31 .44 2.18 1.41 

4.65 .68 2.01 1.13 

24.26 .51 3.92 2.26 

7.45 .50 2.07 1.38 

9.42 0.41 3.07 1.15 

5.52 .42 2.67 1.53 

2.66 .47 1.91 1.07 

4.06 0.62 1.85 1.14 

6.96 .52 1.67 1.01 

5.05 .80 2.07 1.02 

4.20 1.41 1.58 1.77 

8.46 .52 1.26 .75 

5.00 .42 1.58 1.01 

sample analyzed from G-2 contains 74.0 ppm of 

total extractable hydrocarbons. The nitr">gen, 

sulfur, and oxygen contents of the Upper Cr~taceous interval in the COST No. G-1 well are about 

five times greater than in the Upper Creta~eous 

of the COST No. G-2 well (tables 1-4, figs. 40 and 

41). 

The gas chromatograms of the saturated 

paraffin-naphthene hydrocarbons of the T Jpper 

Cretaceous from the two wells are shovrn in 

figures 42 and 43. The resolved alkanes in th~ Upper Cretaceous strata from the G-1 (1 ,090-1,130 

and 2,080-2,110 ft; 332-344 and 634-643 m) have 

a molecular composition and boiling-point range 

that extends from about n-C15 to n-C32 and a CPI 

ratio that averages 1.20. The resolved alir"atic 

components are dominated by a broad, bin1odal, 

113 
I 

UJ 

U) 

z: 

0 

a.. 

U) 

UJ 

0:: 

0:: 

UJ 

Q 

0:: 

0 

u 

CARBON NUr1BER 

10 12 14 16 18 20 22 24 26 28 30 

LEONARDITE 

ASPHALTIC SUBSTANCE 

COST G-2 

15~000-15~050 FT 

4572-4587 M 

~ TIME-TEfi>ERATURE -

C

15 + FARAFFIN-NAPHTHENE 

ANALYSIS 

926-CONTAMINANT 

GEOCHEM INCORPORATED 

NAPHTHENES 

FIGURE 39.-Gas chromatographic analyses of (upper left) saturated paraffin-naphthene hydrocarbons in lignosulfonate 

(leonard.ite), (lower left) an asphalt-like substance isolated from the 15,000- to 15,050-ft (4,572- to 4,587-m) interval of the 

COST No. G-2 well by the USGS, and (at right) a solid black hydrocarbon substance isolated by GeoC'1em Laboratories, 

Inc., from the COST No. G-2 well at about 14,000 ft (4,267 m). 

unresolved complex mixture. In contrast, the extractable paraffin-naphthene hydrocarbons from 

the Upper Cretaceous rocks of G-2 (2,180-

2,210 ft; 664-674 m) are characterized by highly 

resolved alkanes that range from n-C1s to n-C2s 

and dominate over the much less pronounced bimodal, unresolved complex mixture. The predominant normal aliphatic species occur in the n-C15 

to n-C20 range and have a CPI ratio of 2.36 

(tables 3 and 4; figs. 42 and 43). The narrow range 

of the resolved alkanes (n-C15 to n-C20) is consistent with a thermally mature hydrocarbon assemblage and is similar to molecular distribution of 

diesel fuel. The pristane and phytane isoprenoid 

hydrocarbons are dominated by the resolved 

normal alkanes, a signature that is usually associated with mature saturated hydrocarbons. However, the shallow burial depth and the thermalpyrolysis maximum yield temperatures that 

range from 837° to 860° F (447° to 460° C) (tables 

3-6) are inconsistent with the extractable hydro114 

carbon chemical maturity signatures. The degree 

of convertibility of the sedimentary organic matter to petroleum hydrocarbons may be expressed 

by the ratio of the total pyrolytic hydrocarbons 

(S1 + S2) to total organic carbon (Claypool and 

others, 1977; Miller and others, 1979, 1980). This 

convertibility ratio for the Upr~r Cretaceous 

strata averages 8.9 percent for G-1 and 7.6 percent for G-2. Such values imply a strong influence of hydrogen-poor kerogens. The thermal 

pyrolytic measurements and geocl, ~mical sourcerock parameters indicate that the organic matter 

in the Upper Cretaceous strata is thermally immature and would be a poor source for liquid 

petroleum hydrocarbons in both wells of the 

Georges Bank basin. 

LOWER CRETACEOUS 

The Lower Cretaceous strata in the COST Nos. 

G-1 and G-2 wells range from 2,680 to 5,290 ft 
(817 to 1,612 m) and from 2,600 to 5,960 ft (792 to 

1,817 m), respectively. Alternating units of 

glauconitic, unfossiliferous sandstones and 

shales containing trace amounts of coal, pyrite, 

and plant fragments (with small amounts of silty 

dolomite near the base of the interval) characterize the Lower Cretaceous of the G-1. In contrast, the Albian sandstones of G-2 (2,500 to 

3,950 ft; 762 to 1,204 m) contain glauconitic 

pellets and shell fragments, plant debris, thin 

coal streaks, and carbonaceous dark-gray shales. 

Underlying these units is a bioclastic limestone 

intercalated with argillaceous micrites, calcareous claystones, and silty mudstones (3,950 to 

4,500 ft; 1,204 to 1,372 m). From 4,500 ft to 

5,320 ft (1,372 m to 1,622 m) are thickly bedded, 

poorly consolidated sandstones with thin beds of 

coal and lignitic shales (tables 1 and 2) (Lachance, 

1980; Simonis, 1980). 

Based on the combustion oxidation method, the 

Lower Cretaceous strata of the G-1 well contain 

very low amounts of total organic carbon: 0.04 

weight percent between 3,190 and 3,220 ft (972 

and 981 m), and 0.12 weight percent between 

4,000 and 4,030 ft (1,219 and 1,228 m). The exception is the interval from 5,140 to 5,170 ft (1,567 to 

1,576 m), which contains 1.97 weight percent 

total organic carbon. In comparison, the Lower 

Cretaceous strata from the COST No. G-2 well 

contain total organic carbon ranging from 0.42 to 

1.06 weight percent (tables 3 and 4). The total 

extractable hydrocarbon content for the Lower 

Cretaceous in the G-1 and G-2 averages 49 and 

103 ppm, respectively. The total organic carbon 

and total extractable hydrocarbon values indicate 

that the Lower Cretaceous strata of the Georges 

Bank basin have comparatively low source-rock 

quality and richness. The average total hydrocarbon to total organic carbon values are 1.07 percent for G-1 and 1.3 percent for G-2; total 

hydrocarbon to extractable organic matter ratios 

average 0.51 and 0.56 for G-1 and G-2 respectively; and saturated paraffin-naphthene to 

aromatic hydrocarbon ratios average 1.60 and 

3.10, respectively, for the Lower Cretaceous of 

G-1 and G-2 (tables 3 and 4). The saturated 

paraffin-naphthene to aromatic hydrocarbon 

ratio is unusually high, but may reflect the thermal history of the rocks as well as the type and 

amount of the organic matter and the preferential 

destruction of aromatic hydrocarbons (Baker, 

1972; Baker and Claypool, 1970; Louis and 

115 

Tissot, 1967). The low hydrocarbon to total 

organic carbon and total hydrocarbon to e::-·tractable organic matter ratios, and the averag~ CPI 

values of 2.88 for the G-1 and 1.98 forth~ G-2 

well suggest that the organic matter in the Lower 

Cretaceous strata is thermally immature with 

regard to liquid hydrocarbon generation (tables 3 

and 4). 

The saturated paraffin-naphthene hydrocarbon 

gas chromatograms for the Lower Cretr~eous 

from the No. COST G-1 well are characteriz-ed by 

a moderately strong bimodal, unresolved complex mixture (fig. 42). The resolved aliphatic 

hydrocarbons have a molecular compositio"1 and 

distribution that ranges from n-Cl5 to n-Cso· 

With the exception of those in the 4,000- to 

4,030-ft (1,219- to 1,228-m) interval, the rerf)lved 

normal alkanes are equal to or dominant ov~r the 

unresolved branched and cyclic paraffin env~lope. 

The resolved aliphatics also show significant concentrations of the n-C22 to n-Cso plant-wax 

hydrocarbons probably associated with terestrially derived organic matter. In comparison, saturated paraffin-naphthene hydrocarbon gas chromatograms for Lower Cretaceous strata fro:-n the 

COST No. G-2 well show a well resolved, strong 

predominance of the normal aliphatics ovnr the 

unimodal unresolved complex envelope (fig. 43). 

The narrow range of molecular compositior and 

distribution of the normal alkanes (n-Cl5 to n-C22) 

in these Lower Cretaceous strata tend to resemble those of thermally mature hydroc::-~~bon 

assemblages, whose presence may also be indicated by the predominance of the normal ar-:anes 

over the isoprenoid hydrocarbons pristane and 

phytane. Inconsistent with an interpretathn of 

maturity, however, is the odd-carbon preiominance indicated by an average CPI ratio of 1.98, 

which suggests thermal immaturity (tab l.e 4). 

However, because of the restricted range of the 

resolved normal alkanes the CPI ratio of 1.98 is 

considered to be of limited use as an indica tor of 

thermal maturity (Swetland and others, 1978; 

Miller and others, 1979, 1980; figs. 42 aiJd 43; 

tables 3 and 4). Although the influence of diesel 

fuel cannot be totally disregarded, the nm-row 

molecular range and distribution of the ref">lved 

aliphatics probably reflects a marine algal s·ource 

of the aliphatics (Hunt, 1979). 

The thermal pyrolysis convertibility para"lleter 

(S1+S2)/0rg. C of the Lower Cretaceous rocks 
TOTAL PARAFFIN- AROMATICEXTRACTABLES NAPHTHENE HYDROCARBONS ELUTED NSO (ppm) 

(ppm) (ppm) (ppm) 

400 500 0 ,o __ ~,oo~--,---~3oo~ __ To-r~2ro.-40~~sor.~so~~or,~2~o~~40r-,so~~sor.-T-.~~~~~~~~~~~ 

3000 1000 

6000 

!h 

a: 

w 

1-

w 

~ 

~ 

1-

w 

w 

u. 

o- ~ 

:I 

1-

II. 

w 

~ 9000 II. 

w 

0 0 

4000 

5000 
....... 

Iii 

~ 

2000 

4000 

8000 

8000 

~ 10.000 

Ul 

~ c 

12.000 

14,000 

6.000 

18,000 

TOTAL ORGANIC 

CARBON(%) 0.4 0.8 1.2 1.8 2.0 2.4 0 

TOTAL HYDROCARBON PARAFF1N-NAPHTHENE 

TOTAL ORGANIC CARBON(%) AROMATIC HYDROCARBON 

2.0 4.0 

FIGURE 40.-Summary of organic-richness analyses on C15+ hydrocarbon extractables of samples from the COST No. G-1 well. 

1000 

2000 

II'J 

a: 

~ Ul 

~ 

3000 ~ 

4000 

&000 

Ul 

~ c 
TOTAL PARA.Ft=W- AROMATICEXTRACTABLE& NAPHTHENE HYDROCARBONS ELUTED NSO 

(ppm) (ppm) (ppm) (pprn) 

o 200 aoo 1200 1 eoo o 200 400 eoo o eo 180 240 320 o 200 400 aoo soo o~~~~~~-r~~~~~~~~,-T-~~~-r~~~~~~-r~~~~ 

3000 1000 

8000 

2000 

(I) 

It 9000 

3000 ~ 1-

Ill 

Ill 

~ 

Ill 

"' ~ ~ 00 

:I 

:I 

1- t: 12.000 

IL Ill 

4000 ~ 0 

5000 

8000 

21,000 
TOTAL HYDROCARBON PARAFFIN-NAPHTHENE 

TOTAL EXTRAc:T TOTAL EXTRACT 

TOTAL ORGANIC 

CARBON 

(%) 

0 --- --- -·- . ·- ··- .. - - --- - 0 0_2 0.4 0.8 0.8 1.0 

TOTAL HYDROCARBON PARAFFIN-NAPHTHENE 

TOTAL ORGANIC 

CARBON (%) AROMATIC-HYDROCARBONS 

0 4 8 12 18 20 24 28 0 1.0 2.0 3.0 4.0 

Oj I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

1000 

2000 

., ~ I / I / I / ll I / I I ~ I J I l 1/ I ~ I l +-i 

c 

5000 

6000 

FIGURE 41.-Summary of organic-richness analyses on C15+ hydrocarbon extractables of samples from the COST No. G-2 well. 
CARBON NUMBER 

I' I I I I I I I 1'1'1'1 30 28 26 24 22 20 18 16 14 12 10 

HYDROCARBON 

STANDARD 

1090-1130 FT 

332-344 M 

2080-2110 FT 

634-643 M 

3190-3220 FT 

972-981 M 

4000-4030 FT 

1219-1228 M 

5140-5170 FT 

1567-1576 M 

CARBON NUMBEF 

I' I I I I I I I 1'1 

30 28 26 24 22 20 18 16 14 12 10 

- TIME-TEMPERATURE 

~ ~ U) 

LLJ 

0::: 

0::: 

LLJ 

~ 

8 

LLJ 

0::: 

FIGURE 42.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Upper to Low~r Cretaceous rock 

above 5,290 ft (1,612 m), COST No. G-1 well. 

from the COST No. G-1 well averages 11.7 percent, indicating that the most common type of 

kerogens present are predominantly of the 

hydrogen-poor variety, with a temperature of 

maximum pyrolysis (Ts) ranging from 828° to 

878° F (442° to 470° C). In comparison, the 

Lower Cretaceous rocks of the COST No. G-2 

measurements of the solid orgaric matter suggest that the potential for generat.ion of liquid or 

gaseous hydrocarbons in the Lower Cretaceous 

strata is very poor. 

UPPER JURASSIC 

well have thermal pyrolytic convertibility ratios The Upper Jurassic stata of the COST No. G-1 

that average 7.4 percent. From 4,510 to 4,600 ft well are characterized by alternating very fine- to 

(1,375 to 1,402 m) and 5,050 to 5,080 ft (1,539 to coarse-grained sandstone, sligh~ly calcareous 

1,548 m) the convertibility ratios average 90.5 shales with thin beds of silty dohmite, traces of 

percent, suggesting the presence of a zone of coal, pyrite, muscovite, shell frag:'llents, and rare 

hydrogen-rich kerogens. The temperature of max- glauconite. The carbonate conter~ of the Upper 

imum pyrolysis (Ts) for the solid organic matter Jurassic section increases towards the Upperranges from 851 o to 869° F (455° to 465° C) and Middle Jurassic boundary. The Upper Jurassic 

is in the submature to immature temperature lithologies of the COST No. G-2 well are, in 

range (tables 5 and 6). The richness, type, and general, similar to those of the G-1. The G-2, 

maturity characteristics of the extractable however, contains a larger perce:'ltage of brown 

organic matter and the thermal pyrolysis oolitic and algal carbonate rockE" from 6,000 to 

120 
CARBON NUMBER 

I • I I I • I I I I • I • I I I I I fj 

30 28 26 24 22 20 18 16 14 12 10 

HYDROCARBON 

STANDARD 

1190-1220 FT 

363-372 M 

2180-2210 FT 

664-674 M 

CARBON NUMBER 

I I I' 1'1' I I I I 1'1 1 11 1'1 30 28 216 24 22 20 11 16 14 12 10 

3020-3050 FT 

920-930 M 

4130-4160 FT 

1259-1268 M 

6070-6100 FT 

1850-1859 M 

TIME-TEMPERATURE 

I 

LJ.J 

en 

z: 

0 

a.. 

en 

LJ.J 

0:::: 

0:::: 

LJ.J 

~ 0 

u 

UJ 

0:::: 

FIGURE 43.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Tertiary (1,190 to 1,220 ft; 363 

to 372m), Upper Cretaceous (2,180 to 2,210 ft; 664 to 674 m), Lower Cretaceous (3,020 to 4,160 ft; 920 to 1,268 m), and Upper 

Jurassic (6,070 to 6,100 ft; 1,850 to 1,859 m) samples, COST No. G-2 well. 

7,000 ft (1,829 to 2,134 m) (tables 1 and 2) others, 1978; Miller and others, 1979, 1980\ The 

(Lachance, 1980; Simonis, 1980). Upper Jurassic rocks of the COST No. G-2 well 

The Upper Jurassic strata in the two wells have have an average total extractable hydrocarbon 

similar average total organic carbon values of content of 155 ppm and a total hydrocarbon to ex0.73 percent (G-1) and 0.62 percent (G-2). The tractable organic matter ratio of 0.60. These 

average hydrocarbon to total organic carbon values are higher than those for equivalent COST 

ratios of 0.88 percent (G-1) and 2.62 percent No. G-1 well strata, which average 39.0 ppm 

(G-2) suggest that the extractable organic matter total extractable hydrocarbons and 0.31 total 

of the Upper Jurassic units is approaching ther- hydrocarbon to extractable organic ntatter 

mal maturity in the G-2. However, because of the (tables 3 and 4). The polar nitrogen, sulfur, and 

effect that small absolute concentrations may oxygen concentrations range from 10 to 20(' ppm 

have on a specific geochemical ratio, the inter- for Upper Jurassic units in the COST No G-1 

pretation of maturity must be viewed with cau- well and are usually less than 150 ppm in the 

tion (Claypool and others, 1978; Swetland and COST No. G-2 well. Although G-2 contains more 

121 
TABLE 5.-0rganic carbon and thermal analysis (Rock-Eval pyrolysis) data for samples from the COST No. G-1 well 

(Organic carbon analyses, wet oxidation method by Rhinehart Laboratories, Inc., Arvada, Colo. Rock-Eval pyrolysis by Jeff Baysinger, U.S. Geological Survey. The 

parameter S, (CO, derived from kerogen) was not determined in this study) 

Depth 

Feet Meters 

Total 

organic 

carbon 

(weight 

percent 

s1 

(mgHC/g) 

(ppt) 

S2 (mgHC/g) 

(ppt) 

S1+S2 

(weight 

percent) 

S~Org. C 

{ mgHC :\ 

\_gOrg. C-} 

S1+S2 

Org.C 

(percent) 

Upper Cretaceous 

1,090- 1,120 

2,080- 2,110 

2,350- 2,380 

332- 341 

634- 643 

716- 725 

0.10 

.88 

.59 

0.045 

.014 

.012 

0.11 

.41 

.36 

0.016 

.042 

.037 

110 

46 

61 

470 

450 

452 

0.29 

.03 

.03 

15.5 

4.8 

6.3 

Lower Cretaceous 

2,920- 2,950 

3,280- 3,310 

4,180- 4,210 

4,870- 4,900 

5,140- 5,170 

5,050- 5,080 

890- 899 

1,000-1,009 

1,274-1,283 

1,484-1,494 

1,567-1,576 

1,539-1,548 

0.34 

.10 

.12 

4.22 

2.18 

4.66 

0.019 

.044 

.013 

.066 

.056 

.057 

0.16 

.15 

.07 

4.40 

2.97 

6.54 

0.018 

.019 

.008 

.447 

.303 

.660 

47 

150 

58 

104 

136 

140 

442 

447 

455 

452 

470 

455 

0.11 

.23 

.16 

.01 

.02 

.01 

5.3 

19.4 

6.9 

10.6 

13.9 

14.2 

Upper Jurassic 

6,030- 6,040 

6,210- 6,220 

6,960- 6,970 

7,050- 7,060 

7,140- 7,150 

7,650- 7,660 

7,740- 7,750 

8,550- 8,560 

9,540- 9,550 

1,838-1,841 

1,893-1,896 

2,121-2,124 

2,149-2,152 

2,176-2,179 

2,332-2,335 

2,359-2,362 

2,606-2,609 

2,908-2,911 

1.45 

.39 

.28 

.20 

.32 

.38 

.26 

.26 

.18 

0.015 

.012 

.008 

.012 

.023 

.008 

.015 

.013 

.011 

0.89 

.20 

.14 

.08 

.12 

.09 

.09 

.07 

.05 

0.091 

.021 

.016 

.009 

.014 

.010 

.011 

.008 

.006 

61 

51 

50 

40 

38 

24 

35 

27 

28 

457 

460 

458 

452 

456 

464 

442 

462 

465 

0.02 

.06 

.05 

.13 

.16 

.08 

.14 

.16 

.18 

6.2 

5.4 

5.3 

4.6 

4.5 

2.6 

4.0 

3.2 

3.4 

Middle Jurassic 

10,530-10,540 

11,250-11,260 

11,850-11,860 

12,210-12,220 

12,480-12,490 

12,790-12,800 

12,960-12,970 

13,020-13,030 

13,440-13,450 

3,210-3,213 

3,429-3,432 

3,612-3,615 

3,722-3,725 

3,804-3,807 

3,898-3,901 

3,950-3,953 

3,968-3,972 

4,097-4,100 

0.33 

.24 

.62 

.26 

.23 

.17 

.18 

.17 

.18 

0.015 

.016 

.018 

.021 

.026 

.020 

.018 

.016 

.021 

0.19 

.12 

.31 

.14 

.12 

.09 

.12 

.07 

.08 

0.021 

.014 

.033 

.016 

.015 

.011 

.014 

.009 

.010 

58 

50 

50 

54 

52 

53 

67 

41 

44 

460 

462 

485 

456 

1

(375) 

468 

1

(392) 

460 

460 

0.07 

.12 

.05 

.13 

.18 

.18 

.13 

.19 

.21 

6.2 

5.7 

5.3 

6.2 

6.4 

6.5 

7.7 

5.1 

5.6 

Lower Jurassic 

14,040-14,050 

14,340-14,350 

15,040-15,050 

15,100-15,110 

4,279-4,282 

4,371-4,37 4 

4,584-4,587 

4,602-4,606 

0.32 

.21 

.19 

.17 

0.026 

.030 

.040 

.032 

0.16 

.16 

.15 

.13 

0.019 

.019 

.019 

.016 

50 

76 

79 

77 

1

(400) 

450 

460 

1

(379) 

0.14 

.16 

.21 

.20 

5.8 

9.1 

10.0 

9.5 

Cambrian 

15,640-15,650 

16,010-16,020 

4,767-4,770 

4,880-4,883 

1

No definite pyrolysis peak. 

0.21 

.31 

0.26 

.32 

organic-rich sediment than G-1, the organicrichness properties of total organic carbon and 

total extractable hydrocarbons suggest that the 

Upper Jurassic rocks of the Georges Bank basin 

area have very poor source-rock quality (tables 3 

and 4; figs. 40 and 41). 

The saturated paraffin-naphthene hydrocarbon 

gas chromatograms for the Upper Jurassic rocks 

in the COST No. G-1 well, with the exception of 

the 9,030- to 9,070-ft (2,752- to 2,765-m) interval, 

show a strong unresolved bimodal envelope of 

branched and cyclic paraffins. The resolved 

0.10 

.09 

0.013 

.012 

48 

29 

450 

1

(380) 

0.21 

.26 

6.0 

3.9 

aliphatics range from n-C15 to n-C30 and have an 

average CPI of 1.88. The isoprenoid pristane continues to predominate over both the isoprenoid 

phytane and n-C17• There is no c<Plsistent change 

in the molecular composition anc distribution of 

the resolved aliphatics or in the character of the 

unresolved complex envelope ,.,ith increasing 

depth of burial in the Upper Jurar~ic strata of the 

COST No. G-1 well (fig. 44). In comparison, the 

resolved aliphatics of the Upper Jurassic strata 

from the COST No. G-2 well continue to dominate the unresolved envelope ani are character122 
TABLE 6.-0rganic carbon and thermal analysis (Rock-Eval pyrolysis) data for samples from the COST No. G-2 we1

l 

[Organic carbon analyses, wet oxidation method by Rhinehart Laboratories, Inc., Arvada, Colo. Rock·Eval pyrolysis by Jeff Baysinger, U.S. Geological Surrey. The 

parameter S, (C02 derived from kerogenl was not determined in this study] 

Depth 

Feet 

1,130- 1,160 

1,550- 1,580 

2,150- 2,180 

2,510- 2,540 

3,110- 3,140 

3,530- 3,560 

4,130- 4,160 

4,510- 4,600 

5,050- 5,080 

5,560- 5,590 

6,010- 6,040 

6,550- 6,580 

9,730- 9,740 

10,230-10,240 

10,730-10,740 

11,230-11,240 

11,730-11,740 

12,230-12,240 

12,740-12,750 

13,230-13,240 

13,250-13,260 

13,750-13,760 

14,250-14,260 

14,740-14,750 

15,250-15,260 

15,750-15,760 

16,240-16,250 

16,740-16,750 

17,250-17,260 

17,750-17,760 

18,250-18,260 

18,750-18,760 

Meters 

344- 354 

472- 482 

655- 664 

765- 774 

948- 957 

1,076-1,085 

1,259-1,268 

1,375-1,402 

1,539-1,548 

1,695-1,704 

1,832-1,841 

1,996-2,006 

2,966-2,969 

3,118-3,121 

3,271-3,27 4 

3,423-3,426 

3,575-3,578 

3,728-3,731 

3,883-3,886 

4,033-4,036 

4,039-4,042 

4,191-4,194 

4,343-4,346 

4,493-4,496 

4,648-4,651 

4,801-4,804 

4,950-4,953 

5,102-5,105 

5,358-5,361 

5,410-5,413 

5,563-5,566 

5,715-5,718 

Total 

organic 

carbon 

(weight 

percent 

0.65 

1.04 

.83 

.65 

0.83 

.74 

.54 

.37 

3.09 

1.73 

0.84 

.71 

.48 

.72 

.42 

.53 

.33 

0.38 

.267 

.33 

.29 

.20 

.50 

.43 

.51 

.46 

.27 

.22 

.41 

.29 

.53 

1.10 

sl 

(mgHC/gl 

(pptl 

s2 

(mgHC/gl 

(pptl 

Tertiary 

0.310 1.20 

Upper Cretaceous 

0.090 

.100 

.045 

0.42 

.81 

.41 

Lower Cretaceous 

0.045 

.045 

.090 

2.000 

8.000 

6.600 

1.000 

.660 

.630 

.550 

.390 

.340 

.290 

0.33 

.43 

.47 

2.10 

13.70 

8.00 

Upper Jurassic 

1.80 

1.00 

.87 

1.02 

.64 

.68 

.56 

Middle Jurassic 

0.320 

.170 

.530 

.240 

.160 

.310 

.230 

.200 

.460 

.151 

.110 

.150 

.074 

.175 

1.700 

0.49 

.31 

1.01 

.61 

.30 

1.66 

.58 

.66 

1.22 

.38 

.29 

.51 

.27 

.85 

5.24 

Sl+S2 

(weight 

percentl 

0.151 

0.051 

.091 

.046 

0.038 

.048 

.056 

.410 

2.170 

1.460 

0.280 

.166 

.150 

.157 

.103 

.102 

.085 

0.081 

.048 

.154 

.085 

.046 

.197 

.081 

.086 

.168 

.053 

.040 

.066 

.034 

.103 

.694 

S~Org.C 

/. mgHC ~ 

\.g Org. cJ 

185 

40 

98 

63 

40 

58 

87 

568 

443 

462 

214 

141 

181 

142 

152 

128 

170 

129 

119 

306 

210 

150 

332 

135 

129 

256 

141 

132 

124 

93 

160 

476 

460 

447 

ND 

451 

465 

460 

456 

455 

465 

460 

482 

457 

470 

452 

472 

462 

464 

462 

446 

448 

454 

ND 

464 

468 

456 

460 

448 

446 

456 

436 

450 

460 

0.205 

0.176 

.110 

.099 

0.120 

.095 

.161 

.488 

.369 

.452 

0.357 

.398 

.420 

.350 

.379 

.333 

.341 

0.395 

.354 

.344 

.282 

.348 

.157 

.284 

.233 

.274 

.284 

.275 

.227 

.215 

.171 

.245 

SI+S2 

0r"l'.C 

(pereentl 

~3.2 

4.9 

11.0 

7.0 

4.5 

6.4 

10.4 

110.8 

71.2 

8.4 

3".3 

2:'.4 

31.3 

21.8 

24.5 

19.2 

2::-:.8 

21.3 

18.5 

4~.7 

2'1.3 

23.0 

3'1.4 

18.8 

16.9 

3fi.5 

20.0 

18.2 

16.1 

11.9 

19.3 

63.1 

ized by a rather narrow range of normal alkanes 

with an average CPI of 1.54 extending from n-C15 

to n-C22, which are probably of a marine algal 

origin (figs. 43 and 45 ). 

The average thermal pyrolysis convertibility of 

the Upper Jurassic strata from the COST No. 

G-2 well is 25.6 percent, which is significantly 

higher than the 4.4 percent of the COST No. G-1 

well. This difference is thought to reflect the 

hydrogen-rich nature of the Upper Jurassic kerogens in the G-2, associated with shallow-water 

marine algal carbonates, as opposed to the predominance of hydrogen-poor humic-type kerogens present in the G-1. The transformation 

ratios (S1/(S1 +S2)) for the Upper Jurassic s·trata 

can be grouped into two distinct populations with 

the higher ratios predominating in the COS~ No. 

G-2 well samples. This difference may indicate 

greater thermal evolution of the more hydr~"'q:enrich Upper Jurassic kerogens in the COST No. 

G-2 well. The temperature of maximum pyr<'lysis 

yield (T s) for the solid organic matter in thP. Upper Jurassic rocks ranges from 828° to 8f~° F 

(442° to 465° C) for the COST No. G-1 well. With 

the exception of the 6,010- to 6,040-ft (1,8~2- to 

1,841-m) interval, which is 900° F (482° C), the 

123 
5940-5950 FT 

1811-1814 M 

7020-7060 FT 

2140-2152 M 

CARBON NUMBER 

I I I' I' I I I I I' 1'1 '1'1 30 28 26 24 22 20 18 16 14 12 1 0 

8040-8080 FT 

2451-2463 M 

9030-9070 FT 

2752-2765 M 

CARBON NUME ER 

I I I I' I I I I I I I 1'1' I 'I 30 28 26 24 22 20 18 16 14 12 10 

9540-9580 FT 

2908-2920 M 

10,020-10,060 FT 

3054-3066 M 

- TIME-TEMPERATURE 

FIGURE 44.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Upper Jur!lssic rocks between 

5,290 ft (1,612 m) and 10,100 ft (3,078 m), COST No. G-1 well. 

temperature of maximum pyrolysis yield ranges 

from 846° to 882° F (452° to 472° C) for the Upper Jurassic strata of the COST No. G-2 well 

(tables 5 and 6). A maximum pyrolysis temperature of 878° F (470° C) is believed to be the 

critical temperature required to indicate the onset 

of maturation (Claypool and Baysinger, 1978). 

This temperature is also influenced by kerogen 

type, lithology, and design of the pyrolysis 

system (Hunt, 1979). For the COST No. G-2 well, 

the Upper Jurassic rocks appear to be slightly 

below the critical temperature threshold. 

MIDDLE JURASSIC 

The Middle Jurassic strata of the COST No. 

G-1 well occur from 10,100 to 14,000 ft (3,078 to 

4,267 m) and are characterized by interbedded 

124 

pelletal carbonates, siltstones, sandstones, and 

gray shales that grade downward into dolomites, 

anhydrites, and thin shales. Traces of coal and 

pyrite occur from about 10,000 to 13,000 ft (3,048 

to 3,962 m). The Middle Jurassic strata from the 

COST No. G-2 well range from 11,800 ft 

(3,597 m) down to at least 18,010 ft (5,486 m). 

Below 18,000 ft (5,486 m) and to the total well 

depth of 21,874 ft (6,667 m) it is possible that 

Lower Jurassic or Triassic strata may be present; 

however, because of the lack of micropaleontological control, the exact age of these older rock 

units cannot be determined (Behout, 1980). The 

Middle Jurassic interval in the G-2 well contains 

a much thicker section of brown to gray micritic 

and oolitic limestones, micrOCJ77Stalline to fine 

crystalline dolomites, and anhyirites with co~­

siderably less shale and sandstor~ than occurs m 
CARBON NUMBER 

I I I I I I I I I I I I I I I I I I I I I 

30 28 26 24 22 20 18 16 14 12 10 

7000-7030 FT 

2134-2143 M 

7990-8020 FT 

2435-2444 M 

9010-9040 FT 

2746-2755 M 

CARBON NUMBER 

I I I I I I I I I I I I I I I I I ij I I 

30 28 26 24 22 20 18 16 14 12 tO 

10~490-10,510 FT 

3197-3203 M 

11,500-11,510 FT 

3505-3508 M 

12,520-12,540 FT 

3816-3822 M 

- TIME-TEMPERATUR':: 

1 

LJ.J 

(/) 

z: 

0 

a.. 

(/) 

LJ.J 

0::: 

0::: 

LJ.J 

~ 0 

u 

LJ.J 

0::: 

FIGURE 45.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Upper Jurassic (7,000 to 

9,040 ft; 2,134 to 2,755 mt, and Middle Jurassic rocks down to 12,540 ft (3,822 mt, COST No. G-2 well. 

the G-1 well (tables 1 and 2). The Middle Jurassic 

strata probably were deposited in a shallowwater, restricted (supratidal to subtidal) environment (Lachance, 1980; Simonis, 1980). 

The total organic carbon contents of the Middle 

Jurassic rocks from the COST Nos. G-1 and G-2 

wells average 0.25 and 0.20 weight percent, 

respectively (tables 3 and 4). These values are 

slightly below the 0.3 percent considered adequate for some carbonate strata to be termed 

source rocks (Hunt, 1967). However, fine-grained, 

dark-colored carbonate rocks may be capable of 

generating more hydrocarbons than some shales 

that contain the same amount of total organic 

125 

matter. Carbonate rocks commonly contain only 

amorphous organic matter derived from algae. 

This kind of organic matter has the highest. yield 

of petroleum. among the kerogen types, which 

may explain why dark-gray to medium-gray carbonate rocks commonly yield more oil than shales 

that have the same total organic-carbon content 

(Hunt, 1979). The question of how much organic 

carbon is needed to make an excellent, go~, or 

poor carbonate source rock is highly cont ... oversial. From a qualitative point of view, ho-r~ever, 

limestones and dolomites that are predominantly 

gray to dull brown or black commonly have an extractable hydrocarbon content equivalent t"' that 
CARBON NUMBER 

I I I I' I I I I 1'1 I I 'I 30 28 26 24 22 20 18 16 14 12 10 

13,500-13,520 FT 

4115-4121 M 

14,480-14,500 FT 

4414-4420 M 

15,490-15,510 FT 

4721-4727 M 

CARBON NUMBER 

I I I I I I I I I I I' I I I 'I 

30 28 26 24 22 20 1' 16 14 12 10 

15,900-151 920 FT 

4846-4852 M 

16,450-16,470 FT 

5014-5020 M 

17,020-17,540 FT 

5188-5346 M 

J 

'II, 

- TIME-TEMPERATURE 

L..L..I 

(/) 

= 0 

a... 

(/) 

L..L..I 

0::: 

0::: 

L..L..I 

Q 

0::: 

0 

<.....> 

L..L..I 

0::: 

FIGURE 46.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Middle Jurassic rocks from 

13,500 to 17,540 ft (4,115 to 5,346 m), COST No. G-2 well. The 17,020- to 17,540-ft sample is a comp<J<:~ite of two samples 

from 17,020-17,040 and 17,520-17,540 ft (5,188-5,194 and 5,340-5,346 m). 

associated with good source rocks, whereas lightcolored, recrystallized carbonate rocks generally 

have very few, if any, indigenous hydrocarbons 

(Hunt, 1979). In addition, it has been demonstrated that organic matter and bitumen content 

increases with an increase in the clay content of 

carbonate strata (Hunt, 1967). Thus, the lightgray to black, argillaceous, fine-grained carbonate rocks of the Middle Jurassic section could 

be considered as potential source rocks. 

A major difference exists between the average 

total extractable hydrocarbons of the Middle 

Jurassic sediments from the COST Nos. G-1 and 

G-2 wells. The G-1 rocks contain an average 

of 36 ppm, whereas the G-2 strata average 

170 ppm. Although these values are both low in 

terms of source-rock richness, the difference in 

quality may be related to the nearshore character 

126 

of the Middle Jurassic in the COf'T No. G-1 well. 

The Middle Jurassic section of th~ G-2 contains a 

much larger percentage of marine carbonate 

rocks and anhydrites. The average total hydrocarbon to total organic carbon rrtios may signal 

the begining of the intense oil ge:'leration process 

below 10,000 ft (3,050 m) in the Middle Jurassic 

(table 3 and 4). Between 15,000 and 18,000 ft 

(4,572 and 5,486 m) in the COST 1To. G-2 well, the 

Middle Jurassic rocks contain a higher concentration of nitrogen, sulfur, and oxygen compounds 

than occurs in the Upper Jurassic or Cretaceous 

rocks (fig. 41). This higher concrmtration of the 

polar compounds is believed to reflect the nature 

and type of organic matter present in this interval. Traces of a black, asphalt-like substance, soluble in carbon disulfide, was pres•:mt in several of 

the cutting samples between 15,500 and 18,000 ft 
CARBON NUMBER 

I I I' I I I I I I I I I I 1'1 I 1'1 

30 28 26 24 22 20 18 16 u 12 10 

17,470-17,520 FT 

5325-5340 M 

17,980-18,000 FT 

5480-5486 M 

18,470-18,500 FT 

5630-5639 M 

CARBON NUMBER 

I I I' I I I I I I I I I I 1'1' 11 1 

30 28 26 24 22 20 18 16 14 12 10 

18,980-19,030 FT 

5785-5800 M 

19,500-19,530 FT 

5944-5953 M 

19,950-20,010 FT 

6081-6099 M 

- TIME-TEMPERATUR:: 

LL.J 

(/) 

:z: 

0 

a... 

(/) 

LL.J 

c:: 

c:: 

LL.J 

0 

c:: 

0 

u 

LL.J 

c:: 

FIGURE 47.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Middle Jurassic rocks from 

17,470 to 20,010 ft (5,325 to 6,099 m), COST No. G-2 well. 

(4, 724 and 5,486 m). A gas chromatogram of the 

saturated paraffin-naphthene hydrocarbons from 

a similar substance isolated by GeoChem Laboratories, Inc., in samples from below 14,000 ft 

(4,267 m) is shown in figure 39. If this substance 

is indigenous, it supports the interpretation of 

low thermal maturity; however, the possibility is 

equally good that the substance may be a mud 

contaminant. Because this substance was present 

only in a few samples from a limited interval, its 

interference with the paraffin-naphthene signatures of this interval is believed to be minimal except where noted. 

The saturated paraffin-naphthene hydrocarbon 

gas chromatograms for the Middle Jurassic 

strata from 12,520 to 21,540 ft (3,816 to 6,565 m) 

127 

in the COST No. G-2 well show an irregula"" and 

inconsistent change in the magnitude o~ the 

unresolved bimodal branched and cyclic paraffins 

relative to the resolved aliphatics (figs. 4~. 4 7, 

48). This inconsistent change may be due m part 

to possible background interference by mu; additives. Except in the 12,520- to 12,f<t0-ft 

(3,816-to 3,822-m) interval, the major porti,<>n of 

the resolved aliphatic hydrocarbons are the n-C15 

to n-C22 molecular species, which predominate 

over the isoprenoid hydrocarbons pristan£. and 

phytane. Although not completely source-sp~cific 

because of the masking effects of catagensis, the 

pristane/phytane ratio varies throughout the 

Middle Jurassic between 1.1 and 2.0, prol·ably 

indicating the influence of mixed marine-,qjgal, 
CARBON NUMBER 

I I I' I I I I I I I I I I I' I I I 'I 

30 28 26 24 22 20 18 16 14 12 1 0 

20,480-20,520 FT 

6242-6254 M 

20,970-2L030 FT 

6392-6410 M 

2L 460-2L 540 FT 

6541-6565 M 

~ TIME-TEMPERATURE 

LJ.J 

(/) 

z: 

0 

0.... 

(/) 

LJ.J 

0::: 

0::: 

LJ.J 

0 

0::: 

0 

u 

LJ.J 

0::: 

FIGURE 48.-Gas chromatographic analyses of saturated 

paraffin-naphthene hydrocarbons of Middle Jurassic rocks 

from 20,480 to 21,540 ft (6,242 to 6,565 m), COST No. G-2 

well. 

herbaceous, and woody organic matter. At about 

18,500 ft (5,639 m), the resolved normal alkanes 

begin to predominate over the unresolved complex envelope and shift toward the lower molecular weight ranges, and the CPI ratio approaches 

unity (figs. 47 and 48). Such characteristics indicate that thermal maturation processes have 

been active. However, at a depth of 21,460 to 

21,540 ft (6,541 to 6,565 m), the resolved normal 

aliphatics, the molecular distribution and composition, and the unresolved napthenic envelope 

still do not resemble those of thermally mature 

petroleum hydrocarbons and may be influenced 

by mud additives (fig. 48). 

In the COST No. G-1 well, the Middle Jurassic 

section is much thinner than in the COST No. 

G-2 well, extending from 10,1('~ to 14,000 ft 

(3,078 to 4,267 m). The resolved n~rmal aliphatics 

occur predominantly in the n-Cu to n-C22 range, 

except for the 12,360- to 12,4QO-ft (3,767- to 

3,780-m) sample, and generally ar~ dominated by 

a strongly bimodal, unresolved, complex mixture, 

a signature that usually incicates a lowtemperature thermal history for the liquid c15 + 

hydrocarbons (figs. 49 and 50). Throughout the 

Middle Jurassic section, the r~solved normal 

aliphatic hydrocarbons dominat~ over the isoprenoids pristane and phytane. The generally low 

concentration of the aliphatics in the n-C21 to 

n-C36 range, the predominance of the resolved 

normal aliphatics from n-Ct4 tc n-C22, and an 

average CPI ratio of 1.2 are cl,~racteristics of 

hydrocarbons that are conside::ed to have a 

marine origin. 

The temperatures of maximum thermal pyrolysis yield for the Middle Jurassic strata in the 

COST Nos. G-1 and G-2 wells average 867° F 

(464 o C) and 849° F (454 o C), respectively. These 

temperatures are consistent witli the interpretation of a relatively low degree of thermal maturation, which is in general agreeme:"'t with the lowthermal-maturity signatures of the saturated 

paraffin-naphthene hydrocarbon gas chromatograms (tables 5 and 6; figs. 45-5f\ 

LOWER JURASSIC AND CAMf'~IAN 

Lower Jurassic and Cambrian rocks were 

penetrated in the COST No. G-1 well. The Lower 

Jurassic rocks extend from 14,(10 to 15,630 ft 

(4,267 to 4,764 m), and the Cambrian from 15,630 

to 16,061 ft (4,764 to 4,895 m). The Lower 

Jurassic is characterized by light-gray to buff 

dolomites, anhydrites, and mica ~eous siltstones 

that grade downward into coarse-grained sandstones and red hematitic mudr~ones (table 1). 

Only traces of dolomite are present below a depth 

of about 15,000 ft (4,572 m). Chips of black, 

graphitic schist, present from 16,056 to 16,061 ft 

(4,894 to 4,895 m), yielded K-Ar ages of 450 to 

550 million years (Steinkraus, 1980). 

The total extractable hydrocarbons for the 

Lower Jurassic and Cambrian rocks averaged 

39 ppm, and these intervals haY~ average total 

organic carbon values of 0.11 and 0.14 weight percent, respectively. The ratio of t<Jtal hydrocarbon 

128 
CARBON NUMBER 

I I I' I I I I I I I I I I I I I I 'I 

30 28 26 24 22 20 111 16 14 12 10 

10,440-10,480 FT 

3182-3194 M 

10,950-10,970 FT 

3338-3344 M 

11,220-11,260 FT 

3420-3432 M 

11,850-11,890 FT 

3612-3624 M 

12,360-12,400 FT 

3767-3780 M 

CARBON NUMBER 

I I I' I' I I I I I 11 1 I I 'I 

30 28 26 24 22 20 18 16 14 12 10 

12,960-13,000 FT 

3950-3962 M 

~ TIME-TEMPERATURE 

w 

(/) 

:z: 

0 

a... 

(/) 

w 

0::::: 

0::::: 

w 

~ 0 

u 

w 

0::::: 

FIGURE 49.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Middle Jurassic rocks above 

13,000 ft (3,962 m), COST No. G-1 well. 

to total organic carbon averages 5.37 percent for 

the Lower Jurassic and 4.52 percent for the Cambrian rocks. The average ratios of total hydrocarbon to extractable organic matter are 0.43 and 

0.61, saturated hydrocarbon to aromatic hydrocarbon ratios are 2.48 and 2.00, and Carbon 

Preference Indices (CPI) are 0.88 and 1.10 for the 

G-1 Lower Jurassic and Cambrian, respectively 

(table 3). The progressive increase in the average 

values from the Upper through Lower Jurassic 

strata indicates progressively increasing thermal 

maturation. The saturated paraffin-napthene 

hydrocarbon gas chromatograms, however, continue to show a strong bimodal distribution of the 

unresolved complex mixture with a predominance 

129 

of the naphthenes over the resolved n-alkanes, a 

signature that may indicate mud additive effects 

(fig. 50). These gas chromatographic chara~teristics of thermal immaturity are inconsistent with 

the extractable hydrocarbon ratios that indicate 

a time-temperature history characterist~ ~ of 

mature sources. The low average convertjbility 

((S1+S2)/0rg. C) of 8.6 indicates the predomi~ance 

of hydrogen-poor organic matter. The average 

thermal-pyrolysis maximum-yield temperature 

for the Lower Jurassic and Cambrian rock;-- was 

calculated to be 847° F (453° C) where dcmute 

thermal peaks were present (table 5). This 

temperature of maximum yield indicates that the 

solid organic matter in the Lower Jurassi ~ and 
CARBON NUMBER 

I I I I' I I I I I' 1'1 1 I 'I 30 28 26 24 22 20 18 16 14 12 10 

13,530-13,570 FT 

4124-4135 M 

14,040-14,080 FT 

4279-4292 M 

14,550-14,590 FT, 

4435-4447 M 

15,040-15,080 FT 

4584-4596 M 

15,540-15,570 FT 

4757-4775 M 

CARBON NUMBER 

I I I' 1'1 I I I I I I' 1'1' I I 30 28 26 24 22 20 18 16 14 12 10 

15,030-15,070 FT 

4885-4898 M 

- TIME- TE~'PERATURE 

FIGURE 50.-Gas chromatographic analyses of saturated paraffin-naphthene hydrocarbons of Middle J·.•'rassic (13,530 to 

13,570 ft; 4,124 to 4,136 m), Lower Jurassic (14,040 to 15,080 ft; 4,279 to 4,596 m), and Cambrian (15,640 to 16,070 ft; 4,767 

to 4,898 m) rocks, COST No. G-1 well. 

Cambrian rocks are apparently still thermally immature with respect to the generation of liquid 

hydrocarbons. This temperature of maximum 

yield may be influenced by the low total organic 

matter content of the rocks. The S1/(S1+S2) production index ratio, which is a measure of maturation, does however, show a consistent increase 

from 0.14 at 14,040 to 14,050 ft (4,279 to 4,282 m) 

to 0.26 at 16,010 to 16,020 ft (4,880 to 4,883 m) 

and indicates significant thermal maturity. 

The low total organic carbon (average 0.12 

weight percent) and the thermal-pyrolysis and 

gas chromatographic maturity characteristics of 

the organic matter in the Lower Jurassic and 

Cambrian rocks suggest that this interval in the 

COST No. G-1 has a very poor oil and gas sourcerock potential. 

130 

KEROGEN TYPES AND THERMAL MATUI''TION FOR THE 

COST NO. G-1 WELL 

The geochemical parameters used to classify 

the kerogens in the COST No. G-1 well are 

relative type and abundance, hydrogen to carbon 

ratios, stable carbon isotope com:nositions (o13C), 

and thermal pyrolysis hydrogen iriex (SiOrg. C), 

(fig. 51). The sediments of the COST No. G-1 

down to a burial depth of about 6,000 ft (1,820 m) 

contain mainly amorphous aiJ d herbaceous, 

hydrogen-rich kerogens (fig. 51). Below 6,000 ft 

(1,829 m), there is a considerable decrease in the 

abundance of amorphous keroger and a significant increase in the herbaceous, w'lOdy, and coaly 

types. This predominance of hydrogen-poor kerogen extends into the Lower Jurr4Ssic and Cambrian rocks below 14,000 ft (4,267 m) and is be-
RELATIVE KEROGEN 

ATOMIC 

HYDROGEN/ 

TYPE AND ABUNDANCE CARBON 

(%) (ratio) 

0 0 20 40 60 80 100 0.4 0.6 0.8 1.0 

... 

w 

w 

LL 

~ 

:I 

3000 

6000 

li: 9000 w 

0 

12.000 

15.000 

[27] AMORPHOUS D WOODY 

I ••••• I HERBACEOUS IQ;3J CO ALLy 

GEOCHEM LABS 

AMOCO 

PROD. CO. 

8c 13 (per mil) 

X . . X• 

•X 

. x.o 

X 

.. . X 

. X• 

. . X 

X• .. . X • X . 

. •X 

e.ox .. X 

X . 

.. ASPHALTENE 

X TOTAL EXTRACT 

• SATURATED HYDROCARBON 

PHILLIPS PETROLEUM CO. 

SMITH. 1880 

ORGANIC CARBON 

(mgHC/gC) 

50 100 150 

20"0 C/) 

a: 

w 

... 

w 

::! 

~ 

:I 

... 

Q. 

301'>0 w 

0 

USGS 

FIGURE 51.-Summary profile of indicators of types of organic matter present in the COST No. G-1 well as a function of depth 

of burial. 

lieved to reflect the influence of the terrestrially 

derived organic matter associated with nearshore 

sedimentary facies. 

In the COST No. G-1 well, the hydrogen to carbon ratios of the kerogens range from 0.5 to 0.9. 

The hydrogen-poor character of these kerogens is 

also indicated by their average thermal pyrolysis 

hydrogen indices (SJOrg. C), which range from 38 

in the Cambrian to 118 in the Lower Cretaceous 

(table 5). Such values are generally consistent 

with poor-quality source rocks that contain 

predominantly hydrogen-lean, type Ill, gasprone kerogens. The stable carbon isotopic compositions of the asphaltene, ·total extracts, and 

131 

saturated paraffin-naphthene fractions are rl:town 

in figure 51. Yen (1972) has reported thrt:. the 

asphaltene fraction of an oil should have a o13C 

value similar to that of the kerogen from wl'ich it 

was derived. This isotopic relationship is ~ue to 

the structural and chemical similarities be~ween 

the asphaltene and kerogen. Stahl (1978\ confirmed the isotopic similarity between genetically 

associated kerogens and asphaltenes from crude 

oils. In the COST No. G- well, no o13C values of 

the kerogens were available for comparisor with 

those of the asphaltenes. However, if it is assumed that a genetic asphaltene-kerogen chemical structure relationship does exist (Yen, 1972; 
Stahl, 1978) and that this relationship can be extended to include the asphaltene fractions associated with the total bitumen extractables of the 

source shales (believed to represent that portion 

of the generated hydrocarbons remaining at the 

place of origin), then the o13C values of the 

asphaltene fraction of the source shales may be 

interpreted as being representative of the o13C 

ratio of the source kerogens. The o13C values for 

the asphaltene fractions of the COST No. G-1 

well are predominatly between -26 and 

-28 permil. Such o13C values are, however, inconsistent with the o13C values of the predominantly 

terrestrial kerogen types described from well cuttings. With the exception of those from the Cretaceous strata, the kerogens of G-1 are considered 

to have a predominantly terrestrial source, as indicated by their relative abundances determined 

by optical microscopy methods (fig. 51). 

The distribution and concentration of the C1 to 

c7 hydrocarbons, the percent gas wetness, and 

the n-C4 to n-C7 ratios for the COST No. G-1 well 

are shown in figure 52, and the thermal maturation geochemical characteristics for G-1 are 

shown in figure 53. The maximum C1 to C4 light 

hydrocarbon concentrations range from 15,000 to 

27,000 ppm in the 4,500- to 6,500-ft (1,372- to 

1,981-m) Cretaceous-Jurassic interval, and generally the strata have less than 10 percent gas wetness. These Cretaceous-Jurassic rocks contain lignitic and peaty types of organic matter. The 

extractable organic matter from this interval is 

characterized by the highest total organic carbon, 

total extractable saturated paraffin-naphthene, 

and aromatic hydrocarbons. The nitrogen, sulfur, 

and oxygen compound concentrations in this interval range from 50 to 200 ppm. The apparently 

low thermal maturity of the extractable organic 

matter, and low gas wetness, as well as the 

presence of terrestrial organic matter associated 

with these Cretaceous-Jurassic sandstones and 

shales, suggest that the light hydrocarbons in 

this interval are probably unrelated to indigenous, thermally produced, mature liquid 

petroleum hydrocarbons. This interpretation is 

consistent with the bimodal distributions of the 

saturated paraffin-naphthene hydrocarbon gas 

chromatograms, the CPI ratios that show a 

predominance of odd-carbon chain hydrocarbons, 

the moderately low temperatures of maximum 

thermal pyrolysis yield (846° to 878° F; 452° to 

132 

470° C), and TAl values that ra"1ge from 1.5 to 

1.8 (figs. 41, 43, 44, and 49-53). 

Where the n-CJn-C7 profile sh'lws values that 

are less than unity, the possibility exists that 

diesel fuel contamination may be present (7 ,000-

10,000 ft, 2,134-3,048 m; 1~:,000-13,000 ft, 

3,658-3,962m; and 14,000-15,000ft; 

4,267-4,572 m) (fig. 52). However, the n-CJn-C7 

ratio compares molecular sped~s that are in 

gaseous and liquid physical states. Because of the 

possibility of preferential loss of the lower 

molecular weight species due to t:he difference in 

vapor pressures, this ratio may be misleading and 

should be used with caution; the presence of 

diesel fuel should not be inferrE'ri on the basis 

of this ratio alone. The molecular distribution 

and concentrations of the saturated paraffinnaphthene hydrocarbons do not reflect the presence of diesel fuel in the litholo:'ric units below 

6,500 ft (1,981 m). Although an ir~onsistency exists with the n-CJn-C7 ratio-:o~, the normal 

saturated paraffin-naphthene hydrocarbon distributions and the thermal-matura+ion interpretations are not believed to be influ <'!Deed by diesel 

fuel effects. 

If vitrinite reflectance (R0 ) values are determined on primary (first-cycle) vitrinite macerals 

and the geothermal gradient is assumed to be 

constant, then for a sedimentar:-r basin with a 

simple burial history involving r 'l loss of overburden by erosion, vitrinite reflectance is the only 

thermal maturation parameter thc-t is believed to 

increase exponentially with therm~ maturity and 

to be unaffected by kerogen con1position (Dow, 

1977). The slope of the vitrinite reflectance profile 

is a function of the maximum f:'~othermal gradient and the age of the lithologic units or, more 

specifically, the length of the time of heating. In 

those instances where sedimentary units have 

experienced varying geothermal gradients, segmented maturation gradients may occur. If the 

R0 values are plotted on a log scale and depth on a 

linear scale, the relationship be~ween the two 

parameters for each segment wfl usually be a 

straight line (Dow, 1977). Vitririte reflectance 

values determined on well cutt~~gs, however, 

may give anomalous results. Sucl' factors as the 

presence of oxidized vitrinite or recycled 

material, natural variations, and statistical and 

technical errors in not selecting first-cycle 

vitrinite, can produce abnormally high R0 values, 
TOTAL C,-C4 (ppm) TOTAL Cr-C7 (ppm) GAS WETNESS (%) C,JC7 

0 1000 3000 15000 7000 8000 0 80 180 240 0 20 40 80 80 0 2.0 4.0 6.0 8.0 10.0 o~--~--~--r-~r-~--~---.--~--~--.-----~~~r-~--~---.--~--~--,-~~~r-"~~~~-.-.-.-..-.-.-,-~~~r4 

3000 1000 

8000 

2000 ~ 

I!! e.. 

Ill 

... £; 

::! 

Ill 

Ill 

u. 

l: ~ 

~ ~ I: 8000- ~ t: ~ ~ 3000 ~ 

12,000 

4000 

1&.000 

L-~---L--~---L-~----L--~--L-~----L------L~~---L--~---L-~----L--~~~~~~~~~~~~~~~~~~~~~~ 

GEOCHEM LABS GEOCHEM LA88 GEOCHEM LABS GEOCHEM LABS 

FIGURE 52.-Summ.ary of C, to c7 hydrocarbon analyses of samples from the COST No. G-1 well. 
~ 

VITRINITE 

THERMAL ALTERATION INDEX REFLECTANCE (Ro) CPI 

TEMPERATURE MAXIMUM 

PYROLYSIS YIELD TS2 j°C 

1.0 1.5 2.0 2.5 3.0 3.5 0.2 o.e 1.0 1.4 1.8 o -·- ··- ··- -·- -·- -·- -·- ~-- ~-- -·- -·- -·- - ~-- ··- -- o 

Iii 

Ill 

II. 

~ 

~8000 

! 

12.000 

15,000 

GE:OCHEM LABS 

X 

' i. 

'x 

ICx .. 

. 

W. DOW SUII'£RIOft OIL CO. 

-;~============-- ----- --- * 

* NO DEFINITE PYROLYSIS PEAK 

FIGURE 53.-Maturity profiles of organic matter as a function of depth of burial for samples from the COST No. G-1 well. 

1000 

2000 • 

! 

~ 

~ 

:I 

3000~ Ill 

Q 

4000 

6000 
whereas cavings, rough vitrinite, and mud contamination can result in abnormally low R0 

values (Dow, 1977; Bostick and others, 1978). 

The R0 values from the COST No. G-1 well 

were reported as having been determined on 

primary vitrinite except in the 5,500- to 6,500-ft 

(1,676- to 1,981-m) interval, where cavings from 

overlying coals may have given abnormally low 

R0 values (Smith and Shaw, 1980). The slope of 

the R0 profile for the sedimentary section from 

about 6,500 ft (1,981 m) to the bottom of the well 

(16,071 ft; 4,898 m) is less steep than the profile 

from 2,000 ft (610 m) down to 6,500 ft (1,981 m) 

(fig. 53). The change in slope of the R0 profile at 

about 6,500 ft (1,981 m) suggests a cooler thermal 

history for the overlying Cretaceous-Jurassic 

rocks and a higher geothermal gradient for the 

older Jurassic rocks below this depth. These 

vitrinite data suggest that a complex thermal and 

burial history may have existed for the Cretaceous and Jurassic. The effect of possible removal 

of overburden on the vitrinite profile is open to 

question. The degree of thermal maturity indicated by the vitrinite reflectance values below 

6,500 ft (1,981 m) is also not consistent with the 

TAl values, odd-even carbon preference indices 

(CPI), or temperature of maximum pyrolysis 

yield (Ts ). If the range of R0 values (0.62 to 1.8) 

below 6,SOO ft (1,981 m) is representative of indigenous, first-cycle vitrinite, then the existence 

of a higher thermal gradient is suggested for the 

more deeply buried Jurassic rocks. 

This history of higher temperatures is not totally corroborated, however, by the other comparative thermal maturation parameters. The 

vitrinite reflectance data suggest paleotemperatures have already exceeded those needed for the 

first-order chemical reactions that are responsible 

for the formation of petroleum and have passed 

into the temperature range where dry gas may be 

formed. However, because of the inconsistencies 

between the level of thermal maturation indicated by the vitrinite-reflectance (R0 ) values 

and the other geochemical maturation parameters, the paleotemperatures are believed to have 

been lower than those required for peak gas 

generation. The threshold for intense oil generation as defined by Hunt (1979) is placed at 

10,500 ft (3,202 m) and is based on the significant 

increase in the concentration of the c4 to c7 

gasoline-range hydrocarbons (fig. 52). Peak oil 

generation appears to have occurred between 

135 

13,000 and 15,000 ft (3,965 to 4,575 m). The 

change in the slope of the R0 profile below 

6,500 ft (1,981 m) may have been influenc~d by 

oxidized vitrinite or recycled organic Irs:ttter, 

which would yield an anomalously high palE''ltemperature history for the strata down to at least 

15,630 ft (4, 764 m). Below this depth, the degree 

of influence that Cambrian metamorphisir may 

have had on the strata is unknown. Similarly, 

there is no clear evidence for a massive Jurassic 

thermal event associated with plate brealrup in 

the COST No. G-1 well. 

KEROGEN TYPES AND THERMAL MATURATION FO~ THE 

COST NO. G-2 WELL 

The data on the relative kerogen type:~ and 

abundance in the COST No. G-2 well are inconsistent (fig. 54). The analyses reported by Core 

Laboratories, Inc., show a relatively large percentage of inertinite and exinite along with a comparatively small contribution of amorphou~-algal 

kerogen. The relative percentages of kerogen 

types and abundances determined by GeoChem 

Laboratories, Inc., show a significant amo•lnt of 

marine, amorphous-herbaceous organic matter 

(fig. 54). Whether this inconsistency in the 

kerogen characterization is due to samp1 '1 contamination, analytical procedure, or inh<''Dogenous sample suites is not known. Smith (1980) 

has suggested that the Core Laboratories procedure may have inadvertently regardeq the 

amorphous, sapropelic type of organic matter as 

a mud contaminant and that the GeoChem Laboratories, Inc., estimates of amorphous kl'~rogen 

may have been slightly high. 

The stable carbon isotope ratios for tll e Tertiary and Cretaceous kerogen and solvent-r'lluble 

fractions (paraffin-naphthenes, aromatics, total 

extractable hydrocarbons) range from -24 to 

-28 permil. With the exception of one sarr.1'Jle interval (16,200 ft; 4,938 m), the stable-carbonisotope ratios range from -22 to -29 permil for 

organic matter from the Upper Jurassic (5,960 to 

11,800 ft; 1,817 to 3,597 m) and Middle Jurassic 

strata (11,800 to 18,000 ft; 3,597 to 4,586 n1). The 

Middle Jurassic rocks below 18,000 ft (5,486 m) 

have o13C values that range from -24 to 

-28 permil (fig. 54). The o13C compositio:'l of a 

number of Cretaceous and Jurassic keroge11 s were 

reported to range from -22 to -28 permil 
~ 

RELATIVE KEROGEN RELATIVE ATOMIC CARBON ISOTOPIC 

TYPE AND KEROGEN TY~ AND HYDROGEN/CARBON COMPOSITION S7'C ORGANIC 

ABUNDANCE (%) ABUNDANCE (%) (ratio) (~C 3poB) <rnsaHC/vCI 

o 20 40 eo eo 1000 20 40 eo eo 100 o 0.2 o.4 o.e o.e 1.0 1.2-30 -28 -28 -24 -22 -2o o 100 200 300 400 600 eoo 

0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

3000 

6000 

9000 

1-

Ill 

Ill 

II. 

z 

- 12.000 

:I 

1-

CL 

Ill 

0 

16.000 

18.000 

21.000 

GEOCHEM LABS * (20% of ..,....,lnaludMI with 

-~ ..... lit 2.3715 ft. 

COM LAa8 

CORE LAII8 

.. .. . 

. . . ... 

• ~ IJ 

.. . 

~ 

: 

. .. .. - . .. .. tli.: 

.·~ 

... . .. ... ... ... . ... ~ ... 

. 

••• 

. k 

.. 

.~· -... 

.. 

.. . . • TOTAL EXTRACT 

• SATURATES 

• AROMATICS 

~IPS PET'AOL.EUM CO. 

FIGURE 54.-Summ.ary profiles of indicators of types of organic matter present in the COST No. G-2 well as a function of depth of burial. 

1000 

2000 

3000 t/) 

a: 

Ill 

1-

Ill 

~ 

~ 

4000 ~ CL 

Ill 

0 

5000 

6000 
(Degens, 1969). Such an isotopic spread is believed to be characteristic of organic matter 

derived from predominantly open-marine sources 

and is consistent with the stable carbon isotope 

ratios in almost all of the Cretaceous and Jurassic 

kerogens in the COST No. G-2 well. 

There is a difference of 4 permil between the cPSC 

values of saturated paraffins-naphthenes, 

aromatic hydrocarbons, and total extractable 

hydrocarbons, and those of the kerogens from the 

COST No. G-2 well (fig. 54). This spread of values 

suggests that a genetic relationship probably 

does not exist between the extractable bitumens 

and the kerogens. However, it is possible that 

thermal-maturation processes can induce carbon isotopic fractionation and exchange during 

catagenesis and metagenesis (Galimov, 1973; 

Tissot and Welte, 1978) and that the o1

SC balance 

in kerogen is generated at an early stage of 

diagenesis when all the humic acid enters the 

kerogen structure (Galimov, 1980). 

The kerogen types and abundances reported by 

Core Laboratories, Inc., show major amounts of 

woody to coaly (type Ill) kerogen and a very 

small amount of the amorphous algal (type I) 

variety in the COST No. G-2 well (fig. 54). In contrast, the kerogen types and abundances as determined by GeoChem Laboratories, Inc., show that 

the amorphous and herbaceous (type I and II) 

varieties compose 40 to 50 percent of the solid 

organic matter present in the Cretaceous and 

Jurassic strata (fig. 54). The stable carbon isotope 

ratios reported in this study were determined on 

the kerogen and bitumen extracts prepared by 

GeoChem Laboratories, Inc. (fig. 54), but other 

stable carbon isotope ratios reported by Phillips 

Petroleum Co. are consistent with the type and 

abundance of kerogens reported by GeoChem 

Laboratories, Inc. If, however, the woody and 

coaly-humic (type Ill) kerogens were the most 

abundant species in the GeoChem Laboratories, 

Inc., samples, then the o13C ratios determined on 

the bitumen extracts and kerogen isolates should 

have been isotopically lighter, trending toward 

the -30 to -31 permil range characteristic of 

more terrigenous kerogen. 

For that part of the Lower Cretaceous section 

between 4,510 and 6,000 ft (1,375 and 1,829 m), 

the thermal pyrolysis hydrogen index (SJOrg. C) 

averages 491 mg HC/g Org. C and suggests the 

presence of a more hydrogen-rich type of kerogen 

that is suitable for the generation of liquid 

petroleum hydrocarbons (fig. 54; table 6). Por the 

underlying Upper and Middle Jurassic rocks 

below 6,000 ft (1,829 m), the more hydrogen-poor, 

gas-prone kerogens have thermal-py:":"olysis 

hydrogen indices (SJOrg. C) that average 161 and 

193 mg HC/g Org. C, respectively (fig. 54). Hunt 

(1979) has shown that the hydrogen to carbon 

ratios for the inertinite type of kerogen fall within 

the 0.3 to 0.45 range, whereas the woody type of 

humic kerogen has hydrogen to carbon ratios 

from 0.3 to 1.0. The hydrogen to carbon ratios for 

these Cretaceous and Jurassic sediments are in 

the 0.5 to 0.8 range and are more consistert. with 

a woody humic type rather than a coaly (inertinite) type of kerogen (fig. 54). 

Below about 9,600 ft (2,926 m) the Upp~l." and 

Middle Jurassic strata of the COST No. G--2 well 

are predominantly calcareous shales, limert.ones, 

dolomites, and anhydrites. The carbonat~ and 

evaporite strata are believed to have been 

deposited in shallow-water, restricted marine environments, and contain only small amounts of 

terrestrially derived (type Ill) kerogens (fi ~. 54). 

The terrestrial (type Ill) kerogens pres~nt in 

these carbonate strata are believed to be largely 

recycled. Highly carbonized organic matte:-- such 

as inertinite is fairly resistant to weatherir~ and 

may be transported without significant f·1rther 

loss of hydrogen to new depositional basir~ and 

mixed with young, thermally immature O''"ganic 

matter (Tissot and Welte, 1978). If the o:":"ganic 

matter that has been identified as inertirite or 

coal in the COST No. G-2 well is truly as abundant as indicated by Core Laboratories, Inc., then 

the potential for generation of gas is very poor 

(fig. 54). On the other hand, if the woody-ltumic 

type III kerogens are more abundant, f'<q the 

hydrogen to carbon ratios seem to suggest. then 

the potential for gas generation may be significant, depending upon the abundance of primary 

solid organic matter and the time and intenr1.ty of 

thermal maturation. 

137 

The possibility of mud additive contami'lation 

or coaly cavings cannot be discounted as a cause 

of the inconsistent kerogen-type determinl'tions. 

Moreover, the probability of two laborrtories 

receiving totally and consistently diss'imilar 

sample suites seems rather remote. Therefo:we, the 

reported differences in the kerogen type~ and 

their relative abundances may be related to the 

analytical techniques and methods employed in 
the preparation and identification of the kerogen 

types. 

The T AI, vitrinite reflectance (R0 ), CPI, and 

temperature of maximum pyrolysis yield (T s) 

maturation parameters for the G-2 well samples 

are shown in figure 55. During the thermal 

maturation process (as the burial depth and 

temperature increase), the breaking of carboncarbon bonds occurs more and more frequently, 

and, depending upon the predominant type of 

organic matter, varying proportions of light (C1 

to C .. ) hydrocarbons and gasoline range (C4 to C7) 

hydrocarbons are produced (Tissot and Welte, 

1978). The profiles of the concentrations of the C1 

to c .. and c5 to c7 hydrocarbons, the percent gas 

wetness, and the n-CJn-C7 molecular ratio are 

shown in figure 56. Although the n-CJn-C7 ratio 

is less than unity in several isolated intervals of 

the COST No. G-2 well, the effect of diesel fuel on 

the thermal maturation characteristics of the 

c15+ liquid hydrocarbons below 12,000 ft 

(3,660 m) is believed to be minimal. The total concentration of C 1 to C7 hydrocarbons in the Cretaceous and Jurassic strata is low, usually less than 

1500 ppm, which may be related to the poor 

source-rock quality. 

The two sets of T AI data are inconsistent in 

their description of the levels of thermal maturity 

for similar burial depths (fig. 55). Because the 

T AI profile established by Core Laboratories, 

Inc., includes samples down to a burial depth of 

only 12,000 ft (3,658 m), their data do not permit 

the development of a complete, comparative thermal maturation interpretation of the COST No. 

G-2 well and will not be discussed further. The 

T AI values reported by GeoChem Laboratories, 

Inc., include samples from the entire well and are 

discussed below. The level of thermal maturation 

indicated by Core Laboratories, Inc., vitrinite 

reflectance (R0 ) measurements is inconsistent 

with and abnormally high when compared with 

the level of thermal maturation indicated by the 

liquid C15+ hydrocarbon CPI ratios and the thermal pyrolysis yield (Ts) values, and by the TAl 

values reported by GeoChem Laboratories, Inc. 

Below 3,500 ft (1,067 m) the vitrinite reflectance values appear to be grouped into several 

families of straight-line relationships, each with a 

slightly different slope, that may suggest the 

presence of different past geothermal gradients. 

Any offset at the breakpoint of the straight-line 

relationship has been interpreted by Dow (1977) 

to signify a possible unconformity (fig. 55). The 

possibility of recycled organic mri:.ter as a factor 

in the unusually high vitrinite reflectance measurements must not be discounted. If the level of 

thermal maturation were as advr'i'nced, for such 

shallow burial depths, as the vitrinite reflectance 

values suggest, then the concent-ations of C1 to 

c .. light hydrocarbons and c .. to c7 gasoline-range 

hydrocarbons generated would be. expected to be 

much greater. Furthermore, the saturated 

paraffin-naphthene hydrocarbon nolecular distribution and composition would be expected to 

show a more mature character. Ba.cause the TAl 

values determined by GeoChen1 Laboratories, 

Inc., and the CPI values and thermal pyrolysis 

measurements made by the USGS are in agreement, it is believed that the threrl10ld of intense 

oil generation begins between 9,000 and 10,000 ft 

(2,743 and 3,048 m) in the COST No. G-2 well, 

and peak generation and maturation processes 

occur between about 14,000 and 18,000 ft (4,267 

and 5,486 m). It is important tc note that the 

threshold or transition temperature of intense oil 

generation tends to be higher or to occur at 

greater burial depths in carbonates than in 

shales. This tendency is consistert with the idea 

that the activation energy for ker<Jgen decomposition in limestones and dolomites Fould be higher 

than in clays because of the catalytic effect of the 

clays (Hunt, 1979). Loc~lized zones 

of high heat flow may play a significant role in 

thermal maturation within the Georges Bank 

basin and the possibility may exist for dry gas 

generation in the Jurassic of the COST G-2 area 

below 18,000 ft (5,486 m). Howe·ver, because of 

the poor-to-fair quality of the source rocks, 

the potential for significant resources 

may be reduced. 

SUMMARY AND IMPLICATIONS FOR OIL AND 

GAS GENERATION 

The Tertiary strata of the COST No. G-1 well 

(1,013 to 1,030 ft; 309 to 314 m) and the COST 

No. G-2 well (1,100 to 1,310 ft; 35~ to 399m) are 

characterized by thin layers of unconsolidated, 

coarse quartz sands and light-rellow to buff 

calcareous muds and siltstones. respectively. 

Because of the extremely shallow burial depths, 

the thermally immature nature of the lignitic to 

138 
~ 

1-

w 

w 

IL 

z 

THERMAL AL TERATtON VITRINITE REFLECTANCE 

INDEX CPI-8 

TEMPERATURE MAXIMUM 

PYROLYSIS YIELD 

Ts2 (CIC) 

0 0 1.4 1.8 2.2 2.8 3.0 0.2 0.8 1.0 1.4 -- --- --- --- - 0.5 1.0 1.5 2.0 2.6 440 450 480 470 480 

. 3000-l 

·~ I : 

I / I / 11000 

. ' 

. 

6000j ~~ I . / ~ ~2000 . . . 

. 

. . 9000 . 

. 3000 ~ . . 

. w . 1-

w . . . ~ . . - 12,000 . ~ I: 

~ w 

a 

16.~] 

18,000 

I 

21,000 

) 

I 

GEOCHEM LABS 

CORE LABS 

I 

. . . . .. . 

. . 

.. 

. 

. . 

. 

CORE LABS 

? s . 

. . 

. . . . 

. . ' >· ... I ~ I 

• SIDEWALL CORES USGS USGS 

• CUTTINGS 

FIGURE 55.-Maturity profiles of organic matter as a function of depth of burial for samples .from the 0~3T No. G-2 well. 

4000~ w 

a 

r6000 

~6000 
TOTAL C,-c4 (ppm) 

(X 1n~ 

TOTAL c.-c7 (ppm) 

(X 102) CJC7 . - , , ...... "- , GAS WETNESS (%) 

0 o 1 3 & 7 8 11 o 1 3 5 7 8 11 13 15 o 10 20 30 40 50 eo o 2 4 a a 10 12 14 

3000 1000 

8000 

2000 

9000 

rn 

a: 

w 

1-

w 

1-

w 

Ill 

IL. 

~ 

~ -~ ~ 12.000 0 :J: 

4000 ~ 

a. t: Ill 

Ill 

a 

a 

5000 

6000 

21.000 

GEOCHEM LABS GEOCHEM LABS GEOCHEM LABS GEOCHEM LABS 

FIGURE 56.-Summary of c. to c7 hydrocarbon analyses of samples from the COST No. G-2 well. 
woody kerogens, and the character of the extractable organic matter, the Tertiary is not considered a target for oil or natural gas exploration 

in the Georges Bank region. 

Cretaceous strata were penetrated in the COST 

No. G-1 well from 1,030 to 5,290 ft (314 to 

1,612 m) and in the COST No. G-2 well from 

1,310 to 5,960 ft (399 to 1,817 m). Source-rock 

richness characteristics for the Cretaceous in 

these two wells are in the poor-to-fair quality 

range. This interpretation is based on the average 

total organic carbon values of 0.46 to 0.85 (weight 

percent), and average total extractable pydrocarbons of 33 and 93 ppm for the G-1 and G-2 wells, 

respectively. The Cretaceous kerogens have 

hydrogen to carbon ratios that range from 0.63 to 

0.97. Such ratios are comparable with type II and 

III terrestrially derived, hydrogen-poor, humic, 

gas-prone kerogens. The molecular distribution 

and concentration of the C15+ saturated paraffinnaphthene hydrocarbons, the low temperature of 

maximum pyrolysis yield (T8 ), and TAl levels of 

1.4 to 1.6 suggest that the Cretaceous extractable 

organic matter and kerogens have not yet experienced a sufficient time and temperature 

history to allow the generation of petroleum 

hydrocarbons and gas. 

The vitrinite reflectance values suggest that a 

much higher degree of thermal maturity may 

have existed during the Cretaceous of the 

Georges Bank basin than is suggested by the 

other light optical, pyrolysis, and geochemical 

maturation parameters. This inferred higher level 

of thermal maturation may be the result of prior 

thermal histories imprinted on recycled organic 

matter. The indigenous extractable hydrocarbons 

present in the Cretaceous sediments down to 

6,000 ft (1,829 m) in the COST Nos. G-1 and G-2 

wells are believed to be thermally immature and 

have not been produced by petroleum-generating 

processes. 

The potential for mud-additive influence from 

diesel fuel or other additives such as barite, 

spersene, bentonite, carboxymethylcellulose, pipe 

dope, and lignosulfonate (leonardite) cannot be 

disregarded. The mud-additive effects are not 

believed to have been pervasive but rather are 

restricted to certain zones, influencing the 

character of the indigenous cl5+ hydrocarbons at 

specific intervals in the Jurassic below 12,000 ft 

(3,660 m). The mud-additive effect on the extractable organic matter is believed to be localized 

and restricted because of the consistently low 

total organic carbon values and the lack of a 

uniform mud-additive fingerprint on the hydrocarbon molecular composition and distributi~n of 

the entire suite of samples. 

The Middle Jurassic strata of the COST No. 

G-2 well below 13,650 ft (4,161 m) are chart'~terized by abundant shallow-water dolomite, limestone, and anhydrite-evaporite facies. The J·lrassic section of the G-1 (5,290 to 15,630 ft; 1,612 to 

4,764 m) has a higher percentage of sand anc silt, 

and less carbonate and argillaceous sedi"'llent 

than the G-2. This difference is also reflected in 

the distribution and type of the solid organic matter in the samples. The Jurassic kerogens in the 

G-1 are predominantly terrigenous, humic, and 

gas-prone (type Ill), with little of the hydrogenrich, oil-prone (type I) variety. The Jur~~sic 

strata of the G-2 (5,960 to 21,874 ft; 1,817 to 

6,667 m) contain amorphous and algal (tY]'le I) 

gas-prone and herbaceous (type II) and w~y 

(type Ill) kerogens. In the COST No. G-1 well, 

the average total organic carbon values for the 

Upper, Middle, and Lower Jurassic sample~ are 

0. 73, 0.25, and 0.11 weight percent, respecti" 7ely, 

and the values for total extractable hydrocar.,ons 

in these strata are 38, 36 and 39 ppm, respect;ively. These source-rock organic-richness value~ are 

considered to be very poor to poor. For the U"lper 

and Middle Jurassic shales of the COST No. G-2 

well, the average total organic carbon value:;-o are 

0.62 and 0.23 weight percent, and the avE:rage 

total-extractable-hydrocarbon concentrationr are 

155 and 170 ppm, respectively. Although the 

source-rock organic-richness characteristicr of 

the G-2 Jurassic strata appear to be better than 

those of the Jurassic in the G-1, such values only 

indicate a poor-to-fair oil and gas source -1'()Ck 

potential. 

141 

The possibility exists that oxidized vitrinite or 

recycled organic matter in the Jurassic of the 

COST Nos. G-1 and G-2 wells may have influenced the vitrinite reflectance values by im'"larting abnormally high thermal-maturity level~ acquired from earlier thermal histories. Becau~e of 

the consistent agreement between the tem,erature of maximum pyrolysis yield (T8 ), the thermal alteration index, and the molecular distribution and concentration of the C15+ hydrocar~'>ns, 

the peak of liquid hydrocarbon generation is 

placed at burial depths of about 13,001 to 

15,000 ft (3,962 to 4,572 m) in the COST G-1. The 
depth of peak petroleum generation is believed to 

occur in the COST G-2 between 14,000 and 

18,000 ft (4,267 and 5,486 m). 

In the COST No. G-1 well, the thermalchemical maturation processes may be influenced 

by the presence of localized metamorphism. How 

representative the thermal maturity data from 

the COST Nos. G-1 and G-2 wells may be for a 

regional view of the Georges Bank basin is open 

to question, because the basin appears to be 

characterized by a complex thermal and burial 

history, and the effects of possible overburden 

loss in the Tertiary and Cretaceous have not yet 

been evaluated. Localized zonefl of abnormally 

high heat flow may have exie"*.ed along with 

patches of organic-rich Jurassic evaporite-reefal 

carbonate rocks. Such factors ar~ believed to be 

critical in controlling the maturation processes 

and occurrence of possible dee~ Jurassic gas. 

Because of the predominance o~ the hydrogenpoor kerogens, the potential for generation may 

exist at greater depths in the vicinity of the 

COST No. G-2 well. However, because of the 

poor to fair source-rock quality, the commercial 

attractiveness may be significantly diminished. 

142 
Thermal History of the Georges Bank Basin 

Michael A. Arthur 

A study of the thermal history of the Atlantic 

continental margin basins is necessary for an 

evaluation of the possibility of generating 

hydrocarbons from potential source rocks. The 

depths at which petroleum and thermogenic gas 

may have been generated can be estimated from 

present-day thermal gradients taken from well 

temperature logs (Tissot and others, 197 4), but 

this approach is more useful for near-surface, 

younger sedimentary horizons (100-120 m.y. old), 

which probably have not been affected by burial 

temperatures higher than those existing today. 

However, the older, more deeply buried strata, 

particularly those deposited within 50-70 m.y. 

after the initiation of rifting along the Atlantic 

continental margin, may have been initially subjected to higher temperatures and may have 

generated hydrocarbons early in their evolution. 

The thermal gradient probably decreases both 

through time and with depth in sedimentary 

basins along rifted passive margins (Royden and 

others, 1980). Also, older strata such as those in 

thinner sedimentary sequences on the continental 

rise may have been heated sufficiently to produce 

significant amounts of petroleum or gas early in 

the history of sedimentation without deep burial. 

Therefore it is important to know the thermal 

history of a sedimentary basin as well as its 

modem thermal gradient, because generation and 

preservation of petroleum hydrocarbons is a function of both time and temperature (Waples, 1980). 

The purpose of this paper is to discuss aspects 

of the present-day thermal gradient and the thermal history of the Georges Bank basin based on 

data from the COST Nos. G-1 and G-2 wells. 

Aspects of basin subsidence, sedimentation, and 

continental margin evolution are discussed with 

regard to the indications of thermal maturity in 

sedimentary organic matter and possible hydrocarbon generation in the Georges Bank basin. 

The discussion of thermal history is based largely 

143 

on recent models of the thermal evolutic, of 

passive margins (Steckler and Watts, 1978; Royden and others, 1980; Angevine and Turc"ltte, 

1981) and is intended only to place some Iimi+s on 

estimates of the petroleum potential of the landward part of the Georges Bank basin. 

PRESENT-DAY THERMAL GRADIENT 

Figure 57 illustrates the downhole temperr~ture 

profiles for the COST Nos. G-1 and G-2 wells 

based on Schlumberger temperature logs (Scholle 

and others, 1980). The geothermal gradient~ calculated by applying linear regression analyri s to 

these data (Jackson and Heise, 1980; Heise and 

Jackson, 1980) are 1.26° F per 100ft (23.0° C/km) 

for the G-1 well and 1.34° F per 101 ft. 

(24.4C/km) for the G-2 well. Jackson and Peise 

(1980) and Heise and Jackson (1980) have "corrected" the temperature log data at several 

depths to remove the effects of drilling (no:-:malized to a 25-hr post-drilling period) and co.termined revised gradients of 1.17° F per 100ft 

(21.3° C/km) and 1.46° F per 100ft (26.6° C/km) 

for the G-1 and G-2 wells respectively. Corrr~cted 

bottom-hole or near-bottom-hole tempera~ures 

were 247° F (119° C) at 16,400 ft (5,000 m) in the 

G-1 and 360° F (182° C) at 21,790 ft (6,640 m) in 

the G-2 well. 

The present-day temperature gradients from 

the Georges Bank COST wells are compared to 

those of other Atlantic margin COST wellr and 

several other localities in table 7. The gradient at 

the G-2 well is the highest measured along the 

Atlantic margin, while that at the G-1 w~ll is 

close to the average for wells on other parts <'f the 

margin. However, it is likely that abs~lute 

temperatures and thermal gradients in the lower 

part of G-1 were once higher because of higher 

heat flow associated with the extensional thinning of the crust during the rifting in I atest 
DOWN HOLE 

TEMPERATURE 

(oF) 

100 300 

I I I 

1M-

~~ 

j~ 

-

~ 

...... 

-.... 

,. 

.... 

.. 

..... 

... 

.. 

• 

.... 

~ 

~ 

... 

Ro 

(MEAN VITRINITE REFLECTANCE) 

0.0 0.6 1.4 2.2 3.0 

I I I I I I 1 I I I I I I 

• G-1 WELL DATA 

• • G-2 WELL DATA 

• • 

t 

' • 

• 

• 

• 

• 

.• 

• • 

t 

• • • 

• 

• • 

• • • ... • • 

• • 

• 

4 

• 

1- -

• 

• I 

I 

• -

• I 

I 

• I 

• 

• 

• 

.. 

t 

• • • ... ... 

THERMAL 

AL TERATlON 

INDEX 

2 3 4 

C'EPTH 

FEET METERS 

0 0 

1000 

3000 

9000 

10.000 

11.000 

SEA 

LEVEL 

500 

1000 

1500 

FIGURE 57.-Downhole temperature profiles from temperature logs (Scholle, Krivoy, and Hennes:~y. 1980; Scholle, 

Schwab, and Krivoy, 1980), mean vitrinite reflectance values (Superior Oil Co. and Core Laboratorir~s. Inc.), and thermal alteration indices (TAl; GeoChem Laboratories, Inc.) for the COST Nos. G-1 and G-2 wells. 

144 
DOWN HOLE 

TEMPERATURE 

(oF) 

100 300 

I I I 

.,. 

--

-

-

.. 

""" 

• 

....IL 

-

.. 

~ 

• 

~ 

-

• 

-

• 

-

• 

• 

Ro 

(MEAN VITRINITE REFLECTANCE) 

0 0 0.6 1.4 2.2 3.0 

I I I •• 1 I I I I I I I I 

• 

• 

• • 

. 

• .. 

• 

• 

• • 

• 

j~ 

• 

~ 

~· 

•• 

~16 • 

• 

~ • 

• 

A 

• 

• 

• 

• 

• 

• 

4 

~ 

·I· ~ 

I • 

~ 

• 

• 

• • 

•• 

• 

• 

A 

THERMAL 

ALTERATION 

INDEX 

2 3 4 

DEPTH 

FEET METEP.S 

FIGURE 57.-Downhole temperature profiles from temperature logs (Scholle, Krivoy, and Hennessy, 1980; Schnlle, 

Schwab, and Krivoy, 1980), mean vitrinite reflectance values (Superior Oil Co. and Core Laboratories, Inc.), and t'termal alteration indices (TAl; GeoChem Laboratories, Inc.) for the COST Nos. G-1 and G-2 wells.-Continued 

145 
TABLE 7.-Geothennal gradients on passive continental margins 

[Data from Jackson and Heise (1980) and Robbins and Rhodehamel (1976)) 

Gradient 

Area Well °F/100 ft °C/km 

Georges Bank .............. . Do ..................... . Baltimore Canyon .......... . Do ..................... . Southeast Georgia 

embayment .............. . Scotian sheH ............... . Texas Gulf Coast ........... . North Sea basin ............ . 

1 Average from several wells. 

G-1 

G-2 

B-2 

B-3 

GE-l 

(1) 

(1) 

(1) 

1.2 

1.5 

1.3 

1.2 

.9 

1.2 

1.6 

1.7 

22 

27 

24 

22 

16 

22 

29 

32 

Triassic-Early Jurassic time. The present-day 

gradients suggest that there has been no significant hydrocarbon generation above 8,000 ft 

(2,440 m) in the G-1 well and above 6, 700 ft 

(2,040 m) in the G-2 well, based on the generalizations offered by Pusey (1973) for the "oil 

window" (150°-300° F; 66°-149° C). Dry gas 

may be expected below about 18,000 ft (5,490 m) 

in the G-2 well and below about 16,000 ft 

(4,870 m) in the vicinity of the G-1 well. Generation of hydrocarbons is a function of time as well 

as temperature (Lopatin, 1976), and the organic 

geochemical and thermal maturation data (Miller 

and others, this volume) generally agree with the 

estimates given above. 

SUBSIDENCE AND THERMAL HISTORY 

The subsidence history of the Cost Nos. G-1 

and G-2 wells was examined using the method of 

Steckler and Watts (1978). In this method the 

sedimentary section recovered in the well is 

"backstripped" in order to examine the sequential subsidence history of a given part of the continental margin. Sediments of each defined time 

interval are restored to their former thickness by 

correcting for compaction, and the amount of subsidence induced by sediment loading is calculated 

incrementally using the Airy isostatic model and 

assuming local loading of the crust. The depth to 

basement after removal of the effects of local 

sediment (and water) loading are obtained by 

using the following equation: 

Y=S* (pm-ps) +W -flSL=:-pm __ :--

(pm-pw) d (pm-pw) 

146 

where 

Y =depth to basement with no loading ("tectonic component of subsidenc~") 

S* =interval sediment thickness corrected 

for compaction 

pm=density of the upper n1antle (assumed 

3.3 g/cm3

) 

ps=initial density of a given sediment 

package (calculated) 

pw=density of seawater (assumed 1.03 g/cm3

) 

W d=average water depth during a given 

time interval 

llSL=eustatic sea level chanf.'~ (relative to today). 

The value of S* was calculated for a given 

thickness of sediment by determimtg the change 

in porosity during compaction. The lithology of 

much of the COST Nos. G-1 ar1 G-2 wells is 

variable, so the assumption of constant grain density does not hold and the single porosity reduction curve with compaction used by Steckler and 

Watts (1978) and Watts and St~~kler (1979) in 

"backstripping" the COST No. B-2 well is not 

applicable. Therefore, in this study the sedimentary sequence was subdivided into time intervals 

using the biostratigraphic age assignments of 

Poag (this volume). These age as<"\i~ments may 

be in error, particularly for the c.lurassic part of 

the sequence in which fossils w1~re sparse. The 

ratios of sand and shale to carbonate and to 

evaporite sediments was calculauti for each sediment interval using lithologic descriptions (Arthur, this volume; Scholle, Krivoy, and Hennessy, 

1980; Scholle, Schwab, and Krivo~r, 1980). Clastic 

sediments were assigned an initial porosity of 52 

percent, carbonate sediments a po:--osity of 30 percent, and evaporites a porosity of 10 percent. The 

precision of this method is inherently low in such 

generalized calculations. 

Estimates of water depth at the time of deposition are based on those of Poag (tl'is volume), and 

the sea level curve derived by Watts and Steckler 

(1979) was used to make the eustR.tic correction. 

The data and calculations for the COST No. G-2 

well are shown in table 8, and this subsidence 

history is illustrated in figure 58. 

Assuming that the amount of "tectonic" subsidence is related to the amount of crustal thinning 

during initial rifting, Royden and others (1980) 
TABLE B.-Data used and results of calculations of basin subsidence at the COST No. G-2 well 

[Depth figures are feet below Kelly Bushing (1 ft=0.3048 m). -, not applicable; (?), uncertain! 

Age Depth 

to top to top Interval Cumulative Average Average Corrected 

Interval horizon horizon thickness thickness porosity Lithology1 density thickness 

(m.y.) (feet) (feet) (feet) (percent) (percent) (glcma, s• (feet) 

Water ........................ 272 21,920 

Holocene and Pleistocene ........ 0 351 749 21,648 52 95-5-0 2.00 749 

Pliocene and Miocene ........... 1.8 1,100 150 20,820 45 95-5-0 2.10 158 

Eocene ....................... 38 1,250 74 20,670 45 95-5-0 2.10 78 

Lower Santonian ............... 80 1,324 376 20,596 42 95-5-0 2.15 409 

Coniacian ..................... 83 1,700 420 20,220 40 95-5-0 2.10 466 

Lower Turonian ................ 90 2,120 150 19,800 37 90-10-0 2.10 169 

Upper and middle 

Cenomanian ................. 92 2,270 60 19,650 37 90-10-0 2.10 68 

Aptian 0 0 0 •• 0 0 0 •• 0 •••••••• 0 ••• 107 2,330 480 19,590 35 90-10-0 2.10 551 

Barremian ••• 0 ••• 0 •••••••• 0 ••• 115 2,810 1,110 19,110 33 90-10-0 2.15 1,296 

Hauterivian . . . . . . . . . . . ........ 120 3,920 590 18,000 30 82-18-0 2.25 696 

Valanginian . . . . . . . . . . . ........ 126 4,510 930 17,410 25 85-15-0 2.35 1,150 

Berriasian ••• 0 ••• 0 ••••••• 0 0 ••• 131 5,440 480 16,480 25 58-42-0 2.55 565 

Tithonian ..................... 135 5,920 780 16,000 20 58-42-0 2.65 958 

Upper Kimmeridgian ........... 137 6,700 960 15,220 20 70-30-0 2.45 1.204 

Lower Kimmeridgian ........... 140 7,660 1,000 14,260 25 80-20-0 2.45 1,226 

Oxfordian(?) . . . . . . . . . . . . . ...... 142 8,660 1,440 13,260 20 60-40-0 2.50 1,774 

Callovian(?) •••• 0 •• 0. 0 0 •••••• 0. 150 10,100 2,000 11,820 5 42-53-5 2.65 2.665 

Bathonian(?) .................. 156 12,100 2,000 9,820 5 20-75-5 2.65 2.568 

BX~!:!i!(?f~ ................. 164 14,100 900 7,820 7 5-62-33 2.95 1.058 

Toarcian(?) and Upper 

Pliensbachian(?) .............. 174 15,000 1,900 6,920 2 12-64-24 2.85 2.391 

Lower Pliensbachian(?) 

and Sinemurian(?) •••• 0 •••••• 0 180 16,900 1,100 5,020 2 8-80-12 2.85 1,401 

Hettangian(?) and 

Rhaetian(?) .................. 189 18,000 3,870 3,920 1 17-50-33 2.85 4.882 

Rhaetian(?) . . . . . . . . . . . . . . . . . ... 192 21,870 >50 50 4 0-0-100 3.00 50 

Corrected Estimated Total 

Corrected Cumulative Non-load water non-load Sea level Corrected Cumulative 

Interval density thickness subsidence depth subsidence correction subsidence subs~dence 

ps (glcm:; (feet) (feet) (feet) (feet) (feet) (feet) (foot) 

Water ........................ Holocene and Pleistocene ........ 2.0 21,970 479 272 751 185 566 1:J,871 

Pliocene and Miocene ........... 1.99 21,171 92 200 292 185 107 1S,305 

Eocene ....................... 1.99 21,027 45 200 345 351 -6 13,198 

Lower Santonian ............... 1.98 21,022 240 600 840 596 244 13,204 

Coniacian ..................... 1.89 20,771 292 600 892 596 292 12,960 

Lower Turonian ................ 1.86 20,261 108 200 308 432 -124 12,668 

Upper and middle 

Cenomanian ................. 1.85 20,105 44 300 344 400 -66 12,792 

Aptian 0. 0 0 ••• 0 0 ••• 0 •• 0 0 •• 0 0 •• 1.83 20,136 359 50 409 80 329 12,858 

Barremian • 0 ••••••• 0 ••• 0 ••• 0 •• 1.84 19,818 841 50 891 60 831 12,529 

Hauterivian ................... 1.91 18,647 421 50 471 81 390 11,698 

Valanginian ................... 1.90 18,158 715 50 765 120 645 11,308 

Berriasian • 0 •••••• 0 •••• 0 ••• 0 •• 2.17 17,110 285 300 585 135 450 10.663 

Tithonian ..................... 2.16 16,718 487 60 547 135 412 10,213 

Upper Kimmeridgian •• 0 0 •• 0 •••• 1.95 15,976 722 50 772 135 637 9.801 

Lower Kimmeridgian •• 0 ••• 0 •••• 2.00 14,993 709 50 759 135 624 9.164 

Oxfordian(?) ................... 2.03 14,086 1,003 50 1,053 (?) 1,053 8.540 

Callovian(?) • 0 ••• 0 •••• 0 •• 0 0 •• 0. 1.99 12,792 1,553 50 1,603 (?) 1,603 7,487 

Bathonian(?) 0 ••• 0 •••• 0 ••• 0 •• 0. 2.06 10,529 1,418 0 1,418 (?) 1,418 5.889 

BX~!:!i!(?f~ ................. 2.51 8,212 377 0 377 (?) 377 4.466 

Toarcian(?) and Upper 

Pliensbachian(?) .............. 2.26 7,584 1,112 10 1,122 (?) 1,122 4.089 

Lower Pliensbachian(?) 

and Sinemurian(?) 0 •••••••• 0 •• 2.24 5,500 664 10 674 (?) 674 2,967 

Hettangian(?) and 

Rhaetian(?) .................. 2.26 4,932 2,271 10 2,281 (?) 2,281 2.293 

Rhaetian(?) .................... 2.80 50 12 0 12 (?) 12 12 

1Relative abundance of clastic, carbonate, and evaporite sediments, respectively. 

147 
AGE IN MY 

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 

0 -----,-----,---,-------,--~,--,-------,------,----,------,----,----,---,--,---~ 

"t 12 

13 

14 

15[ 

:: ~ 

18 19 f 

20 

21c- COST NO G-2 WELL 

22~_j ___ l___ __ j__________..___L ___ l 

DUE TO TECTONIC 

DRIVING FORCES 

J.•oo 

j

3000 

------- 4000 

1-

Jooo ., 

FIGURE 58.-Subsidence history of the basement (194 m.y. 

B.P.) and sedimentation at the COST G-2 well. Stippled 

area shows subsidence due to sediment loading assuming 

local loading and Airy isostasy. The clear portion is that 

part of the subsidence due to cooling after crustal thinning 

or dike intrusion following rifting. See text and table 8 for 

details of reconstruction. 

and Angevine and Turcotte (1981) have demonstrated that the history of heat flow in continental margins can be modeled. The heat flow 

models allow reconstruction of the general thermal history of sedimentary horizons of different 

ages, assuming decay of the initial heat flux 

without addition of heat from other sources, an 

average thermal conductivity for the basin sediment sequence, and continuous thermal equilibrium within the sequence. These are all reasonable assumptions for the Georges Bank basin. 

Royden and others (1980) have constructed 

thermal models for crust of various thicknesses. 

They defined a factor,')', which equals 0 for normal 

continental crust and 1 for oceanic crust. The 

crust at the COST No. G-2 well was thinned to a 'Y 

value of 0.6 on the basis of the calculated amount 

of "tectonic" subsidence (Sawyer and others, in 

press), while the crust at the COST No. G-1 well 

was thinned to a 'Y value of 0.4. Sawyer and others 

(in press) arrived at these values using modeling 

techniques more sophisticated than those used in 

this study. The total tectonic subsidence derived 

here (fig. 58) is about 1,640 to 1,969 ft (500-600 

m) greater than in the Sawyer and others model. 

148 

Figure 59 shows the model of Royden and 

others (1980) for the evolution of geotherms in a 

basin in which the initial thinning occurred at 

about 200 m.y. B.P. and had a 'Y value of 0.6 (the 

COST No. G-2 estimate). Estima+es of the burial 

history of several sedimentary h~rizons are also 

illustrated. From these data, time-temperature 

profiles can be constructed (Wapi ~s, 1980). These 

are shown in table 9. 

TIME-TEMPERATURE INDIC:ES AND 

HYDROCARBON MATU~'TION 

On the basis of temperatur€R of maximum 

pyrolysis, thermal alteration indi,~es, and the concentrations of C15+ hydrocarbons, Miller and 

others (this volume) have inferred that peak thermal maturation of hydrocarbons occurs between 

13,000 and 16,000 ft (3,960 and 4,570 m) in the 

COST No. G-1 well and between 14,000 and 

18,000 ft (4,270 and 5,490 m) in the COST No. 

G-2 well. Miller and others (this volume) place 

the "threshold of intense oil gen€ration" at about 

9,000 to 10,000 ft (2,750 to 3,050 m) in the COST 

Nos. G-1 and G-2 wells. The est.imated "oil window" occurs between about 8,000 and 16,000 ft 

(2,440 and 4,570 m) in the G-1 vrell and between 

6,700 and 17,000 ft (2,040 and 5,180 m) in the G-2 

well. There is a general agreem~nt between the 

very general estimates of the ''oil window'' and 

organic geochemical indicators <'f thermal maturity of organic matter. 

Vitrinite reflectance values, co:'11IIlonly used indicators of thermal maturity, are shown in figures 

60, 61, and 62, (analysis by Super,:or Oil Company 

for the COST No. G-1 well and by Core Laboratories, Inc., for the COST No. G-2 well). Thermal 

alteration indices (TAl, figs. 57 and 60) were 

determined by GeoChem Labo·atories, Inc. A 

vitrinite reflectance (R0 ) value of 0.6 is believed to 

represent the onset of thermal maturation and 

hydrocarbon generation (Dow, 1f77; Hunt, 1979). 

This value occurs at an an01r 1\lously shallow 

depth of about 3,800 ft (1,160 m\ in the G-2 well 

in Cretaceous sediments and at about 7,000 ft 

(2,130 m) in the G-1 well in Upper Jurassic 

sedimentary rocks. The "oil flCJ~r" (R0 = 1.35) 

should occur at about 13,500 ft (4,120 m) in the 

G-1 well and 11,500 ft (3,510 m) in the G-2 well. 

However, Miller and others (this volume) have 

discussed the other indications of organic 
TIME IN M.Y B. P. 

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 

0.-~--~--~--~~--~--~--~--~~~==~----~----~,--.---,--.------. 

2 

\ 

\ 

-..... 

' " 

----------------, 

......... 

--------------75°C----------------------~ 

~ 

~ 3 

z 

J: 

1-

CL 

w 4 

0 

---------

125°C ------------------1 

150°C ------------------~ 

175°C -----·-------------1 

FIGURE 59.-Thermal model based on the amount of crustal thinning ('y=0.6) at the COST No. G-2 well (after Royd1n and 

others, 1980). The burial histories of sediments approximately 191, 156, 140, and 107 m.y. old (dashed lines) are shown 

relative to the time-temperature field. These traces were used to calculate the time-temperature indices in table 9. 

maturation, which conflict with the vitrinite 

reflectance data in the COST No. G-2 well. 

Figure 60 suggests that vitrinite reflectance 

values are generally too high when compared 

with TAl in the same samples. 

It is possible that the anomalous reflectance 

values are from reworked or highly oxidized 

vitrinite derived from a previous sedimentary 

cycle, or that there is some nonsystematic error in 

the reflectance determinations. The first possibility is geologically reasonable, but the COST 

Nos. G-1 and G-2 wells do not exhibit the same 

pattern of reflectance values with depth, as would 

be expected if the sediment at both wells was 

derived from the same source. The reflectance 

values increase normally and systematically 

downhole in the G-1 well (figs. 61, 62), and R0 

values of equivalent strata in the G-2 well are 

considerably higher, which suggests errors in the 

149 

measurements for the G-2 well or bias towards 

the higher rank vitrinite in each sample. 

Figure 62 is a semilog plot of vitrinite reflectance and downhole temperature. The G-1 data 

plot on a straight line segment with relet.ively 

little scatter, suggesting that the valu~s are 

reasonable and that they increase in a predi~table 

fashion with increasing temperature. Tho G-2 

data define several line segments having dif~erent 

slopes. The values from about 12,750 ft (3,r90 m) 

to the bottom of the hole define a line }' 'lving 

about the same slope as the G-1 data This pattern suggests that the G-2 data fron the 

Jurassic and older section may be accurB te. In 

fact, they reflect a somewhat lower refle~tance 

value for a given temperature than do th~ G-1 

data The problem occurs in the refle~tance 

values from 914 to 12,750 ft (278 to 3,890 m) in 

the G-2 well. These data suggest an anmnalous 
TABLE 9.-Time-temperature indices for representative horizons in the COST No. G-2 wel,: 

[TTl, time-temperature index; rD, assumed increase in rate of maturation relative to the 100 °-110 oc interval, as described in Waples (1980)] 

Temp. 

interval a Time Interval Total Equivalent 

(oC) rD (m.y.) TTl TTl m.y.B.P. Ro 

191-m.y.-old sediment (now at 20,000 ft (6,096 m)) 

20-30 2 8 1.0 .004 .004 190 <0.3 

30-40 2-7 0.5 .004 .008 189.5 <.3 

40-50 2-6 0.5 .008 .016 189 <.3 

50-60 2-5 10 .32 .33 179 <.3 

60-70 2-4 4 .26 .59 175 <.3 

70-80 2-3 2 .25 .84 173 <.4 

80-90 2-2 14 3.5 4.34 159 .5 

90-100 2-1 4 2.0 6.34 155 .55 

100-110 1 3.5 3.5 9.84 151.5 10.6 

110-120 2 4 8 17.8 147.5 I .65 

120-130 22 9 36 53.8 138.5 I ,9 

130-140 23 4 32 85.8 134.5 11.05 

140-150 24 2.5 40 125.8 132 11.2 

150-160 26 8.5 272 397.8 123.5 1.7 

160-170 26 11 704 1,108.8 112.5 2.1 

170-180 27 6 768 1,869.8 106.5 3.8 

180-190 28 110 28,160 30,029.8 4.2 

156-m.y.-old sediment (now at 12,100 ft (3,688 m)) 

20-30 2 8 6 .024 .024 150 <0.3 

30-40 2-7 3 .024 .048 147 <.3 

40-50 2-6 3.5 .056 .114 143.5 <.3 

50-60 2-5 3.5 .112 .226 140 <.3 

60-70 2-4 6 .384 .610 134 <.3 

70-80 2-3 9 1.13 1.73 125 .45 

80-90 2-2 7 1.75 3.48 .5 

90-100 2-1 118 59 62.48 118 2 .95 

140-m.y.-old sediment (now at 7,680 ft (2,340 m)) 

20-30 2 8 9 .036 .036 131 <0.3 

30-40 2-7 6 .048 .084 125 <.3 

40-50 2-6 4 .064 .148 121 <.3 

50-60 2-5 32 1.02 1.17 89 .4 

60-70 2-4 89 5.70 6.87 3 .55 

11n empirical oil-generation window between 11,480 and 15,580 ft (3,500 and 4,750 m) burial depth (only 50 m.y. after deposition). 2

In oil-generation window at approximately 95 m.y. B.P. at burial depth of 9,500 ft (2,900 m). 3

Immature. 

thermal event that affected only the Upper 

Jurassic through Upper Cretaceous section of the 

COST No. G-2 well. Although such a thermal 

event would not be impossible, it is unlikely that 

the heating would have increased vitrinite rank 

without altering T AI values or other indicators of 

thermal maturity. Therefore the anomalously 

high average R0 values probably do not reflect 

such an event. 

Despite the problem with the vitrinite reflectance values in the G-2 well, the estimates of 

thermal maturity by Miller and others (this 

volume) are in general agreement with the thermal model approach. Different estimates are obtained from models of the thermal history of the 

sediments. The thermal model constructed in 

figure 59 was used to calculate time-temperature 

indices (TTl shown in table 9; method outlined by 

150 

Waples, 1980) for the following }''lrizons at the 

COST No. G-2 site: 191 m.y. (20,000 ft; 6,100 m 

present depth); 156 m.y. (12,000 ft.= 3,690 m present depth); 140 m.y. (7,680 ft; 2,340 m present 

depth); and 107 m.y. (2,330 ft; 710 m present 

depth). The burial history of each of these 

sedimentary layers is shown super~.mposed on the 

theoretical depth distribution of temperature 

through time in the Georges Bank basin. The 

calculation of TTl for each heizon gives a 

general indication of the thermal rr.fiturity of each 

horizon, based on the data of Wap1o.s (1980). 

The organic matter in the stratr. near the base 

of the G-2 well is overly mature on the basis of 

the calculated TTl; that is, b~low the "oil 

window" but still within the dry gas stability 

field. The TTl history indicates that these strata 

reached the oil window within 50 m.y. after their 
THERMAL ALTERATION INDEX 

1 2 14 16 18 20 22 24 26 28 30 

03 

04 

05 

06 

1/1. 

0 07 

~ 

w 08 

() 

z 

<( 09 

1-

() 1 0 

w 

...J 

u. 11 

w 

a: 1 2 

w 

1- 1 3 z 

a: 1 4 1-

> 1 5 

z 

<( 1 E w 

~ 1 7 

1 8 

1 9 

20 

. . . 

• G-1 WELL 

4 G-2 WELL 

4 

: ~ 

44 

FIGURE 60.-Mean vitrinite reflectance values versus thermal 

alteration indices (TAl) for samples from COST wells G-1 

and G-2. Line indicates optimum relationship between the 

two values. 

deposition (at a burial depth of about 11,500 ft 

(3,500 m)). The TTl values also indicate that 

these strata remained within the "oil window" for 

only 15 m.y. TTl estimates suggest that those 

units presently buried deeper than 18,000 ft 

(5,490 m) are overly mature. 

The onset of thermal maturation of the organic 

matter in the sediments deposited about 156 m.y. 

B.P. is estimated to have occurred about 95 m.y. 

B.P. at a depth of about 9,514 ft (2,900 m). The 

stratum is still within the zone of hydrocarbon 

generation based on calculated TTl values. 

The organic matter laid down at 140 m.y. B.P. 

is still immature on the basis of TTl values. 

Sediments near the G-2 well above about 8,500 ft 

(2,600 m) have TTl values that apparently indicate thermal immaturity, which is consistent 

with the organic geochemical data. 

The models suggest that the thermal history of 

the area surrounding the COST No. G-1 well was 

similar to that at the G-2 well except for 

somewhat lower temperatures at given depths in 

G-1. Therefore the maturation horizons should 

be lower in the G-1 well, which is in agreement 

with the present-day difference in thermal gradient at the two wells, but not with the organic 

maturation indicators. 

151 

50 

03 

04 

05 

06 

07 

08 

09 

10 

11 

~ 1 2 

0 1 3 ~ 

w 1 4 

t) 

z 1 5 <( 

1- 1 6 t) 

w 

_J 1 7 u.. 

w 18 a: 

w 19 t:: 

z 20 a: 

1- 21 

> 

z 22 

<( 

w 23 

~ 24 

25 

26 

27 

2 8 

29 

30 

3 1 

32 

33 

TEMPERATURE (°F) 

90 130 170 210 250 290 330 370 410 

• G-1 WELL 

• G-2 WELL 

---9000' 

.t..t. (-142-150 m.y.BP(G-2)) 

.t. -156 myB~ (G-1) 

• 

.. .. 

• 

FIGURE 61.-Mean vitrinite reflectance (R0 ) versus present in 

situ temperature (linear plot) for samples from COS1' wells 

Nos. G-1 and G-2. Note differences between the tw" wells. 

CONCLUSIONS 

There is conflicting evidence of the degree of 

thermal maturation of organic matter in the 

COST Nos. G-1 and G-2 wells. The estimrt.es of 

Miller and others (this volume) are that peak thermal maturation occurs between 13,000 and 

15,000 ft (3,960 to 4,570 m) in the COST No. G-1 

well and at 14,000 to 18,000 ft (4,270 to 5,490 m) 

in the COST No. G-2 well, with the "thresl''lld of 

intense oil generation'' occurring in both w~lls at 

about 9,000 to 10,000 ft (2,750 to 3,050 m). These 

estimates are based mainly on the concent ... ation 

of c15+ hydrocarbons, the temperatures of maximum pyrolysis, and thermal alteration index 

(TAl) values. The modern thermal gradient at the 

two wells, the vitrinite reflectance values, and 
MEAN VITRINITE REFLECTANCE (Ro)% 

• 10 w,...c:omo o ooooo 

0 

0

,--------,----,--------,o,---,o_o,----r-o --,-o -,o~ ~--,-1 --,-----,l,---,~-'"r-.-"

1 .-"'1 "',;, { 

(G-1) 1500' -

.. (G-1) 6750' - ·; 

(G-1) 10,900' -

\ .. 

\u~ 

- 1200' (G-2) 

- 3700' (G-2) 

- 6500' (G-2) 

- 9100' (G-2) 

- 10,900' (G-2) 

(G-1) 15,000' - ~ • - 12,750 (G-2) 

•:t. 

• G-1 WELL 

--• G-2 WELL 

~~.. - 16,600' (G-2) 

~ .... \ .. 

\.·· 

~~ 

\ - 22,8_50' (G-2) 

FIGURE 62.-Semilog plot of mean vitrinite reflectance (R0 ) 

versus present in situ temperature for samples from COST 

wells Nos. G-1 and G-2. 

152 

thermal models and calculated t~me-temperature 

indices (Trl) suggest that the cnset of thermal 

maturation should occur at sli ~htly shallower 

depths in the two wells; a depth of 8,500 ft 

(2,590 m) in the G-2 well seems rE'~onable for the 

beginning of thermal maturity. TAl values below 

this depth are around 2 and the carbon preference 

index (CPI) is about 1.5 and decr~ases downhole. 

These values are taken as an indication of the 

onset of thermal maturity. 

Previous estimates of the depth of the beginning of maturation in other Atlantic area COST 

wells are about 9,000 ft (2,750 1n) in the GE-l 

well, 11,300 ft (3,450 m) in the B-2 well, and 

14,300 ft (4,350 m) in the B-3 well. The COST No. 

G-2 well does have the highest present-day geothermal gradient of these wells; b':lwever, thermal 

maturation is affected by the richness and type of 

organic matter in the sediment. Therefore the 

prospects for significant generation and accumulation of oil and gas from in situ sources in 

the Georges Bank basin near the COST No. G-1 

or G-2 well are not good, regardless of the thermal history of the basin. (See Miller and others, 

this volume.) 
Geophysical Studies of the 

COST Nos. G-1 and G-2 Wells 

David J. Taylor and R. C. Anderson 

Digital well log data from the COST Nos. G-1 

and G-2 wells were used to compute subsurface 

velocities and synthetic seismograms. The 

interval-traveltime log from each well was integrated over each respective depth range, producing a relationship between depth and two-way 

traveltime for a seismic wave propagating 

through the subsurface. This relationship was 

used to convert the suite of well logs recorded as a 

function of linear depth to linear functions of 

time. The interval-traveltime log also provided 

other velocity information relevant to seismic 

reflection processing and interpretation. Synthetic seismograms were also computed using the 

velocity and density logs from the wells. The synthetic seismograms were bandpass filtered to 

match the seismic field data for correlation, and 

then spliced into the seismic line at the appropriate location. 

VELOCITY INFORMATION 

The average velocity function, shown in figure 

63 for the COST No. G-1 well and figure 64 for 

40~~~~~~~~~~~·-2~~~~~~3 

Two-way travel time, seconds 

FIGURE 63.-Average velocity (V avg) and root-mean-square 

velocity (V nns) as a function of two-way traveltime from 

sea-level datum for the COST No. G-1 well. 

153 

the COST No. G-2 well, can be used to compute 

the depth of a seismic reflection given its or.~way 

time position. Average velocities are also u~oo. in 

the migration processing of seismic data in areas 

of geologic structure. The root-mean-r~uare 

velocity shown on the same plots can be us~d for 

computing normal-moveout times, an imp'lrtant 

step to perform prior to the stacking proc~ss of 

multifold seismic reflection data. These velocities 

are only applicable in areas where the subs~uiace 

layers are relatively flat. 

The curve that relates depth to two-way traveltime below the sea floor is shown in figure 65 for 

both wells. Because the wells are fairly cl·'lse to 

each other, the curves nearly overlap throughout 

the extent of the logs. This crossplot can be used 

directly to determine the depth of a reflector 

given its two-way time position on the seismic 

line. 

SEISMIC DATA 

Two multichannel seismic reflection line~ were 

recorded for the USGS in 1977 by Digicon, Inc. of 

Cost G-2 

2 

Two-way travel time, seconds 

3 

'0 

c: 

0 

u 

Q) 

3~ E 

.>1! 

FIGURE 64.-Average velocity (Vavg) and root-mear-square 

velocity (V nns) as a function of two-way traveltime from 

sea-level datum for the COST No. G-2 well. 
5 

s= 

-a. 

Q) 

c 

15 

20 

0 1 2 3 4 

Two-way travel time, seconds 

FIGURE 65.-Twcrway traveltime below sea-level datum as a 

function of depth for the COST No. G-1 and COST No. G-2 

wells. 

Houston, Tex., to tie the COST Nos. G-1 and 

G-2 wells into the regional network of USGS 

multichannel seismic reflection lines on the 

Atlantic Outer Continental Shelf (AOCS). The 

orientations of these seismic lines with respect to 

regional USGS seismic reflection lines and the 

Cost Nos. G-1 and G-2 well locations are shown 

in figure 66. Line 77-1 crosses the COST No. G-1 

well at shotpoint 95, and line 77-2 crosses the 

COST No. G-2 well at shotpoint 96. Both lines 

were recorded for 36-fold common-depth-point 

(CDP) multiplicity with a record length of 7 

seconds two-way time. Shotpoint 350 on line 77-1 

intersects USGS line 12 at shotpoint 10,800. 

Shotpoint 205 on line 77-2 intersects USGS line 1 

at shotpoint 1,200. 

154 

Both seismic lines 77-1 and 77-2 were recorded 

on a 48-channel streamer at a 4-millisecond 

sampling interval. The data processing of each 

line consisted of the following prxedures. After 

demultiplexing and applying exponential gain to 

the field tapes, velocity analyses were performed 

on both seismic lines at 1-mi (1.6-lrm) intervals for 

normal-moveout correction and stacking. To attenuate multiple reflections and reverberations, 

two deconvolution filters were applied to the 

stacked data After deconvolutior a set of bandpass filters of 10 to 35Hz from 0 to 1.6 seconds, 

and 5 to 25 Hz from 1.6 to 4.0 Sf'~onds were applied to remove extraneous noise left on the data 

A final gain process (AGC) bas~~d on 1-second 

sliding windows was applied to ba1ance the amplitudes on the section. 

SYNTHETIC SEISMOGRAMS 

Using the digitized interval-traveltime and density logs from the two COST wells, zero-offset 

synthetic seismograms were computer generated 

and correlated to the multichannel reflection 

seismic lines described in the pre,ious section. A 

reflection coefficient series was fir;--t generated by 

converting the log data from dep+h to time, and 

computing the change of acoustic impedance 

(product of density and velocity) a~ross each time 

layer. These reflection coefficie:"lts were then 

filtered with a bandpass filter wltose passband 

was chosen to match that of sersmic reflection 

lines 77-1 and 77-2. 

The generation and utilization of synthetic 

seismograms is well described by Sengbush and 

others (1961) and Peterson and otl'~rs (1955). The 

shortcomings of the methods us~<i in constructing accurate synthetic seismog~ams are that 

plane waves are assumed, the so·rrce wavelet is 

usually not known, interbed multiples are not 

properly modeled, absorption and attenuation are 

not computed, and the effects o~ noise are not 

added. The effects of these problems are not corrected and degrade the comparisnn of synthetic 

seismograms to field data, although correlations 

are still worth making. 

The seismic lines were deliberately recorded 

close to the two COST wells to allow a reliable 

correlation of well data with seisiJlic data Based 

on the results in figures 67 and 68, there are certain areas of the log where the correlations to the 
·-a 

so 0 

40°30' + 

I 

68°30' 

+ 

0 

I 

68°00' 

5 

I 

10 

I 

0 5 101520km 

15 

I 

.... )')' 

• • • v~ • ? • 0 • 170 • 

oo. + . 

+ 

67°30' 

20 Nautical miles 

I 

+ 

FIGURE 66.-Locations of seismic lines 77-1 and 77-2 with respect to the COST wells and other regional USGS seismic reflection lines. 

seismic data are very good, while at other locations there are reflection amplitudes on the synthetic seismogram that are not as prevalent on 

the seismic data We suspect that the seismic 

data provide the more accurate description of the 

subsurface geology, and it is the well log data 

that is in error, mainly because of the inaccurate 

measurement of the true formation velocities by 

the interval-traveltime log. The log data were not 

edited prior to the generation of the synthetic 

seismograms, although the data were smoothed 

to reduce noise. 

Selected data-versus-depth curves from both -

wells were converted to two-way traveltime and 

plotted with the synthetic seismograms for G-1 

155 

(fig. 69) and for G-2 (fig. 70). These curves include 

caliper, gamma ray, conductivity, neutron porosity, and interval velocity derived from the 

interval-traveltime curve. Age boundaries and a 

condensed description of lithology are also included in these figures. The figures show the correlation of lithology and porosity with seismic 

reflection expression, and demonstrate (under 

ideal conditions) the "detectability" of particular 

geologic horizons. Obtaining a reasonably good 

correlation of the synthetic seismogram data to 

the seismic reflection field data is desirable, so 

that major geologic boundaries can accurately be 

defined and carried away from the well to other 

regional seismic lines. 
-

c: 

·c; 

a. 

-0 

.s::. 

(/) 

0 N (') 

SpU009S '9W!J 19ABJJ ~BM-OM! 

156 
(I) 

"0 

c: 

0 

u 

Q) 

(I) 

oi 

E 

:;; 

~ Cii 

> 

as 

!:; 

>-

as 

~ 

I 

0 

~ 

1-

0 

2 

3 

II 

~ rl 

tt 

·I 

~ 

~ 

~ 

Cost G-2 well 

Shot point 200 150 100 ~Synthetic seismogram 

lllllllll

0

tltlllllllllll l llllltlllt l llllllll ll lllllllllllllllllllllllllllllll t llllllllllllt l lll lll '1 ttllllllllt t ll t tl lltllllllll l l tllllllllll 

~ 

... 

~w 

................... 0 

1'.'.' .. : "'''!.'I)!Jli\H'.\ \:Itt)i\\\J't',"1,·, ,·,·,, ,\ 1.,,11 ! '•,f• ,'.',i' '' 

Utu , 

--;)·;-;-

\I 

I~ .i!tthllilt\ii,il;,ll/1!1 tww::: 

·."\: (((_fi 

Juu ~ I' 

•

1

.mYI\ 1 :~~::~:::::: ~~~~~~:~~;;~: •.•• ',\: :': :: ~;w 

.,.., 

... .. .. , .'.'.' " ." ; . 

.-,· ~' : l. lt w, \·~t ,u······"·'' ·- '2.':__ ~E.~~~~:~ ::::..~:::_-_ · •. ~ 

-fMt;;;, ~~~ 1U ''·''""•Mil ,,,,,,,,,[,,,,,, ,, ,,t;,_,,,\utnorou•••'' ''''' 

~:::'1 1/lli ll ::mttWii •.• ·; ·1 .. , .,11,,. . ... 1

) " ': ,.',', 

Ji t· ' ' '.·' 1/{1/{\'.'.\ ..... ')1/!'"'·'ticlliii 111'1 

..... ,,.. ........ . ~·-- ,, ,, .... ,, ... ''''''"'~ ... ~~ ... • •~•hlll'~nm ..... t~ltttttn"': 

':'~:-~ · 2 

'l !~~~7~r 

•"""'*! -~-- ""' z a ... ". !~:;.;!.lit 

--~~~··rftho"!ol'lfhtt~ll•t~t 

3 

::t~!(fV};I' 

1!. 

iliii/m(((l l ............... . l))))il\)iliJ' . 1 . • 

''''"' ' I :.wit 

4 .ll~~~ .... l.o 4 "' '"'"''"'' 

FIGURE 68.-Seismic reflection line 77-2 with the spectrally matched synthetic seismogram from the COST No. G-2 well spliced into the line. 
~ 

0 

Caliper, inches 

Gamma ray, 

API units 

~o or-~~~-, •oo 

Conductivity, 

mhoslm % Porosity 

Interval vek>city, 

1000's ftls 

0 0 40 5 10 15 20 25 .--,-----, 

Synthetic seismogram 

; ~---~ :·;. ·:-:. ~ > ..... ·f r 'f 

Age 

Peleogene 

s .. on.an 

~ 

T""~" 

cenon.,...n 

Alb•&n +Aphan 

Apt .. n 

Period/ 

Se<ies 

,.. 

~ 

~ 

~ , 

! 

u 

~ g 

. , 

. 

0 

u 

~ 

. 

u 

Description 

Calcareous -"&ly QUartz 

unds and 

tight to medium gray 

gumf:IOI and IM .. I 

= . 

0 

0 

~ 

£ 

• " 0 

0 

[ ~ I 1 5 

~ \ f f f J ; . ,• .• .• 

~' ~ ~ !~ 

;}} 

~ ~ j ; " ; l l } 

B•remial'l · 

to Valengr,.,,.n 

T•tPlOnoan 

KommertdQ•a" 

. 

~ 

~ 

Allernallng units of 

shaty coarse sandstone 

and gray shale 

T1'11n atternallf'IO calcareous 

tandllone and shale wrth 

thin beds ot sitty dotomrte 

Alternarong stlaly sandstone 

•nd red-gray sh.lle with ll'lln 

limestone •?d dolom•te beds 

Hi ;! . > > 

~~~ .. ~. ~ 

~ i · ~1".-! b-l 1rr 

Odord .. n HI 

Callovian !11to 

Ba,ac .. nHI 

Toarc,.n HI 

• & 

:::> 

~ 

~ 

-'l 

~ :lE 

Cambrian m 

Allernatong shaly coarse 

sandstone w1th gray and 

redd-Ish brown sh.lle 

lncreasng thin beds ol 

tt gray butt limestone 

and dOIOI'nlte 

PelOidal carbonates, shale . calc at 

Shale. carbonate,calc as, siltatone 

Shale, sparse ss and slat, carbonate 

Shale, sandstone. sitlstone. liltteatone 

Shale, carbonet"-sparaa as slat. anti 

Dolomfla. anhydrite. ''*' shale 

Beds . Minor sandstone 

,_lntlfbd dol, ss.shaHI.antly 

Dolomite. aandatone. shale. Trace anh 

C~ltlc- aandatone. shale. 

Minor dolcMtlila and tt'ace anh 

Sandstone . eon-glomerate, minor 

amo.nts ot sl\ale and cubonetas 

Seroclte. metadolomita. 

metaquanzlte and 

graot'litie ptty•t• 

8 

10 

12 

14 

16 

FIGURE 69.-Selected log curves and the synthetic seismogram from the COST No. G-1 well plotted as a linear function of time. Age boundaries 

and lithologic descriptions from Amato and Simonis (19801. 

E 

,. 

" a 

. 

0 

.-o 

0 .5 
~ » 

.. 

~ 

~ 

0 

Gamma ray, Conducltvoty, 

Caliper, inches API unots mhos/m % Porosoty 

10 20 0 100 2 I 0 0 40 

.---r--1 

rr J .. 

{ 

~ 

.; 

~ 

~ ~ 

} 

10 

I 

\ 

Interval velocoty, 1000's lt/s 

15 20 

I 

25 

Synthetoc seosmogram 

r 

) 

. t )I • 

~ ~ 

'• ~ ~ 

r 

j 

i 

·~ ~ 

~ ! _L~ 

r -r . .. .. , .. ·~ ·: ~ ~ ::.!.~~ ,. ,. ,. ,. 

~ ~ ~ ~ )I .. 'tt .. . ..... '~ ·~ t ·~ ·~ \ t t 't 

~ 

Age 

Albtan 

Apt•an 

Barrem•an 

Hauter•v•an-

~ 

8err+as•an 

TtthomanI <" 1 1 ..._... 1 .~ I Kommerodgoen 

~ ~ ~ ~ ....... 

·, ·, • • I I O•fordttm m ' ., ' ' r .r .r · .r 1-~ II e:_ II }}~} 

t r :r r Caltov .. n l?) 

~ ( 

!-

r ~ 

LW 

~ ~ ~ 

·.~ .i ·r ·.r 

l l i i .~ '; '; .~ ~ ~ l ~ 

~ ~ ~·.~ 

to Batoctan 171 

Early 

JuraSSIC 

IO 

Tnass•cH) 

Period/ 

Series 

,.. 

.. 

., 

... 

::;) 

::;) 

~ 

Oescroptoon 

Unconsolidated Quartz sand 

wtth tnterbedded clavev stltstone 

Calcareous claystone and 

clayey stltstone rangtng 

to argtllaceous chalky limestone 

Ltmestone, calcareous sandstone 

Coarse sandstone wtlh 

tnterbedded Stlty mudstone 

Stlly muOstone Interbedded 

wllh coarse sandstone 

umestone ana snate, few ss 

Th1c;k bedded sandstone w1th shale 

and coal mterbeds 

~y caTc-ar&OUs mudstone Interbedded wllh few S\ and Is 

Limestone Interbedded w1th 

S1lly calcareous shale 

Sanastone, rea ana grey snate, 

streaks of coal 

Ooht1c limestone 

Carbonates wtth few claystone 

Mostly shale 

Th1ck limestone 

~ o------..=., ___ ...... - .. --•-·- ·•-•-

~ 

j 

" .., 

..J 

Th1ck sect1on of 

dolom1te, limestone 

and anhydnte 

Limestone wtlh few~ 

II) L1mestone, dolomne, annyante 

~ Rea shale ana stlty mudstone=:::::::: 

~ Limestone, stlty dolomtte ::;) 

Salt 

111 I 111 

FIGURE 70.-Selected log curves and the synthetic seismogram from the COST No. G-2 well plotted as a linear function of time. Age boundaries 

and lithologic descriptions from Amato and Simonis (1980). 

:: 

.. 

0 

0 

0 

0 

~ 

rO 

10 

12 

14 

16 

~18 

20 

~ 

~ 

g 

0 

0 

05 

4 

6 
Basement Structure, Sedimentation, and Te~tonic 

History of the Georges Bank Basin 

Kim D. Klitgord, John S. Schlee, and Karl Hinz: 

INTRODUCTION 

The sediment-filled basins beneath Georges 

Bank formed as the continental margin subsided 

during and following the rifting of Africa from 

North America. We shall develop a tectonic 

history for this region by examining the crustal 

foundation beneath these basins and by outlining 

the stages in sedimentary buildup. The analysis 

of magnetic and gravity data integrated with 

seismic reflection profiles provides clues as to the 

nature of basement rocks, their depth of burial, 

-composition, and tectonic setting. The interpretation of seismic reflection profiles and the correlation of seismic stratigraphic units with lithostratigraphic units at the COST Nos. G-1 and 

G-2 wells gives a history of basin filling over the 

past 200 m.y., including major trends in rock 

types and their thicknesses, relative ages of interregional unconformities, and the relationship of 

the basin sedimentation to the construction of the 

adjacent continental slope and rise. 

Before the G-1 and G-2 wells were drilled, 

most of the information concerning the subsurface of Georges Bank was derived from a combination of geophysical data and the extrapolation of 

stratigraphy from the Shell Mohawk well on the 

Scotian shelf. (See, for instance, Ballard and 

Uchupi, 1972; Mattick and others, 1974; Schlee 

and others, 1976, 1979; Klitgord and Behrendt, 

1979; Austin and others, 1980.) In this report, 

magnetic and gravity data are used in conjunction with multichannel seismic reflection data 

(fig. 71) to outline the basement structures, to 

interpolate seismic basement features between 

seismic lines, and to provide depth estimates 

for basement in regions of limited acoustic 

penetration. 

The seismic stratigraphy for the Georges Bank 

shelf, slope, and rise was determined from correlation with the lithostratigraph~r at the Shell. 

Mohawk well (Schlee and other:--~, 1976), at the 

COST Nos. G-1 and G-2 weHs (Amato and 

Bebout, 1980; Amato and Simonis, 1980; Poag, 

this volume), at the Nantucket 'f17ell (Folger and 

others, 1978), and at Deep Sea Drilling Project 

(DSDP) sites (Klitgord and Grow, 1980). Additional information concerning the shallow 

stratigraphy was provided by the 1976 Atlantic 

Margin Coring Project (AMCOR) (Hathaway and 

others, 1976, 1979) and other multichannel seismic data (Austin and others, 1980). The correlation of deep-sea and shelf seisnic stratigraphy 

is tenuous, because a buried she] f edge of Lower 

Cretaceous and older carbonate rocks (Schlee and 

others, 1979) obscures the acoustic record of the 

transition across the shelf and slope. 

Interval velocities determined from the USGS 

multichannel seismic data have b ~en used to correlate the seismic stratigraphy on the seismic 

lines with the lithostratigraphy in the various 

drill holes (Schlee and others, 1976; Ditty, 1980; 

Waetjan, 1980; Poag, this volume). This same 

velocity information has also be~n used to produce depth sections (fig. 72), iso:"lach maps, and 

structure contour maps (fig. 3 in Schlee and 

Klitgord, this volume). The interval velocities 

were determined from the mult~~hannel profile 

velocity scans using the method of Taner and 

Koehler (1969). 

BASEMENT STRUCTURE 

MAGNDIC ANOMALY D,,TA 

Magnetic surveys of the Georf"~S Bank region 

were conducted in 1965-19f~ by Project 

MAGNET (U.S. Naval Ocean<'~aphic Office, 

1966; Taylor and others, 1968; ¥. ane and others, 

160 
~ 

72°W 71°W 65°W 

~ 

STATUTE MILES 

0 2f? 'P !P 

0 20«1!10fll00 

KILOMETERS ~ .... 41 °N 

fc~ L~:t 7oow 

·~ 69°W COP 

LINE 

21 

8~~, 65°W 64°W 63°W 

23 16 22 20 

FIGURE 71.-Multichannel seismic reflection profiles in the Georges Bank region. U.S. Geological Survey common depth point (CDP) profiles 

(24- or 48-channel stacks) and Bundesanstalt fiir Geowissenschaften und Rohstoffe (BGR) profiles (48-channel stacks) are shown as solid lines 

with crossticks at 10-km intervals. Woods Hole Oceanographic Institution (WHOI) CDP profiles (6-channel stacks) are indicated by dashed 

lines. Bathymetric contours, in meters, are from Uchupi (1966). Continental Offshore Stratigraphic Test (COST) drill sites and Atlantic 

Margin Coring Program (AMCOR) drill sites are shown by circles. 
COP LINE #19 

(/) 

..... 

I'll 

"V 

:tl:: 

N 

INTRUSIVE 

MAIN BASIN BODY 

NW MAGNETIC DEPTH ESTIMATES-· SE 

SHOT POINT # 1000 2000 3000 4000 

FIGURE 72.-Typical cross section and magnetic anomaly profile for the Georges Bank basin based on CDP line 19. The dashed 

basement beneath the breakup unconformity is inferred from adjacent seismic profiles and magnetic drta. The locations of 

the COST Nos. G-1 and G-2 wells are projected onto the cross section. Ages of seismic stratigraphic units are from Poag 

(this volume). Solid dots show locations of depth-to-magnetic-basement estimates from Klitgord and Behrendt (1979). 

1972) and again in 1975 by LKB Resources, Inc., 

for the USGS (Klitgord and Behrendt, 1977, 

1979). The magnetic anomaly contour map (fig. 

73) is a composite of these two surveys plus some 

data published by the Geological Survey of 

Canada (Haworth and Macintyre, 1975). A 

50-nanotesla (1 nT=1 gamma) contour interval 

was used for the entire map (2 nT and 10-nT contours are ·"also available for the LKB/USGS 

survey; Behrendt and Klitgord, 1979). Flight 

lines for the LKBIUSGS survey have a spacing of 

2.5 km (1.5 mi) at an elevation of 300 m (984 ft) 

over eastern Georges Bank and 3.2 km (2.0 mi) at 

an elevation of 450 m (1 ,4 7 5 ft) over western 

Georges Bank. The Project MAGNET survey 

(U.S. Naval Oceanographic Office, 1966) was 

flown at an elevation of 7 50 m (2,461 ft), and flight 

line spacing was about 8 km (5 mi). For a more 

complete discussion of these two surveys, see 

Taylor and others (1968) and Klitgord and 

Behrendt (1979). 

Basement structures were mapped using inferred magnetic source depths to interpolate seismic basement structures between seismic lines. 

Depth-to-magnetic basement estimates were 

determined for the entire LKBIUSGS survey (fig. 

7 4) (Klitgord and Behrendt, 1979). A comparison 

between these depth-to-magnetic basement estimates and a seismic depth section (fig. 72) demonstrates the close correlation between magnetic 

and seismic basement. Also, low magnetic 

162 

anomalies correlate well with shallow grabens 

(fig. 7 5 ); narrow magnetic highs l'"lrder the edges 

of the grabens and may be caused by intrusive igneous features along the edges of the grabens. 

GRAVITY ANOMALY DATA 

The gravity anomaly map (fib. 76) is a composite of several maps (Kane ar~ others, 1972; 

Haworth and Macintyre, 1975; G-ow and others, 

1976; 1979) that were based on marine profiles 

and measurements from a few l'~ttom stations. 

Free-air gravity anomalies with a 10-mGal contour interval were used offshore south of lat 

42° N. and simple Bouguer gravity anomalies 

with a 10-mGal contour interva1 were used onshore and offshore north of lat 42° N. The most 

prominent gravity feature in this area is the large 

peak and trough at the shelf brea"". This anomaly 

is produced by the horizontal c"l~nsity contrast 

between sediment and water in the vicinity of the 

shelf break and slope (Worzel and Shurbet, 1955). 

The calculation of Bouguer anomalies or isostatic 

anomalies (Talwani and Eldholm~ 1973; Rabinowitz, 1974; Rabinowitz and LzBrecque, 1977; 

Grow and others, 1979) remov£.~ most of this 

edge-effect anomaly. An exampln of this can be 

seen in the Bouguer anomaly contours north of 

lat 42° N. and in the isostatic anc?)laly calculated 

along CDP line 5 (fig. 77). 
Gravity anomalies over the shelf reflect the 

same general basement structure indicated by the 

magnetic and seismic data. The northeasttrending gravity highs over Martha's Vineyard 

and Nantucket, and between Step #1 and Step #2 

(lat 42° N., long 68° W.), are located above basement highs. The northeast-trending gravity low 

around lat 41 oN., long 69° W., coincides with the 

deepest part of the Georges Bank basin (Schlee 

and others, 1976) and extends to the northeast 

over the broad basement sag just north of the 

Yarmouth arch. The gravity field over the main 

basin seaward of the Yarmouth arch is dominated 

by the edge-effect anomaly at the shelf break. 

SEISMIC BASEMENT 

Seismic reflection profiles across the Georges 

Bank region (fig. 71) show great variability in 

depth and character of seismic (acoustic) basement. Except in the vicinity of the carbonate 

buildup associated with the ancient shelf edges 

(Schlee and others, 1976, 1979) there is a general 

seaward deepening of seismic basement. We use 

the term crystalline basement to refer to the surface that is the bottom of the sedimentary fill and 

the top of metamorphic or igneous rocks. Seismic 

basement is the surface of maximum interpretable acoustic penetration, and the depth to that 

surface can vary between seismic lines, depending upon data quality. We have attempted to interpret those regions where seismic basement 

does not coincide with crystalline basement. 

The deep structure for Georges Bank can be 

divided into four characteristic zones: (1) a lowrelief zone of Paleozoic or older metamorphic and 

igneous rocks that is present on the shallow 

stable platforms; (2) a block-faulted zone of 

Paleozoic or older metamorphic or igneous rocks 

that deepens seawards in distinct steps; (3) a zone 

of very thick sediments with prograding carbonate deposits at its seaward edge; and (4) a 

zone of oceanic basement that was generated by 

sea-floor spreading. Crystalline basement and 

seismic basement usually coincide in zone 1 (continental crust) and zone 4 (oceanic crust). The 

seismic basement in zone 1 is characterized by a 

very strong reflector associated with shortwavelength undulating relief in some areas, sets 

hyperbolic echoes and generally low relief. 

The most complex area of basin development is 

in zones 2 and 3, where seismic basement rarely 

coincides with crystalline basement. On many of 

the seismic profiles the breakup unconformity 

(Falvey, 1974) coincides with seismic basement, 

and the nature of crystalline basement somewhere beneath it can be inferred only from the 

character and shape of this unconformity surface. 

Across the block-faulted zone 3, a number of halfgrabens that form subbasins lie beneath the 

breakup unconformity. Sediments within these 

grabens appear as zones of seaward- or landwarddipping reflectors truncated by the breakup unconformity (fig. 78). The unconformity deepens 

abruptly over the downthrown side of the graben 

(shotpoint 900, fig. 78) and then levels off until 

encountering the next graben (shotpoint 1220, 

fig. 78). The diffraction pattern and rough seismic 

basement on the upthrown side of the half-graben 

(shotpoint 1200, fig. 78) may indicate crystalline 

basement; on some profiles, this rough basement 

can be traced beneath the dipping reflectors. On 

profiles where the breakup unconformity coincides with seismic basement (fig. 79), these same 

narrow zones of steep dips (separated by more 

gently dipping segments) give the seismic basement a steplike appearance. We infer that crystalline basement, as illustrated in figure 78, is probably a series of half-grabens beneath these steps. 

Seaward of this block-faulted zone, seismic basement is usually an interval of chaotic reflectors, 

either directly beneath or at the breakup unconformity. The recovery of halite at the bottom of 

the COST No. G-2 well (Amato and Simonis, 

1980), from the stratigraphic unit that we would 

place directly below the breakup unconformity 

suggests that salt forms seismic basement. The 

patches of chaotic reflectors directly below the 

unconformity have been interpreted by Poag (this 

volume) as carbonate mounds. Seaward of the 

COST No. G-2 well, seismic basement becomes 

shallower because of a prograding carbonate 

buildup near the Jurassic and Lower Cretaceous 

shelf edge. We cannot identify crystalline basement in this region. 

DISCUSSION 

of diffraction patterns in other areas, and negligi- The basement structure map for the Georges 

ble relief in still other areas.· The seismic base- Bank region (fig. 73) combines magnetic basement in zone 4 is characterized by closely space ment (fig. 7 4) and seismic basement information. 

163 
~ 
8: 

55•w 

8 -f.. 

STATUTE MILES 

20 40 60 

~PALEO SHELF EDGE 

~ SCARP-EDGE 

--BENCH 

0 ·- - · 20 - "!:Q__ 60 BQ_________JOQ 

KILOMETERS 

54•w 

mmrm DROP IN BREAKUP UNCONFORMITY TTTTTT1 DEEPENING BASEMENT 

- - MAJOR TECTONIC BOUNDARY ~ BASEMENT HIGH 

T T T DEEPENING BASEMENT INFERRED FROM MAGNETICS 

FIGURE 73.-Magnetic anomaly maps of the Georges Bank area, composited from the maps of Klitgord and Behrendt (1977) and Haworth and 

Macintyre (1975). Contour interval 50 nT; Universal Transverse Mercator projection. A, USGS and BGR multichannel seismic line locations 

superimposed. B, Tectonic structure (Schlee and Klitgord, this volume, fig. 4) superimposed. 

4 2•N 

41°N 
g: 

39°N 

72°W 70°W 69°W 

:· .·GULF OF MAIN~ 1-..'l: 

i 

i-

~AY~NANTUCKET 

9 

.. .. . .......... . 

70°W 

EORGES BANK BASIN 

EXPLANATION 

\;;::;::.:o~ Depth to magnetic basement,in kilometers 

--~2-Depth to seismic basement, in kilometers 

"' Seamounts 

cosT e Drill site, Continental Offshore Stratigraphic G-1 Test 

·· ... 100m. .. .Bathymetric contours, r. meters 

9tatt1111Milll 

0 20 10 ~ 

o 20 40 .. _ 60 eo y> 

1--~ 

~ -<(U';-

~~ ~<( 

..rllfll""" 

.. 4VV" 

65°W 

:·:·· 

FIGURE 74.-Depth to magnetic basement in the Georges Bank area. Contour interval! km (0.62 mi); Universal Transverse Mercator projection. 

Depths were determined using magnetic depth estimates to interpolate between CDP lines 1, 4, 5, 7, 8, 12, and 13. From Klitgord and 

Behrendt (1979, fig. 7C). 

43°N 

:·: .·· ."i 42°N 
~ 

~ 

COP SEISMIC LINE # 19 

400 

t- /MAGNETIC ANOMALIES 

c:: 

-c_j 

w 

(/) 

-

w 

~ 

I-

_J 

w 

~ 0:::: 

I-

~ 

~ 0 

3: 

I0 

NW SE 

SHOT POINT 

NUMBERS • 200 300 400 500 600 700 800 900 I 

O I I , ,I I ~~m~- -='-..., , ... ,.. 1 __ • _ _ _ I I ,;;___i J w b· = __ i!i:±:Ei ... tt : ii¥2~ff.~<??¥V.: 4Z&%£!$5¥Alr~-- E?!St,n§L i¥##~ , ~ .. .,_JJNL _ 44::?%&:-m 

2 

3 

4 

FIGURE 75.-Magnetic anomaly and seismic reflection profiles for a portion of CDP line 19 across Step #1. Note the correspondence between the 

magnetic high and the basement high, and between the magnetic low and the basement trough. See figure 71 for location. 
168 

z 

0 

N 

"" 

z 

0 

<t 

··. 
$ 

!J()OO•····· 

j B 

I ......... IIJ(JO• ······· j.. 

... (.. . I 

I 

STATUTE MILES 

20 40 60 

44°N 

43°N 

42°N 

~~'\. ~ t r•v _ __ ,_ jo l ~ ~ ' • ~ ... ·· I I(ILOMETERS 41 N 

----· ---··· _ .... !... :~£.:. ~ __ f..""? ~~··· -.. ~... ,.."7! ... 

0 

~PALEO SHELF EDGE 

TTTTT SCARP-EDGE 

--BENCH 

nmmn DROP IN BREAKUP UNCONFORMITY nnm DEEPENING BASEMENT 

- - MAJOR TECTONIC BOUNDARY ~ BASEMENT HIGH 

T T T DEEPENING BASEMENT INFERRED FROM MAGNETICS 

FIGURE 76.-Gravity anomaly maps of the Georges Baillk area, composited from the free-air gravity anomaly map of Grow and others (1976) and 

the Bouguer gravity anomaly maps of Kane and others (1972) and Haworth and Macintyre (1975). Contour interval 10 mGal; Universal 

Transverse Mercator projection. A , USGS and BGR multichannel seismic line locations superimposed. B, Tectonic structure (Schlee and 

Klitgord, this volume, fig. 4) superimposed. · 
USGS LINE 5- CAPE COD 

/"···· .•. /T COAST ANOMALY (ECMA) 

!1 . MAGNETIC FIELD ! ··.. 0 

. 50 /V\(00""'" I \\ - 200 ~ ~ ...... / .............. ~ 

~ 0~--~----~~~== ~--~~~~~======~=·- .. ;. ;:;. _~- --=- ~--: ... ~---~- -400 ~ ......... ···· 

~ 

/MASS ANOMALY OF MODEL -600 

3~00 

~OBSERVED FREE -AIR ANOMALIES 50 

1 

ACOUSTIC BASEMENT (COP)-----

M-E BENEATH TIC BASEMENT ECNA ******* 

250 

20 

30 

D!STANCE (KM) 

FIGURE 77.-Two-di.mensional gravity model for CDP line 5. Sediment thickness and densities are inferred from the multichannel velocities. Magnetic basement from Klitgord and Behrendt (19791 was used for the base of the sediments in the 

vicinity of the East Coast magnetic anomaly, where seismic basement is the top of the Jurassic shelf-edge bank. The upper 

and lower crust were assumed to have densities of 2.7 and 3.0 g/cm' respectively, although no refraction data are available. 

The relative shape of the crust-mantle boundary was modified to fit the gravity data, but the absolute depth-to-Moho could 

be in error by several kilometers. This line typifies the narrow zone of progressively deepening small subbasins between 

stable platforms of continental crust (just to the left of the profilel and oceanic crust (to the right of the 200-km markl and 

demonstrates a rapid crustal thinning over a distance of only 100 km (62 mil. From Grow, Bowin, and Hutchinson (1979, fig. 

51. 

Shallow, stable platforms lie northeast, north, 

and northwest of Georges Bank, where seismic 

basement is less than 2 km (6,600 ft) deep. The 

block-faulted zone seaward of the platforms is 

divided into two segments, one southeast of the 

Long Island platform and the other southeast of 

the Gulf of Maine platform. These two segments 

are separated by a set of east-west structures 

near lat 41 o N. Seismic basement depths at the 

top edges of the grabens and basins range from 

170 

less than 2 km (6,600 ft) to more than 6 km 

(19,700 ft); several thousand meters of sediments 

fill isolated basins beneath the breakup unconformity. Seaward of the block-faulted zone, the 

main basin lies beneath the outer Georges Bank 

and contains more than 6.5 km (21,500 ft) of sediments. The Jurassic-Lower Cretaceous shelf edge 

forms the seaward border of both the main basin 

and the small subbasins to the west. Oceanic 

basement can be traced landward to within 50 km 
c:_j 

w 

(f) 

I 

w2 

~ 

I-

_J 

<X: ~3 ...... a:: ~ I-

>-

~4 

0 

S: 

I5 

6 

NW CDP SEISMIC LINE # 19 

FIGURE 78.-A portion of CDP line 19 showing the landward-dipping reflectors beneath the breakup unconformity for the half-grabens that form 

Steps #2 and #3. The basement hinge for Step #2 is at shotpoint 1200; the hinge for Step #3 is at shotpoint 1500. Drops in the breakup 

unconformity area indicated by triangles. See figure 71 for location. 

SE 
"""' ..., 

NW COP SEISMIC LINE #I SE ) NT Rs -100 200 300 400 500 6C 

o. L ... :::;:!;;; t 1. I I I I ··..:1!.:.:=.- I ... I 0 --- ,..;r..,..CL ............... ~ ----···--··· ---- c_j 

w 

(f) 

w 

t= ~2-w-~:;.~~~~;;,r...;,~-t~;:-,;, -~~- ~'- ::'-:: -t:~, __ .:::>.!"-~:-. ---~ ~-~~~ ·;q r --x••·•t EE~¥i£C::•~IOP~~~-~ ~F~~~~-:·_-~::_~~- ~l'f-~g~;;~~~~~~--_;:~~2 

_j 

w 

> 

~4-E.~~ki~~~~~~;-~ 'S ~ :- --:.'?-;;).,~::--~--~.;~~ B~~~~~6RMITY --~?;_ ~:;?:!;- _ $sifi.~~~-JLSE~l-4 1-

~ ~ 

1-

FIGURE 79.-A portion of CDP line 1 over the buried steps. See figure 71 for location. Notice the drops in the breakup unconformity (triangles) to 

the left of Steps 112, between Steps 113 and 114, and to the right of Step #4. Steps #2 and #3 have merged on this line. The small basement high 

that the COST No. G-1 well penetrated is seen as a small rise in the breakup unconformity. The deep reflectors at 6 sec to the right of Step #4 

may be real (Schlee and others, 1976), indicating a thick sequence of prerift and synrift sediment in this region. Also, these deep reflectors 

possibly are pegleg multiples off landward-dipping synrift sediments obscured by the acoustic reflectors associated with the breakup unconformity (3 to 4 sec depth) but similar to those shown in figure 78. 
(31 mi) of the axis of the East Coast magnetic 

anomaly (ECMA) on most of the seismic profiles 

and to within 20 km (12.4 mi) of it on some lines. 

The depths of these structures are shown in the 

series of cross sections in figure 80. 

en 

-i 

"' ., 

'fl: 

"' 

COP LINE # 18 

SHOT 

en-< 

,.,. 

"'"' "!: 

0 

c 

-i 

I 

YARMOUTH SAG 

YARMOUTH 

ARCH 

L J 

The block-faulted zone southeast of the Gulf of 

Maine platform deepens in a series of steps into a 

broad sag (the Yarmouth sag) before abutting 

against the Yarmouth arch. There may be a small 

subbasin beneath the breakup unconformity at 

5 

MA IN BASIN 

10 

10 

0 25 

I I 

KILOMETERS 

•• - .::: .. - .. ----:.SALT~ ~ 

en 

-i 

"' ., 

it 

len 

, .... 

"' ., 

* .. 

en-< )>l> I 

C>~ I 

0 

c 

-i 

I 

FIGURE 80.-Interpretive cross sections of the Georges Bank basin seaward of the Gulf of Maine platform along CDP lines 4, 

18, 19, and 1. See figure 71 for locations. UK, Upper Cretaceous; LK, Lower Cretaceous; UJ, Upper Jurassic; MJ, Middle 

Jurassic; LJ, Lower Jurassic(?). 

173 
each of these steps but these subbasins can be 

seen on only some of the seismic profiles. Step # 1 

is a linear trough that is well defined on most 

multichannel seismic profiles (fig. 75; basin at 

OOOOh on line 17-19, fig. 5 of Austin and others, 

1980) and even on some single-channel profiles 

(such as fig. 3B of Ballard and Uchupi, 1972, and 

fig. 4 of Oldale and others, 197 4). Step #1 lies at 

the hinge zone between the Gulf of Maine platform (which contains a number of the other 

Triassic grabens; Ballard and Uchupi, 1972) and 

the deepening basement to seaward. Steps #1 and 

#2 are separated by a broad basement high (fig. 

75) that is associated with a large positive 

magnetic anomaly and a high gravity anomaly. 

These two potential field highs suggest that a 

mafic intrusive body separates the two basins. 

Step #2 is a half-graben that is well defined on 

common-depth-point (CDP) line 4 (Grow and 

Schlee, 1976) and line 19 (fig. 78). On CDP lines 1, 

7, and 18, the breakup unconformity dips steeply 

along the landward edge of the step. This graben 

can also be seen on some single-channel seismic 

profiles (such as fig. 3C of Ballard and Uchupi, 

1972). Step #3 also clearly appears as a halfgraben on line 19 (fig. 78), but the other seismic 

lines show only a small basement high on each 

side of the step. Between Step #3 and the Y armouth arch, the broad Yarmouth sag (including 

Step #4) overlies a major gravity low. The Yarmouth sag deepens to the southwest and includes 

a small basement high on CDP line 4 (Grow and 

Schlee, 1976) and line 18 (fig. 78). The basin 

becomes very deep where it is crossed by CDP 

lines 7, 19 and 1. Only the steeply dipping sides of 

the Yarmouth sag can be seen on lines 7 and 19 

but suggestions of a deep crystalline basement 

can be seen on CDP line 1 (shotpoints 550 to 850, 

fig. 79). On line 1 the drop in the breakup unconformity is visible at both edges of Step #4, but the 

drop is negligible on lines 18 and 7. We consider 

the Yarmouth arch the seaward end of this blockfaulted zone. The arch deepens to the southwest 

until on line 19 (shot point 2250, fig. 80) it is only 

a small basement high with a possible carbonate 

mound on top (Poag, this volume). The small 

basement high on CDP line 1 (shotpoint 880, fig. 

79) is interpreted, using the magnetic data, to be 

a continuation of the small east-west basement 

high encountered on CDP lines 8 and 20, which 

was drilled into at the COST No. G-1 well (fig. 

73). It may be connected to the Yarmouth arch. 

The small east-west basin just north of this high 

is either a continuation of the Yarmouth sag or a 

separate subbasin. 

The basement of the block-faulted zone to the 

southeast of the Long Island platform does not 

deepen in a steplike fashion, but it does contain 

four small, elongate subbasins (fig. 73). The depth 

to the tops of these subbasins increases gradually 

to the southeast, as shown in figure 81. All of 

these basins deepen to the south, where their 

seaward margins are obscured by the carbonate 

buildup near the Jurassic-Lower Cretaceous shelf 

edge. The Nantucket subbasin is well defined on 

CDP lines 5 (Grow and Schlee, 1976) and 36, and 

the northwestern part of the basin can be seen on 

line 22. The rest of the outline of the subbasin was 

determined from the magnetic data (fig. 7 4) and 

the gravity data. Nowhere do the margins of the 

Nantucket subbasin exceed 4 km (13,000 ft). 

There is a seismic basement high (fig. 81) 

associated with a large magnetic high and gravity high between the Nantucket subbasin and subbasin A. We interpret this basement high to be 

the upper surface of a mafic body similar to that 

noted previously between Steps #1 and #2. Subbasin A (fig. 81) gradually deepens to the south, 

but its margins do not exceed 5 km (16,400 ft) 

depth; it appears as a half-graben on CDP line 22. 

Subbasin B also appears on CDP line 5 (fig. 81) 

where it is deeper and broader than Subbasin A. 

The deepest of this western set of subbasins, Subbasin C, broadens to the east and may merge with 

the main basin (fig. 73). Subbasin C is bounded on 

the west by a small basement high that may 

represent an intrusive igneous feature; to the 

northeast is a larger basement high. As with the 

other three subbasins, the seaward edge of Subbasin C is obscured by the carbonate buildup near 

the Jurassic-Lower Cretaceous shelf edge. 

The main basin of the Georges Bank lies between the Yarmouth arch and the ECMA. The 

region of greatest sediment accumulation (Schlee 

and Klitgord, this volume, fig. 3) encompasses 

this main basin and the Yarmouth sag. The COST 

No. G-2 well was drilled into the main basin and 

encountered salt at a depth of about 21,300 ft 

(6.5 km) (Amato and Simonis, 1980). This salt 

unit forms seismic basement beneath most of the 

main basin, but there are deeper reflectors 

beneath the salt layer towards the edges of the 

main basin. There may be an additional 3 to 4 km 

(9,800 to 13,100 ft) of Mesozoic sediments 

174 
CJl 

NW COP S~ISMIC LINE #5 SE 

.Q I . ,I. : I I ~ ¥ 1 

~ t --~- :' -=: :: ., -c~a.; _ ii§J ~~~:±:t-- at ~ ··fk( -f.::f?S.;k¢1 -<Y- ~~-- -- "_ ;~ti9 

w 

~2 

f-

_J 

w 

~ o::4 

f-

~ :s: 

06 

~ 

f0 

w 

(/) 

NW 

FIGURE 81.-A portion of CDP line 5 across the prerift or synrift basins. See figure 71 for location. Note the changes in slope in the breakup unconformity and the basins beneath the unconformity. 

COP SEISMIC LINE #I SHOT POiN T 

NUMBE RS -1500 1600 1700 1800 1900 2000 2100 2200 

FIGURE 82.-Portion of CDP line 1 across the Jurassic shelf edge. See figure 71 for location. The identification of the deep sea Jurassic units are 

from Klitgord and Grow (1980). The age identification of the shelf seismic units are from Poag (this volume). Note how the deep reflectors J,, 

J,, and J, onlap the buried benches and the Upper Jurassic shelf edge, respectively. 

SE 
beneath this seismic basement. A buried igneous 

body is located just east of the COST No. G-2 

well in the main basin and it may protrude more 

than 3,300 ft (1 km) above the salt layer (line 19, 

shotpoint 3300, fig. 80). The seaward edge of the 

main basin is formed by a series of three benches 

(figs. 72, 80, and 82) that form descending steps 

seaward. The most landward bench is the same 

Upper Jurassic-Lower Cretaceous shelf edge that 

has been identified along the entire margin 

(Schlee and others, 1979). The two most seaward 

benches may be the erosional relics of Middle and 

Lower Jurassic shelf edges or elevated blocks of 

crystalline basement. The seismic reflectors J 1, J 2, 

and J 3, which onlap these three benches, have 

been identified as the tops of Upper, Middle, and 

Lower(?) Jurassic units respectively (Klitgord 

and Grow, 1980). The seismic basement just landward of the Upper Jurassic shelf edge is the top of 

the prograding carbonate buildup. The magnetic 

basement (fig. 7 4) reflects the deep main basin, 

the Yarmouth sag, the small high between them, 

and the buried intrusive feature in the main 

basin. The shallow ridge in the magnetic basement beneath the landward edge of the ECMA 

coincides with the most seaward bench. Although 

the estimated depth of magnetic basement is 

slightly shallower than the depth of seismic basement, the error associated with such estimates 

(Klitgord and Behrendt, 1979) would permit the 

two basement depths to be about the same. 

The crystalline basement seaward of the ECMA is primarily igneous rock that forms the top 

of oceanic crust. Seismic basement to within 

50 km (31 mi) of the ECMA is marked by hyperbolic echoes, a signature typical of oceanic basement (Grow, Mattick, and Schlee, 1979; Klitgord 

and Grow, 1980). Seismic basement and crystalline basement coincide to the east of a basement 

scarp 50 km (31 mi) east of the ECMA (fig. 73B). 

The acoustic horizon J 3 terminates at this scarp 

and forms seismic basement on most of the multichannel seismic profiles southwest of the New 

England Seamounts. The irregular, hyperbolic 

echo type seismic basement beneath the J 3 reflector can be traced landward of this scarp on CDP 

lines 5 (fig. 83) and 22 to within 20 km (12.4 mi) of 

the ECMA. This suggests that oceanic basement 

(and the underlying oceanic crust) may continue 

landward to the ECMA (Grow, Mattick, and 

Schlee, 1979). Crustal velocity information for 

the area off the New Jersey coast within 50 km 

176 

(31 mi) of the ECMA indicates that crustal structure is similar to that normally found for oceanic 

crust (Sheridan and others, 1979). In the vicinity 

of the New England Seamounts, the seismic basement has a shingled character (fig. 5 of Schlee and 

others, 1976) that can be traced landward to the 

axis of the ECMA. This acoustic characteristic of 

shingle-like reflections is common for a carbonate 

buildup, but it also could result from volcanic 

debris from the New England Seamounts or an 

overlapping of sedimentary and volcanic layers 

near a spreading center. 

The New England Seamount chain intersects 

the margin of the Georges Bank at the southwestem edge of the main basin and the three benches 

described above. This point of intersection, where 

Bear Seamount lies within the gap in the ECMA, 

coincides with the zone of east-west structures 

that separates the block-faulted zone seaward of 

the Long Island platform from the block-faulted 

zone seaward of the Gulf of Maine platform. The 

most likely igneous intrusive features landward 

of Bear Seamount are the body within the main 

basin, one feature between subbasins A and B, 

and one feature between subbasins Band C. The 

seismic data from the two highs between subbasin C and the main basin suggest that these are 

more likely structural basement highs. 

BASIN FILL 

The 6,350 km (3,943 mi) of multichannel CDP 

seismic reflection profiles collected for the USGS 

over the Georges Bank area (fig. 71) have allowed 

a clear look at deeper basement structures and 

the mapping of key reflectors within the sedimentary section. Analysis of the sedimentary sequences interpreted from these profiles indicates 

the existence of rift and postrift basin fill above 

an extensively block-faulted basement. The 

geometry of the several subbasins (fig. 3, Schlee 

and Klitgord, this volume) determined from the 

reflection profiles is similar to the pattern obtained using the depth-to-basement estimates inferred from the magnetic data (fig. 7 4). 

Two profiles (figs. 84 and 85) demonstrate the 

arrangement and character of reflectors in the 

Georges Bank basin. Bundesanstalt fiir Geowissenschaften und Rohstoffe (BGR) line 209 (fig. 

84) crosses the site of the COST No. G-2 well, and 

the 60-km (37 -mi) section of line 20 shown in 
::::J 

USGS. SEISMIC COP LINE #5 

0 I I I I I : . j ~AC:T """h UA~Tr! AounuAt£ J SOUTHEAST 1 I I I o 

NORTHWEST 

SHOT POINT N.NBER 

FIGURE 83.-Portion of CDP line 5 across the Jurassic sheH edge. See figure 71 for location. Note the deep reflector J, that onlaps basement near 

shotpoint 2300 and the lack of the benches seen on CDP line 1 (fig. 82). 
SHOT POINT 200 

0 

<n2 

0 

z 

0 

~3 (f) 

400 

w 

~4 

I-

~ IV~ COST G-2 

~ 0 5 IOKm WELL SITE 

600 800 

2 

3 

4 

SE 

_,<I:Qt CX) 0:: SEAFLOOR OUAT I I • ·0 METERS SEA LEVEL 0 

I- 000 :f"/K • T T- TEll!. ----T __ T_ --. 

~ :s: 

I 

~ I- 2 

3 

4 

1_ .. T----

1----- 0 0 0 

T T------• 

MARINE SHELF DEPOSITS ------ 0 0 0 ---- .•:'• 

~~-:- --::::::==:·- :=::·:·:.-.:-::·. ··:!:iii!~- -- - --- - - -- UJ ::>non 

NONMAR"NE · ·REbREssJvt'·.·-taN"Gui··-·· -~ -·:.:; -,:.·.·.·:~:·.::·: .. ·:.·.· 2 _:· _;:·· ·.· .... .. :_':· .... ,.. 

MJCARBONATE- EVAPORITE MARINE SHELF DEPOSITS 

--LJ-r3 

FAULT 

~ -r----r::~~ 

REEF-LIKE BUILDUP SALT 4 

~ GRAVEL AND SAND ~ SHALE, MUDSTONE D SANDSTONE ~ CARBONATE ROC K ~ EVAPORITE ROCK 

FIGURE 84.-A part of BGR line 209 across central Georges Bank basin. The actual time-scaled profile is shown and an interpretation of the 

stratigraphy is given below it. Also superimposed on the interpretation section is the lithology of the COST No. G-2 well at the approximate 

position where the profile crossed the drill site. T/K, Tertiary/Cretaceous boundary; CENO., Cenomanian; UJ, near the top of the Upper 

Jurassic section; MJ, within the Middle Jurassic section; W, near the base of the Lower Jurassic(?) section. T marks a thin transgressive unit. 

0 marks the correlation with the "0 marker"-a zone of limestone within the Missisauga Formation beneath the Scotian margin (Jansa and 
" ~ 

~ '--

~ f::: 

~ :s: 

..0 

'-l ~ f...:: 

)..... 

~ ' t\j 

2900 2800 2700 2600 2500 2400 2300 2200 2100 SHOT 

POINTS 

0 

2 2 

4 J 4 ;:;:s::: ... :·:~ 

NW SE 

0 

T- T . L PROGRADATION 

REGRESS/Vf.SEQUENC£- T• ;z T TRANSGRES5'0N 0 _.,_ T ----T T - - T T -- T -- -==-~-=::::..- -- r===== 

- ~AIC _PROGRADATION 

2 MIXED COASTAL AND 2 

MARINE SHELF CARBONATE ROCKS 

4 4 

0 KILOMETERS 10 20 30 40 

FIGURE 85.-A part of line 20 across the west-central part of Georges Bank basin. Below, the interpretation of the profile gives main strati· 

graphic sequences thought to compose the sedimentary section, and inferred environments of deposition. T/K, Tertiary/Cretaceous boundary; 

K/J Cretaceous/Jurassic boundary; CENO., Cenomanian; MJ, within the Middle Jurassic section; LJ, near the base of the Lower Jurassic(?) 

section. T marks a thin transgression unit. See figure 71 for location. 
figure 85 spans the west-central part of the basin. 

Beneath the subhorizontal, parallel arrangement 

of reflectors above an irregular seismic basement 

is a second set of reflectors tilted at a low angle. 

It is important to distinquish between the 

horizontal reflectors and those with a low-angle 

tilt, because they represent the two main kinds of 

deposits in the basin: synrift and postrift 

sedimentary rocks. The boundary between these 

two reflectors is interpreted to be Falvey's (1974) 

breakup unconformity, which resulted from the 

change in tectonism from block-faulting to broad 

crustal extension as the thinned crustal foundations of the basin sank during the separation of 

Africa from North America. The key unconformity is best developed in the area where platforms 

and basins meet. Within the central part of the 

main basin, the deposits are comformable. 

Rln DEPOSITS 

The acoustic character of the sediments 

beneath the breakup unconformity can be seen 

most clearly beneath the landward half of 

Georges Bank. As shown by part of line 18 (fig. 

86) across the eastern side of the bank (fig. 2, 

Schlee and Klitgord, this volume), seismic basement appears at slightly less than 2-1/2 seconds 

tw~way traveltime around shotpoint 1360, drops 

to slightly more than 3 seconds in the central part 

SP 1400 1500 1600 

of the profile, and then rises again to 2-1/2 seconds around shotpoints 1800-1900 (fig. 86). Reflectors dip gently to the northwest (left) beneath 

a probable unconformity (arrow, fig. 86) within a 

graben 15 km (9.3 mi) across. These reflectors are 

inferred to be part of a rift sequence that formed 

prior to the main phase of basin subsidence 

(parallel reflectors above the unconformity). 

The character of reflectors within the rift sequence changes across the main basin. On line 18, 

more or less continuous reflectors that show 

strong acoustic reflectivity are interpreted to be 

marine shelf deposits of interbedded carbonate 

and evaporite rocks. On two other profiles (figs. 

84 and 85), inferred rift deposits display similar 

reflector characteristics. Yet on the northwestward continuation of profiles 18 and 20, equivalent reflectors become discontinuous, and their 

amplitude is variable; both charactistics are indicative of a nonmarine clastic sedimentary sequence, similar to the section drilled in the lowest 

part of the COST No. G-1 well. For line 20 

bordering the Long Island platform, the reflectors below horizon LJ (correlated with the 

breakup unconformity) are areally restricted by 

irregular highs in seismic basement (fig. 85). Seismic reflectors are moderately continuous to 

discontinuous and show a wide range of seismic 

amplitude and a splayed arrangement. The sequence is interpreted to consist of interbedded 

marine (carbonate-evaporite rock) and nonmarine 

1700 1800 1900 

00~~~~~~~~~~~~~~ w 

(f) 

w 

2 

f--

_J 

w 

> 

~ &RE 

63~~~ :5: 

f--

FIGURE 86.-A part of seismic line 18 between shotpoints 1360 and 1900. Notice conspicuous unconformity (arrow) forming 

the upper boundary of inferred rift deposits within a graben. See figure 71 for location. 

180 
clastic rocks that filled a rift prior to continental 

separation. Basement rocks are not obvious on 

BGR line 209 (fig. 84), probably because they are 

masked by the thick beds of limestones and 

anhydrite encountered in the lower part of the 

COST No. G-2 hole. BGR line 209 crosses the 

site of the COST No. G-2 well, where the deepest 

rock drilled was halite, which is of unknown age 

but probably correlates with the Argo Formation 

(Early Jurassic? to Late Triassic?) on the Scotian 

margin (Given, 1977; Barss and others, 1979; 

Poag, this volume). Reflectors associated with 

horizon W (Lower Jurassic?) are bowed-up areas 

of inferred carbonate accretion (possible reef). The 

largest of these, at shotpoint 680 (fig. 84), is 8 km 

(5 mi) across and appears to have been built over 

a basement high which can be seen on crossline 

33. Between these bowed-up areas reflectors are 

horizontal and are thought to represent marine 

shelf deposits that accumulated over the central 

southern part of the basin. 

EARLY POSTRin DEPOSITS 

Above the breakup unconformity, the character 

of seismic reflectors varies within the basins. On 

the western flank of the LaHave platform, there 

are a few moderately continuous reflectors and 

many discontinuous ones of low to high seismic 

amplitude. This pattern of reflectors indicates a 

mixed marine and nonmarine sequence similar to 

the interbedded sandstone, shale, and limestone 

sampled in the COST No. G-1 well. 

On BGR line 209, reflectors are parallel and 

weakly to strongly continuous. The zone of low 

continuity parallel reflectors between horizons 

MJ and LJ (Middle Jurassic and Lower Jurassic? 

on fig. 84) is interbedded limestone and anhydrite 

and a few beds of sandstone and siltstone. Reflector continuity and amplitude within this interval 

(MJ-LJ) increases to the southeast, indicating 

density contrasts between groups of strata that 

are not evident on BGR line 209 near the site of 

few thin streaks of coal (Scholle, Schwal,, and 

Krivoy, 1980; Simonis, 1980), thought to have 

been deposited in water depths of less than 30 m 

(100 ft) (Bielak and Simonis, 1980; f~holle, 

Schwab, and Krivoy, 1980). 

Line 20 (fig. 85) displays some of thE: same 

changes in reflector characteristics noted in BGR 

line 209. The profile between horizons W a11d MJ 

is marked by strong high-amplitude, cont~'luous 

reflectors. They continue to the southeast (to the 

right on fig. 85) where individual reflect.ors in 

foreset arrangement climb to the right, indicating 

that the margin in this area prograded Sf't:tward 

during the Jurassic. Between horizons M:J and 

UJ (Middle Jurassic and Upper Jurassic), there 

are less continuous and variable-amplitude reflectors which become even more prevalent to the 

northwest. As on BGR line 209, these zc101es of 

discontinuous variable-amplitude reflqctors 

extend as tongues from the northwest.. The 

moderate- to low-continuity reflectors are interpreted to be sequences of nonmarine sand stones 

and shale that change laterally to mixed littoral 

and inner-shelf sediments. One of these tongues 

above horizon UJ projects well into the basin 

(shotpoint 2400, fig. 85) and is in an interval in 

which a few reflectors appear to be modorately 

continuous; these zones of continuous ref~tors 

are interpreted to be marine shelf deposi~s laid 

down during transgressive phases of margin 

sedimentation (T-T symbol, fig. 85). Seaw~~d (to 

the right) of this uppermost tongue (shotpoint 

2400), reflectors are faint and dip seawari at a 

low angle, an arrangement that probably indicates a deltaic progradation of the shelf in this 

area during the Early Cretaceous. The pat .. ern of 

outbuilding is similar to that described by Jansa 

and Wade (1975b) for the Early Cretaceous Missisauga Formation on the northern f-~otian 

margin, although sediments there are thicl~er. 

LATE POSTRin DEPOSITS 

the COST No. G-2 well. The upper part of the Cretaceous and younger sedimentary rocks 

early postrift section (to horizon UJ) shows the in- make up the third broad group of dist~nctive 

terfingering of probable alluvial and sublittoral reflectors beneath Georges Bank (figs. 84 and 85). 

coastal deposits and carbonate shelf deposits. A They occupy the upper 1.2 seconds (t~~o-way 

zone of weakly continuous, low-amplitude reflec- traveltime) of the seismic records and are charactors extends to the southeast (to the right on fig. terized by thin zones of fairly continuous reflec84) before changing acoustic character. In the tors of moderate amplitude, usually one or two 

COST No. G-2 well, rocks equivalent to this in- wavelets thick, separated by thicker intervals of 

terval are gray sandstone, shale, limestone, and a weakly continuous reflectors. Toward tho outer 

181 
part of the shelf are faint reflectors arranged in 

broad foresets. The difference in acoustic character between this group of reflectors and the 

underlying group is the absence of the tonguelike, 

discontinuous reflectors of variable amplitude. 

In the COST No. G-2 well, this youngest group 

of reflectors is produced by a section of interbedded claystone, siltstone, sandstone, and a few 

thin beds of limestone of Barremian, Aptian, 

Cenomanian, and Coniacian Ages (Simonis, 1980; 

Scholle, Schwab, and Krivoy, 1980; Poag, this 

volume). Some of the limestone beds can be correlated with the persistent thin zone of reflectors 

described on BGR line 209; one group of strong 

reflectors marked by the symbol o-o-o on figure 

84, is thought to correlate with the 0 marker 

delineated in wells on the Scotian margin. The 0 

marker off eastern Canada is a zone of thin Barremian limestone beds approximately 1.6 ft (0.5 m) 

thick within the Missisauga Formation (Mel ver 

1972; fig. 4 of Given 1977). 

Rocks from the COST Nos. G-1 and G-2 wells 

suggest a change in environment from shoreline 

conditions in the Early Cretaceous to shorelinemarine shelf conditions in the middle Cretaceous. 

Middle to outer shelf conditions ~xisted at the 

COST No. G-2 well during the Lzte Cretaceous 

and early Tertiary (Bielak and Simonis, 1980; 

Scholle, Krivoy, and Hennessy, 1980; Scholle, 

Schwab, and Krivoy, 1980; Lachann.e and others, 

1980; Poag, this volume). There a ... e hiatuses in 

the COST Nos. G-1 and G-2 wells (see Poag, this 

volume) between the Barremian and Hauterivian, 

the Aptian and Cenomanian, the Ce"lomanian and 

Turonian, the Turonian and Conia ~ian, and the 

Santonian and Tertiary. Some oft]'~ unconformities in the Cretaceous seem to be aqsociated with 

marine transgressions inferred fro"ll thin zones 

of continuous reflectors in the BarremianHauterivian (fig. 84; o-o-o) and the Cenomanian. 

There are hiatuses in other areas of the Atlantic 

Continental Shelf. At the COST No. B-3 well in 

72° 700 42° 69° 68° ~--~~~~~~~--~~~~~~~----~--------------~-------,------,,67° 

KILOMETERS 

6SO 

FIGURE 87.-lsopach map of synrift deposits in the Georges Bank basin. Contours are in kilometers, and dots indicate data 

points obtained from spot calculations along the grid of seismic-reflection profiles. 

182 
the Baltimore Canyon trough, unconformities 

were detected between rocks of the Hauterivian 

and Barremian, the late Cenomanian and Turonian, the early Turonian and Coniacian, the Late 

Cretaceous and Eocene, and the late Eocene and 

late Oligocene (Poag, 1980b). In the Scotian margin wells, Ascoli (1976) lists major hiatuses in 

rocks of Berriasian, Aptian-early Albian, 

Cenomanian-Turonian, and Maestrichtian-late 

Eocene age. These intervals of widespread erosion during the Barremian, Cenomanian, and 

Late Cretaceous-early Tertiary indicate numerous short-term changes in sea level on the Atlantic margin and support the generalized coastal 

onlap-offlap curve of Vail and others (1977). The 

occurrence of marine shelf conditions in Late 

Cretaceous-early Tertiary time that resulted in 

similar seismic characteristics on widely spaced 

profiles is further evidence of a widespread 

marine transgression (Pitman, 1978; Vail and 

others, 1977) that affected continental margins 

bordering most of the world's oceans. 

BASIN GEOMETRY OF SEDIMENTARY FILL 

As noted by Schlee and Klitgord (this volume) 

the Georges Bank basin is a collection of rmaller 

subbasins (fig. 73). Interpretations from a grid of 

multichannel seismic reflection profiles s·.tggest 

that the area has been built in rift pha"'e and 

postrift phase (figs. 87 and 88). 

Sediments of the rift phase are thick, irregularly distributed, and areally restricted to several 

elongate subbasins bordering the platforrr<il. The 

subbasins have a northeast trend and contF~n 1 to 

3 km (3,300 to 9,800 ft) of probable E'~liest 

Jurassic and older red beds, limestone:;-, and 

evaporites. The thickest rift deposits are under 

the south-central part of the bank in th ~ Y armouth sag and in the main basin, where ar much 

72° 7Cf 4~ 69° 68° ~--~~~--~~~--~~~~--~~-----L---------------L------r-------u67° 

FIGURE 88.-lsopach map of postrift sedimentary section (Jurassic and Cretaceous only) for the Georges Banl~ basin. 

Contours are in kilometers, and dots indicate data points obtained from spot calculations along the grid of seismic-reflection 

profiles. 

183 
as 6 to 8 km (20,000 to 26,000 ft) of sediment appears to be present (fig. 87). During the postrift 

phase of basin history the pattern of subsidence 

changed from narrow rifts to a broad subsiding 

area that encompassed the earlier formed rifts 

and had a sedimentary blanket as much as 6 to 

7 km (20,000 to 23,000 ft) thick (fig. 88). Large 

amounts of both rift and postrift sediments accumulated in the south-central part of the 

Georges Bank marking this area as the main 

basin. Much less sediment (1 to 2 km; 3,300 to 

6,600 ft) accumulated on the landward periphery 

of the set of subbasins, even above earlier formed 

rifts where 2 to 3 km (6,600 to 9,900 ft) of sediment was deposited earlier. A comparison of the 

two isopach maps (figs. 87 and 88) indicates that 

subsidence was rapid and localized at the beginning of basin formation, but slowed and covered a 

larger area in the late Mesozoic. 

The postrift basin geometry was controlled by 

the formation of a continental shelf, slope, and 

rise as the new Atlantic ocean basin was created 

to the east. The buildup of a carbonate bank-reef 

complex near the shelf break trapped a thick ac-

~mulation of sediments on the shelf during the 

Jurassic and Early Cretaceous (Schlee and others, 

1979). This shelf edge formed the seaward edge of 

shelf edge (east of line 20) put it consistently 

beneath the landward edge of the PCMA (fig. 73), 

suggesting that a common structural control for 

the shelf edge and the ECMA de,.reloped during 

the earliest stages of the margin d~velopment. 

TECTONIC HISTORY 

The tectonism associated with the rifting and 

continued separation of Africa from North 

America provided the dominant cc1'ltrol for basin 

development and the sedimentar"' wedge construction. The rate of crusW subfilidence on different parts of the margin was pro..,ably strongly 

influenced by the early tectonic hi~tory (Steckler 

and Watts, 1978; McKenzie, 197f'~ Royden and 

others, 1980). The distribution of the numerous 

subbasins and the accumulation history of the 

sedimentary fill provide the basic data to determine subsidence rates, from which can be inferred 

thermal history (Royden and others, 1980) and 

tectonic history. 

PALEOGEOGRAPHIC RECONSTRf~CTION 

the series of coalescing Atlantic marginal basins Prior to Early Jurassic time (fig. 89A), northand its position has varied through time (Grow, west Africa was adjacent to the Georges Bank 

Mattick, and Schlee, 1979; Schlee and others, region (Bullard and others, 1965; LePichon and 

1979). During the Cretaceous, the overall rate of others, 1977; Klitgord and Schouten, 1980). The 

sediment accumulation decreased on the shelf, locus of rifting during the Late Trit'c:;sic and Early 

and there may have been a slight landward Jurassic suggests that the region now occupied 

retreat of the shelf edge (Schlee and others, 1976, by Georges Bank lay in a shear zone between the 

1979; Uchupi and others, 1977). In the Cenozoic, Triassic grabens in New Jersey arq Connecticut 

the major realm of sedimentation was offshore and those in Northwest Africa and the Iberian 

(Tucholke and Mountain, 1979) and only a thin Peninsula (Van Houten, 1977; Manspeizer and 

veneer accumulated on the shelf (Schlee and others, 1978). As a result, num<:)rous grabens 

others, 1976; Austin and others, 1980). formed in the Georges Bank region in the latest 

The location of the shelf edge during the Triassic or earliest Jurassic (Ballar-i and Uchupi, 

Jurassic is not clearly defined but the seismic and 1972). During the earliest stages of rifting and 

magnetic evidence suggest a small seaward pro- continental drift, crustal blocks for:ned by offsets 

gradation on the western side of Georges Bank just south of Georges Bank and ju~t southeast of 

(Mattick and others, 1981), and a landward the southern tip of Nova Scotia along the breakup 

retreat on the eastern side. As already mentioned, edge (fig. 89B) probably restricted water circulathe arrangement of reflectors on line 20 suggests tion. As the continents continued to drift apart, 

a seaward-prograding carbonate sequence (fig. these ocean basins merged to form the early 

85) similar to that seen in the Baltimore Canyon Atlantic Ocean basin. The restrict.ed water cirtrough (Grow, 1980). On the profiles east of line culation in the Middle and Early Jurassic led to 

20, the retreat or cutting-back of the shelf during salt deposition. Thick salt accumulations to the 

the Jurassic is suggested by the buried benches north of the offset off the southe1~ tip of Nova 

that form ascending steps landward (fig. 82). Our Scotia may account for the perva~ive diapirism 

estimates of the location of the Early Jurassic north of Georges Bank. 

184 
EARLY 

MIDDLE 

· SALT 

LATE TRIASSIC-EARLY 

JURASSIC BASINS 

TTTTn- HINGE ZONE 

"\,. MAJOR CONTINENTAL 

" EDGE OFFSET 

_.EAST COAST MAGNETIC 

I 

.· 

o, WEST AFRICAN MAGNETIC ANOMALY 

c=::> BLAKE SPUR MAGNETIC ANOMALY 

FIGURE 89.-Reconstructions of the Atlantic Ocean during the Early and Middle Jurassic. Note the possible barriers to water 

circulation during the early period of ocean opening just to the northeast and just to the southwest of the Georges Bank 

basin. The locations of Lower Jurassic(?) and Upper Triassic(?) salt deposits are indicated. From Klitgord and Schouten 

(1980). 185 
TECTONIC STAGES 

The development of the Georges Bank basin 

began with the rifting of Paleozoic or older crust 

during the Late Triassic as at least three or four 

graben-like, northeast-oriented subbasins formed 

along the edge of the Long Island-Gulf of Mexico 

platform. Their trend was parallel to the landward edges of the Carolina trough, the Baltimore 

Canyon trough, and the Scotian basin. Prerift and 

synrift sediments filled these subbasins, which 

were tilted by later tectonic activity on the 

borders of the structures. As the two continents 

began to separate, the intrusion of igneous rock 

probably altered and broadened what now forms 

the main basin seaward of the Yarmouth arch 

(fig. 73). The restricted oceanic circulation at this 

time (late rifting stage to early drifting stage) 

would have resulted in evaporite deposition over 

much of the region. 

At the end of the Early Jurassic, a new ocean 

basin was beginning to form. The sediment fill 

which had been previously trapped within the 

subsiding marginal subbasins, eventually spilled 

over into the ocean basin forming a continental 

shelf, slope, and rise. A less restricted basin circulation at this time probably facilitated the 

building of a broad carbonate platform and is 

marked in the stratigraphic data by the breakup 

unconformity. As crust cooled, subsidence was 

greatest near the earlier igneous intrusions and 

slower near the edges of the old platforms, 

resulting in increased subsidence to the southeast 

away from the Long Island platform and the Gulf 

of Maine, and to the southwest away from the 

LaHave platform. This pattern of Early and Middle Jurassic differential subsidence can be seen in 

the undulating pattern of the breakup unconformity above the synrift sediments. The breakup 

unconformity dips gently seaward over large 

distances but drops rapidly within a number of 

narrow zones, giving it a stair step appearance. 

During the Middle and Late Jurassic, the infilling of sediments continued on a rapidly subsiding 

shelf while a thin wedge of sediments accumulated on the slope and rise. The position of 

the shelf edge changed during this time as sea 

level fluctuated (Vail and others, 1977). 

Numerous subbasins coalesced into a broader 

186 

basin beneath the south-central Georges Bank; 

its extension to the northeast was divided by the 

Yarmouth arch into a shallower landward limb 

(the Yarmouth sag) and a deeper seaward limb 

(the Scotian basin). By the Cretaceous, shelf sediment accumulation had slowed and the accumulation pattern was more uniform over the whole 

shelf, no longer reflecting the deeper basement 

structures. 

The Cenozoic tectonic history of Georges Bank 

has most likely been one of local and regional 

response to forces such as sea level fluctuation, 

sediment loading, and ice sheet loading and rebound. The subsidence from crustal cooling was 

negligible by then (Steckler and Watts, 1978), and 

only a thin veneer of sediments accumulated on 

the shelf. The shallowest of the rift subbasins 

identified from seismic data, Step #1, lies along 

the northern edge of the bank and may have controlled its location. The shelf break was cut back 

as a result of erosion associated with the continuing sea level fluctuations. Evidence for Cenozoic 

tectonic activity, aside from slumping near the 

shelf break, is minimal, although Uchupi and 

others (in press) have found evidence of possible 

faulting near the northeast channel. 

TECTONIC SmiNGS OF THE COST NOS. G-1 AND G-2 WELLS 

The COST Nos. G-1 and G-2 wells are only 

about 65 km (40.4 mi) apart but the basement 

beneath them may be significantly different. The 

COST No. G-1 well was drilled on a small basement high adjacent to the Yarmouth sag, which 

we have inferred to be part of a Triassic or older 

graben system. This area remained well landward 

of the shelf edge throughout its history. The 

COST No. G-2 well lies seaward of this small 

basement high, and basement beneath the well 

may have been intruded by Lower Jurassic igneous rocks associated with continental breakup. 

Both wells were drilled in what probably was part 

of the early rift basin system, which included 

sites of salt accumulation. In contrast to the G-1 

well, the G-2 well is located in a region that was 

close enough to the shelf edge throughout its 

history to record significant facies changes 

associated with shelf margin migrations. 
Conclusions 

1. The COST No. G-1 well drilled through 

16,071 ft (4,898 m) of sedimentary rocks in 

the Georges Bank of the North Atlantic 

Outer Continental Shelf. Seismic correlation 

with other cored sites on the continental 

shelf suggests the presence of Tertiary 

strata above 1,030 ft (314 m), which are 

disconformable over Cretaceous (santonian) 

rocks. Foraminifers, calcareous nannofossils, and palynomorphs indicate that the 

rocks are Cretaceous from 1,030 to 5,400 ft 

(314 to 1,646 m) and Late Jurassic in age 

from 5,400 to 10,100 ft (1,646 to 3,079 m). A 

K/Ar date of 550 m.y. for a phyllite from 

16,050 ft (4,892 m) indicates the well bottomed in Cambrian strata 

2. No rocks were recovered from the COST No. 

G-1 well above 1,030 ft (314m), but Eocene 

calcareous nannofossils and foraminifers in 

the uppermost samples suggest the presence of an Eocene limestone that appears on 

reflection profiles and in conventional cores. 

Down to 9,900 ft (3,018 m) the strata are 

coarse-grained unconsolidated sands and 

loosely cemented sandstones with beds of 

gray shale, lignite, and coal. From 9,900 to 

12,400 ft (3,780 to 3,018 m) the strata are 

predominantly gray shale, sandstone, limestone, and dolomite. There are predominantly red shales, sandstones, and conglomerates below 12,400 ft (3,780 m) down 

to 15,600 ft (4,755 m). Below this are black 

graphitic slate, phyllite, schist, metadolomite, and metaquartzite. 

3. The COST No. G-2 well (drilled 42 mi (68 km) 

east of COST No. G-1) penetrated 21,874 ft 

(6,668 m) of sedimentary rocks. Conventional cores and seismic correlation indicated that above 1,300 ft (396 m) are Tertiary strata, which lie unconformably over 

Cretaceous (Santonian) rocks. The microfossils indicate that Cretaceous strata extend 

from 1,300 ft (396 m) to 5,920 ft (1,804 m) 

and that Late Jurassic age strata occur 

from 5,920 to 10,100 ft (1,804 to 3,079 m). 

Below this depth, the rocks contain few 

microfossils and are tentatively dated as 

Middle and Early Jurassic. The well bottomed in rocks tentatively assigned a Late 

Triassic age. 

4. No rocks younger than Santonian (Cretaceous) 

were recovered at the G-2 site, but rich 

foraminiferal assemblages from the uppermost sample suggest the presence of Eocene 

and younger limestones down to 1 ,300 ft 

(396m). From 1,300 to 4,000 ft (396 to 

1,219 m) are unconsolidated sands, sandstones, and calcareous shales. From 4,000 to 

13,500 ft (1,219 to 4,115 m) are limestones 

with interbedded sandstones, and from 

13,500 to 21,830 ft (4,115 to 6,654 m) are 

alternating beds of limestone, anhydrite, 

and dolomite. The bottom 40ft (12m) of section contains salt and anhydrite. 

5. The oldest sedimentary rocks at the COST 

Nos. G-1 and G-2 sites are post-rift Jurassic (possibly Late Triassic) evaporitic and 

terrigenous deposits. Through the Jurassic 

and Cretaceous the depositional environment varied between near-shore subaerial to 

sublittoral and inner to outer shelf conditions. Through the Cretaceous the water 

was deeper over the G-2 site than over the 

G-1 site, but shelf conditions prevailed at 

both until the Paleogene, when slope conditions are inferred. 

6. Above 10,000 ft (3,048 m) in the COST No. G-1 

well, porosities range from 15 to 33 percent 

and average 26 percent; below this depth the 

average porosity is 16 percent. In the COST 

No. G-2 well above 10,000 ft (3,048 m), 

porosities range from 15 to 39 percent and 

average 24 percent; below this depth the 

average value is 12 percent. The permeabilities are highly variable in both wells: in G-1 

0.1 to 8,600 mD above 9,000 ft (2,733 m) and 

0.1 to 16 mD below; in G-2 0.1 to 7,100 mD 

above 10,000 ft (3,048 m) and 0.1 to 0.2 mD 

below. 

187 
7. The present-day geothermal gradients are 

1.26° F/100 ft (22.3° C/km) for the COST 

No. G-1 well and 1.34° F/100 ft (24.4° C/km) 

for the COST No. G-2 well. The temperature 

gradient at the COST No. G-2 well is the 

highest yet measured on the Atlantic 

margin. 

8. Measurements of vitrinite reflectance, color 

alteration of visible organic matter, and 

various organic geochemical properties indicate that the Tertiary and Cretaceous 

strata of both wells appear to have poor 

petroleum source-rock potential because the 

organic matter is thermally immature and 

the total organic carbon contents are less 

that 1 percent. The Jurassic rocks may have 

poor-to-fair potential for gas generation. The 

Jurassic hydrocarbons are thermally 

mature, but the average organic carbon contents are also less that 1 percent, and the 

organic matter is largely of terrestrial 

origin. 

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Planktonic Microfossils, Rome,1970, v. 2, p. 1337-1340. 

Amato, R. V., and Bebout, J. W., eds., 1980, Geologic and 

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Amato, R. V., and Simonis, E. K., eds., 1980, Geologic and 

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