UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

Depositional history of Louisiana-Mississippi outer 

continental shelf

by

Jack L. Kindinger, Ronald J. Miller 

Charles E. Stciting, and Arnold H. Bouma

OPEN-FILE Report 82- /O77

This report is preliminary and has not 

been reviewed for conformity with Geological 

Survey editorial standards or nomenclature. 

Use of brand names in this report is for 

identification only and does not imply 

endorsement by the U.S. Geological Survey.

1982
CONTENTS

	Page

Abstract ------------------------------ 1

Introduction ---------------------------- 1

Methodology related to the collection of seismic data ------- 3

Trackline map -------------------------- 5

Geologic setting -------------------------- 5

Product presentation ------------------------ 6

Bathymetry ----------------------------- 6

Surface and shallow subsurface features -------------- 6

Sedimentary sequences ----------------------- 10

Geologic history -------------------------- 35

Geologic features ------------------------ 35

Sediment distribution ----------------------- 40

Methods ----------------------------- 40

Discussion ----------------------------- 44

Surface drift patterns ----------------------- 44

References ----------------------------- 48

Appendix ------------------------------ 49
ILLUSTRATIONS

Page

Figure 1. Index map of study area ----------------- 2

2. Trackline map of study area --------------- 4

3. Bathymetric map of study area -------------- 7

4. Surface and shallow subsurface structure map ------ 8

5. Surface faulting (within 5 m of sediment surface) - - - - 9

6. Subsurface faults (not reaching 5 m of sea floor) - - - - 11

7. Graben of upper slope described from air gun profile - - 12

8. Diapiric activity of area ---------------- 13

9. Diapir collapse on upper slope ------------- 14

10. Horizons A, C, and D minisparker interpretation ----- 16

11. Isopach map of Unit 2------------------ 17

12. Structure contour map of Horizon D ----------- 18

13. Channel pattern of Unit 2---------------- 19

14. Channel pattern of earliest stage of stream

erosion during theperiod of Unit 2 ---------- 20

15. Channel pattern of middle stage of stream

erosion during the period of Unit 2---------- 21

16. Channel pattern of youngest stage of stream

erosion during period of Unit 2------------ 22

17. Extent of deltaic outbuilding of Unit 2--------- 24

18. Isopach map of regressive sediments

overlying Horizon C------------------ 25

19. Structure contour map of Horizon C ----------- 26

20. Isopach map of transgressive sediments

forming Unit 1 -------------------- 27

21. Channel pattern of Unit 1---------------- 28

22. Structure contour map of Horizon A ----------- 29

23. Distribution of buried oyster reefs ----------- 30

ii
ILLUSTRATIONS cont inued

Figure 24. Oyster reef interpretation from 3.5-kHz

profiles ----------------------- 31

25. Isopach map of St. Bernard Delta ------------ 32

26. Distribution of gas-charged sediments

of Unit 2 ---__---__-__-_------- 33

27. Example of shallow gas interpretations

from 3.5-kHz profile ----------------- 34

28. Location of line 114 -----__---_------ 36

29. Profile of Horizon D described from line 114 ------ 36

30. Stage two of shelf development of line 114 ------- 37

31. Stage three of shelf development of line 114 ------ 37

32. Stage four of shelf development of line 114 ------ 38

33. Stage five of shelf development of line 114 ------ 38

34. Stage six of shelf development of line 114 ------- 39

35. Stage seven of shelf development of line 114 ------ 39

36. Location of grab sampling stations ----------- 41

37. Surficial sediment distribution of area -------- 43

38. Current drifter release stations ------------ 45

39. Surface current drift patterns of study area ------ 46

iii
ABSTRACT

A geological study was undertaken in 1981 in the Louisiana-Mississippi 

outer continental shelf for the Bureau of Land Management. The study 

included a high-resolution seismic reflection survey, surficial sediment 

sampling and surface current drifter sampling. Approximately 7100 sq km of 

the Louisiana-Mississippi shelf and upper slope were surveyed.

The sea floor of the entire area is relatively smooth except for 

occasional areas of uplift produced by diapiric intrusion along the upper 

slope. Characteristics of the topography and subsurface shelf sediments are 

the result of depositional sequences due to delta outbuilding over 

transgressive sediments with intervening periods of erosion during low sea 

level stands. Little evidence of structural deformation such as faults, 

diapirs, and shallow gas is present on the shelf and only a few minor faults 

and scarps are found on the slope.

Minisparker seismic records in combination with air gun (40 and 5 cu 

in) and 3.5-kHz subbottom profile records reveal that seven major stages of 

shelf development have occurred since the middle Pleistocene. The shelf 

development has been controlled by the rise and fall of sea level. These 

stages are defined by four major unconformities, several depositions of 

transgressive sediments, sequences of river channeling and progradational 

delta deposits.

Surficial sediment sample and seismic records indicate tat the last 

major depositional event was the progradation of the St. Bernard Delta lobe. 

This delta lobe covered the northwestern and central regions. Surficial 

sediments in most of the study area are the product of the reworking of the 

San Bernard Delta lobe and previous progradations.

INTRODUCTION

A geologic study was undertaken in 1981 in the Louisiana-Mississippi OCS 

area for the Bureau of Land Management. This area, east of the Mississippi 

River delta, covers the southeastern part of the Mobile quadrangle and the 

eastern half of the Breton Sound quadrangle (Fig. 1). The purpose of the 

study was to provide an interpretation of the geologic framework and 

geologic history of the area since the middle Pleistocene, and to present 

the regional distribution of geologic features that can be hazardous to 

offshore gas and oil production. The project was funded by the Bureau of 

Land Management as part of their program to map geologic features that may 

affect offshore development and to locate geomorphic features that may 

indicate possible cultural resource sites. Maps and reports from this study 

will become part of the Marine Geologic Atlas Series for the Gulf of Mexico 

OCS.

The main aspect of the field data collection was the utilization of 

several types of high-resolution, single channel seismic-reflection systems. 

In addition, a grid pattern was used to collect surficial sediment samples, 

and to drop drifters for establishing the surface current system.

Through personal communication with H. L. Berryhill, stratigraphic 

units of similar time frame and sedimentological characteristics to those in 

the western Gulf of Mexico were selected for this study. Interpretation and 

organization of presentation were patterned after Berryhill, 1980.
Figure 1. Index map of study area, showing 2° sheets used in mapping
The majority of the maps produced from this study are presented 

separately on plates at a scale of 1:250,000. To facilitate reading, 

photographic reductions are inserted in the text with reference in each 

caption to which plate the illustration refers.

METHODOLOGY RELATED TO THE COLLECTION OF SEISMIC DATA

Seismic data were compiled during three phases. The first phase 

consisted of obtaining high-resolution seismic records from archives at the 

U.S. Geological Survey, Conservation Division, Metairie, Louisiana. These 

records provided preliminary information and helped to establish the most 

advantageous seismic grid for an overall survey. The second phase dealt 

with the collection of high-resolution seismic data by the U.S. Geological 

Survey aboard the R/V GYRE (Cruise 81-G-6) in April 1981. Using the survey 

grid established during phase one, the R/V GYRE ran tracklines parallel and 

perpendicular to the shelf break, with 5 km spacings. The third phase was 

the completion of seismic tracklines into waters too shallow for the R/V 

GYRE. For this the R/V CARANCAHUA was used during which a total of 700 km 

of high resolution seismic data was collected by U.S. Geological Survey 

personnel in July 1981. In total, 3200 km of high-resolution seismic 

reflection data were collected by both vessels (Fig. 2).

During the 2500 km of tracklines run by the R/V GYRE, the following 

seismic systems were operated:

1) 400-joule minisparker

2) 3.5-kHz subbottom profiler

3) 40-in^ and 5-in^ airguns

4) 12-kHz precision depth recorder (PDR)

The minisparker system provided mid-range penetration (0-500 m). The 

recorder setting was at 1/2 second sweep and the filter settings were placed 

at 200 Hz to 2000 Hz. Bubble pulse interference in the upper sediments in 

the minisparker records made it necessary to use a 3.5-kHz subbottom 

profiler to obtain data in that zone. The penetration ranged from 0 to as 

much as 100 m; the recorder sweep was set at 1/4 second. The 40-in^ airgun 

provided deep penetration (0-1500 m) and was used in water depths greater 

than 100 m. In waters shallower than 100 m, a 5-in^ airgun was used because 

although it gave less penetration than the large airgun, its multiples were 

not as overwhelming. Filter settings for both sizes of airguns were 20 Hz 

to 120 Hz. The 12-kHz precision depth recorder provided continuous 

bathymetry of area. Analog records were made for each system in addition to 

taping all information consisting of the seismic systems, voice annotation, 

time and navigation data. Navigation for the R/V GYRE was an integrated 

system consisting of Loran C, Satellite, and Gyro compass. The navigation 

system also marked the analog seismic records every 300 m. Navigators kept 

the trackline maps up-to-date by plotting in real time the positions of the 

shot points. Regularly updated copies were used by the seismic 

interpreters.

The third phase of seismic data gathering was carried out aboard the 

R/V CARANCAHUA using an ORE monopulse boomer system, which was very 

successful in shallow water. This system, ideal for small boat use, 

provided high-resolution seismic records of both shallow and moderate depth 

of penetration (0-250 m). The analog recorder was set at a 1/4 second sweep 

and the filter settings at 200 Hz-4000 Hz. All information was taped
Dauphin I stand

Ship Island Petit Bait Island

\

Chandeleur

Islands

Figure 2. Trackline map of study area

4

=? KM. 

=?N.M.
including seismic signals, time, shotpoint, and navigation. Navigation was 

obtained from a Northstar Loran C receiver and the navigators provided a 

real-time track map. Shotpoints were plotted every 5 minutes and also 

annotated on the analog records.

Interpretation of seismic records collected by the R/V GYRE started as 

soon as work copies of the analog records were available. Most 

interpretation activities were directed toward correlation of stratigraphic 

units throughout the area, and preliminary isopach maps were prepared. 

Bathymetry and trackline maps were completed in rough draft. All this 

preliminary work provided valuable assistance when more detailed 

interpretations and finalizing of statigraphic units began using 

post-plotted navigation maps.

Trackline Map

A trackline-shotpoint map was produced plotting all seismic lines 

collected aboard the R/V GYRE and the R/V CARANCAHUA. Two sets of 

preplotted tracklines for the principal cruise aboard the R/V GYRE were 

chosen. One ran northwest-southeast, and the other ran northeast-southwest. 

The main reason for deviation line headings from the traditional north-south 

and east-west headings was to obtain seismic lines parallel and 

perpendicular to the shelf-break. To avoid confusion with shotpoint 

numbers, tracklines running in northwest to southeast directions were 

numbered from 100 to 122, and those lines running from northeast to 

southwest from 200 to 222. In both cases, numbering started at the northern 

end of the area and increased toward the south. Tracklines were spaced 5-km 

apart, and shotpoints were labelled at 300-m intervals. The navigation 

post-plot system of the U.S. Geological Survey plotted every second point 

and labelled every tenth shot point. Seismic lines were positioned near 

preploted tracklines except in cases where avoidance of course obstacles, 

such as platforms, was necessary for ship safety. The additional seismic 

lines collected aboard the R/V CARANCAHUA increased the accuracy of geologic 

interpretation and filled in missing areas. Line headings were chosen 

according to geology as well as to provide tie lines with the seismics 

collected aboard the R/V GYRE. Shotpoints were numbered consecutively. The 

combined postplots of both vessel operators are presented in Figure 2.

GEOLOGIC SETTING

The topography and subsurface sediment characteristics of the 

Louisiana-Mississippi continental shelf and upper continental slope are the 

result of depositional sequences of delta outbuilding over transgressive 

sediments with intervening periods of erosion during low sea level stands. 

Little evidence of structural deformation such as faults, diapirs, and 

shallow gas is present on the shelf. In contrast, the upper slope has 

indications of occasional diapirs with associated faulting. In addition, 

the upper sedimentary column of the continental slope contains a few minor 

faults and scarps resulting from sediment slumping. Surface sediments over 

the entire area relate to several different depositional periods and can be 

seen as complete sequences, although they are not present at all locations 

of the shelf and upper slope (Frazier, 1974).
PRODUCT PRESENTATION

All original seismic data records were microfilmed and good quality 

vellum copies were made. Navigational post-plots were used to produce a 

trackline map with numbered shotpoints and labeled line numbers. Using the 

information from the 12-kHz precision depth recorder, a bathymetry chart was 

prepared. Interpretation of seismic records resulted in the following maps:

1) surface and near-surface structure

2) diapir and fault distribution

3) buried stream channels

4) shallow gas and buried oyster banks

5) buried delta lobes

6) isopachs of two stratigraphic units, and

7) structure contour of three stratigraphic horizons.

In addition to the above-mentioned products, we produced surface 

sediment distribution and surface water current maps along with base maps of 

the sampling and drift bottle drop stations.

BATHYMETRY

Bathymetric charts (Fig. 3) of the Louisiana-Mississippi continental 

shelf and upper continental slope were compiled using uncorrected velocities 

because of the shallowness of the area. Depth was calculated using the 

velocity of sound as 1500 meters per second and mean sea level as datum. 

These charts compare favorably to the National Ocean Survey 1972 map 

(NOS 0906N-14). Any differences are likely due to density differences of 

data points. The NOS data formed a considerably tighter grid than the 5-km 

grid of the present project. Our bathymetric charts were needed to 

facilitate the basic understanding of the area, and also because the data 

points for the NOS map were unavailable.

The bathymetry of the entire area is rather smooth. The area was 

divided arbitrarily into three regions on the basis of average slope 

gradient. The Louisiana-Mississippi continental shelf is a broad, flat, 

very gently sloping, sea floor ranging in water depth from about 10 to 75 m. 

The average slope gradient across the shelf is <0.1°. The shelf break is 

located at a depth of 75 m and its orientation is east-northeast to 

west-southwest. The second region between depths of 75 to 400 m is a gently 

sloping sea floor of relatively equal width with an average slope of 1.0°. 

The third region, covering water depths of 400 to 940 m, is located in the 

southeast corner of the area. This region has a relative steep slope with 

an average gradient of 2.0° to 2.5°.

SURFACE AND SHALLOW SUBSURFACE FEATURES

The high-resolution seismic records obtained with the 3.5-kHz system 

were used to produce a surface and shallow subsurface structure map (Fig. 

4). Surface features mapped were principally areas of topographic relief 

and faults breaking the sediment surface or coming within 5 m of sediment 

surface (Fig. 5). The continental shelf in the area contains few 

significant faults and the main topographic features are sand waves or the 

remains of relic barrier beaches (Frazier, 1974) found at several locations. 

The largest and best defined area is just southeast of the Chandeleur
tf'oo'

Figure 3. Bathymetric map of shady area,
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Figure A. Surface and shallow subsurface structure map
JO'IS jjCT

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FAULTS CROSSING MORE THAN 

ONE DATA LINE

FAULTS ONLY SEEN IN 

ONE DATA LINE

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Figure 5. Surface faulting (within 5 ms of sediment surface). Hachures on 

downthrown side.
Islands. In this region the sand waves or relic barrier beaches trend 

northeast-southwest with several crest and trough sequences. The relief of 

these sandy features can be as high as 5 m, ranging from -1 m to +4 m when 

compared to the surrounding area. Not only were shelf faults uncommon, but 

associated structures were not obvious. Subsurface faults (not coming 

within 5 m of surface) appear scattered throughout most of the shelf 

(Fig. 6).

The upper slope, designated by the bathymetric gradient change, 

contains more faults and several large topographic features. Most of the 

faults are related to sediment movement perpendicular to the shelf break or 

with sediment shifting caused by diapiric action. An exception was the 

impressive graben system (Fig. 7) that is located perpendicular to the shelf 

break at the south end of the area. The graben extends down almost the 

entire slope (Jim Coleman, pers. commun.). Mass sediment movement such as 

slumping is not seen. Only minor faulting parallel to the shelf break 

indicates slight sediment movement down slope. The main features of the 

upper slope are six diapirs (Fig. 8). Three of these diapirs disrupt 

surface sediments and the others show topographic relief but do not disrupt 

surface sediments. The latter only shows sediment disturbance at depth and 

have intruded only near enough to bow-up surface sediments forming rounded 

minor topographic highs.

The three diapirs showing disruption of the sea floor exhibit different 

stages of development. The apparently oldest diapir is located at the shelf 

break and has approximately 15-m relief. The top of the uplift is planar 

and exhibits an angular unconformity on the seaward side. This indicates 

the top is an erosional surface. There are progradational sediments 

landward but are absent on top. The beds below the erosion show drag and 

truncation on the diapir's sides. The diapir appears to have principally 

moved previous to the last lowstand of sea level. Apparently during the 

lowstand, the emergent diapir was eroded to sea level and was submerged as 

sea level rose. The recent sediment disturbance along the diapir flanks 

indicate continuing movement. The second form of diapir is on the ou-ter 

shelf and has a topographic relief of approximately 20 m with possibly an 

associated hard bank. There are fold-parallel beds on top of the diapir but 

the beds are not greatly deformed. The internal diapir mass is chaotic. 

The parallel beds surrounding the diapir show upward drag and truncation. 

There are progradational sediments on either side of the feature and no 

erosion is apparent. This indicates that the uplift movement occurred 

before the delta deposition of Unit 2 but after the most recent low stand of 

sea level. The third type and largest of the diapirs is located on the 

upper slope. The diapir has a very hummocky surface and a chaotic 

subsurface. This intrusion appears to have pushed up and then collapsed 

(Fig. 9). Even after collapse, topographic relief of some parts is 

approximately 100 m above the surrounding surface. There is no evidence of 

erosion. The surrounding beds are truncated and have been dragged up along 

the sides of the diapir. The top of the diapir does not have sediment drape 

or indication of recent sedimentation. This implies that movement of this 

diapir is very recent and may be continuing today.

SEDIMENTARY SEQUENCES

A sedimentary sequence is defined as a seismic stratigraphic unit 

containing a major regression and a major transgression, with all associated

10
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FAULTS ONLY SEEN IN 

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Figure 6. Subsurface faults (not reaching 5 ms of seafloor) 

downthrown side.

11

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Figure 7. Graben of upper slope, described from air gun profile.

12
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Figure 8. Diapiric activity of area,

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events included. Therefore, the division of geologic events is controlled 

by the relative rise and fall of sea level (Beard and others, 1982). The 

base of the lower sequence is bounded by a shelf-wide erosional 

unconformity, and the majority of succeeding deposition was formed by 

transgressive sediments and progradational delta deposits. The upper 

sequence also has a shelf-wide erosional unconformity as its base, which is 

overlain by a major transgressive deposition and recent deltaic sediments of 

the St. Bernard Delta.

Four major unconformities were originally selected for mapping. They 

were called, from younger to older, horizons A, B, C, and D and correlated 

well with Berryhill (pers. commun., 1982). Erosion during the forming of 

horizon A and little deposition following the underlying horizon B made a 

consistent separation of these two horizons impossible and therefore the 

horizon A-B will be discussed as A only. Horizons A, C, and D were mapped 

throughout most of the area (Fig. 10). Horizon D is the only one that can 

be carried across the shelf break while horizons A and C disappear on the 

outer shelf. Although horizon C could not be mapped across the shelf break, 

a more or less parallel reflector (horizon C 1 ) could be mapped on the upper 

slope. The seismic character of the sediments deposited upon horizon C 1 

indicates that their deposition may have occurred during the formation of 

horizon C.

The mapped horizon D is the base of the lower sequence designated here 

as Unit 2 (Fig. 11). This horizon, referred to as an erosional 

unconformity, is an even surface with little relief and with a very gentle 

slope toward the shelf break (Fig. 12). Although no evidence of horizon D 

can be found on the upper continental slope, it was probably related and 

partly formed by a low stand of sea level. With the shelf being eroded to a 

flat surface, a transgressive sea would quickly cover most of the shelf. 

This is evident in the thickness of transgressive sediments on the inner 

shelf and their relative thinness on the outer shelf (Frazier, 1974). 

Deposition on the inner shelf area is evidenced seismically by a 

parallel-type bedding (transgressive sediments) which shows heavy channels. 

This suggests that any stillstands of sea level following the transgression 

did not contribute much sediment to the area. The channeling of the inner 

and mid-shelf (Fig. 13), that occurred during the ensuing regression, can be 

divided into three groups according to the location of the channel within 

the unit (Figs. 14, 15, 16). These indicate at least three levels in 

channel patterns and may reflect pulses in the total regression of the sea.

The earliest stage of stream erosion occurred along the inner shelf 

with the channels cutting through the entire Unit 2. These streams showed 

little meandering and had a narrow flood plain. The second stage of erosion 

occurred when the regression stopped at the mid shelf. Most streams during 

this stage did not channel to the bottom of the unit, but reworked sediments 

deposited during the previous stage. The streams of this second stage 

meandered slightly more than during the first stage; however, they did not 

link with the streams of the first stage which suggests a change in the 

drainage pattern. The last stage of stream erosion of Unit 2 affected only 

the uppermost sediments, again indicating a reworking of the sediments 

deposited during the earlier stages. This set of streams terminated at what 

appears to be the shelf break of that time period. There was only a slight 

change in drainage pattern from the second stage with the sediments of the 

prograding delta controlling the drainage. A major stillstand occurred

15
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Figure 10. Horizons A, C, and D, as interpreted from a Minisparker 

seismic section.

16
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Figure 11. Isopach map of Unit 2,

17
Figure 12. Structure contour map of Horizon D.

18
30-19 j-

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S O S

N

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Figure 13. Channel pattern of entire Unit 2 inferred from seismic reflection 

profiles. Center lines = channel axes. Surface coverage of the channels 

is shaded.

19
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z»-oo' jFigure 14. Channel pattern representing the earliest stage of stream erosion 

during the period of Unit 2.

20
S_____O_____3_____10_____IS

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Figure 15. Channel pattern representing the middle stage of stream erosion 

during the period of Unit 2.

21
N

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iroai jFigure 16. Channel pattern representing the youngest stage of stream erosion 

during the period of Unit 2.

22
midway through the regression leading to an outbuilding of a series of 

progradational deltaic deposits beginning at mid-shelf and building out 

laterally to the shelf break. These deltaic deposits formed the thickness 

portion of Unit 2 and are characterized by megaforeset and bottomset 

bedding. The lateral extent of the delta system to the east, south, and 

west is shown in Figure 17. The northern limit is not apparent because of 

the limitations of the survey coverage. In support of the seismic data, 

well borings in the general area cored through sediments from Unit 2 and 

suggest deltaic deposition (i.e. clay overlain by fine sandy clay with 

shells). Near the shelf break, delta lobes with topset, foreset, and 

bottomset bedding are discernible. /The slope sediments in front of the 

delta deposition are seismically characterized by thinner parallel-type 

bedding. The final delta lobe appears to have been deposited during a 

higher stand of sea level indicating a temporary rise of sea level before 

the final plunge to the low stand near or beyond the shelf break.

Horizon C is an erosional unconformity formed during the low stand of 

sea level following deposition of Unit 2. The onlapping slope sediments 

(Fig. 18) overlying horizon C 1 were probably deposited during shelf erosion 

and the point of onlap on the slope was possibly just below the location of 

sea level during formation of horizon C. Again the shelf was eroded and 

horizon C was a relatively flat surface in this area (Fig. 19). The 

following transgression was probably rapid and only a thin drape of sediment 

was deposited on the outer shelf with no measurable deposit on the shelf 

break. The east side of the area shows a uniform increase in thickness of 

the transgressive sediments landward (Fig. 20) indicating a steady rise in 

sea level. Data from borings in this area show that the lower part of Unit 

1 was made up of soft gray clayey silt.

Before reaching the present sea level, at least one minor regression 

occurred which lowered sea level to the mid-shelf. This formed a channeling 

system (Fig. 21) and horizon A which is an erosional unconformity that 

disappears at mid shelf (Fig. 22). Once the sea started to rise again, 

shallow areas in the northwest part of the area became covered with oyster 

reefs (Fig. 23). The reefs were interpreted from seismic records as hard 

jagged horizons with acoustic blank zones located directly beneath them 

(Fig. 24). The oyster reefs appear to have grown upon horizon A and 

therefore indicate an estuarine environment during the early Holocene.

As present day sea level was reached, very little deposition occurred 

in the area until the St. Bernard Delta complex started to form. This 

Mississippi River deposition was the most recent geologic event and covered 

the northwest corner of the region. It thins evenly from the northwest to 

the southeast and has very little internal seismic structure except for 

minor foreset bedding at pinchout on the shelf (Fig. 25). Almost all 

interpreted shallow gas occurs in the St. Bernard Delta sediments just 

offshore of the Chandeleur Islands chain (Fig. 26). Interpretation of gas 

pockets from high-resolution seismic records are based on the commonly 

accepted practice dealing with small areas with no acoustic return (Fig. 

27). The rapid deposition of highly organic sediments during the St. 

Bernard Delta deposition was probably responsible for shallow gas formation. 

Coleman (1976) provided an extensive discussion of the St. Bernard 

progradation and subsequent reworking. Data from borings show normal 

deltaic sequences (i.e. clay with sandy silt overlain by clay with sand, 

overlain by a fine sand) which are still in the process of being reworked.

23
0

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DELTA FRONT PRESENT

DELTA FRONT NOT PRESENT

DELTA EXTENT UNKNOWN

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CENTER LINES INDICATE 

DRAINAGE PATTERN

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Figure 17. Extent of deltaic outbuilding of Unit 2

24
N

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5______0 5_____ 10 15

CONTOUR INTERVAL 

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Figure 18. Isopach map of regressive sediments overlying Horizon C 1

25
2m TO 70 METER DEPTH 

5m TO MAXIUM DEPTH

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Figure 19. Structure contour map of Horizon C,

26
30V

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CONTOUR INTERVAL 

1 METER

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Figure 20. Isopach map of the transgressive sediments forming Unit 1,

27
N

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Figure 21. Channel pattern observed in Unit 1, 

surface. Center lines - channel axes.

Shaded area - channel

28
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Figure 22. Structure contour map of Horizon A.

29
53*'5 - K

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AREA OF PATCH REEFS

Figure 23. Distribution of buried oyster reefs (shaded area)

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0.5

KM

ST. BERNARD DELTA SEDIMENTS OYST

KM
 I 

CONTOUR INTERVAL 

1 METER

19-00 j- -l l»'C

Figure 25. Isopach map of St. Bernard Delta,

32
CO 

CD

zs-oc I 

Figure 26. Distribution of gas-charged sediments in Unit 2

33
LU

I to

CVJ

o

to 

o

I 

to

N 

O

to

CVJ

I 

to

CV1

o

IO

o

I

IO 

N 

O

O

i

10

CVl

u spuooes

Figure 27. Example of shallow gas ^Interpretations from 3.5-kHz profiles

34
GEOLOGIC HISTORY

The geologic history of the eastern Louisiana-Mississippi continental 

shelf, indicated by this study, shows seven major stages of shelf 

development since the middle Pleistocene. Seismic interpretations were 

combined to form an idealized composite of shelf and upper slope 

stratigraphy (Fig. 28). The oldest stage was an erosional shelf surface 

probably exposed by a low stand of sea level (Fig. 29). This was followed 

by a rising sea depositing transgressive sediments (Fig. 30). The position 

of the high stand of sea level may have been higher than present sea level. 

The river channeling of the shelf transgressive deposits indicates that the 

third stage of development (Fig. 31) was begun by a lowering of sea level. 

This regression was probably not a smooth recession of the sea, but a 

stepped withdrawal producing at least three levels of river cutting. One 

stillstand produced progradational delta deposits and probably a minor 

transgression followed (Fig. 32). This development is considered a major 

event because of the directly related large volume of sedimentation. The 

slightly higher sea level partly backfilled river channels and produced a 

delta lobe at a slightly higher elevation than previous delta deposits. The 

fifth stage was formed during the most recent low stand of sea level (Fig. 

33). During this time the exposed shelf was eroded and regressive sediments 

were deposited on the upper slope. Rising sea level brought transgressive 

sedimentation to the inner shelf and stage six of development (Fig. 34). A 

minor regression during this rise in sea level formed small river channels 

on the inner shelf and portions of the area developed oyster reefs. The 

most recent stage of shelf development was produced as the sea reached 

present day level (Fig. 35). The St. Bernard Delta was formed by the 

Mississippi River and prodelta deposits reached into the area. Since the 

depocenter of the Mississippi River is now outside the area and sea level is 

presently at a stillstand, little deposition is occurring on the 

Louisiana-Mississippi continental shelf.

Geologic Features

This study provides geologic information important to offshore 

development of the Louisiana-Mississippi continental shelf and upper slope. 

The shelf surface is relatively flat with only minor areas of slight relief. 

The only surface features of interest that appear on the upper slope are 

diapiric action that has created a few large protrusions on the sea floor. 

Shelf faulting is random and in most cases is minor. The upper slope has a 

few apparently active faults mainly associated with diapiric uplift. Some 

upper slope faulting is found parallel to the shelf break indicating 

slumping but most of these faults are small and no sign of mass movement is 

found. Relatively large progradational delta sediment lobes are found at 

the shelf break and shoreward for several kilometers. Although delta 

sediments are usually formed rapidly and may be somewhat unstable, no 

indications of sediment adjustment are seen. Shelfwide river cutting 

produced outer shelf delta deposition and inner shelf erosion, but main 

river channels were not greatly developed. The shelf rivers seem to have 

been shallow and widely distributed. Further inshore, oyster reefs appear 

to have developed on a high area in the northwestern part of the study area. 

These reefs appear rugged and blanketing sediments seem disturbed but no 

surface indications are seen. These sediments are thought to be part of St. 

Bernard Delta deposition. The only shallow gas pockets observed are in the 

sediments of the St. Bernard. Although almost no gas was seen escaping from

35
LO

50 0 100 200 KM

Figure 28. Location of line 114.

PRESENT SEA LEVEL

SEA LEVEL

0 2-

HORIZON 0

VERTICAL EXAGGERATION 40i

Figure 29. Profile of Horizon D described from line 114. Depth in seconds: two
SECONDS

SECONDS

OQC

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03
the sediment into water column, apparently gas disturbed areas are observed 

very near the seafloor surface. In general, the study area is stable with 

almost no sediment movement on the shelf and only a few localized areas of 

movement on the upper slope. The geologic features of the entire area are 

almost all minor with only the diapirs of the upper slope creating any 

possible problems.

SEDIMENT DISTRIBUTION 

Methods

Sediment samples were collected from 75 sites throughout the LouisianaMississippi OCS area (Fig. 36). Sites were located at alternating 

intersections of the seismic grid (10 km spacings), and were selected to 

provide a reasonable coverage of the continental shelf and upper continental 

slope areas. Samples were collected from the upper 18 cm of sea-floor 

sediment by means of a clam-shell grab sampler. Fifty-eight samples were 

collected during R/V GYRE cruise G-18-6 in April 1981; the remaining 17 

samples were collected during R/V CARANCAHUA cruise C-81-2 (Appendix 1). 

Navigation during the R/V GYRE cruise was accomplished with an integrated 

navigation system, while LORAN-C was used during the R/V CARANCAHUA cruise.

Textural analyses were performed in the laboratory on representative 

splits of the sediment samples. The organic matter was removed by oxidation 

in a 30 percent hydrogen peroxide solution. The samples were washed to 

remove soluble salts, and then dispersed in a 0.5 percent calgon (sodium 

hexametaphosphate) solution. After dispersion, the samples were separated 

by means of wet-sieving into gravel (>2 mm), sand (2 mm-63 urn), and mud 

(<63 ym) fractions. The term "mud" as used in this report covers the 

combined silt and clay-sized fractions of the sediment.

Grain-size distributions of the mud fractions were determined using a 

16-channel model TA-II Coulter Counter. All Coulter analyses were conducted 

using a combination of 200-ym and 30-ym tube apertures, thus providing for 

an effective composite analytical range of 64 ym-0.630 urn size range. The 

electrolyte consisted of a 4 percent calgon solution prefiltered through a 

0.45 ym filter. For a more detailed description of the techniques of 

sediment analyses by the Coulter Counter, the reader is referred to Shideler 

(1976).

Grain-size distributions of the sand fraction were determined using a 

Rapid Sediment Analyzer settling tube similar to the instrument described by 

Schlee (1966). Sediment particle fall times were converted to phi-size 

cumulative percentages at a 0.5?J interval.

The analyses of the sand and mud fractions were integrated to produce a 

composite grain-size distribution at a 0.5^ interval over a 2 mm-0.49-um 

size range. The following textural relationships were derived using a 

computer program: 1) single component percentages - gravel, sand, silt, and 

clay (Appendix 1); 2) two component ratios - sand/mud and silt/clay; 3) 

composite classification based on mixed percentages of sand-silt-clay; and 

4) statistical grain-size parameters-moment measures of mean diameter, 

standard deviation, skewness, kurtosis, and modal diameters. The 

description of sediment properties given here is restricted to the composite 

classification based on mixed percentages of sand-mud.

40
"3

 7

^

4-:

8

to

* fa.

N

'/f

 3s-

*3(

 yy V?

' 70

MX

"fro

7/

*73

"70-

Figure 36.. Distribution of grab sample stations

41
DISCUSSION

Surficial sediments in the Louisiana-Mississippi OCS area are generally 

sand enriched. The average sand percentage of samples collected on the 

continental shelf (stations 1-66) is 56 percent; the average sand/mud ratio 

for those same set of samples is 8.88 percent. Accordingly, distribution of 

the surficial sediments is best illustrated by a composite classification 

emphasizing the sand-size fraction. Sediment type was determined using a 

two-component diagram (triangle) with the intervals patterned after Shepard 

(1954). The terminology for each sediment type is based on the percentage 

of sand-size material. Sediment types (Appendix 1) used in this report are: 

sand (75-100%); muddy sand (50-75%); sandy mud (25-50%); and mud (0-25%).

The distribution of the surficial sediments (Fig. 37) in the Louisiana 

Mississippi OCS area is the product of fluctuating sea level during late 

Quaternary. The sands on the southeast side and in the northeast corner are 

the oldest sediments in the study area. These orthoquartzite sands were 

derived from the Cretaceous and younger sedimentary mantle of the 

Appalachians (van Andel and Poole, 1960), and were emplaced as fluvial 

and/or beach deposits on the subaerial continental shelf during the last 

major low stand 18,000 years B.P. (Ludwick, 1964; Frazier, 1974). Ludwick 

reports these sands are probably a continuation of the sand basal facies of 

the central and Rio Grande shelf areas of the northwestern Gulf of Mexico 

(Curray, 1960). The seismically determined sand waves in the southeastern 

area have been interpreted as relic shoreline deposits formed during a 

temporary stillstand about 18,500-15,000 years B.P. (Frazier, 1974). Our 

findings are consistent with Frazier's interpretation.

The next major event affecting surficial sediments of the

Louisiana-Mississippi OCS area was the progradation of the St. Bernard Delta 

lobe over the eastern sands (Ludwick, 1964). The muds extending over most 

of the central region are prodelta clays. These muddy sediments are the 

approximate basinward limit of the finite zone of clay deposition during 

Recent times (Frazier, 1974). The muddy sands to the north, east, and south 

of the muds occur in a transition zone where lateral and vertical mixing of 

the prodelta clays and eastern sands has taken place. The two small areas 

of sandy mud within the prodelta clay are the result of mixing with the 

eastern sands (north) and Chandeleur Island sands (south). The southern end 

of the muddy sediment is a mixture of St. Bernard sediment and sediment 

presently being deposited by the active birdfoot delta of the Mississippi 

Delta. Seaward of this transition zone, the muddy sediment becomes finer, 

and the clay-sized muds of the continental slope are mainly pelagic.

About 450 years B.P., sea level rose transgressing over the St. Bernard 

subdelta, and the Mississippi River altered its course. Sand from the 

distributary-mouth sand bars was reworked in a landward direction by wave 

attack on the subsiding delta. Sand from the coalescing sand bars form the 

Chandeleur Islands, and Chandeleur and Breton Sound behind them (Ludwick, 

1964). The sand waves located in the sandy area southeast of the Chandeleur 

Islands are a relic shoreline that probably formed during a temporary 

stillstand. Murray (1976) reports that ebb-directed tidal flushing of the 

turbid Chandeleur-Breton Sounds estuary waters flow to the north and south 

of the Chandeleur Island chain. The patch of muddy sand, therefore, either 

represents settling of this finer-grained sediment into the naturally 

occurring depression, or may possibly be reworked lagoonal/tidal flat

42
t-"

Figure 37. Surficial sediment distribution of area.

43
sediments deposited behind the barrier ridge. The muddy sand and sandy mud 

north of the Chandeleur Island sands represent mixing with the prodelta 

clays. Modern sediments from the Chandeleur-Breton Sounds estuary and from 

the Mississippi Sound are also being deposited within the transition zone. 

The muddy sand and sandy mud south of the Chandeleur Island sands reflect 

the mixing of both the Chandeleur Island sand and St. Bernard prodelta clays 

with silty clays from the modern Mississippi Delta.

SURFACE DRIFT PATTERNS

In order to gain more insight into the surface circulation patterns of 

the Louisiana-Mississippi OCS area, three ballasted surface drifter bottles 

were released at 76 stations (Fig. 38) during R/V GYRE cruise G-81-6 in 

April 1981. Because of the paucity of circulation data in the area, 

comparison to previous studies was not possible. The purpose herein, is to 

report the results of this drifter study relative to the conditions during 

the study period.

A total of 228 bottles was released, and 79 (35%) bottles were 

recovered. The surface current patterns shown in Figure 39 are based on all 

returns, regardless of recovery interval. Drift bottles recovered within 

100 km of the release point are plotted with a medium arrow if recovered in 

0-42 days, and with a fine arrow if recovered more than 42 days after 

release. Drift bottles recovered over 100 km from the release point are 

plotted with the boldest arrow. Most of the bold arrow drifters were 

recovered beyond 42 days as they were recovered on the west coast of Florida 

(7 bottles), Florida Keys (1 bottle), east coast of Florida (3 bottles), or 

west of the Mississippi delta (Louisiana-7 bottles, Texas-15 bottles). The 

only bold arrow drifters recovered in less than 42 days were released from 

stations 38 (35 days), 60 (20 days), and 74 (13 days); the second bottle 

recovered from station 74 was recovered in 47 days. Release and recovery 

information for each bottle recovered is listed in Appendix 2.

The current patterns show four sectors of varying drift direction. The 

bottles released at the northeast stations drifted to the east along the 

Mississippi-Alabama-Florida coast. Movement in an easterly direction is 

consistent with the semi-permanent currents in this area (Scruton, 1956). 

The bottles at the five stations in the northwest corner were released on 

April 19, 1981, except for station 18 (April 15) and all bottles drifted to 

the southwest. Those five stations reflect a northeast wind for that date 

as recorded in Mobile, Alabama. Bottles released in the central portion of 

the study area were set to the northwest except for stations 38, 41, and 53 

which drifted to the southwest. Finally, the bottles released in the 

southern portion of the study area drifted to the southwest, and were 

recovered west of the delta, except station 63 which was set to the 

northwest.

Daily wind speed and azimuth as compiled by the National Oceanic and 

Atmospheric Administration (Daily Weather Maps, Week Series) indicate that 

the winds at Mobile, Alabama, were generally blowing from the northeast 

during the period from April 11-June 5, 1981. Comparison of wind speed and 

azimuth at New Orleans, Louisiana, in the same publication indicated the 

same general wind pattern.

44
30'/f' \-

 y

V7

 30

*'.??

%//»

'3c> 31

sz>

"1,0

70 "71

 7V

13

-7(f ^

Figure 38. Current drifter release stations

45
 1 

N

V \

Zf-00 [-

Figure 39. Surface current patterns of the area. Large arrows - greater than 

100 km. travel. Small arrows - less than 100 km. travel. Arrow/segments 

equal number of drifters recovered.

46
The general circulation pattern suggests that a combination of 

wind-stress induced circulation, semi-permanent currents discharge of water 

from the Mississippi River, and tidal motion around the Chandeleur-Breton 

Sounds estuary and the Mississippi Sound were interacting to produce a 

clockwise gyre in the study area. Drift bottles released in the southern 

area were not affected by discharge from the eastern distributary channels, 

and were driven by the wind to the west of the delta. River discharge and 

tidal motion north of the delta resulted in a northerly longshore current 

that deflected surface waters along the Chandeleur Islands and bent east 

along the Mississippi-Alabama barrier island chain. The recovery of a 

bottle released from station 12 on the west side of the delta could have 

resulted from movement from the northern end of the study area clockwise in 

the gyre to an area where the wind-induced northeast currents set it south 

of the delta.

Recoveries stretched from Freeport, Texas (356 miles to the west) to 

Flagler Beach, Florida (828 miles to the east). The results of this one 

drift bottle study indicates that substantially more studies are required in 

this area.

47
REFERENCES

Beard, J. H., Sangree, J. B., and Smith, L. A., 1982, Quaternary chronology, 

paleoclimate, depositional sequences, and eustatic cycles, American 

Association of Petroleum Geologists Bulletin, v. 66, no. 2, p. 158-169.

Coleman, J. M., 1976, Deltas: Processes of deposition and models for

exploration, Continuing Education Publication Company, Inc., 102 p.

Curray, J. R., 1960, Sediments and history of Holocene transgression,

continental shelf, northwest Gulf of Mexico, iti F. P. Shepard, F. B., 

Phleger, and T. H. van Andel, eds., Recent sediments, northwest Gulf of 

Mexico: Tulsa, Okla., AAPG, p. 221-266.

Frazier, D. E., 1974, Depositional episodes: their relationship to the

Quaternary stratigraphic framework in the northwestern portion of the 

Gulf basin, Bureau of Economic Geology, The University of Texas at 

Austin, Geological Circular 74-1, 28 p.

Ludwick, J. C., 1964, Sediments in northwestern Gulf of Mexico, in R. L. 

Miller, ed., Papers in Marine Geology, Shepard Commemorative Volume: 

New York, Macmillan Co., p. 204-238.

Murray, S. P., 1976, Currents and circulation in the coastal waters of

Louisiana, Louisiana State University, Center for Wetland Resources, 

Tech. Rept. 210, 32 p.

Schlee, J., 1966, A modified Woods Hole Rapid Sediment Analyzer, Journal 

of Sedimentary Petrology, v. 36, no. 2, p. 403-413.

Scruton, P. C., 1956, Oceanography of Mississippi Delta sedimentary

environments, American Association of Petroleum Geologists Bulletin, v. 

40, no. 12, p. 2864-2952.

Shepard, F. P., 1954, Nomenclature based on sand-silt-clay ratios, Journal 

of Sedimentary Petrology, v. 24, no. 3, p. 151-158.

Shideler, G. L., 1976, A comparison of electronic particle counting and 

pipette techniques in routine mud analysis, Journal of Sedimentary 

Petrology, v. 46, no. 4, p. 1017-1025.

van Andel, T. H., and Poole, D. M., 1960, Sources of Recent sediments in the 

northern Gulf of Mexico, Journal of Sedimentary Petrology, v. 30, no. 

1, p. 91-122.

48
APPENDIX 1. Surficial sediments: Station locations, sediment type, gravel percentage 

sand, silt, clay percentage (percentages of nongravel (<2mm) fraction)

Station 

number

1*

2*

3*

4*

5*

6

7

8*

9

10

11*

12*

13

S 14

15*

16

17

18*

19

20

21A

21B

22

23

24

25

26

27

28

29*

30

31

Latitude (N)

30°10.0'

30°10.0'

30°10.0'

30°06.3 ?

30°06.3'

30°06.26'

30°06.17 ?

30°02.7'

30°02.71'

30°02.60'

29°58.7 f

29°58.7'

29°58.80'

29°58.48

29°55.4'

29°55.57 ?

29°54.90'

29°51.6'

29°51.70'

29°51.74

29°51.64 ?

29°51.64 ?

29°47.30'

29°47.49 ?

29°47.14'

29°43.65 !

29°43.53 ?

29°43.23'

29°43.59'

29°40.0'

29°40.07'

29°40.09'

Longitude (W)

88°41.1'

88°32.7'

88°23.9'

88°46.4'

88°36.9'

88°28.61'

88°19.74 ?

88°41.1 ?

88°32.69'

88°24.06'

88°46.4'

88°36.9'

88°28.62'

88°19.81'

88°41.1'

88°32.70'

88°23.98'

88°46.4'

88°36.86'

88°28.61'

88°19.72'

88°19.47'

88°40.99'

88°32.83'

88°24.02'

88°46.36'

88°36.78'

88°28.69 ?

88°19.50'

88°49.2'

88°40.98'

88°32.83

Sediment type

Muddy sand

Sand

Sand

Sandy mud

Sand

Sand

Sand

Sandy mud

Sand

Sand

Muddy sand

Muddy sand

Muddy sand

Muddy sand

Sandy mud

Mud

Muddy sand

Muddy sand

Mud

Mud

Sand

Muddy sand

Sandy mud

Mud

Muddy sand

Sand

Mud

Mud

Muddy sand

Sand

Sandy mud

Mud

Gravel 

percentage

0.72

0.81

0.23

4.34

0.95

0.17

0.38

0.35

2.43

0.60

3.86

0.17

1.24

1.46

2.49

0.26

1.16

0.05

0.03

0.28

0.41

1.22

1.98

0.21

0.50

2.29

0.17

0.10

1.34

0.03

0.39

0.17

Sand 

percentage

74.46

97.62

98.58

38.87

92.79

98.81

98.67

44.50

78.66

94.24

51.22

51.86

62.96

74.40

30.98

20.82

61.22

68.38

11.25

21.03

75.55

72.91

32.96

9.11

59.14

96.38

14.37

9.48

68.02

95.46

47.32

12.26

*Samples collected during R/V CARANCAHUA Cruise C-81-2; other samples collected during 
Station 

number

32

33*

34

35

36

39*

40

41

42

43*

44*

45

46

47

48

49*

g 50

51

52

53

54*

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

Latitude (N)

29°39.88'

29035.9.

29° 35. 74'

29°36.00'

29°35.84'

29°32.2'

29°32.16'

29°31.99'

29°33.07'

29°28.3'

29°28.3'

29°28.21'

29°27.87'

29°28.26'

29°28.33'

29°45.5f

29°24.60'

29°24.53'

29°24.42f

29°24.62

29°20.8'

29°20.87'

29°20.94'

29°20.67'

29°20.84'

29°17.21f

29°17.17'

29°17.48'

29°17.20'

29°13.45'

29°13.47'

29°13.69'

29°13.59'

29°09.67'

29°09.76'

29°09.99f

29°05.79'

29°05.77f

Longitude (W)

88°23.82'

88°53.6'

88°46.49f

88°36.96f

88°28.40f

88°49.2'

88°40.95'

88°32.09'

88°23.70f

89°02.0f

88°53.6

88°46.10'

88°36.68f

88°28.48f

88°19.80f

88°57.5'

88°48.45f

88°41.20f

88°32.46f

88°23.77f

88°53.6f

88°46.24f

88°36.97f

88°28.50 f .

88°19.79f

88°49.08f

88°41.04'

88°32.74f

88°23.83f

88°46.30'

88°36.72f

88°28.77f

88°19.76'

88°41.06'

88°32.59f

88°23.68f

88°46.34'

88°36.57f

Sediment type

Muddy sand

Sand

Muddy sand

Sand

Sandy mud

Sand

Sand

Mud

Muddy sand

Muddy sand

Sand

Sand

Sandy mud

Mud

Sand

Muddy sand

Sand

Mud

Mud

Sand

Sandy mud

Mud

Mud

Muddy sand

Sand

Mud

Mud

Muddy sand

Sand

Mud

Mud

Mud

Sand

Mud

Mud

Mud

Mud

Mud

Gravel 

percentage

0.19

0.03

0.26

0.01

0.74

0.18

0.44

0.13

1.57

0.05

0.03

0.38

0.10

0.14

1.33

0.01

0.04

0.03

0.75

0.54

0.05

0.02

0.02

1.75

2.90

0.02

0.10

0.96

0.33

0.00

0.07

0.02

5.07

0.46

0.00

0.04

0.09

0.05

Sand 

percentage

57.28

94.78

51.63

95.11

46.13

74.98

97.37

14.56

64.05

72.38

97.86

92.39

29.41

21.08

86.76

52.15

75.04

11.04

21.38

81.41

47.92

3.07

9.54

67.70

95.08

2.71

3.13

71.75

93.60

0.83

21.84

7.50

86.52

5.00

41.46

1.07

5.82

0.68
Station 

number

72

73

74

75

76

Latitude (N)

29°05.93'

29°06.06'

29°02.53'

29°02.90'

29°02.39'

Longitude (W)

88°28.A1'

88°19.61

88°40.91'

88°32.29'

88°23.97'

Sediment, type

Mud

Mud

Mud

Mud

Mud

G ravel 

percentage

0.02

0.01

0.06

0.02

0.04

Sand 

percentage

1.13

2.41

0.62

0.75

1.53
APPENDIX 2. Surface Drift Patterns: 

recovery data

Station location, drift bottle numbers, and relea

Station 

number

1

1

2

2

2

3

4

5

6

7

8

9

10

11

11

11

12

13

14

14

15

15

15

16

17

18

18

Latitude (N)

30°10.74'

30°10.74'

30°10.41'

30°10.41'

30°10.41'

30°10.44'

30°06.94'

30°06.66'

30°06.36'

30°06.26'

30°03.20'

30°02.79'

30°02.50'

29°58.99'

29°58.99'

29°58.99'

29°59.20'

29°59.01'

29°58.77'

29°58.77'

29°55.26'

29°55.26'

29°55.26'

29°55.57'

29°55.15'

29°51.63'

29°51.63'

Longitude (W)

88°39.47'

88°39.47'

88°31.35'

88°31.35'

88°31.35'

88°24.01'

88°44.83'

88°35.73'

88°27.57'

88°19.24'

88°40.89'

88°31.73'

88°23.24'

88°44.60'

88°44.60'

88°44.60'

88°36.54'

88°27.66'

88°19.29'

88°19.29'

88°40.46'

88°40.46'

88°40.46'

88°32.51'

88°23.67'

88°44.86'

88°44.86'

Drift 

bottle 

number

3394

3395

3397

3398

3399

3424

3489

3391

3401

3430

3389

3502

3503

3504

3493

3387

3403

3405

3409

3410

3411

3482

3517

3518

Release 

date

4-18-81

4-18-81

4-18-81

4-18-81

4-18-81

4-20-81

4-19-81

4-18-81

4-18-81

4-21-81

4-19-81

4-18-81

4-18-81

4-19-81

4-19-81

4-19-81

4-19-81

4-18-81

4-18-81

4-18-81

4-19-81

4-19-81

4-19-81

4-19-81

4-18-81

4-15-81

4-15-81

Recovery 

date

5-3-81

7-1-81

5-23-81

6-9-81

5-3-81

6-4-81

5-23-81

6-5-81

7-15-81

6-5-81

5-9-81

7-4-81

5-2-81

5-3-81

6-4-81

11-8-81

6-12-81

9-29-81

4-30-81

8-1-81

6-14-81

6-2-81

4-18-81

4-18-81

Recovery 

interval

15

74

35

52

15

45

34

48

88

 45

21

76

13

14

46

204

48

164

11

98

56

45

3

3

Reco

Dauphin I

Horn Isla

Petit Boi

Petit Boi

Dauphin I

from west 

Destin, F

Curlew Is

Destin, F

Sugarloaf 

American 

Pensacola 

No bottle

Chandeleu

lighthous

No bottle

Chandeleu

Chandeleu

Chandeleu

lighthous

Grand Isl

Flager Be

Lauderdal

Titusvill

cross ove

Curlew I

Chandeleu

St. Andre

No bottle

Chandeleu

Chandeleu

88°50.0'W

Chandeleu

88°50.0'W
Station 

number

18

19

20

21A

21B

22

23

24

25A

25A

25A

25B

25B

26

27

28

29

30

30

31

31

31

32

34

35

35

36

Latitude (N)

29°51.63I

29°51.38I

29°51.68f

29°51.29f

29°51.75I

29°47.88f

29°47.42'

29°47.35'

29°44.76f

29°44.76'

29°44.76f

29°44.24f

29°44.24f

29°44.39f

29°43.42f

29°43.80f

29°39.82'

29°40.72f

29°40.72'

29°40.27'

29°40.27f

29°40.27'

29°39.90f

29°36.71f

29°36.95'

29°36.95'

29°36.03'

Longitude (W)

88°44.86'

88°36.25f

88°28.28'

88°19.45'

88°19.66f

88°40.86'

88°31.97'

88°23.91'

88°45.39f

88°45.39'

88°45.39'

88°44.70'

88°44.70'

88°37.10f

88°28.66'

88°19.60f

88°48.16'

88°41.14f

88°41.14f

88°32.55'

88°32.55f

88°32.55'

88°23.88f

88°44.90'

88°37.10f

88°37.10f

88°28.19f

Drift 

bottle 

number

3519

3501

3514

3515

3516

3427

3428

3523

3545

3541

3474

3512

3513

3526

3527

3528

3476

3509

3510

3530

Release 

date

4-15-81

4-19-81

4-19-81

4-19-81

4-21-81

4-15-81

4-19-81

4-21-81

4-15-81

4-15-81

4-15-81

4-21-81

4-21-81

4-15-81

4-21-81

4-22-81

4-14-81

4-15-81

4-15-81

4-15-81

4-15-81

4-15-81

4-19-81

4-14-81

4-15-81

4-15-81

4-15-81

Recovery 

date

4-18-81

6-1-81

4-18-81

9-5-81

5-2-81

5-2-81

5-2-81

4-18-81

6-1-81

6-7-81

4-18-81

5-3-81

5-30-81

8-15-81

5-3-81

4-29-81

4-25-81

12-15-81

4-25-81

4-24-81

Recovery 

interval 3

433

143

17

11

113

41

464

18

45

122

18

14

11

244

109

Chan

88°

No b

Daup

Gulf 

No b

No b

No b

No b

No b

Cha

of 

Horn 

end

Cha

Cha

of 

Cha

of 

Cha

of 

Cat 

Dee

Cur

Cha

woo

Cha

Hor

Hor

sou

Cha

No 

Cha

Pt.

Cha

Cha

cha

Cur
Ln

Station 

number

36

37

38

39

AO

Al

Al

42

AA

A5

A6

A7

48

A9

50

51

52

53

54

55

56

56

57

58

59

60

61

62

63

Latitude (N)

29°36.03f

29°36.03'

29°32.A8f

29°32.74f

29°32.95f

29°33.00f

29°33.00f

29°32.53f

29°28.A9f

29°32.36f

29°30.19f

29°29.20f

29°28.A3'

29°25.20f

29°2A.68f

29°26.AO'

29°26.37f

29°25.27f

29°21.AAf

29°20.93f

29°21.87f

29°21.87f

29°22.15f

29°21.5A !

29°17.67f

29°17.A8f

29°18.39'

29°18.86f

29°13.78f

Longitude (W)

88°28.19f

88°19.65f

88°56.76f

88°52.15f

88°A0.82f

88°32.89f

88°32.89f

88°2A.19f

88°52.66f

88°A8.5Af

88°37.91 !

88°28.96f

88°19.86f

88°57.26'

88°A8.60f

88°A2.20f

88°33.91f

88°2A.65f

88°51.17f

88°AA.50f

88°38.31f

88°36.31f

88°29.39f

88°20.52f

88°A9.08f

88°A0.75f

88°33.59f

88°26.98f

88°AA.93f

Drift 

bottle 

number

3531

33A2

3505

3506

35 3 A

3339

3467

3435

3336

3438

3A51

33A5

3331

3A60

3A61

3449

332A

3AAA

3352

Release 

date

4-15-81

4-19-81

4-12-81

4-14-81

4-14-81

4-15-81

4-15-81

A- 15-81

4-12-81

4-14-81

4-14-81

4-15-81

4-15-81

4-12-81

4-12-81

4-14-81

A- 14- 81

4-15-81

4-12-81

4-12-81

4-14-81

4-14-81

4-14-81

4-15-81

4-12-81

4-12-81

4-14-81

4-14-81

4-12-81

Recovery 

date

4-25-81

5-17-81

7-29-81

12-16-81

5-7-81

5-1A-81

4-25-81

6-8-81

5-30-81

5-16-81

6-9-81

6-4-81

4-25-81

6-1-81

7-A-81

6-12-81

5-2-81

5-23-81

5-16-81

Recovery 

interval

10

35

105

2A5

22

32

11

55

A8

32

55

53

13

A8

81

58

20

39

3A

Rec

Chandele

Gulf side

No bottl

Elema Is

Caminada 

No bottl

No bottl

Grand Is

Pt. aux 

Chandele

lighthou

Chandele

Redfish 

Chandele

Mobile B

No bottl

No bottl

No bottl

Chandele

No bottl

Chandele

Redfish 

Timbalie

Perdido 

Chandele

High Isl

12A inte

Bolivar 

Rollover 

No bottl

Florida 

Pensacol

No bottl

Grand Is

No bottl

Chandele

pipeline

North Is
Station 

number

64

65

65

66

67

68

69

69

70

71

72

73

73

74

74

75

76

Latitude (N)

29°13.39'

29°14.40'

29°14.40'

29°15.06'

29°10.01'

29°09.62'

. 29°11.36f

29°11.36f

29°07.00'

29°06.19'

29°05.64'

29°06.79'

29°06.79'

29°02.39'

29°02.39'

29°02.29'

29°01.95'

Longitude (W)

88°36.40'

88°29.43'

88°29.43'

88°21.91'

88°40.82'

88°32.47'

88°26.23'

88°26.23'

88°45.94'

88°36.79'

88°28.18'

88°21.37'

88°21.37'

88°42.88'

88°42.88'

88°32.50'

88°24.10'

Drift 

bottle 

number

3327

3382

3383

3445

3355

3379

3380

3375

3360

3320

3376

3377

3371

3372

3362

3316

Release 

date

4-12-81

4-14-81

4-14-81

4-14-81

4-12-81

4-12-81

4-14-81

4-14-81

4-13-81

4-13-81

4-12-81

4-14-81

4-14-81

4-13-81

4-13-81

4-13-81

4-12-81

Recovery 

date

5-31-81

6-1-81

6-1-81

5-29-81

6-9-81

5-31-81

6-4-81

6-7-81

6-6-81

6-3-81

6-3-81

6-3-81

4-26-81

5-30-81

6-29-81

7-4-81

Recovery 

interval

49

48

48

45

58

48

51

55

54

52

50

50

13

47

77

83

Re

Boilers 

road to 

High Is

124 int

McFaddin 

Rim Sta

McFaddin 

Rim Sta

Crystal 

Port Bo

No bott

High Is

Hwy 124

High Is

Cameron

Ship Ch

High Is

Shorty'

Alligat

High Is

Cameron 

Grand I

Pass)

Galvest

High Is

Galvest