GEOLOGICAL SURVEY CIRCULAR 773

Stratigraphic Test Well, 

Nantucket Island, 

Massachusetts
Stratigraphic Test Well, 

Nantucket Island, 

Massachusetts

By D. W. Folger, J. C. Hathaway, R. A. Christopher, 

P. C. Valentine, and C. W. Poag

GEOLOGICAL SURVEY CIRCULAR 773

Description of Triassic(?) basalt and Upper 

Cretaceous to Pleistocene sediments 

recovered from 514 meters of 

test coring

1978
United States Department off the Interior

CECIL D. ANDRUS, Secretary

Geological Survey

W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 78-600008

Free on application to Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, Ma. 22202
CONTENTS

Abstract ___________.

Introduction _____________.

Purpose ________-__. 

Setting ____________. 

Previous work ___________

Acknowledgments ___________.

Methods ______________.

Results ___________________

Stratigraphy ____________

General lithology ______

Upper zone ________

Middle zone ______

Lower zone ____

Saprolite and basalt 

Paleontology _________

Coskata well _____

Pleistocene ___.

Page

1 Results Continued.

1 Stratigraphy Continued

1 Paleontology Continued

2 Pliocene or Miocene

3 Eocene ______ .

4 Paleocene _______ .

5 Borehole 6001 ______.

6 Pleistocene ________

6 Eocene __ ______

6 Upper Cretaceous _.

6 Porosity and permeability _.

7 Discussion _________ ___ _ ___.

8 Regional stratigraphy ______ .

8 Regional structure _____________

15 Hydrology .

15 Summary ______ ___ .

15 References cited ____ _ ________

Page

15

16

16

16

16

17

17

18

18

18

22

23

26

26

ILLUSTRATIONS

Page

FIGURE 1. Index map of Nantucket Island and the surrounding area _ 2

2. Cross section showing structure of part of Continental Shelf

south and west of Nantucket ____ _- 4

3. Columnar section of borehole 6001 ___ ___ - 6 

4-6. Diagrams showing variations for the following chemical components in the basalt and saprolite zones of borehole 6001:

4. Chemical elements and minerals __________ __ _____ 14

5. TiC-2 and P205 _________________ 15

6. Mn02 and CaO ____________________________ 15

7. Stratigraphic sections showing regional correlation of Nantucket 

boreholes with other holes drilled in the Atlantic Coastal 

Plain to the west and south _______________ ____ 19

8. Section from New Jersey to Georges Bank showing environment

of deposition of sediments _____________________________ 21

9. Map showing gravity anomalies in Nantucket region ___ _ 23

10. Seismic reflection profile through Great Round Shoal Channel and

Nantucket Sound ________________________________ 24

11. Graph comparing salinity of interstitial water with electrical

conductivity and lithology in borehole 6001 ___________ 25

TABLES

TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and 

saprolite ________________________ _ _

2. Porosity and permeability analyses ___________ _____________

Page

9

18

III
Stratigraphic Test Well, Nantucket Island, Massachusetts

By D. W. Folger, J. C. Hathaway, R. A. Christopher, P. C. Valentine, and C. W. Poag

ABSTRACT

The U.S. Geological Survey, in cooperation with the 

Massachusetts Water Resources Commission and the 

Nantucket Conservation Foundation, continuously cored 

514 m of sediment and volcanic rock in a Stratigraphic 

and water-quality test.

Stratified sediments were divided texturally into 

three zones: the upper zone (0-128 m) contains mostly 

coarse sand and gravel; the middle zone (128-349 m) 

contains mostly silty clay and a few beds of sand and 

silt; and the lower zone (349-457 m) contains soft, 

unconsolidated, clayey sand. Below the lower zone, a 

saprolite, composed mostly of clay, grades abruptly 

downward at 470 m into partially altered basalt that 

extends to the bottom of the hole at 514 m.

Fossils are sparse throughout the cores, but Pleistocene, Eocene, and Upper Cretaceous assemblages were 

identified. On the basis of limited foraminifer and 

ostracode assemblages, Pleistocene deposits are inferred to extend to a depth of about 85 m. A Lower 

Eocene section 25 m thick is defined on the basis of 

palynomorph and dinoflagellate assemblages. (However, samples from a water well drilled in 1933, 10 

km to the north, contain Pliocene and Miocene, early 

Eocene, and Pal eocene foraminifers.) Upper Cretaceous 

beds, inferred to extend from 128 to 349 m, are identified mostly on the basis of pollen and spores. The 

oldest datable fossiliferous sample at 345 m is earlyto-middle Cenomanian in age.

Samples found below 345 m are barren of indigenous 

fossils and are assigned an Albian Age on the basis 

of electric log correlations. Paleontologic evidence suggests that the Pleistocene section was deposited under 

nearshore marine conditions, the Tertiary section under open-shelf marine conditions, and most of the 

Upper Cretaceous section under nonmarine conditions.

The unstratified clay that makes up the saprolite 

was probably formed by subaerial weathering of basalt 

similar to that which underlies the saprolite. Chemical 

evidence suggests that the basalt was probably deposited as a series of flows. The oldest K-Ar date obtained in the basalt was 183±8 m.y. (Early Jurassic); 

however, because of alteration, this probably represents a minimum age.

Lignites and coal in the Upper Cretaceous section 

are of low rank and, on the basis of their thermal immaturity, have probably never been buried deeply; thus,

local generation of petroleum hydrocarbons in this 

shoreward area of the continental margin is unlikely. 

Freshwater or low-salinity brackish water was 

found in sediments far below the depth predicted by 

the Ghyben-Herzberg principle. These interstitial 

waters are probably relict ground water emplaced 

during times of low sea level during the Pleistocene.

INTRODUCTION

PURPOSE

In 1975, the U.S. Geological Survey (USGS), 

in cooperation with the Massachusetts Water 

Resources Commission, planned to drill a 122-m 

hole near the geographic center of Nantucket 

Island to assess the total thickness of freshwater in the sediments. Calculations based on 

the Ghyben-Herzberg principle predicted a zone 

of freshwater 120-150 m thick (Kohout and 

others, 1977). This principle is the theory of 

hydrostatic equilibrium between freshwater 

and more dense seawater in a coastal aquifer; 

it states that for each meter of ground-water 

elevation above sea level, the freshwater lens 

will depress the saltwater interface about 40 m 

below sea level. The USGS later proposed to 

deepen the test to about 500 m, the approximate 

depth of a prominent acoustic reflector (Oldale, 

1969), which was assumed to be basement. The 

primary objective of the additional drilling was 

to obtain new Stratigraphic information near 

the shoreward margin of the Georges Bank 

basin. Seismic reflection and refraction surveys 

by oil companies and by the USGS have been 

carried out for several years in the region of 

Georges Bank, where leasing of tracts and exploratory drilling are imminent.

The nearest pre-Pleistocene sedimentary 

strata exposed on land are Tertiary and Cretaceous clay and sand that crop out at Gay 

Head, Martha's Vineyard (fig. 1). However,
NANTUCKET SOUND

MASSACHUSETTS BAY 4I°25'-

Great Point

COSKATA 

BOREHOLE

( T.D. 102m)

Sankaty Head 

41° 15'-

USGS BOREHOLE 

NO. 6001

(T.D. 514m)

70°00'

USGS BOREHOLE 

NO. 6016

0 10

70° 00

USGS BOREHOLE

NO. 6018 

© and

COST G1

STRATIGRAPHIC

TEST

FIGURE 1. Index map of Nantucket Island and surrounding area showing location of Nantucket stratigraphic 

test well (USGS borehole No. 6001) and other boreholes in the region. T.D. shows total depth of some of 

the boreholes.

they are dislocated and highly folded and 

faulted, apparently from loading or "bulldozing" by glacial ice (Kaye, 1964), and they do 

not provide a clear picture of the stratigraphy. 

The Nantucket test-well site is located farther 

seaward from Martha's Vineyard, and it provided an opportunity to gain data where sediments are thicker, closer to the basin center, 

and presumably less affected by ice movements. 

Furthermore, penetrating the sedimentary section and identifying basement would be useful 

in the interpretation of geophysical data collected to assess the resource potential of the 

area.

SETTING

Nantucket Island is about 25 km long, as 

much as 10 km wide, and lies 40 km south of

the coast of Cape Cod, Mass., on the eastern 

Continental Shelf of the United States. It has 

a maximum elevation of only 33 m (Folger 

Hill), and encompasses a total area of 132 km2 .

Exposed surficial sediments are mostly glacial sand, gravel, and some clay (Richards, 

1962; Woodworth, 1934). These deposits are 

part of the Ronkonkoma-Vineyard-Nantucket 

moraine and its outwash plain that extends 

eastward to form part of Georges Bank (Pratt 

and Schlee, 1969). Controversy has surrounded 

the age of shelly deposits underlying the sand 

and gravel at Sankaty Head (fig. 1), but most 

evidence available suggests that they are also 

of Pleistocene age (Richards, 1962; Gustavson, 

1976).

The well site (borehole 6001) is at lat 

41°15/54.9// N. and long 70°02'16.72" W. near
the geographic center of the island on land 

owned by the Nantucket Conservation Foundation, which, because of its interest in island 

water resource evaluation, kindly granted the 

USGS permission to drill. The site was conveniently located 60 m from Milestone Road, the 

main highway between Nantucket and Siasconset (fig. 1), in a long linear depression 

known as Madequecham Valley that was probably eroded by a proglacial melt-water stream. 

Ground surface elevation at the site is 10.9 m 

above mean sea level.

PREVIOUS WORK

Discussions concerning sediments of Nantucket date back to Desor (1849) who suggested 

that fossils exposed at the base of cliffs at 

Sankaty Head were Tertiary in age. In subsequent work, this conclusion was hotly contested 

and a Pleistocene age for them was established 

(Merrill, 1896; Cushman, 1906; Richards, 

1962) ; thus, most work on the geology of the 

island has concerned its glacial evolution 

(Shaler, 1889; Woodworth, 1934). However, 

extensive study of Tertiary and Cretaceous exposures on Martha's Vineyard at Gay Head, 

contiguous shores, and in pits located inland 

laid the basis for conjecture concerning the 

subsurface stratigraphy of Nantucket (Woodworth, 1934; Kaye, 1964, 1972).

Fourteen deep boreholes drilled on lower 

Cape Cod penetrated as much as 137 m of glacial clastic deposits and 172 m of bedrock composed of schist and granite (Koteff and Cotton, 

1962; Oldale, 1976). Sediments of Tertiary age 

(Eocene) were recovered in three holes drilled 

near Provincetown, at the northern tip of Cape 

Cod (Zeigler and others, 1960). A hole has recently been drilled on Martha's Vineyard to a 

total depth of 262.2 m; the core contains a condensed but similar stratigraphic section to that 

penetrated on Nantucket (Raymond E. Hall, 

USGS, written commun., 1977).

On Nantucket, a water well was drilled in 

1933 using a manually operated cable-tool rig 

at Coskata, about 10 km north of USGS borehole No. 6001 (fig. 1). No freshwater was recovered, but the hole penetrated 44 m of sand 

and gravel overlying 58 m of silt and clay. 

Cuttings from the hole were assembled in 1936 

by Walter Barrett, then a Nantucket High

School student, and examined for microfossil 

content with the help of J. A. Cushman. On the 

basis of Foraminifera that he discovered in the 

fine-textured sediments, he assigned them a 

Tertiary age. This work, remarkable for a high 

school student, remained unpublished until now. 

The Coskata samples, which had been saved by 

Mr. Barrett, provided for us a Tertiary section 

that is mostly absent in the USGS borehole.

Geophysical investgiations of the island to 

our knowledge have been sparse. Weston Geophysical Co. conducted a refraction seismic and 

resistivity survey in 1966 (Massachusetts 

Water Resources Commission, written commun.). One refraction line was long enough to 

reach a high velocity (5.7 km/s) refractor at

-509 m near the western end of the island. A 

shorter line laid out along Milestone Road revealed two refracting horizons less than 46 m 

deep close to the location of the USGS hole. 

Oldale (1969) shot several refraction lines 

along the beaches, but none was long enough to 

reach refractors with velocities in excess of 

2.8 km/s. He did, however, compile all available 

data in the Cape Cod, Martha's Vineyard, and 

Nantucket area to construct a depth-to-basement map. Though he had only the one site 

from Weston's unreversed line at which higher 

velocity material was penetrated, his prediction 

of basement depth at the USGS borehole of

-500 m was within a few meters of the depth 

at which basalt was penetrated.

A deep CDP (common depth point) seismic 

line (No. 5) was shot by the research vessel 

Gulf Seal, operated by Digicon Geophysical, 

Inc., for the USGS Outer Continental Shelf 

Resource Assessment Program, 20 km west of 

Nantucket (Grow and Schlee, 1976). There, 

sediments overlying basement thicken from less 

than 1 km nearshore to 8 km offshore beneath 

the Continental Slope. Figure 2 shows the processed record and our interpretation of seismic 

line No. 5. West of Nantucket, the line appears 

to cross several subsurfurce basins that may be 

down-faulted. These have been interpreted on 

the basis of previous work to be Triassic or 

Jurassic grabens (Grow and Schlee, 1976, map 

2; Ballard and Uchupi, 1975; Ballard and Sorensen, 1968; Uchupi and Emery, 1967; Uchupi, 

1968).

On the basis of magnetic data, Nantucket
NW SHOT POINT NUMBER

600 700 800

SE

70°

EXPLANATION

Q, Quaternary 

T, Tertiary 

K, Cretaceous 

J, Jurassic 

1, Triassic 

M, Multiple

LOCATION MAP

FIGURE 2. Cross section of part of Continental Shelf showing processed record and interpretation of USGS seismic line No. 5 (CDP) south and west of Nantucket. Mi, M2 , and M3 are interpreted as multiples of reflector 

at base of Cretaceous. The geologic setting of borehole 6001 may be represented by location B on the profile (near shot point 400) with respect to its position relative to the inferred Triassic-Jurassic basin. The 

basalt found in borehole 6001 may be represented by the strong reflector at a reflection time of about 0.7 

seconds (between shot points 110 and 230 below location A), because this reflector occurs in the area of 

seismic line No. 5 at a depth below sea level similar to the depth of the basalt in the borehole.

lies close to the northern end of a northeasttrending basement ridge that is bordered on 

the northwest by a parallel broad basin that 

underlies Nantucket Sound and extends southwestward under the Continental Shelf (Klitgord and Behrendt, 1977).

ACKNOWLEDGMENTS

F. A. Kohout l and M. H. Bothner set up the 

equipment and conducted on-site determinations 

of tests of salinity and pH of interstitial water

1 All persons mentioned in these acknowledgments are from the 

USGS unless an affiliation is otherwise indicated.

squeezed from the cores recovered from the 

borehole. E. G. A. Weed described and sampled 

cores during virtually the entire period of the 

drilling operations, managed the logs of the 

data obtained, and aided in training and supervising the technicians who assisted from time to 

time in processing cores. E.G. Rhodehamel participated in on-site operations during the drilling of the saprolite and basalt in the lower part 

of the borehole and during the final logging of 

the well. He also interpreted the logs and provided tentative correlations of these with other 

wells of the Atlantic Coastal Plain.
J. A. Commeau made partial chemical analyses of the core materials by X-ray fluorescence. 

L. J. Poppe prepared X-ray diffraction patterns 

and made qualitative mineralogic analyses of 

the cores.

S. A. Wood assisted in part of the on-site 

work with the cores and also assembled and 

proofed some tabular material and parts of the 

text and assembled information from some of 

the references.

E. H. Walker participated in the early onsite salinity determinations and provided advice 

on local ground-water conditions on Nantucket.

W. S. Barrett of Nantucket, Mass., gave important assistance in arrangements with local 

groups and contractors on Nantucket, lent advice and counsel on local conditions, and provided history, samples, and original paleontologic analyses from the well drilled in 1933 at 

Coskata.

The following assisted in the work of describing, sampling, photographing, and packing 

cores at various times during the coring of the 

well: Susan Wieber, Rebecca Belastock, Charles 

O'Hara, Ellen Davie, Raymond Hall, Robert 

Commeau, John Schlee, James Robb, W. M. 

Ferrebee, Lyle McGinnis, Anna Sundberg, 

Christina Schoen, John Dunlavey, David Delaney, Patricia Forrestel, Stanley Locker, and 

Paul Cousins.

John Baker and Michael Frimpter supervised 

the original arrangements for the water resources test well and lent advice and counsel 

during later stages of the program. David Delaney aided extensively in the interstitial water 

chemistry studies during the drilling operations.

James Lentowski, executive secretary of the 

Nantucket Conservation Foundation, arranged 

for the clearing of the site prior to the drilling 

and for the restoration of the site after completion of the project.

The late Austin Tyrer, local water-well drilling contractor, drilled freshwater supply wells 

for the program and rendered assistance in 

numerous logistic problems that arose during 

the operations.

Larry J. Nutter ran electric logs (self-potential and resistivity) of the upper 125 m of the 

well.

H. Peyton Herman supervised the crew of the 

U.S. Army Corps of Engineers, who ably conducted the drilling and coring operations despite severe winter conditions. Janet R. Moller 

of Falmouth, Mass., drafted most of the illustrations for this paper.

METHODS

The U.S. Army Corps of Engineers began 

drilling on November 9, 1975, with a Failing 2 

2000 rotary rig. Our objective was to core the 

entire hole to provide as much stratigraphic 

information as possible. Several methods, including split-spoon coring, punch or 'driven barrel coring, as well as rotary coring, were used 

to improve recovery in the upper unconsolidated 

glacial sands and gravels. Nevertheless, recovery was poor (10.3 percent) throughout the 

upper 120 m of section until casing (24.5 cm or 

9% in. I.D.) was set at 125 m. From that point 

on, best recovery (45.5 percent) was obtained 

in clay-rich sediments using a core barrel 15.2 

cm (6 in.) I.D. by 6.1 m (20 ft) long, designed 

by the Corps of Engineers. Where hard rock 

was penetrated, a conventional petroleum core 

barrel with a diamond rock-coring bit (Hycalog 

9.1 m (30 ft) long; 6.35 cm (2V2 in.) I.D.) was 

used and obtained 73 percent recovery.

Immediately after recovery, cores were described, photographed, and sampled for textural, hydrocarbon, mineralogic, paleontologic, 

and water analyses. Squeezing for pore water 

analysis was carried out immediately by a hydraulic press (Manheim, 1966) and salinity 

values obtained using an Endeco type 102 refractometer. Some microscopic examination of 

the samples was carried out on the well site.

In the laboratory, samples were examined for 

microfossils, including Foraminifera, nannofossils, pollen, and spores. At places where lithologic changes were seen or at one depth in each 

core, mineral content was assessed by L. J. 

Poppe, using a Norelco X-ray diffractometer 

equipped with a graphite curved-crystal monochromator and a proportional counter alined 

to record copper K« radiation (A= 1.5418 A). 

Textural analyses were carried out with a 

Rapid Sediment Analyzer (Schlee, 1966) and a 

Coulter Counter Model TAII by Sally Wood, 

Peter Johnson, and Wayne M. Ferrebee. Hydrocarbons were assessed by Robert Miller, David

- Trade names in this publication are used for descriptive purposes only, and do not constitute endorsement by the U.S. Geological Survey.
Schultz, and George Claypool of the USGS by 

soxhlet extractions and gas chromatography. 

Two potassium-argon ages were determined by 

R.F. Marvin, H. H. Mehnert, Kinyoto Futa, and 

Violet Merritt. Potassium content was determined using an Instrument Laboratories Flame 

Photometer with a lithium internal standard. 

Permeability and porosity measurements were 

carried out by Core Lab., Inc. Chemical compositions were obtained by Judith A. Commeau, 

using a Diano XRF 8000 automated X-ray 

fluorescence analyzer. Sample preparation was 

by the methods of Rose, Adler, and Flanagan 

(1963). Carbon-14 date W-3542 was measured 

in the laboratory of the USGS by Meyer Rubin.

RESULTS

STRATIGRAPHY

GENERAL LITHOLOGY

To a depth 3 of 457 m, the borehole penetrated unconsolidated and semiconsolidated 

sedimentary clastic detritus that ranges in texture from clay «0.004 mm) to cobbles (128 

mm). Below 457 m, a saprolite, composed 

mostly of clay, grades abruptly at about 470 m 

into partially weathered or altered basalt that 

extends to the bottom of the hole at 514 m.

The sedimentary section can be divided into 

three lithologic zones. The upper zone, from the 

surface to 128 m, is dominated by coarse sand 

and gravel and a few thin beds of clay and silt; 

the middle zone, from 128 to 349 m, is composed 

mostly of silty clay showing increasing consolidation as the depth increases, interbedded with 

a few clayey, silty, sandy beds (3-12 m thick) 

and indurated siltstone beds as much as 30 cm 

thick. The lower zone, from 349 to 457 m, contains soft, unconsolidated, water-saturated, 

clayey sand interrupted by clay layers 3 to 6 m 

thick.

The lithology of the section from the borehole is shown in columnar section in figure 3.

UPPER ZONE

Lithology. In the upper zone (0-128 m), 

sands range in texture from medium to very 

coarse grained and range in color from light 

tans, grays, and olives to bright green. Pea-size 

(<1 cm) gravel is most common but coarse 

gravel and cobbles apparently are scattered

LITHOLOGIC 

COLUMN

GROUND LEVEL 0 FT

SEA LEVEL 

35.9 FT (I0.9M

SP

0 METERS

GAMMA RAY API

-GAMMA RAY

-BASE OF CASING

TD 1686 FT 

514 M

OHMS M /M 

RESISTIVITY 

0. .100

1 All depths are from ground level (10.9 m above sea level).

FIGURE 3. Columnar section of borehole 6001 

showing lithology, core recovery (solid black, 

left side of column; small arrows indicate driven 

cores), self potential (SP), caliper, induction resistivity, and gamma ray logs. See figure 7 for 

explanation of lithologic symbols.
throughout the section, especially between 60 

and 80 m. Two thin zones cored at 35 and 63 m 

contain a mixture of gravel, sand, silt, and 

clay, and may be glacial tills or weathered soil 

zones. Shell fragments, as much as 7 cm across, 

form layers that are most common between 38 

and 61 m. Greensand having a matrix of silt 

and clay-size glauconite was first found at 91 m 

and, though recovery was poor, appears to 

dominate at least to 107 m and perhaps as deep 

as 126m.

Mineralogy. Dominant clay minerals in the 

upper 120 m of the section are illite and minor 

kaolinite; chlorite and dioctahedral vermiculite 

are also common in several intervals. Smectite, 

which was observed in several samples from 

this zone, is probably contamination from the 

drilling mud because it shows extremely sharp 

and well ordered X-ray diffraction peaks, quite 

unlike the mixed-layered assemblages usually 

found in such detrital sediments. The coarse 

fraction comprises mainly quartz and plagioclase feldspar. Calcite and aragonite are present 

in strata containing shells.

MIDDLE ZONE

Lithology. The middle zone (128-349 m) 

contains mostly variegated clay and fewer 

interbeds of light-gray sand. The dense, compact, and silty clay ranges in color from white 

to red, yellow, brown, purple, olive gray, and 

black; in many places, it is mottled in combinations of these colors. The black and darkgray layers contain abundant lignite and many 

leaf imprints; at least one interval contains 

lignite/subbituminous coal at 328 m (described 

below). Particles of lignite are also scattered 

throughout most of this middle zone. Interbedded sands are commonly gray to brown, 

highly micaceous, kaolinitic, and contain 

abundant lignite. Very fine to medium-grained 

sand is most abundant, but coarse to very 

coarse material is present. Sand is more common than clay from about 128 to 213 m, whereas clay tends to be more common below 213 m. 

The sediments are more indurated toward the 

base of the zone at 349 m; some layers are hard 

cemented siltstone.

Mineralogy. Clay minerals are the most 

common constituents of this zone. Of these, 

kaolinite is most abundant accompanied by

minor amounts of illite and smectite; chlorite 

is absent. Minor amounts of mixed layer smectite-illite are found toward the base of the zone. 

Quartz, rare amounts of plagioclase feldspar, 

goethite, gibbsite, hematite, siderite, and occasionally anatase constitute the main non-clay 

fraction. The mineralogy of this interval is thus 

characteristic of a heavily weathered and 

leached soil, probably formed under tropical, 

humid conditions.

Coal. A bed of lignite/subbituminous coal 

at least 20 cm thick was found at 328 m. When 

the core was first recovered, freshly exposed 

surfaces were dark brown but turned black 

within seconds after exposure to the air. Analyses by George E. Claypool, USGS, showed that 

it is a relatively pure coal containing 58.8 percent organic carbon. Soxhlet extraction yielded 

2.68 percent bitumen. Of this, 0.14 percent is 

composed of saturated hydrocarbon, 0.18 percent is nominal aromatic hydrocarbon material, 

and the balance of 2.36 percent is nonhydrocarbon extractable organic matter. Its total hydrocarbon concentration of 3,181 ppm and a 

hydrocarbon-to-organic carbon ratio of 0.54 are 

typical of low-rank coals. The saturated-toaromatic hydrocarbon ratio of 0.76 is much 

higher than typical humic coals, suggesting a 

higher content of waxy tissues in this coal. 

Thermal analysis/pyrolysis showed only 12.2 

percent of the organic carbon recoverable as 

pyrolytic volatiles. This relatively small amount 

indicates that the organic matter of the coal 

would be a relatively inefficient generator of 

petroleum hydrocarbons.

Gas chromatography of the products of pyrolysis showed that, although the coal is capable 

of generating light (C10-C2n ) paraffin hydrocarbons, it is thermally immature and has not 

done so. The temperature of maximum pyrolysis 

yield (450°C) indicates a low-temperature history, or lignite/subbituminous rank (G. E. 

Claypool, written commun., 1975). These results indicate that sediments in this part of the 

shoreward edge of the Atlantic continental margin sediment wedge have never been buried 

deeply enough to generate mature petroleum 

hydrocarbons. Thus, unless migration has taken 

place, any accumulations of petroleum hydrocarbons probably occur far seaward of the Nantucket site in areas where source sediments
have been buried much more deeply than those 

at Nantucket.

LOWER ZONE

Lithology. In the lower zone (349-457 m), 

sandy sediments are predominant; they are unconsolidated and mostly light gray or occasionally tan, and contain rare pebbles (<1 cm) and 

layers of yellowish clay. The sand is fine to very 

coarse grained and has an abundant matrix of 

clay that is mostly kaolinite. The cores recovered were usually soft and watery. Interbedded 

clay horizons, a few meters to 10 m thick, are 

light gray, red, and yellow, commonly mottled, 

very sandy, silty, and micaceous.

Mineralogy. The abundant sand in the 

lower zone contains mostly quartz and minor 

plagioclase feldspar. Clay minerals are mainly 

kaolinite, lesser amounts of illite, and rare 

smectite. Neither chlorite nor vermiculite was 

observed.

In summary, the upper 128 m zone of sediments is almost entirely sand and gravel, the 

middle 221-m zone is mostly clay and silt, and 

the lower 108 m zone is mostly sand.

SAPROLITE AND BASALT

Lithology. At 457 m, the stratified sands 

and clays are in contact with an unbedded maroon clay containing many rounded blebs and 

veins of white clay. The white structures closely 

resemble those in the veined amygdaloidal basalt that underlies the clay zone. We concluded 

that the maroon and white clay is a saprolite 

derived by weathering-in-place of igneous rock 

having similar structure. At about 470 m, the 

clay grades into hard partially weathered or 

altered basalt that is maroon to brown and 

aphanitic to finely crystalline; the basalt is 

veined with calcite and has vesicles filled with 

zeolite or saponite. Toward the bottom of the 

hole at 514 m, the basalt is bluish gray and contains many amygdules and veins consisting of 

red, white, and green zeolites, saponite, and calcite.

Two samples of the basalt were dated by the 

K-Ar methods. A sample from 485.7 m gave an 

age of 183±8 m.y. (Early Jurassic); the other 

sample taken at 513.8 m, was dated at 164±3 

m.y. (Middle Jurassic). Because the basalt in 

both samples was partially altered, however,

these probably represent minimum ages, and 

the basalt may well be at least Triassic in age.

The types of clay and other alteration minerals in the basalt are not the result of weathering processes as is the kaolinite of the saprolite 

zone. Alteration within the basalt itself probably took place as a result of hydrothermal 

processes early in the history of the rock, and 

thus the ages obtained may not be as much in 

error as the existence of alteration might otherwise suggest. The saprolite, however, is probably the result of later subaerial weathering.

Chemistry. Chemical analyses (table 1) for 

Si02 , Al2 0:i , Fe2 03 , MnO,, MgO, CaO, Na2 0, 

K2 0, TiOL>, and P2 05 and modal mineralogical 

analyses by X-ray diffraction were made for 

samples taken from the cores at 1- to 3-m intervals. Fluctuations in abundances (fig. 4) of 

some elements (expressed as oxides) appear to 

reflect mainly the extent of weathering and 

leaching. For example, the saprolite zone from 

about 470 m to 457 m shows upward decreasing 

concentrations of MgO, Si02 , P2 0D , CaO, and 

Na2 0 and increasing concentrations of A12 03 , 

Fe2 0:; , and Ti02 . The first five elements thus 

have been removed, apparently as deep weathering has proceeded with time, and the last 

three have concurrently increased as part of 

residual, refractory mineral constituents. The 

K2 0 and Mn02 contents show only slight decreasing trends in this interval.

Below 470 m, variations are more complex. 

Several samples in which MgO content and the 

ratio of Si02 /Al2 0:: are large correlate with the 

occurrence of the mineral saponite. Saponite 

(not to be confused with the term "saprolite" 

above) is a magnesium-rich smectite (montmorillonite group minerals) having relatively 

low aluminum content. Its idealized structural 

formula (Ross and Hendricks, 1945) is:

Na0 . :-i,

r 

Mg3 {Si 3 . B7 A10 .,3 > 010 {OH2 )

The chemical composition for sample 6001- 

120-5 (55-58 cm) gives the following calculated structural formula:

{Na0. n ;i Kn.oi Ca0 .i0 }

t T 

{Mg2 . 49 Fe0 . 20 A10 . 10 > {Si.,.^ A10 .« 3 > 010 {OH2 }

8
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite

[Chemical analyses by J. A. Commeau; X-ray diffraction analyses by L. J. Poppe and J. C. Hathaway]

Sample No.1 _________.

Depth (m) 

Material _.

6001-116-1 6001-116-2 6001-116-2 6001-116-2 6001-116-3 

(15cm) (10cm) (60cm) (90cm) (107cm)

456.5 

Gray 

sedimentary 

clay.

457.5 

Maroon 

clay with 

white 

blebs.

458.0

Maroon

clay with

white

blebs.

458.3 459.6 

Maroon Dark red 

clay with clay, 

white 

blebs.

6001-116-4 

(25-50 

cm) 

460.0

Yellow 

blebs.

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

Si02 __________________ 38.51 26.80 19.37 33.01

A1203 ________________ 27.45 18.41 28.53 21.27

Fe2 03 _________________ 2.21 27.30 24.89 13.34

Mn02 ________________ .03 .11 .12 .05

MgO ___________________ .96 .83 .78 .46

CaO __________________ .11 .13 .12 .14

Na2 0 _________________ .37 .50 .58 

K2O __________________ .00 .00 .005 .02

Ti02 _________________ 3.18 2.91 3.06 .85

P2On __________________ .00 .04 .05 .06

Partial total _____________ 72.82 77.03 77.505 69.20

____ ___ Estimated modes from X-ray diffraction

Kaolinite ______________ 99 75 72 75 75 87 

Smectite (montmorillonite

group other than saponite) ___ 

Saponite ____________ 

Mixed layered smectite-chlorite _ 

Chlorite _____________ 

Illite _-_______________ _____ _____

Talc _______________________ _____ _ _ _

Heulandite _______________ 

Stilbite _______________ _______

Analcime _______________ 

Prehnite ____________ 

Potassium feldspar ______ 

Plagioclass feldspar ________ 

Calcite ________________ Tr. 

Hematite ______________ 25 28 25 25 13

Other ____________________ Quartz tr. Quartz tr.

Sample No.1 _____________ 6001-116-4 6001-116-5 6001-116-6 6001-117-1 6001-117-2 6001-117-3

(90cm) (40cm) (20cm) (50cm) (55cm) (55cm)

Depth (m) _____________ 460.5 461.2 462.0 462.7 464.0 465.2

Material ___ _____________ Maroon Maroon Maroon Maroon Dark- 'Maroon **

clay with clay with clay with clay with maroon clay

white white white white clay with with white

blebs. blebs. blebs. blebs. green amygdukg

	amygdules

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

SiO, __________________ 31.37 34.54 43.64

Al.0.1 _________________ 23.31 20.09 14.87

Fe.O, _________________ 20.36 23.04 15.76

MnO, _________________ .11 .11 .05

MgO _________________ .00 .33 1.98

CaO __________________ .17 .53 1.13

Na,0 ________________ .49 .98 1.68

K,O _________________ .16 .77 .89

TiO2 __________________ 2.96 3.14 2.67

P2O5 _________________ .19 .21 .35

Partial total ___________ 79.12 83.74 83.02

Estimated modes from X-ray diffraction

Kaolinite _________________

Smectite (Montmorillonite

group other than saponite) ___ 

Saponite _______________

Mixed layered smectite-chlorite _

70 90 79 75 30

55

15

69
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued

	Estimated modes from X-ray diffraction

Chlorite ______________ ___ 

Illite _________________ _____ _ _ 

Talc __________________ _____ _____

Heulandite ______ ___________ 

Stilbite _______________ 

Analcime ___________________ 

Prehnite _____________________ 

Potassium feldspar ___________ Tr. 

Plagioclase feldspar _________ Tr. 

Calcite ________________ 

Hematite ______________ 20 10 21 25 10 16

Other _________________ Quartz tr. Quartz tr.

Sample No. 1 _____________ 6001-117-4 6001-118-1 6001-118-3 6001-118-3 6001-118-3 6001-119-1

Depth (m) 

Material _.

(25 cm)

465.4 

Maroon 

clay with 

white 

amygdules

(3-5 cm) (47-49 (109-110 (110-111 (l-2cm)

cm) cm) cm)

465.5 467.8 468.4 468.5 469.4 

Red clay Amygdules Red clay Veins and Red basalt

amygdules.

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence _____

SiO. _ _________ _ _____ 42.30 46.73 47.53 54.29 40.96

Al-6:, _--___________----- 17.79 14.74 15.77 16.83 15.70

Fe,O, ________________ 15.88 8.75 16.77 5.83 14.42

MnO. _____________ ___ .05 .05 .05 .04 .06

MgO _________________ 2.04 2.05 1.10 3.77 .16

CaO ________ ____ ___ 1.24 .82 1.40 .78 4.82

Na.O ___ _; ______ __-_ 1.48 3.32 2.04 3.64

K.O __________________ .16 .34 1.18 .42 .95

TiO, _____ ___ __ _ 1.96 .82 2.45 .69 2.09

P»O, __________ ____ _ .40 .08 .31 .06 .27

Partial total _____________ 83.30 74.38 89.88 84.75 83.07

Estimated modes from X-ray diffraction

Kaolinite ______________ 15 20 

Smectite (montmorillonite

group other than saponite) __ 69 65 90 53 90 20

Saponite __________________ 

Mixed layered smectite-chlorite _ 

Chlorite _______________ 

Illite _________________ 

Talc __________________ ______ _____

Heulandite ___________________ 

Stilbite _______________ 

Analcime ____________________ 

Prehnite _________________ 

Potassium feldspar ___________ Tr. 

Plagioclase feldspar _______ 30 Tr. 70

Calcite _____________________ Tr.?

Hematite _____________ 15 15 8 17 6 15

Other _________________ Quartz 1 Unidentified Unidentified

	mineral. mineral.

Sample No.1 _____________ 6001-120-1 6001-120-1 6001-120-4 6001-120-4 6001-120-5 6001-120-5

(4-6 cm) 2 (95-96 (48-49 (66-69 (44-46 (55-58

cm) 2 cm) cm) cm) cm)

Depth (m) _____________ 472.7 473.6 476.5 476.7 477.6 477.8

Material _________________ Maroon Basalt White White Red vein Yellow

basalt with green calcite vein calcite vein vein 

amygdules

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

SiO2 _______________-__ 39.94 38.93 1.54 18.84 37.62 45.55

AlsOa _________________ 12.40 12.37 .37 4.74 8.65 8.45

Fe2 03 _________________ 11.51 11.78 .46 1.05 6.01 3.61

Mn02 _________________ .17 .16 .70 .59 .33 .00

MgO _________________ 5.14 4.51 4.71 4.48 12.61 22.61

CaO __________________ 7.63 6.23 46.89 33.93 7.62 1.29

10
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued 

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

Na2O _________________ 4.68 2.80 3.08 2.65 2.51 3.26

K2O ___________________ .54 1.04 .00 .56 .49 .11

TiO2 __________________ 1.55 1.51 .00 .00 .01 .00

P^Os __________________ .19 .18 .13 .07 .00 .00

Partial total ____________ 83.75 79.51 57.88 66.91 75.85 84.88

Estimated modes from X-ray diffraction

Kaolinite __________-___ 

Smectite )montmorillonite

group other than saponite) ___ -20 - 68 "10 "62 =100

Saponite ______________ 

Mixed layered smectite-chlorite _ 

Chlorite ____________ 

Illite _________________ _____ ______

Talc _________________ ______

Heulandite _____________ Tr. 20 20 

Stilbite ________________ ______ _____

Analcime _______________ 

Prehnite -_____________ 

Potassium feldspar ________ Tr. 

Plagioclase feldspar _________ 60 4 2 

Calcite _________________ 8 15 99 53 11 

Hematite _____________ 12 12 6 

Other _________________

Sample No.T ____________ 6001-120-5 6001-120-5 6001-121-1 "'6001-121- "6001-121- 6001-121-7

(64-66 (73-75 (22cm) 1(30-31 1(30-31 (27-29

cm) cm) cm) cm) cm)

Depth (m) ____________ 477.9 478.0 479.4 479.5 479.5 485.3

Material _____________ Maroon White White Greenish Maroon Green

basalt crumbly vein amygdules basalt vein 

vein

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

SiO. __________________ 41.34 46.27 6.59 50.44 43.12 38.80

AU), _________________ 12.85 10.32 1.53 15.58 13.99 7.34

Pe2O3 ___-_____________ 13.28 1.51 1.41 4.63 14.21 10.09

MnO2 _________________ .15 .23 .95 .07 .13 .08

MgO _________________ 10.80 12.39 5.32 7.01 6.95 19.45

CaO __________________ 5.72 5.14 42.57 .91 1.59 1.89

Na.O _________________ 3.12 2.32 2.65 2.18 3.30 

K2O _________________ 1.04 .23 .22 .40 .63 .08

TiO3 __________________ 1.77 .01 .06 .18 2.07 .65

P.O.-, __________________ .24 .00 .12 .00 .25 .05

Partial total ____________ 90.31 78.42 61.42 81.40 86.24 78.43

Estimated modes from X-ray diffraction

Kaolinite ___________ 

Smectite (montmorillonite

group other than saponite) _ 3 30 80 80 33 10

Saponite _______________ 15 22 80

Mixed layered smectite-chlorite _ 

Chlorite _______________ _____

Illite ________________ 

Talc _________________ 10 

Heulandite ___________ 10 

Stilbite _______________ 10

Analcime _____________ 

Prehnite _____________ 

Potassium feldspar _______ 

Plagioclase feldspar ____ 42 28 Tr.

Calcite ________________ 10 10 4 90 2 2 

Hematite ______________ 13 3 15 

Other ________________________

11
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued

Sample No.1 _____________ 6001-121-7 6001-121-7 6001-122-1 6001-122-2 6001-123-1 6001-123-2

(64-70 cm) (67-70 cm) (35-37 cm) (90-95 cm) (24-26 cm) (13-15 cm)

Depth (m) _____________ 485.7 485.7 487.1 488.9 489.4 491.3 

Material _ ____ ___ _____ Maroon Maroon Maroon Green Gray Gray

basalt basalt basalt amygdules basalt with basalt

green 

amygdules

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

Si02 _____________ _ ____ 41.19 40.58 38.06 38.61 41.91

AlaOa ___________ _ ____ 14.08 11.77 6.98 10.38 11.96

Fe->O3 _________________ 13.18 14.38 10.91 10.73 11.56

MnO2 _________________ .11 .12 .06 .10 .16

MgO _________________ 6.87 11.41 23.66 9.40 7.59

CaO __________________ 8.92 6.68 .96 6.50 3.31

Na2O _________________ 3.45 2.66 2.87 2.79 4.14

K2O _____________ _ ____ .62 .51 .01 .37 1.14

TiO2 _____________ _ ___ 1.68 1.70 .20 1.41 1.84

P«O- __ __________ __________ 23 22 01 16 24

'llllllllllllll" 9o'.33 9o!o3 SB.12 SQA5 83.'85

Estimated modes from X-ray diffraction

Kaolinite _ __________ _ _______ 

Smectite (montmorillonite

group other than saponite) ___ 10 20

Saponite _________ _____ 20 10 20 89 30 

Mixed layered smectite-chlorite _ 

Chlorite ____ _ _______________ 

Illite _________________ ______

Talc __ _____ _ _______ ___ _ _____ ______

Heulandite _ _ ___ _ _____ _ ____ 

Stilbite _______________ _____ _____

Analcime _ ______ _ _______ _ 

Prehnite ________ _ ________ _ _ 

Potassium feldspar __ ___ __ 

Plagioclase feldspar _ ____ 67 67 65 59 68

Calcite _ _ ______ _ _____ _ _ _ 

Hematite ______________ 13 13 15 11 11 12 

Other _______________________

Sample No.1 _____________ 6001-123-4 6001-124-1 6001-124-3 6001-124-3 6001-124-3 6001-124-4

(13-15 cm) (73cm) (55-58 cm) (74-76 cm) (112-114 (50cm)

	cm)

Depth (m) _____________ 495.4 498.8 503.0 503.2 503.5 505.4

Material ____ _ __ _ ___ _ ___ _ Maroon Maroon Red basalt Orange Red basalt Red

basalt with basalt vein "rotten"

amygdules rock

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

SiO. ____________ _ ____ 44.46 46.08 46.21 55.66 38.89 39.34

ALO, _________________ 13.67 13.82 14.99 19.09 14.99 15.17

Fe,O3 _________________ 12.92 11.77 10.50 9.40 13.85 10.98

MnO2 _________________ .14 .18 .11 .54 .15 .20

MgO _________________ 4.45 8.34 4.35 3.61 5.88 16.32

CaO __________________ 4.37 5.04 1.74 2.73 1.85 5.73

Na2O _________________ 5.86 4.86 5.68 4.33 1.49 1.73

K2O __________________ 1.91 1.17 1.20 1.73 3.12 .55

TiO2 __________________ 2.50 1.70 1.29 1.42 1.40 .64

P2O5 __________________ .33 .22 .11 .23 .10 .13

Partial total ____________ 90.61 93.18 86.18 98.74 81.72 90.79

Estimated modes from X-ray diffraction

Kaolinite _ _____ __ __ ____ 

Smectite (montmorillonite

group other than saponite) ___ 20 18 16 

Saponite _______________ 22 

Mixed layered smectite-chlorite _ 30 30

Chlorite _ __ _ _ _ _ _ _ ____ 

Illite _________________ Tr. 57 

Talc ____________ _ ____ _____ _ _ _

12
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued 

Estimated modes from X-ray diffraction Continued

Heulandite _____________ 

Stilbite _______________ 

Analcime ______________ 32 

Prehnite _______________ 

Potassium feldspar ______ 10 5

Plagioclase feldspar _______ 35 70 66 70 39 54

Calcite ________________ 

Hematite ______________ 13 12 11 9 14 11 

Other _______________________

Sample No.1 _____________ 6001-124-4 6001-125-1 6001-126-1 6001-126-2 6001-126-2 6001-126-5

(80cm) (0-1 cm) (1-2 cm) (18-20 cm) (20-22 cm) (23-24 cm) 

Depth (m) ______________ 505.7 507.2 508.4 509.6 509.6 512.9

Material ___ _______ Maroon Maroon Maroon Gray Maroon Maroon

basalt basalt basalt basalt basalt with basalt

white 

crystals

Partial chemical analyses of major oxides in weight percent from X-ray fluorescence Continued

SiO, __________________ 43.50 43.74 46.91 49.12 38.67 41.60

A12O:! _________________ 12.68 11.73 13.62 16.50 19.42 12.92

Fe2O3 ________________ 11.84 11.63 12.10 12.83 7.42 11.78

MnO2 _________________ .16 .15 .15 .13 .07 .15

MgO _______________.._ 6.43 6.33 6.64 6.60 4.48 7.00

CaO __________________ 5.05 5.13 5.87 9.67 20.35 6.37

Na,O _________________ 5.57 5.80 4.85 1.13 5.63

K2O __________________ .88 .75 .87 .37 .36 .90

TiO2 __________________ 1.76 1.78 2.15 1.71 .82 1.74

P2O, __________________ .21 .20 .21 .24 .15 .22

Partial total ____________ 88.08 87.24 88.52 102.02 93.47 88.31

Estimated modes from X-ray diffraction Continued

Kaolinite ____________________ _ 

Smectite (montmorillonite

group other than saponite) ___ 

Saponite _____________ 

Mixed layered smectite-chlorite _ 15 15 15 10 

Chlorite _______________ _ 10 5

Illite _________________ _____ _____ tr

Talc ___________________ _____ _ _ 

Heulandite _______________ 

Stilbite _______________ 

Analcime _______________ 20 tr 55

Prehnite ______________ _ 15 80 

Potassium feldspar _______ tr tr 20

Plagioclase feldspar _______ 73 53 72 62 20

Calcite __________________ tr 

Hematite ______________ 12 12 12 13 8 

Other _______________________

Sample No.1 ____________ 6001-126-5 6001-126-5 6001-126-5

(85-88 cm) (105-107 (110-114

cm) cm)

Depth (m) ____________ 513.6 513.8 513.9 

Material __________________ Red basalt Basalt Gray basalt

with white

crystals

Partial chemical analyses for major oxides in weight percent from X-ray fluorescence

SiO, __________________ 28.20 48.56

AW), _________________ 11.65 16.34

Fe2 03 _________________ 8.87 12.63

MnO2 __________________ .19 .15

MgO _________________ 6.87 6.84

CaO __________________ 21.31 9.33

Na2O _________________ 1.63 4.20

K2O __________________ .08 .89

Ti02 __________________ .36 1.97

P,O5 _______________ .10 .27

Partial total ____________ 79.26 101.18

13
TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued

Estimated modes from X-ray diffraction

Kaolinite ____-______ _ _ 

Smectite (montmorillonite

group other than saponite) _ 

Saponite _____ 

Mixed layered smectite-chlorite _ 20

Chlorite ________________ 

Illite _________________ Tr.

Talc __________________ 

Heulandite ______ __ 

Stilbite _______________ 

Analcime ___ __ __ ____ 

Prehnite ______________ 10

Potassium feldspar _________ 8

Plagioclase feldspar _____ 15

Calcite _______________- 35

Hematite ___________ 9

Other _____________.__

10

20

69

11

77

13

u As 2 above, but no collapse, even at 750° C. 

* Magnesium calcite (about 18 percent MgCO::). 

5 Amygdules. 

"Host basalt.

MgO

Percent

S,02 /AI 2 03

23456

P2 05 Ti02

Percent Percent

0001 03 0501234 

I ' ' ' ' ' I ' ' ' '

Fe2 03 CaO Mn02 Na20

Percent Percent Percent Percent

10 20 30 0 10 30 50 00 05 10 O I 2 3 4 5 6 0

K 20

c = Analcime Ch = Chlorite Ct=Calcite Hd = Heulandite K = Kaolinite Pr = Prehnite Sm = Smectite Sp = Saponite Tc=Talc

FIGURE 4. Diagram showing variation of chemical elements and minerals as depth increases in the basalt and 

saprolite zones of borehole 6001. See figure 5 for explanation of symbols, which depict type of sample or rock.

These values are within the range of saponite 

composition shown by Ross and Hendricks 

(1945), and Grim (1968).

As shown in figures 4 and 5, Ti02 and P2 0r, 

tend to fluctuate together, except in the upper 

saprolitic zone, where Ti02 increases upward 

and P2 05 decreases.

Manganese content (fig. 6) generally shows 

increases where CaO content is large.

Many of the samples were selected to assess 

the composition of vein and amygdaloidal minerals. Immediately below the saprolite, most 

veins are either calcite or saponite, whereas 

many amygdules are filled by zeolites. As the

14
3.0-

°-2 Percent 0.5

FIGURE 5. Diagram showing variation of TiO,. and P.O.-, in the basalt and saprolite zones of borehole 6001.

O

CL 

0.4

*.-

Percent 30 

CdO

40

a TV i_ 6. Diagram showing variation of MnO, and

CaO in the basalt and saprolite zones of borehole 6001.

depth increases, heulandite and stilbite are succeeded by analcime and prehnite.

PALEONTOLOGY

COSKATA WELL

PLEISTOCENE

In the upper 44 m of sand and gravel, benthic 

and pelagic foraminifers of Pleistocene age are 

identical to those recovered in borehole 6001 

and are indicative of deposition in a nearshore 

shelf environment similar to that present today 

in the New England region.

PLIOCENE OR MIOCFNE

In silty clay from 46 to 55 m, a Pliocene or 

Miocene assemblage contains a sparse foraminiferal fauna. A few planktic specimens appear 

to be Neogloboquadrina pseudopacJiyderm.a 

(Cita, Primoli Silva, and Rossi). Benthic forms

15
include Cibicidoides ftoridanus (Cushman), 

Bulimina marginata (d'Orbigny), Oridorsalis 

umbonatus (Reuss), and Florilus grateloupi 

(d'Orbigny), probably all deposited in a midshelf environment.

EOCENE

In silty clay from 55 to 75 m, early Eocene 

foraminiferal faunas contain numerous benthic 

forms and small planktic specimens, most of 

which belong- to indeterminate species. Those 

species that are recognizable and diagnostic are 

Acarinina broedermanni (Cushman and Bermudez), Morozovella cf. M. trichotrocha (Loeblich and Tappan), Guembelitria cf. G. columbiana (Howe), Bulimina pseudocacumenata 

Olsson, Turrilina robertsi (Howe and Roberts), 

Pseudohastigerina micro, (Cole), Alabamina 

wilcoxensis Toulmin, Gyroidinoides octocameratus (Cushman and Hanna). This assemblage 

was probably deposited in outer continental 

shelf conditions.

PALEOCENE

In silty clay of Paleocene age from 75 to 

102 m, foraminiferal assemblages contain many 

species common to the Aquia Formation of 

Maryland and the Vincentown Formation of 

New Jersey. The planktic and benthic species are 

diverse and include Acarinina tribulosa (Loeblich and Tappan), A. aquiensis (Loeblich and 

Tappan), A. pentacamerata (Subbotina), A, 

strabocella (Loeblich and Tappan), A. esnaensis (Leroy), Morozovella aequa (Cushman and 

Renz), Subbotina triloculinoides (Plummer), 

Pseudohastigerina micra (Cole), Alabamina 

midwayensisC!) Brotzen, Trifarina wilcoxensis 

(Cushman and Ponton), Gyroidinoides octocameratus (Cushman and Hanna), Turrilina 

robertsi (Howe and Roberts), and Anomalinoides midwayensis (Plummer). This assemblage contains more planktic specimens and 

more deep water benthic specimens than 

younger sediments in the hole, but probably still 

reflects outer shelf conditions during deposition.

BOREHOLE 6001

Fossils are scarce in the core, but Pleistocene, 

Eocene, and Upper Cretaceous assemblages 

have been identified; they include benthic

foraminifers, ostracodes, dinoflagellates, and, 

especially, spores and pollen (sporomorphs). 

Pleistocene samples contain only ostracodes and 

foraminifers; Eocene samples yield dinoflagellates and sporomorphs; and Upper Cretaceous 

beds contain sporomorphs, rare agglutinated 

benthic foraminifers, and a few casts of mollusks.

PLEISTOCENE

The Pleistocene microfossil assemblages are 

limited to the medium to coarse quartz sands in 

the interval from 38 m to 45 m. The total Pleistocene section is inferred to extend to 85 m 

depth. Twenty-one species of benthic foraminifers are represented, but specimens are rare. 

The predominant forms are Elphidium orbiculare (H. B. Brady), Elphidium clavatum 

(Cushman), Cibicidoides lobatulus (Walker 

and Jacob), Glabratella wrightii (H. B. 

Brady), Buccella inusitata Andersen, and Buccella frigida (Cushman). Modern representatives of these species inhabit the shallow waters 

adjacent to Nantucket Island, and the Pleistocene sediments containing them presumably 

were deposited under similar conditions.

A small but well-presrved ostracode assemblage was recovered from a depth of 45 m. The 

sample contains abundant molluscan fragments, 

and 19 species of ostracodes:

Baffinicythere emarginata (Sars) ; Bensonocythere americana Hazel; B. sp. A of Valentine (1971) ; B. sp. B of Valentine (1971) ; B. 

sp. D of Valentine (1971) ; B. sp.; Cytheridea 

sp. A of Valentine (1971); Cytherura sp.; 

Finmarchinella angulata (Sars) ; F. finmarchica (Sars) ; Hemicy'there villosa (Sars) ; 

Hemicytherura clathrata (Sars) ; Leptocythere 

angusta Blake; Loxoconcha aff. L. granulata 

Sars of Valentine (1971) ; Microcytherura 

choctawhatcheenis (Puri) ; Muellerina canadensis (Brady) ; M. aff. M. lienenklausi (Ulrich 

and Bassler) of Hazel (1970) and of Valentine 

(1971) ; Sclerochilus sp. C of Valentine (1971) ; 

and Xestoleberis sp.

All the ostracode species range throughout 

the Holocene and Pleistocene, and a few also 

range into the Pliocene. The modern geographic 

distribution of 15 of these species is known 

(Hazel, 1970,1971; Valentine, 1971).

Hazel (1970) established the presence of an

16
ostracode faunal province boundary at Cape 

Cod that delineates the cold temperate Nova 

Scotian faunal province to the north from the 

mild temperate Virginian province to the south. 

The boundary is found somewhat to the north 

of Nantucket Island. The fossil ostracode assemblage from the Nantucket well is composed 

(with two exceptions) of two groups of species: 

those that now range from the Arctic or subArctic to the Nova Scotian-Virginian province 

boundary or into the Virginian province; and 

species that are restricted to the Virginian and 

Nova Scotian provinces. Typical southern forms 

are absent.

The fossil ostracode assemblage, though less 

diverse, resembles the modern Cape Cod assemblage, and therefore confirms the inference 

from the foraminifers that the marine climate 

at the time of deposition approximated the 

present mild to cold temperature climate offshore from Nantucket Island. Deposition took 

place during a period of raised sea level in the 

Pleistocene, possibly during the Sangamon 

Interglaciation, or perhaps marking an interval 

of glacial retreat during the Wisconsin Glaciation. A radiocarbon date based on marine fossils of > 40,000 years B.P. at 57.3 m does not 

confirm this interpretation but at least does not 

invalidate it.

Pleistocene deposits also are found in the sea 

cliffs at Sankaty Head on Nantucket (Cushman, 

1904; Wilson, 1905). In a recent study, Gustavson (1976) reevaluated the age and paleoenvironmental interpretation of the molluscan assemblages from this locality as follows: The 

ranges of living representatives of species from 

the lower Sankaty beds overlap in the area off 

Nantucket; the fossil assemblage may in part 

represent the transition from a Sangamonian to 

a Wisconsinan climatic regime; and, the upper 

Sankaty beds contain a cold-water molluscan 

assemblage of probable Wisconsinan Age. Paleontological correlation of the Sankaty beds with 

the Pleistocene of the Nantucket borehole is 

not possible at this time.

EOCENE

Samples from the greensand collected between 91 m and 98 m yielded sporomorph and 

dinoflagellate assemblages. The dinoflagellates 

are sparse but well preserved, and include

Wetzeliella symmetrica Weiler, W. articulata 

Eisenack, W. sp., Pentadinium sp., Cordosphaeridium fibrospinosum Darcy and Williams, and 

Membranosphaera maestrichtica, Samoilovitch. 

All these forms have been recorded from lower 

Tertiary sedimentary rocks and the assemblage 

is considered to be of Eocene age (Fred May, 

written commun., 1976).

The palynomorphs of the greensand include 

a single specimen of the Paleocene to basal 

middle Eocene genus Thomsonipollis, among an 

assemblage of reworked Cenomanian species 

and modern contaminants. Cenomanian forms 

include Peromonolites allenensis Brenner, Tricolporopollenites triangulus Groot, Penny and 

Groot, Ajatipollis cf. A. tetraedralis (Bolkhovitina) Krutzsch, Cyathidites minor Couper, 

Cicatricosisporites hallei Delcourt and Sprumont, and Retitricolpites minutus Pierce. Modern forms are Quercus sp., Pinus sp., Alnus sp., 

Corya sp., Myrica sp., and members of the 

familes Chenopodiaceae and Ericaceae.

UPPER CRETACEOUS

Upper Cretaceous beds were identified by 

their spore and pollen assemblages, which can 

be correlated with those of the New Jersey 

Coastal Plain formations.

Abundant palynomorphs of latest Campanian 

Age are the youngest Cretaceous forms identified. They were found in the black clay that 

marks the top of the middle lithologic zone at 

128.8 m and are equivalent to the flora of the 

basal part of the Navesink Formation or Mount 

Laurel Sand in New Jersey. Diagnostic species 

include Holkopollenites sp. C, Casuarinldites 

sp., and Betulaceoipollenites sp. At 133.9 m the 

presence of Brevitricolporites sp. B, Proteacidites sp. D, and Triatriopollenites sp. B. indicate 

correlation with the Wenonah Formation 

(upper Campanian). Beds equivalent to the 

Wenonah and Marshalltown Formations are 

present at 136.6 m as indicated by the presence 

of Holkopollenites sp. C and Tricolporites sp. 

W.

Lower Campanian equivalents of the Englishtown Formation or Woodbury Clay were found 

at 141.5 m. Diagnostic forms are Osculapollis 

aeqiialis Tschudy and Brevitricolporites sp. A. 

The presence of Chomotriletes spp., Complexiopollis abditus Tschudy, and Retitricolpites sp.

17
A at 173.2 m suggest an age no younger than 

that of the Englishtown Formation, but its age 

is otherwise not definite.

The highest occurrence of Magothy equivalents (Santonian or possibly lower Campanian) 

was found at 174.2 m, as shown by the presence 

of Trudopollis sp. A, Choanopollenites cf. C. 

transitus Tschudy, and cf. Holkopollenites sp. 

A, The occurrnce of Complexiopollis abditus 

Tschudy and C. sp. B at 211.6 m also indicates 

a Magothy age.

Equivalents of the Woodbridge Clay Member 

of the middle Raritan Formation (middle Cenomanian) were found from 259.2 m to 338.0 m. 

Characteristic fossils are Ajatipollis cf. A. 

tetraedralis (Bolkhovitina) Krutzsch, Atlantopollis spp. and Complexiopollis spp.

Thin intervals of marginal marine strata 

were also observed in the Woodbridge equivalents at 309.9 m, 319.7 m, and 321.1 m. Each 

sample contains a distinct assemblage of 

fragile, agglutinated benthic foraminifers of 

the genera Trochammina and Ammobaculites, 

accompanied by abundant plant fragments and 

fish teeth. These beds may represent the equivalent of the subsurface Bass River Formation of 

Fetters (1976) in New Jersey, which was deposited in a continental shelf environment during the major Cenomanian transgression.

The oldest datable fossiliferous sample 

(depth 345 m) contains Ajatipollis cf. A. tetraedralis (Bolkhovitina) Krutzsch, Tricolpollenites parvuhis Groot and Penny, Retitricolpites georgensis Brenner, R. vulgaris Pierce, 

and Tricolporoidites spp., which sugegst equivalence to the lower or middle part of the Raritan 

Formation (lower to middle Cenomanian). 

Samples collected below this point are barren 

of all indigenous fossils.

POROSITY AND PERMEABILITY

Fourteen undisturbed sand samples were 

analyzed using conventional petroleum industry 

techniques for porosity and permeability. All 

were taken from the Upper Cretaceous section 

between 137 and 307 m. Samples of sand between 350 and 457 m were too unconsolidated 

to obtained undisturbed samples suitable for 

analyses.

Porosity was high and averaged 30 percent 

for all samples and varied from 24.5 to 35.9 

percent with no obvious trend. Horizontal 

permeability in 12 samples (2 were unsuitable 

for analysis) averaged 162 mD (millidarcys) 

and varied widely from 10 to 780 mD (table 

2).

DISCUSSION 

REGIONAL STRATIGRAPHY

We have attempted in figure 7 to correlate 

biostratigraphic and lithostratigraphic units 

defined in borehole 6001 and the Coskata borehole in Nantucket southwest to Long Island 

and New Jersey where the stratigraphic relationships, though controversial, have been

TABLE 2. Porosity and permeability analyses

[Analysts: Core Laboratories, Inc., Dallas, Tex. ]

Sample No. 1

6001-45-1 

6001-50-1 

6001-58-3 

6001-59-1 

6001-60-1 

6001-61-1 

6001-63-1 

6001-67-1 

6001-69-2 

6001-71-1 

6001-72-1 

6001-73-1 

6001-82-1 

6001-87-1

(15-25 cm) 

(28-36 cm) 

(105 cm) 

(70-80 cm) 

(77-87 cm) 

(68-74 cm) 

(37 cm) 

(84-94 cm) 

(100-113 cm) 

(90-95 cm) 

(70-80 cm) 

(73-85 cm) 

(85-95 cm) 

(46-49 cm)

Description

Gray sand 

____do _ _

__ _do.___

_ _do __

__ _do _

_ _do _

__ do__ _

White sand 

Gray sand 

White sand 

Gray sand 

___do____

Laminated silt 

Gray sand

Depth 

(m)

136.6 

159.4 

185.1 

188.3 

192.6 

195.9 

206.1 

222.3 

233.9 

244.3 

247.2 

254.7 

286.0 

306.7

Helium 

porosity 

(percent)

26.9 

32.9 

29.1 

28.5 

32.8 

24.5 

32.1 

35.9 

24.9 

34.7 

26.3 

29.8 

32.1 

31.6

- Horizontal 

permeability 

to air (mD)

10 

431 

25 

780

(3) 

Oil

111

74 

15 

42 

162 

254 

22 

15

1 Sample number is composed of four parts. First four digits give hole number; next two dig-its, core number; last single digit, 

ction number; measurement in. parenthesis shows position of sample within section and equals centimeters below top position of that 

ction.

2 mD = millidarcys.

3 Sample unsuitable for permeability measurement.

18
A B D

ISLAND BEACH

NJ-OC-T-I

Modified from Brown, Miller, 

and Swam (1972)

FORT HANCOCK 5A and 

HIGHLANDS BORO 1973

Composite Secfion 

Modified from Perry and others (1975)

FIRE ISLAND

NY-SUF-T-9

Modified from Brown Miller

and Swam (1972)

BOREHOLE 6001 COSKATA BOREHOLE 

NANTUCKET ISLAND

FIGURE 7. Stratigraphic sections showing regional correlation of the Nantucket boreholes (6001 and Coskata) 

with other holes drilled in the Atlantic Coastal Plain to the west and south. Assignment of Cretaceous 

stages follows Sohl and Mello (1970).

worked out in considerable detail. We used 

microfossils, megascopic lithologic analysis, and 

borehole geophysical logs. Lithostratigraphic 

boundaries were established by Brown, Miller, 

and Swain (1972) in the Fire Island (Suffolk 

County, T-9) and Island Beach (Ocean County, 

T-l) boreholes (they used microfossils to date

some boundaries) ; Fetters (1976) and Poag 

(herein) modified the age boundaries by analyzing foraminiferal faunas. Lithostratigraphic 

boundaries were assigned by Perry and others 

(1975) in the Fort Hancock 5 A well. Most sedimentary materials of Cretaceous age and 

younger in the northern part of the Atlantic

19
Coastal Plain are unconsolidated or at most, 

semi-consolidated. Therefore, they are called 

sediments rather than sedimentary rocks in this 

discussion.

The Pleistocene section in borehole 6001 is 

about twice as thick as that in the other wells, 

which is not surprising because it is much 

closer to Pleistocene terminal moraines than 

the Island Beach well or Fort Hancock well. 

The Pleistocene section thins from 85 m in 

borehole 6001 to 44 m in the Coskata borehole. 

The Coskata borehole lies north of the axis of 

the moraine. Probably the thicker section at 

borehole 6001 is in part due to erosion of underlying Tertiary sediments and subsequent filling by glacial outwash debris.

Tertiary sediments are thin or absent in both 

the Fort Hancock and Fire Island wells. At 

Island Beach, a 340-m section comprises Miocene, Eocene, and Paleocene sediments. Neither 

Pliocene nor Oligocene materials were identified. At Nantucket, the Tertiary boundaries are 

not well defined. An early Eocene fauna was 

identified between 91 m and 98 m in borehole 

6001; on the basis of these fossils and lithology, 

we have assigned a Tertiary age to about 25 m 

of the section. In the nearby Coskata borehole, 

lower Eocene of approximately equal thickness 

was identified on the basis of a sparse planktic 

foraminifer assemblage. This is overlain by a 

thin (10 m) Pliocene or Miocene section (that 

was apparently eroded at the site of the Nantucket borehole), and underlain by almost 30 m 

of Paleocene sediment. Our failure to find the 

Paleocene section only 10 km away in borehole 

6001 may be due to the poor sample recovery in 

this interval.

The Upper Cretaceous section down to the 

top of the Albian is similar in thickness (300- 

400 m) in the Island Beach, Fire Island, and 

Nantucket boreholes. Only at Fort Hancock is 

the section significantly thinner (about 200 m 

thick). This appears to be due mostly to erosion of the Maastrichtian section at the top of 

the Upper Cretaceous strata and to a reduced 

thickness of Turonian sediment.

In detail, the Maastrichtian sediments are 

thickest (60 m) in the Island Beach well and 

thin to almost 35 m in the Fire Island well. 

They were not identified at Nantucket but may

be present in a nonfossiliferous facies. Campanian sediments are about 90 m thick at Island 

Beach, thin to 25 m at Fort Hancock and Fire 

Island, and thicken to a maximum of 80 m at 

Nantucket. In contrast, Santonian and Coniacian sediments are thin at both Island Beach 

( 50 m) and borehole 6001 (~30 m) and are 

thicker at Fort Hancock (85 m) and Fire 

Island (~125 m). Turonian strata are 90 to 

125 m thick at Island Beach and Fire Island, 

but are only about 10 m thick at Fort Hancock. 

About 50 m of Turonian sediments are present 

at Nantucket, but the lower boundary is not 

well defined. Cenomanian sediments are almost 

75 m thick in the three southern holes, but 

double that at Nantucket. Upper and lower 

boundaries of the Cenomanian at Nantucket, 

however, are only partly controlled by fossiliferous samples. Only the Island Beach well contains an Albian section definitely underlain, 

apparently conformably, by Lower Cretaceous 

sediments.

Lithologic variations along the section appear to reflect mainly the changing relative percentages of sand and clay in the Cretaceous 

sediments. Upper Quaternary sediments are 

mainly sand and gravel, whereas Tertiary deposits contain more silt and clay. The Upper 

Cretaceous sediments in the Island Beach well, 

Fort Hancock well, and Nantucket borehole 

6001 contain more sand and clay at the top and 

become clayey toward the middle of the section. 

Sand again becomes more prevalent during 

early Cenomanian and Albian time. The Fire 

Island well, however, appears to have much 

coarser clastic sediments throughout the entire 

Upper Cretaceous section than the other three. 

Thus, the sedimentary facies vary mainly in 

texture finer detritus more common at Island 

Beach and Nantucket, but coarser detritus more 

common at Fire Island.

A paleoenvironmental evaluation of the fauna 

and flora in the sediments of the wells revealed 

that during late Tertiary and Quaternary time, 

at all locations, sediments were deposited in 

nonmarine to marginal marine conditions (fig. 

8). During the early Tertiary, however, sediments were accumulating in a middle to outer 

shelf environment in all areas. Despite the 

similarity in facies along the line of section, the 

environment of deposition during Late Cre20
ISLAND BEACH FIRE ISLAND 

N.J. NY

NANTUCKET 

MA.

USGS 6019

cr LU

LU

o

< 

crIUJ 

Z 

LU 

Q_

200

400-

600-

800

IOOOH

1200-

1400-

I600 J

QUATERNARY*

UPPER 

\;-:: CRETACEOUS: : : :

LONG ISLAND PLATFORM

VERTICAL EXAGGERATION = X528

EXPLANATION

MARGINAL MARINE

W LOWER

CRETACEOUS

GEORGES BANK 

BASIN

OPEN MARINE SHELF

IGNEOUS OR 

METAMORPHIC ROCK

FIGURE 8. Section from New Jersey to Georges Bank along the inner edge of the Continental Shelf showing the 

environment of deposition of the sediments. See figure 7 for location of wells; USGS borehole 6019 is 

located and described in Hathaway and others (1976). The interval labeled Quaternary in the Nantucket 

boreholes contains thin beds of Miocene or Pliocene age which were deposited in marginal marine conditions. 

Depositional environments shown are based on interpretation of paleontologic evidence.

taceous time at Nantucket was significantly 

different from that at Island Beach and Fire 

Island. Both the Island Beach and Fire Island 

wells contain a Late Cretaceous fauna characteristic of a shelf environment, whereas at 

Nantucket a nonmarine sporomorph assemblage

is dominant. The only marine interval detected 

in the Upper Cretaceous sediments at Nantucket was a marginal marine assemblage of 

agglutinated foraminifers deposited during the 

Cenomanian. This apparently reflects the global 

Cenomanian marine transgression, of which

21
Fetters (1976) also found evidence in the 

Island Beach well (represented by his Bass 

River Formation).

The Fort Hancock well apparently bottomed 

in Albian sediments; the Fire Island well bottomed in crystalline basement; and the Nantucket borehole 6001 bottomed in Jurassic or 

Triassic volcanic rocks overlain by barren sediments inferred to be Albian on the basis of 

tenuous correlations of electric logs.

In summary, Upper Cretaceous sediments are 

apparently uniform in thickness along strike 

between Island Beach, N.J., and Nantucket. 

Only at Fort Hancock is the section significantly thinner, but within the time stratigraphic stages, the thickness of sediments does 

vary significantly, possibly indicating changes 

in sediment supply with time. However, paleontologic and well control are insufficient to 

rule out the presence of unconformities or 

faults that also could affect observed thicknesses. Northeast of the Island Beach well, 

where Lower Cretaceous sediments were not 

positively identified, the updip limit of Lower 

Cretaceous sediments apparently lies seaward 

of the line of section.

REGIONAL STRUCTURE

Recently acquired shipboard gravity and 

aeromagnetic data on the Atlantic continental 

margin have been mapped by Grow and others 

(1976 and by Klitgord and Behrendt, 1977). 

The shipboard gravity coverage in waters surrounding Cape Cod, Martha's Vineyard, and 

Nantucket is sparse; however, an ocean bottom 

seismic survey of Cape Cod Bay (Bothner, 

1977) provided additional coverage north of 

Cape Cod. Together, these data reveal a large 

(> +30mGal (milligals)) linear positive gravity anomaly elongated north-northeast that 

passes through the eastern part of Martha's 

Vineyard and crosses Cape Cod just east of the 

Cape Cod Canal (fig. 9). A similar linear 

feature of approximately the same magnitude 

(> +30 mGals) lies to the southeast, and, 

though control is absent, its axis appears to 

pass through the site of the Nantucket borehole 6001. The positive feature passing through 

Martha's Vineyard has been modeled as a large 

mafic body intruded into crystalline basement 

that probably is buried on Cape Cod and under 

Cape Cod Bay only by Pleistocene glacial drift

(Bothner, 1977). Because of sparse control in 

the area of the anomaly that passes through 

Nantucket, no modeling has been done. However, the basalt cored from 457 to 514 m 

beneath Nantucket may account for the equally 

large anomaly there. Thus, the gravity data 

depicts two linear positive anomalies that may 

be caused by basalt intruded into crystalline 

basement beneath Cape Code and Nantucket.

The aeromagnetic survey of the area is based 

on a 3.2 x 32 km line spacing and hence the 

coverage is excellent. A northeast grain is evident that is roughly parallel to the trend of the 

two positive gravity anomalies. The magnetic 

trend is characterized by an area of low magnetic gradients that extends between eastern 

Martha's Vineyard and western Nantucket. 

This is flanked on the southeast and northwest 

by higher gradients and closely spaced anomalies. A possible interpretation of this contrast 

is that the magnetic basement lies closer to the 

surface on the northwest and southeast than in 

the area between the islands where it is more 

deeply buried by sediments (Klitgord and 

Behrendt, 1977). Conceivably, the basalt found 

in the Nantucket borehole is responsible for the 

higher gradients at Nantucket, and a similar 

body or bodies of mafic rocks are responsible 

for the higher gradients to the northwest under 

Cape Cod and Martha's Vineyard.

Several seismic profiles have been run on the 

Continental Shelf, both north and west of Nantucket. The nearest profile to the west (USGS 

seismic line No. 5, CDP) has been interpreted 

by Grow and Schlee (1976) ; the nearest profile 

to the north is an unpublished single channel 

survey conducted by the USGS in 1972. Our 

reinterpretation of the multichannel profile is 

shown in figure 2. We believe that the deeper 

high-angle reflectors are rocks of Jurassic and 

Triassic age that fill possibly faulted basins 

similar to those mapped under the Continental 

Shelf in the Gulf of Maine and beneath Georges 

Bank basin (Uchupi, 1970; Weed and others, 

1974; Oldale and others, 1974; Ballard and 

Uchupi, 1975; Schlee and others, 1976; Schlee 

and others, 1977), and off Canada (King 

and MacLean, 1975). Though borehole 6001 

cannot be projected precisely into these profiles, its location probably lies close to the 

southeastern margin of an extension under

22
42°00'

4I°00' -

40°00' x

70°00

CONTOUR INTERVAL: 10 MILLIGALS

0 10 20 30 40 50KM

7I°00' 72°00' 73°00'

FIGURE 9. Gravity data in the Nantucket region. Two elongated positive anomalies (shaded) pass through the 

Martha's Vineyard and Nantucket areas, respectively (modified from Grow and others, 1976).

Nantucket Island of the basin shown in the 

cross section (fig. 2).

The Jurassic or Triassic basalt penetrated 

may have been injected along a zone of crustal 

weakness associated with flexure or fracture of 

the basin margin and extruded as flows. The 

strong reflector at the northwest end of the 

profile shown in figure 2 may represent such 

flows. Thus, partly on the basis of the information from the borehole, we suggest that the 

geophysical data may best be explained by a 

Jurassic and Triassic basin or graben, with a 

northeast-trending axis, that lies between Nantucket and Martha's Vineyard.

A single channel seismic profile north of Nantucket (fig. 10) shows steeply dipping and 

folded reflectors, which we interpret as part of

the Jurassic and Triassic basin that projects 

north of Martha's Vineyard and Nantucket. We 

interpret a displacement of these reflectors and 

the overlying flat reflectors as evidence of a late 

fault that cuts both the Jurassic and Triassic 

basin and presumed Cretaceous sediments; the 

fault may be as young as Tertiary, but probably does not cut Pleistocene deposits.

HYDROLOGY

The water table at borehole 6001 lies at 

about 3.7 m above sea level or 7.3 m below the 

top of the hole. To a depth of 158 m, pore water 

salinity was less than 1 ppt (parts per thousand). From 158 to 192 m, it increased irregularly to 29 ppt; this interval probably repre23
28 AUGUST 1972

o 

o

LJ

LJ

LJ

or I-ii 

o

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7

Great Round Shoal Channel Off Great Pt. 

Nantucket

t

Nantucket Sound

IOKM IONMI

Nantucket Is.

EXPLANATION

Q, Quaternary 

T, Tertiary 

K, Cretaceous 

J, Jurassic 

~fc, Triassic

LOCATION MAP

FIGURE 10. Single channel seismic reflection profile (R/V F. V. Hunt, USGS, Leg III, August 28, 1972, 

0230-0510 hours), east to west through Great Round Shoal Channel and Nantucket Sound (looking 

south), showing stratigraphic interpretation. We believe that the fault at 0252 cuts both JurassicTriassic and Cretaceous sediments. Sediment, filling stream channels is interpreted as Pleistocene in 

age.

24
the lens,pore water salinity, 

ing to33ppt (thatof seaw 

Nantucket) , decreased again t

o p a . k. m

itead ofincreas- ;er surrounding less than0.5 ppt

to

cm cr *^ *cs

CD >-l *S 

p CD O

« cc y 

2. CD C.

a a a OQ ^- 5 P

CD S° 'T

02

I-H 1 i 1 i.

?s *

£?-ar

ft* 0 

* hjH gPM 3

Mt

gll I"- 8'

P^ a^ CD

If *£.

CD cr

"^ ^ a

03* N

O Si

s= a 2.

a <T> E± T 05 a1^

seawater ina coastal aquifer

"

However, below

hr1 H-t 

CD

t4

cr

M

oq

SL

o' &

a

a' 

Si o'

P<-tCD

05

c-fa4

Pc-tc-tCD

a

05

02'

P

librium between freshwater

P

a

3 

o

CD 

CD

a

05

CD

<j

Pc-h

CD*"*

i '

a

o

r-h

a4

Pr-h

« 

i-S 

CD

Si o' 

<-fCDCL 

cr

*<

<-fCD

Qa4

cr

CD

a

n

a; n'

a4

c-fCD 

c-fCD 

O

O

Ms

a4

ydrostatic equiHJ-JCD

M1.'

P"

^_ r+-'

O 

Ms

r-fCD 

r-fn'

a

CD

05

05

Q

Ms 

r-fCD

Ms

CD

05a4

|

CD

"S

05 

I-1

CD

cr

r-h 

CD

Q a4

cr

CD

a

Herzberg prin-

^3

c-fo

a^

05

r-h

CD 

n

CD 

CD

CL

05

r-fP

o"

CD

CL

Oa4

o

c

p 

a

CL

P

^

Ms

CD ~

S.

?

05

1c-h

a;

CD

05

a'

^r

o

Ms

to

rjCO

a thick freshwater lensbneal

a4

Nantucket that

cr

CDc-f-

^

CD 

CD

a

CO

en

o

P

a

&4 

h^

cn 

-q

3 

P^d

X3 

CD

p 

3

o

^"l

CD

05

<D

p

c-fCD

water andthetransition zon

CD

CO

thus represent

l~"

*<i

n

&^

a4 

o

2. N"

o

a

05

1 1 a

p &.

Si

S; o'

^S 

c-f- a4

CD

05 

P

a 

a

^

05

CD

n

c^o' 

a

zone comprises interbedded lei

sands andlowpermeability

£LP"

CD 

Ms 

CD

05aMS

c5

3

c-fcr

CD

( 

CD<-i

P 

c-fCD

c-fP

cr CD"

cr

cT

^

«

CD

CD

P

2!

1

p

05

es of permeable

^

P

CD

^

N

O

a

CD

05

«

O

cr 

P 

cr

P

CD

P

S.

Ms

>-i

05

02

«

P>-s

PITfCD

CL

a 

oc-t02

3

o 

oc-fcr

P

e

05 

CD

rtCD

?

2.

cT

3

c 

a4

CD

O

u

H3

r-h

P 

c-fto

3 

cr

CD

05

CD

P

a

or-fCD*"*

irfgf a'

Ms

CD

05a4

sents thezone of diffusion to

05

altwater andis

cr

CDr-h

CD 

CD

a

to

to

o

p 

a

to

en

o

3

s

P05

CD

CD

a

805

gL

P

a

o

Cf

o 

o

 a 

5'

as 3 §§'

t-» ^

o

- . Us

SBO fD

pr' w,

Is.

o re

ft.

I

3 

a4

DEPTH, IN FEET BELOW LAND SURFAC

OOOOOOQO

o____o____o____o____o____o____o___

I I I I I I I I I I I I I I 

A/V/V" 

^* 

 ! 1^» *^ y"*1 5 \] " "^*"*^ * """> **\f \ /

i .- * T I I 1 T / 

* ' ' ' I M 

I_______________I_______________1_______________I__

* <* K o

o o o g

o o o o

DEPTH, IN METERS BELOW LAND SURFA
likely that they are connate waters. They may 

have been recharged from Cape Cod or 

Martha's Vineyard, but good recharge areas 

are not obvious and may be revealed only by 

additional drilling. As a third possibility, they 

may be residual from the time of last glacial 

advance when sea level was more than 120 m 

lower than at present (Milliman and Emery, 

1968).

The zones of freshwater occurrence are 

shown in figure 11. These are discussed in detail in Kohout and others (1977).

SUMMARY

The 514-m deep borehole at Nantucket has 

provided the following hydrologic and geologic 

information.

1. A thick (150 m) freshwater lens overlies 

saltwater in approximately the relationship predicted by the Ghyben-Herzberg 

theory. However, beneath the lens are several zones that contain anomalously low 

salinity water (less than 2 °/0o) that may 

be due to recharge, or may be relict from 

glacial time. The lowermost zone is more 

than 100 m thick and extends to the top 

, of the saprolite zone found near the bottom of the borehole.

2. Pleistocene sediments on Nantucket are 

about 85 m thick and comprise mostly 

coarse clastic deposits. A radiocarbon 

date on marine fossils of Pleistocene age 

indicated that the deposits at a depth of 

57.3 m are older than 40,000 years.

3. Marine fossils and glauconite indicate that 

the thin (~25 m) section of Tertiary 

sediment (Eocene) drilled was deposited 

under continental shelf conditions. Ten 

kilometers to the northeast, however, 

Miocene and Pliocene, lower Eocene, and 

Paleocene marine sediments total 60 m 

thick in a water well drilled at Coskata in 

1933.

4. Upper Cretaceous sediments are largely 

nonmarine, even where fossiliferous. 

They appear to have been deposited in 

fluvial to deltaic environments that occasionally gave way to lagoonal or lacustrine conditions. Palynomorphs in semiconsolidated clay (240 m thick) and thin 

interbeds of sand define deposits of late

Campanian to Cenomanian Age; the underlying unconsolidated sand (^100 m 

thick) and thin interbeds of clay are barren but may be of Albian Age on the basis 

of electric log correlations.

Lignite and coal in the Upper Cretaceous are of low rank and are thermally 

immature. These sediments were probably never deeply buried; thus, generation of petroleum hydrocarbons in this 

vicinity or similar shoreward parts of the 

continental margin sediment wedge is 

unlikely.

5. A saprolite zone, 13 m thick, consisting 

mostly of kaolinite, overlies 44 m of partially altered basalt of Jurassic or 

Triassic age. Geochemical data and 

amygdaloidal structure suggest that the 

basalt was deposited as a series of flows, 

and that the upper surface was deeply 

weathered under tropical or humid conditions. The hole bottomed in the basalt.

6. The depth of the basalt and sound velocities 

logged in it agree well with those calculated for a prominent acoustic refractor 

that was detected previously under Nantucket. The well thus established the 

identity of the refractor and showed that 

the basalt is not correlative with the older 

crystalline (acoustic) basement under 

Cape Cod.

7. The presence of Mesozoic basalt under Nantucket, coupled with previously acquired 

gravity, magnetic, and seismic data, suggest that the borehole is close to the 

southeastern flank of a buried Jurassic 

and Triassic basin or graben that trends 

northeast. Its axis lies between the islands of Nantucket and Martha's Vineyard.

REFERENCES CITED

Ballard, J. A., and Sorensen, F. H., 1968, Preglacial 

structure of Georges Basin and Northeast Channel, 

Gulf of Maine: Am. Assoc. of Petroleum Geologists 

Bull., v. 52, no. 3, p. 494-500.

Ballard, R. D., and Uchupi, Elazar, 1975, Triassic rift 

structures in the Gulf of Maine: Am. Assoc. Petroleum Geologists Bull., v. 59, no. 7, p. 1041-1072.

Bothner, W. A., 1977, Gravity study of Cape Cod Bay: 

U.S. Geol. Survey open-file rept. 77-497, 10 p.

Brown, P. M., Miller, J. A., and Swain, F. M., 1972, 

Structural and stratigraphic framework, and spatial

26
distribution of permeability of the Atlantic Coastal 

Plain, North Carolina to New York: U.S. Geol. 

Survey Prof. Paper 796, 79 p.

Cushman, J. A., 1904, Notes on the Pleistocene fauna 

of Sankaty Head, Nantucket, Mass.: Am. Geologist, 

v. 35, p. 169-174.

 1906, The Pleistocene deposits of Sankaty Head, 

Nantucket, and their fossils: Nantucket Maria Mitchell Assoc., pub. 1, no. 1, p. 1-21.

Desor, E., 1849, Deposit of drift shells in the cliffs of 

Sancati Island of Nantucket, in a letter to W. C. 

Redfield: Am. Assoc. Adv. Sci. Proc., v. 1, p. 100- 

101.

Grim, R. E., 1968, Clay mineralogy: New York, McGraw-Hill, 596 p.

Grow, J. A., Bowin, C. O., Hutchinson, D. R., and Kent, 

K. M., 1976, Preliminary free-air gravity map 

along the Atlantic continental margin between 

Virginia and Georges Bank: U.S. Geol. Survey 

Misc. Field Studies Map, MF-795.

Grow, J. A., and Schlee, J., 1976, Interpretation and 

velocity analysis of USGS multichannel reflection 

profiles 4, 5, and 6, Atlantic continental margin: 

U.S. Geol. Survey Misc. Field Studies Map, MF808.

Gustavson, T. C., 1976, Paleotemperature analysis of 

the marine Pleistocene of Long Island, New York, 

and Nantucket Island, Massachusetts: Geol. Soc. 

America Bull., v. 87, no. 1, p. 1-8.

Hathaway, J. C., and others, 1976, Preliminary summary of the 1976 Atlantic margin coring project 

of the U.S. Geological Survey: U.S. Geol. Survey 

open-file report 76-844, 217 p.

Hazel, J. E., 1970, Atlantic Continental Shelf and Slope 

of the United States Ostracode zoogeography in 

the southern Nova Scotian and northern Virginian 

faunal provinces: U.S. Geol. Survey Prof. Paper 

520-E, p. E1-E21.

 1971, Paleoclimatology of the Yorktown Formation (Upper Miocene and Lower Pliocene) of Virginia and North Carolina, in H. J. Oertli (ed), 

Paleoecology of Ostracodes: Centre Recherches Pau 

Bull., v. 5 (supp.), p. 361-375.

Kaye, C. A., 1964, Upper Cretaceous to recent stratigraphy of Martha's Vineyard, Massachusetts: 

[abs.] Soc. America Spec. Paper 76, p. 91.

 1972, Outline of the geology of Martha's Vineyard, Nantucket, and the Elizabeth Islands, Massachusetts: U.S. Natl. Park Service, adm. rept., 

18 p.

King, L. H., and MacLean, Brian, 1975, Geology of the 

Scotian Shelf and adjacent areas: Chart 812H in 

Offshore geology of Eastern Canada, Van der 

Linden, W. J. M. and Wade, J. A., eds.: Canada 

Geol. Survey Paper 74-30, v. 2.

Klitgord, K. D., and Behrendt, J. C., 1977, Mesozoic 

basin distribution along the United States east 

coast Continental Margin: [abs.] Program and 

Abstracts, Am. Assoc. Petroleum Geologists Bull., 

v. 61, no. 5, p. 803-804.

Kohout, F. A., Hathaway, J. C., Folger, D. W., Bothner, 

M. H., Walker, E. H., Delaney, D. F., Frimpter,

M. H., Weed, E. G. A., and Rhodehamel, E. C., 1977, 

Fresh ground water stored in aquifers under the 

Continental Shelf; Implications from a deep test, 

Nantucket Island, Massachusetts: Water Resources 

Bull., v. 13, no. 2, p. 373-386.

Koteff, Carl, and Cotton, J. E., 1962, Preliminary results 

of recent deep drilling on Cape Cod, Massachusetts: 

Science, v. 137, no. 3523, p. 34.

Manheim, F. T., 1966, A hydraulic squeezer for obtaining interstitial water from consolidated and unconsolidated sediments, U.S. Geol. Survey Prof. Paper 

550-C, p. C256-C261.

Merrill, F. J. H., 1896, Post-Pliocene deposits of Sankaty Head [Nantucket, Mass.] : New York Acad. 

Sci. Trans., v. 15, p. 10-16.

Milliman, J. D., and Emery, K. O., 1968, Sea levels 

during the past 35,000 years: Science, v. 162, no. 

3858, p. 1121-1123.

Minard, J. P., Perry, W. J., Weed, E. G. A., Rhodehamel, E. C., Robbins, E. I., and Mixon, R. B., 

1974, Preliminary report on geology along Atlantic 

Continental Margin of Northeastern United States: 

Am. Assoc. Petroleum Geologists Bull., v. 58, no. 

6, p. 1169-1178.

Oldale, R. N., 1969, Seismic investigations on Cape Cod, 

Martha's Vineyard, and Nantucket, Massachusetts, 

and a topographic map of the basement surface 

from Cape Cod Bay to the islands: U.S. Geol. Survey Prof. Paper 650-B, p. B122-B127.

 1976, Generalized geologic map of Cape Cod: 

U.S. Geol. Survey open-file rept. 76-765, 23 p.

Oldale, R. N., and Tuttle, C. R., 1964, Seismic investigations on Cape Cod, Massachusetts: U.S. Geol. Survey Prof. Paper 475-D, art. 145, p. D118-D122.

Oldale, R. N., Hathaway, J. C., Dillon, W. P., Hendricks, J. D., and Robb, J. M., 1974, Geophysical 

observations on northern part of Georges Bank and 

adjacent basins of Gulf of Maine: Am. Assoc. 

Petroleum Geologists Bull., v. 58, no. 12, p. 2411- 

2427.

Perry, W. J. Jr., Minard, J. P., Weed, E. G. A., Robbins, 

E. I., and Rhodehamel, E. C., 1975, Stratigraphy 

of Atlantic coastal margin of United States north 

of Cape Hatteras Brief Survey: Am. Assoc. Petroleum Geologists Bull., v. 59, no. 9, p. 1529-1548.

Petters, S. W., 1976, Upper Cretaceous subsurface stratigraphy of Atlantic Coastal Plain of New Jersey: 

Am. Assoc. Petroleum Geologists Bull., v. 60, no. 

1, p. 87-107.

Pratt, R. M., and Schlee, John, 1969, Glaciation on the 

continental margin off New England: Geol. Soc. 

America Bull., v. 80, no. 11, p. 2335-2342.

Richards, H. G., 1962, Studies in the marine Pleistocene: 

Am. Philos. Soc. Trans., v. 52, pt. 3, 141 p.

Rose, H. J. Jr., Adler, Isidore, and Flanagan, F. J., 

1963, X-ray fluorescence analysis of the light elements in rocks and minerals: Appl. Spectroscopy, 

v. 17, no. 4, p. 81-85.

Ross, C. S., and Hendricks, S. B., 1945, Minerals of the 

montmorillonite group, their origin and relation to 

soils and clays: U.S. Geol. Survey Prof. Paper 

205-B, p. B23-B79.

27
Schlee, John, 1966, A modified Woods Hole rapid sediment analyzer: Jour. Sed. Petrology, v. 36, no. 2, 

p. 403-413.

Schlee, John, Behrendt, J. C., Grow, J. A., Robb, J. M., 

Mattick, R. E., Taylor, P. T. and Lawson, B. J., 

1976, Regional geologic framework off northeastern 

United States: Am. Assoc. Petroleum Geologists 

Bull., v. 60, no. 6, p. 926-951.

Schlee, J. S., Martin, R. G., Mattick, R. E., Dillon, 

W. P., and Ball, M. M., 1977, Petroleum geology 

on the U.S. Atlantic-Gulf of Mexico margins: 

Southwestern Legal Foundation Proc., "Exploration and economics of the petroleum industry," v. 

15, p. 47-93.

Shaler, N. S., 1889, The geology of Nantucket: U.S. 

Geol. Survey Bull. 53, 55 p.

Sohl, N. F., and Mello, J. F., 1970, Biostratigraphic 

analyses, in Owens, J. P., Minard, J. P., Sohl, 

N. F., and Mello, J. F., Stratigraphy of the outcropping post-Magothy Upper Cretaceous formations in southern New Jersey and northern Delmarva Peninsula, Delaware and Maryland: U.S. 

Geol. Survey Prof. Paper 674, p. 28-55.

Uchupi, Elazar, 1968, Atlantic Continental Shelf and 

Slope of the United States Physiography: U.S. 

Geol. Survey Prof. Paper 529-C, p. C1-C30.

 1970, Atlantic Continental Shelf and Slope of 

the United States Shallow structure: U.S. Geol. 

Survey Prof. Paper 529-1, p. 11-144.

Uchupi, Elazar, and Emery, K. 0., 1967, Structure of 

the continental margin off the Atlantic Coast of the 

United States: Am. Assoc. Petroleum Geologists 

Bull, v. 51, no. 2, p. 223-224.

Valentine, P. C., 1971, Climatic implication of a late 

Pleistocene ostracode assemblage from southeastern 

Virginia: U.S. Geol. Survey Prof. Paper 683-D," 

p. D1-D28.

Weed, E. G. A., Minard, J. P., Perry, W. J. Jr., 

Rhodehamel, E. C., and Robbins, E. I., 1974, Generalized pre-Pleistocene geologic map of the northern United States Atlantic continental margin: 

U.S. Geol. Survey Misc. Geol. Inv. Map, 1-861.

Wilson, J. H., 1905, The Pleistocene formation of Sankaty Head, Nantucket: Jour. Geology, v. 13, p. 

713-734.

Woodworth, J. B., Geology of Nantucket and adjacent 

islands, in Woodworth, J. B., and Wigglesworth, 

E., 1934, Geography and geology of the region 

including Cape Cod, the Elizabeth Islands, Nantucket, Martha's Vineyard, No Mans Land, and 

Block Island: Harvard College Mus. Comp. Zoology 

Mem., v. 52, p. 93-116.

Zeigler, J. M., Hoffmeister, W. S., Geise, G. and 

Tasha, H., 1960, Discovery of Eocene sediments in 

subsurface of Cape Cod, Massachusetts: Science, 

v. 132, no. 3437, p. 1397-1398.

28