RC. 267

GEOLOGICAL SURVEY CIRCULAR 267

STRATIGRAPHY AND STRUCTURE 

OF OUTCROPPING PRE-SELMA 

COASTAL PLAIN BEDS OF 

FAYETTE AND LAMAR

COUNTIES, ALABAMA
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 267

STRATIGRAPHY AND STRUCTURE OF OUTCROPPING

PRE-SELMA COASTAL PLAIN BEDS OF 

FAYETTE AND LAMAR COUNTIES, ALABAMA

By Charles W. Drennen

Washington, D. C., 1953

Free on application to the Geological Survey, Washington 25, D. C.
STRATIGRAPHY AND STRUCTURE OF OUTCROPPING PRE-SELMA 

COASTAL PLAIN BEDS OF FAYETTE AND LAMAR COUNTIES, ALABAMA

By Charles W. Drennen

CONTENTS 

Page Page

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

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

Previous investigations ....................... 1

Nomenclature ................................ 3

Stratigraphy....... . ......................... 3

Tuscaloosa group ....................... 3

Coker formation ................... 3

Gordo formation.. . :............... 6

Stratigraphy Continued

Undifferentiated McShan and Eutaw 

formations .......................... 6

Structure ................................... 8

Historical summary ......................... 9

Conclusion ................................. 9

. Selected bibliography ......................... 9

ILLUSTRATIONS

Page

Plate 1. Geologic map of Fayette and Lamar Counties, Ala. ....................................... In pocket

2. Structure contour map of parts of Fayette and Lamar Counties ............................ In pocket

Figure 1 Index map of Alabama................................................................. 2

2. Map and section showing variations in thickness of Coker formation........................ 5

ABSfRACT

The Coastal Plain sediments of Fayette and Lamar 

Counties, Ala., are pre-Selma Late Cretaceous in age 

and are divided into three mappable units, from oldest 

to youngest: (1) the Coker formation, (2) the Gordo 

formation, and (3) a unit composed of the McShan and 

Eutaw formations undifferentiated. The Coker formation as here defined includes the Cottondale, Eoline, 

and Coker formations of earlier workers; the name 

Gordo is used as previously defined. The Coker and 

Gordo formations constitute the Tuscaloosa group. - 

Structure contours on fprmational contacts locally show 

marked irregularities that are partly the result of 

structural disturbances. Some of these disturbances 

were probably of post-Morreville (post-Austin) age.

INTRODUCTION

This report presents the general stratigraphic 

and structural relations of the Coastal Plain sediments 

that crop out in Fayette and Lamar Counties^ Ala., and 

in adjoining small parts of Marion, Pic kens, and 

Tuscaloosa Counties (fig. 1). Coastal Plain units present in the area are the Tuscaloosa group and a unit 

composed of the undifferentiated McShan and Eutaw 

formations, all of pre-Selma Late Cretaceous age.

The geology was mapped on airplane photos and 

data were transferred to U. S. Department of Agriculture

soil maps of Tuscaloosa, Lamar, and Fayette Counties. 

The Lamar County map, 1908, and the Tuscaloosa County 

map, 1911, were adjusted to the newer Fayette County 

map, 1917 a process that introduced some minor inaccuracies in location of control points. Reduction of 

the geologic map (pi. 1) to publication scale necessitated 

further generalizing the contact line*. As a result of 

these generalizations the geologic map does not include 

all the faults and flexures shown on the structure map 

(pl. 2).

PREVIOUS INVESTIGATIONS

The name Eutaw was first proposed by Hilgard 

(1860, p. 62-75) for all the Cretaceous sediments 

between the Carboniferous and his Tombigbee sand 

group. Smith and Johnson in 1887 (p. 95-116) first 

described and named the Tuscaloosa formation to include 

the variegated clay, sand, and gravel between the 

Paleozoic rocks and their Eutaw formation. Hilgard 

had included these beds in his Eutaw group. Smith and 

Johnson, in separating the Tuscaloosa formation from 

Hilgard's Eutaw group, restricted the name Eutaw to 

beds of post-Tuscaloosa age. They added Hilgard's 

overlying Tombigbee group to their redefined Eutaw 

formation.

Monroe, Conant, and Eargle in 1946 divided the 

outcropping Tuscaloosa formation of Smith and Johnson 

of western Alabama into four units of formational rank
________TENNESSEE

'PICKENS TUSCALOOSA^}

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Figure 1. Index map of Alabama. 

2
and raised the name Tuscaloosa to the rank of group. 

Their units, from oldest to youngest, are the Cottondale, Eoline, Coker, and Gordo formations. They 

also divided the Eutaw formation of Smith and Johnson 

of western Alabama into two units of formational rank, 

the McShan formation and the Eutaw formation (restricted) .

Eargle in 1948 published a preliminary chart that 

correlated the pre-Selma rocks of Late Cretaceous 

age in northwestern Alabama with those penetrated by 

wells in the subsurface of Mississippi and showed a 

generalized map of the Tuscaloosa group and the undifferentiated McShan and Eutaw formations in parts 

of northwestern Alabama and northeastern Mississippi.

NOMENCLATURE

Intermittently from 1949 to 1952 the writer made 

a study of beds of Tuscaloosa age, chiefly in Alabama. 

The results of the study are summarized in another 

article (Drennen, 1953). The classification of the 

Tuscaloosa group used in this report follows the classification proposed in that article and differs from 

that of Monroe, Conant, and Eargle (1946).

Only two units of formational rank are here recognized within the Tuscaloosa group lower formation 

for which the name Coker formation is redefined, and 

the upper Gordo formation. The Coker formation contains sediments previously called the Cottondale, Eoline, 

and Coker formations by Monroe, Conant, and Eargle. 

The Cottondale formation is abandoned, for it cannot 

be mapped separately from the Eoline and it contains 

no beds that differentiate it satisfactorily from the latter. 

Neither are the Eoline and Coker formations of earlier 

workers recognized to be of formational rank, for in 

most places they cannot be mapped separately. The 

Eoline and the Coker formations, as defined by those 

workers, however, each contains a distinctive clay 

facies that, where present, serves to distinguish it 

from the other. The Eoline is considered to be the 

lower member of the Coker formation and includes 

beds previously designated Cottondale formation. The 

Coker formation of Monroe, Conant, and Eargle is 

considered to be an unnamed upper member of the Coker 

formation as here defined.

Post-Tuscaloosa sediments are present in the 

area of this report in the western parts of Lamar and 

Pickens Counties. Most of these sediments are at 

the stratigraphic position of the McShan formation, 

but locally in the extreme western parts are some sediments undoubtedly equivalent to the Eutaw formation 

as restricted by Monroe, Conant, and Eargle (1946). 

These sediments are here referred to as the undifferentiated McShan and Eutaw formations.

STRATIGRAPHY 

Tuscaloosa group 

Coker formation

The Coker formation, the lower unit of the 

Tuscaloosa group of Late Cretaceous age, is composed 

of clay, sand, and gravel that rests with great unconformity on sandstone and shale of the Pottsville formation

of Pennsylvanian age. The Coker formation consists 

of two members, a lower Eoline member and an upper 

unnamed member. The contact between the Coker 

formation and the underlying Pottsville formation is 

locally difficult to distinguish with certainty chiefly 

because of the intense weathering to which the rocks 

have been subjected, but also because the predominant 

rock types of both units are similar. Under conditions 

of intense weathering, shale and clay of the Pottsville 

formation resemble clay of the Coker formation, and 

sandstone of the Pottsville becomes so friable that it 

resembles sand of the Coker. Conversely, sand of 

the Coker has locally been sufficiently indurated by 

weathering to resemble superficially sandstone of the 

Pottsville. The best means of differentiating highly 

weathered deposits of Pottsville age from highly weathered 

deposits of Tuscaloosa age are fossil plant material 

or gradations from the weathered materials downward 

into sedimentary rocks that retain primary characteristics.

The two members of the Coker formation are 

not shown separately on the accompanying geologic 

map (pi. 1) because at many places it is not possible, 

on either stratigraphic or lithologic grounds, to ascertain which member is present.

The Eoline member is recognized only by its 

typical facies which is thinly laminated clay having 

partings of glauconitic fine sand. All beds of Tuscaloosa 

age beneath these distinctive but lenticular clay beds 

are also referred to the Eoline member, which is 

characterized throughout by great lithologic heterogeneity. At many places, particularly in the most 

up-dip areas, the basal part of the member is characterized by concentrations of sandy gravel that locally 

attains a thickness of 30 feet. The basal gravel of the 

member in northern Tuscaloosa County and the southern 

two-thirds of Fayette County consists chiefly of quartz 

pebbles, although minor concentrations of chert are 

present locally. Northward, in northern Fayette County 

and southern Marion County, the basal gravel is composed predominantly of pebbles and cobbles of chert. 

The quartz pebbles, probably derived chiefly from 

conglomerates of the Pottsville formation, are generally 

more rounded and of smaller diameter than the pebbles 

and cobbles of chert, which presumably were derived 

from limestones of Mississippian age. In some outcrops a few pebbles or cobbles of friable sandstone, 

undoubtedly derived from the Pottsville formation, are 

interspersed in the gravel beds of the Coker formation. 

Most of the sandstone cobbles and some of the quartz 

pebbles are flattened and resemble beach cobbles, though 

the flaggy character of many sandstones of the Pottsville 

may account for the shape of the sandstone cobbles.

Where gravel is absent in the basal part of the 

Eoline member, the Pottsville formation is generally 

overlain by massive to crossbedded medium to coarse 

sand, but at some places beds of laminated fine sand 

and fissile clay lie only a few feet above the Pottsville 

formation. In some areas lenticular beds of massive 

to subfissile gray clay, which is commonly carbonaceous 

or ferruginous and mottled, form the basal part of the 

member. Locally, compact laminated clay contains 

concretions of earthy or massive siderite as much as 

1 foot in diameter. The massive clay of the Eoline 

locally attains a thickness of about 90 feet. Good 

exposures of such clay are in Fayette County about 

4 airline miles east of Fayette along an east-west gravel
road just south of the Southern Railway; also, about 

7 airline miles northeast of Fayette and about 2f miles 

east of U. S. Highway 43 in cuts of an east-west hardsurfaced farm road that leads east and northeast to 

New Prospect Church; and immediately east of Glen 

Alien, near the Marion County line in northern Fayette 

County, in cuts of the St. Louis-San Francisco Railway (not shown on map).

Most of the Eoline member consists of fine- to 

medium-grained red to yellow and gray sands that 

are commonly glauconitic, but at many places these 

sands are coarse grained and angular; glauconite is 

by no means present in all parts of the member. The 

typical lenticular and thinly laminated clays having 

partings of glauconitic fine sand are chiefly in the 

middle and upper parts of the member, although their 

stratigraphic position is variable. Locally they are 

at least 70 feet thick; in some areas they are absent.

Typical beds of the Eoline member are well exposed just east of Sipsey River in southern Fayette 

County in cuts of a road that trends southeast from the 

town of Fayette, and in northwestern Fayette County 

in cuts of State Route 167 about 2 miles northeast of 

Bluff.

The unnamed upper member of the Coker formation is recognized by its typical variegated and mottled 

massive ferruginous clay that locally is sandy and at 

many places contains spherules of siderite and large 

concretions of massive to earthy siderite. These beds 

of massive clay commonly range in thickness from a 

few feet to 40 feet, but at one place west of Sipsey River, 

in southern Fayette County, is an 80-foot bed of the 

typical mottled massive clay as shown by the following 

section exposed for half a mile south of Martins Creek 

along a north-south gravel road that generally parallels 

and lies just west of the Fayette-Newtonville road, in 

the SWi sec. 25, and the NWi sec. 36, T. 16 S., 

R. 13 W.

Section south of Martins Creek, 

Fayette County

Feet

(approximately)

Gordo formation:

Sand, reddish brown, contains 

much gravel of fine to medium 

chert pebbles; iron-cemented 

chert-pebble conglomerate 

layer 4 to 12 inches thick at 

base; to top of exposure .......... 6

.Coker formation: 

Upper member:

Clay, greenish-gray; purple- and 

yellow-mottled, massive; and 

clayey fine sand having similar 

colors; irregular ironstone layer 

at base ......................... 18

Sand, yellow to light-gray; locally 

stained red, brown, or purple; 

chiefly medium, massively crossbedded, micaceous; upper 15 feet 

contains many layers and films of 

gray clay; ironstone layer at 

base .......................... 65

Feet

(approximately)

Coker formation--Continued 

Upper member Continued

Clay, greenish-gray; purple- and 

yellow-mottled; massive; exposed .......................... 6

Covered ......................... 8

Clay, highly weathered; purple 

mottled in upper 25 to 30 feet, 

lower parts are weathered to 

dark gray-green and purple red, 

massive; locally contains decomposed concretions of siderite..... 80

Sand, reddish-brown to yellow, 

medium, highly crossbedded; 

contains many films of clay and 

stringers of gray and yellow clay 

chips; exposed.................. 2

Some fissile clay is also found in the upper member of the Coker formation. Sand of this member resembles sand of the Eoline member and at some places is 

sparsely glauconitic. As previously mentioned, massive 

variegated clay is also present locally in the lower part 

of the Eoline member, but only those beds stratigraphically higher than the typical laminated clay facies of 

the Eoline are referred to the upper member of the 

Coker formation. At most places the uppermost part 

of the upper member is massive variegated clay, but 

at some places it is thickly to thinly laminated and 

crossbedded varicolored clay and sand, and at a few 

places it is chiefly sand.

Both members of the Coker formation are variably 

ferruginous and commonly have crusts and layers of 

limonite or limonite-cemented sand. The Coker formation is overlain unconformably by gravel of the Gordo 

formation, the upper unit of the Tuscaloosa group.

Other than leaf prints, the only fossils found in 

the Coker formation are borings of organisms. Some 

of the borings resemble those of Halymenites major 

Lesquereux, but many do not have the rugosities that 

are considered typical of Halymenites. Borings are 

found chiefly at the stratigraphic position of the Eoline 

member.

Variations in thickness of the Coker formation 

as determined by surface and subsurface data are 

shown in figure 2. On the surface in central Fayette 

County, about 4-j- miles northeast of the town of Fayette, 

the Coker formation is about 240 feet thick. It thins 

northwestward to about 175 feet in the vicinity of the 

Briggs and Knapp No. 1 Wefel well (NEiSEi sec. 25, 

T. 12 S., R. 14 W.), northeastern Lamar County, 

roughly 21 miles northwest of the town of Fayette, 

Fayette County. About 3 miles northwest of the Wefel 

well, surface measurements indicate a thickness of 

about 90 feet for the Coker. In the Stanolind No. 1-A 

Woods well (NEiSEi sec. 23, T. 14 S., R. 15 W.), 

Lamar County, about 10 miles northeast of Vernon, 

 the Coker is interpreted to be 295 feet thick and thickens 

west-southwestward to 335 feet in the Wilmut No. 1 

Rye well (NE^NEi sec. 22, T. 15 S., R. 17 W.), 

Monroe County, Miss., about 3\ miles west of the 

Alabama State line. The top of the Pottsville formation in these wells (fig. 2) is shown at the depths 

determined by Eargle (1948), but the top of the Coker
J . MARION

MONROE

LOWNDES/

PICKENS

F A Y\E T T E

Fayette

<

 ,________1

|TUSCALOOSA

Surfa

Briggs 

3 No I 

Surface

Figure 2. Map and section showing variations in thickness of Coker formation.
formation as shown in the Stanolind No. 1-A Woods The farthest up-dip observed exposure of the 

well and the Wilmut No. 1 Rye well is interpreted to Gordo formation is in a gravel pit on the top of a high 

be higher than determined by Eargle. hill about 4i airline miles northeast of Fayette,

Fayette County. This locality can be reached by a

Gordo formation generally north-south gravel road that intersects

U. S. Highway 43 at a point about 3-3/4 miles east

The Gordo formation, the upper unit of the of Fayette. The following section is exposed in the 

Tuscaloosa group, is composed of clay, sand, and gravel pit and southward for about 1, 000 feet along 

gravel that rests unconformably on sand and clay of this road, 

the Coker formation. On the outcrop the Gordo formation is about 200 feet thick. The formation is not

divided into members but consists locally of at least Section about 4j miles northeast 

three units, each of which is composed of heterogeneously of Fayette 

bedded clay, sand, and gravelly sand. Each unit has

persistent sandy gravel at the base and persistent Feet 

clay at the top. These units within the formation are (approximately) 

in fact extensive lenses that are traceable with certainty 

for only a few miles. Gordo formation:

Gravel; chiefly of chert pebbles,

In general the Gordo formation in the northern subrounded to subangular, fine 

parts of Fayette and Lamar Counties contains more to large, some cobbles; in 

gravel than it does farther south. This gravel is coarse reddish-brown friable 

composed of subangular to subrounded pebbles and sand; iron-sandstone layer at 

cobbles of chert. The base of the formation is nearly base .......................... 35

everywhere marked by an irregular layer of limonite- irregularly overlies

cemented chert-pebble conglomerate. The basal sandy Coker formation:

gravel of the formation, as distinguished from the more Upper member:

common gravelly sand, attains a thickness of 40 feet. Sand, brown, massive, firm

silty, micaceous; iron-sandSands of the Gordo formation are character- stone layer at base ............. 5

istically medium to coarse, angular to subangular, irregularly overlies 

and massively crossbedded, but fine-grained laminated Silt, gray, finely sandy, micasands are not uncommon. Coloration of the sands ranges ceous; grades downward into 

from red through brown, yellow, and gray to white. thinly laminated firm yellow

sand that grades downward into

The clay of the Gordo formation resembles the gray- and yellow-mottled 

massive clay typical of the upper member of the Coker massive to subfissile silty to 

formation and is commonly gray, mottled by shades finely sandy clay; total exof red, purple, brown, and yellow. This mottling is posed........... i............. 10

attributed to the decomposition of contained ferrugi- Covered ......................... 8

nous compounds: 'At many places,clay of the Gordo, Clay as above, having streaks of

like that of the Coker, contains spherules of siderite micaceous black sand; exposed... i

(commonly weathered to limonite), crusts of limonite, Covered ........................ 4

and zones of ocherous silt. These clay beds locally Sand and clay interbedded;

attain a thickness of 50 feet, but where the Gordo has mammillary ironstone layer at

been observed in contact with the undifferentiated base"; exposed.................. 2

McShan and Eutaw formations, the uppermost clay bed Sand, brown, silty, micaceous, 

of the Gordo formation does not exceed 25 feet in thickly interbedded with silty 

thickness. subfissile gray clay (clay lenses

as much as half a foot thick);

The uppermost part of the Gordo formation ranges clay balls in lower part of sand; 

in composition from variegated and mottled massive iron-sandstone layer at base..... 11

gray sandy clay to mottled clayey sand. At a few places Sand, yellow, highly weathered, firm, 

the uppermost bed consists of thin-bedded sand and clayey; exposed ................ 1

clay. Thin beds of fissile clay are also present locally. Covered ........................ 15

In the west-central and northwestern parts of Lamar Sand, light-brown, massive, firm, 

County the uppermost part of the formation is, in micaceous; exposed ............ 3

general, composed of massive clay that is gray to black

and variably carbonaceous. This black clay of the

formation has not been noted south of the latitude of Undifferentiated McShan and

Vernon. Eutaw formations

Other than comminuted plant matter, the fossils In Alabama and Mississippi early workers were

observed in the Gordo formation are borings that not consistent in mapping the base of the old Eutaw

resemble Halymenites and other borings that lack formation. In Lamar County, Ala., and in Mississippi,

the rugose surfaces considered characteristic of sediments of McShan age were commonly included in

Halymenites. the Tuscaloosa formation, but in much of Alabama they
were included in the Eutaw formation. Eargle 

(1948) was the first to show the true geographic 

position of the top of the Tuscaloosa group in 

Lamar County.

The post-Tuscaloosa sediments in the area 

of this report are chiefly the stratigraphic equivalent of the McShan formation as defined by 

Monroe, Conant, and Eargle (1946). Locally in 

the west-central and southwestern parts of Lamar 

County are some sediments probably equivalent 

to their restricted Eutaw formation. The writer 

has not attempted to map them separately, but 

work to the west and north in 'Mississippi may 

show that they can be differentiated.

Although the contact between the Gordo 

formation and the undifferentiated McShan and 

Eutaw formations is easily traceable in most 

areas of the outcrop, the writer has not found 

it possible in the up-dip areas to separate sediments of the undifferentiated Eutaw and McShan 

formations from the Gordo formation. All the 

sediments in those areas are shown as Gordo 

formation on the geologic map (pi. 1). The areas 

are (1) west-central and, southwestern parts of 

T. 12 S., R. 15 tW., (2) south-central part of 

T. 15 S., R. 15 W., and (3) north-central and 

northeastern parts of T. 16 S., R. 15 W.

The undifferentiated McShan and Eutaw formations are composed of .clay, sand, and gravelly 

sand that rest, generally conformably, on sand 

and clay of the Gordo formation of the Tuscaloosa 

group. The basal few feet of the McShan and 

Eutaw formations consists generally of fine to 

medium, massive to crossbedded, red to brown sand. 

At some places, however, the basal sand is 

coarse and contains some fine pebbles of subangular to subrounded chert and rarely a fragment 

of silicified wood. At many places the basal 

sand of the unit is laminated, crossbedded, and 

contains glauconite. Locally the basal beds consist of evenly bedded and thinly interlaminated 

silt and rippled fine to very fine glauconitic sand.

Clays of the unit are commonly thinly 

laminated like those typical of the Eoline member 

of the Coker formation but are generally more 

silty. The undifferentiated McShan and Eutaw 

formations also contain clays that are massive 

to subfissile, gray to black, and carbonaceousresembling clays of the upper part of the Gordo 

formation in the central and northern parts of 

Lamar County. The unit also contains lenses 

of massive waxy gray-green clay that may be 

bentonitic. Massive clay showing the high degree 

of variegated coloration and mottling typical of 

clay of the Gordo formation has not been noted 

at the stratigraphic position of the Mc.Shan and 

Eutaw.

An excellent exposure of the contact between 

the Gordo formation and the McShan and Eutaw 

formations is on State Route 19 about 5 miles 

south of Sulligent, Lamar County.

Section about 5 miles 

south of Sulligent

Feet

(approximately)

McShan and Eutaw formations undifferentiated: 

Sand, red, fine to medium crossbedded; contains films, balls, and

thin layers of yellow clay, and

many irregular layers and tubes

of ironstone and iron-sandstone ............................. 5

grades downward into 

Sand, red, chiefly fine to medium;

has partings and thin layers

of purplish clay; at base this

sand is coarse grained and

contains granules and very fine

pebbles of chert.................... 6 to 10

Gordo formation:

Clay, gray- and yellow-mottled,

massive; ferruginous layer

locally at base..................... 2 to 3

locally overlies abruptly, but

elsewhere grades downward

into

Clay, blue-gray, massive; contains irregular but persistent

layer (about 1 foot thick) of

black carbonaceous clay............ 10

At several places in west-central and northwestern Lamar County a possibly persistent bed of 

massive carbonaceous clay is present about 80 feet 

above the base of the formation; but, because of the 

high topographic position, it has not been possible to 

obtain enough exposures of this clay to determine its 

continuity. Good exposures, probably of this clay, 

are in Monroe County, Miss., in cuts of a gravel road 

that trends south and west from Gattman, Miss.

One of the best observed sections of the undifferentiated McShan and Eutaw formations is in Lamar 

County in sec. 9, T. 16 S., R. 16 W/, between Wilson 

and Yellow Creeks about 8 airline miles southwest of 

Vernon along a northwest-facing slope of a gravel road 

that leads down to the flood plain of Wilson Creek. At 

this locality about 100 feet of sand, silt, and clay of 

the undifferentiated McShan and Eutaw formations overlies about 35 feet of clay and sand of the Gordo formation.

Section about 8 miles southwest

of Vernon, Lamar County

Feet

(approximately)

McShan and Eutaw formations undifferentiated: 

Sand, dark-gray, fine, massive, 

carbonaceous; contains much 

very fine mica; upper 2 feet is 

fissile; total exposed............... 4
Feet

(approximately)

1 to 4 

2

15

10

2

McShan and Eutaw formations 

undifferentiated--Continued

Silt, gray to yellowish-brown, 

ocherous; interlaminated 

with very fine ferruginous 

sand.............................

Sand, gray, very fine, massive, 

lenticular; contains pale 

glauconite and much very fine 

mica; locally contains weathered 

iron-sulphide concretions..........

Clay, gray, laminated; having 

partings of fine-grained 

glauconitic white sand..............

grades downward into

Sand, red to yellow and white, 

medium, crossbedded, loose; 

contains many lenses (as much 

as 1 foot thick) and films of 

gray clay; ferruginous layer 

marks sharp base.................

Sand, light-brown, very fine, 

micaceous, thickly to thinly 

interlaminated with gray clay; 

highly crossbedded; upper part 

is chiefly clay; exposed............

Covered............................

Clay, dark-gray, slightly redstained, massivej exposed..........

grades downward into

Sand, light-red, fine, indurated. ......

grades downward into

Sand, gray, very fine, laminated, 

silty, highly and very finely 

micaceous; contains thin layers 

of ferruginous sand; upper part 

is weathered and sublaminated 

to massive........................

Sand, brownish-red to light-brown, 

fine to medium, finely crossbedded; 

contains many films of gray clay; 

sharp base........................

Gordo formation:

Clay, greenish-gray, yellow-mottled, 

massive, waxy; lower 15 to 20 feet 

is chiefly fine to very fine, lightred to gray and yellow clayey sand; 

irregular ferruginous layer at 

base.............................

Sand, gray, very fine, massive, 

silty and clayey, very firm; contains much very fine mica; upper 

foot is clayey; irregular ferruginous 

layer at base......................

Sand, gray and light-brown, fine to 

very fine, crossbedded; much very 

fine mica; contains irregular thin 

lenses of finely sandy gray clay; 

to base of exposure................

STRUCTURE

Rocks of the Pottsville formation of Pennsylvanian 

age, which underlie the Tuscaloosa group, were extensively folded and faulted, chiefly by disturbances 

before deposition of the Tuscaloosa. Recent work

25

shows, however, that the Coastal Plain beds in the 

area of this report are also flexed and faulted. Small 

high-angle faults involving these beds are present on 

the outcrop, and structure contours drawn on formation contacts locally show sharp displacements that 

are likely a result of faulting or close folding. Both 

normal and reverse faults have been observed. The 

maximum measured throw on faults involving preSelma Coastal Plain beds in western Alabama is 35 feet.

The character of the faults in the pre-Selma 

sediments of Cretaceous age suggests that they are 

tensional and compressional breaks of slight extent 

that resulted from adjustment of the blanket of Coastal 

Plain strata to minor disturbance at depth. Such faults, 

although more numerous than heretofore recognized, 

do not seem to be persistent either along their strike 

or in depth.

Monroe (1938; Stephenson and Monroe, 1940, 

p. 34) called attention to secondary structure involving 

the Eutaw formation and the Selma chalk (now the 

Mooreville chalk of the Selma group) in east-central 

Lowndes County, Miss, just west of the areas in 

Alabama known to be structurally disturbed. It seems 

probable, therefore, that at least some structural 

irregularities in the pre-Selma sediments of western 

Alabama are post-Mooreville (post-Austin) in age. 

This relatively late disturbance may have affected 

possible oil and gas reservoirs in the Paleozoic rocks.

On the outcrop in the area three contacts are 

persistent enough to serve as horizons for structural 

mapping: (1) the contact at the base of the Tuscaloosa 

group, (2) the contact between the Coker and Gordo 

formations, and (3) the contact at the top of the 

Tuscaloosa group (pi. 2).

The formations strike generally northward and 

dip toward the west. The amount of dip of traceable 

contacts are as follows: Contact between the Pottsville 

and Coker formations, 5 to 75 feet per mile; contact 

between the Coker and Gordo formations, 10 to 100 feet 

per mile; contact at the top of the Tuscaloosa group, 

5 to 45 feet per mile. A few reverse dips and many 

irregular dips have been noted.

Because the Pottsville and Tuscaloosa contact 

is characterized at least locally by notable pre-Tuscaloosa 

topographic relief, contours drawn on that contact are 

probably not indicative of structure at depth. The contact between the Coker and Gordo formations shows 

marked irregularities that are partly the expressions 

of structural disturbance. Most irregularities of the 

contact at the top of the Tuscaloosa are attributed to 

structural disturbance although some undoubtedly are 

a result of differential compaction. At many places 

it is not known to what extent the irregularities of the 

contacts result from structural disturbances and to what 

extent from depositional and compactional phenomena.

Faulting in beds of the Coker formation can be 

seen about half a mile south of Sipsey, Fayette County, 

in cuts of a northwest-facing slope of a northwest-suutheast gravel road. At least two faults are present, arid 

all beds involved probably belong to the Eoline member. 

The amount of displacement is unknown.

In Lamar County, Ala., about 3 airline miles sjuthsoutheast of Gattman, Miss., faults displacing the contact
between the Gordo formation and the undifferentiated 

McShan and Eutaw formations can be observed in cuts 

of the gravel road that leads southward from Gattman. 

Much of this road generally parallels and lies just 

east of Cut Bank Creek.

Faulted beds of the McShan and Eutaw formations 

are exposed on State Route 18 about half a mile east 

of Cut Bank Creek, Lamar County, where the highway 

cut shows two high-angle normal faults, having throws 

of about 15 and 20 feet.

Southwest of Fayette, in the southern part of 

T. 16 S., R. 13 W., Fayette Cqunty, structure contours 

on the contact between the Coker and Gordo formations 

suggest a west-trending zone of faulting. No definite 

faults have been observed in that area, but stratal 

irregularities attributed to structural disturbance and 

possible faults have been noted.

HISTORICAL SUMMARY

The deposits of the Coker formation represent 

essentially continuous deposition in a shallow expanding sea. During early Coker time the most northeastern part of Lamar County and parts of south-central 

Marion County apparently were not submerged. In 

those areas, only a thin section of the Coker formation, 

chiefly equivalent to the upper member, is present 

between the Pottsville and Gordo formations.

The contact between the Coker and Gordo formations represents an unconformity. The Gordo overlaps the Coker regionally, and the basal beds of the 

Gordo mark the first appearance of abundant and persistent chert gravel above the basal gravel of the Coker 

which probably indicates an uplift in the source areas 

(Mississippian outcrop) to the north, possibly in 

Tennessee. It is likely that most of the gravel was 

derived from rocks of Mississippian age on the southern 

flank of the uplift in Alabama, but the major disturbance 

probably occurred farther north. The Gordo formation 

consists locally of at least three units composed of basal 

beds of chert gravel overlain by sand and clay, which 

indicates possibly that pulsating uplifts in the source 

areas occurred throughout Gordo time.

Although locally in some surface areas the contact between the Gordo and McShan formations may 

represent an unconformity, for the greater part of its 

extent in Lamar County, as in other parts of western

Alabama, it seems to be conformable. Apparently no 

widespread withdrawal of the sea occurred at or near 

the end of Gordo time, and no incontrovertible evidence 

for an unconformity has been seen at this horizon by 

the present writer. The undifferentiated McShan and 

Eutaw formations in general seem to be a product of 

a deeper water environment than the Gordo formation.

CONCLUSION

The stratigraphy of the pre-Selma Coastal Plain 

units in the area of this report, particularly in Lamar 

County, will not be fully understood until several wells 

are drilled to determine the subsurface position of 

horizons of stratigraphic reference. It is not now known 

what ratio structural disturbance bears to depositional 

factors as a cause of stratigraphic anomalies.

SELECTED BIBLIOGRAPHY

Drennen, C. W., 1953, Reclassification of the outcropping Tuscaloosa group in Alabama: Am. Assoc.

Petroleum Geologists Bulletin, vol. 37, no. 3,

p. 522-538. 

Eargle, D. H., 1948, Correlation of pre-Selma Upper

Cretaceous rocks in northeastern Mississippi and

northwestern Alabama: U. S. Geol. Survey Oil and

Gas Inv. Prelim. Chart 35. 

Hilgard, E. W., 1860, Report on the geology and

agriculture of the State of Mississippi, 391 p.,

Jackson, Miss.. 

Monroe, W. H., 1938, Columbus anticline, Lowndes

County, Miss.: U. S. Dept. Interior Press Memo.

44947. 

Monroe, W. H., Conant, L. C., and Eargle, D. H.,

1946, Pre-Selma Upper Cretaceous stratigraphy of

western Alabama: Am. Assoc. Petroleum Geologists

Bull., vol. 30, no. 2, p. 187-212. 

Smith, E. A., and Johnson, L. C., 1887, Tertiary

and Cretaceous strata of the Tuscaloosa, Tombigbee,

and Alabama Rivers: U. S. Geol. Survey Bull. 43. 

Stephenson, L. W., and Monroe, W. H., 1938,

Stratigraphy of Upper Cretaceous series in Mississippi.

and Alabama: Am. Assoc. Petroleum Geologists

Bull., vol. 22, no. 12, p. 1639-1657. 

_______ 1940, The Upper Cretaceous deposits

L of Mississippi]: Mississippi Geol. Survey Bull. 40. 

United State Department of Agriculture, 1908, Soil

map of Lamar County, Ala.

_______ 1911, Soil map of Tuscaloosa County, Ala. 

_______ 1917, Soil map of Fayette County, Ala.

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CARBONIFEROUS CRETACEOUS QUATERNARY
GEOLOGICAL SURVEY CIRCULAR 267 PLATE 2

R. 16 W. R.I5W. 

MARION COUNTY

R. 14 W.

10 Miles

Gottmon

Contour interval 25 feet 

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FAYETTE__CO _ 

TUSCALOOSA CO

R.I6 W.

Unmapped 

R. 15 W. R. 14 W.

R.I3 W. R.I2 W. R. 11 W. R IOW. 

Geology by C.W. Drennen,l952

EXPLANATION

Contour ot top of 

Gordo formation

Contour ot top of 

Coker f emotion

Contour at top of 

Pottsville formation

Contours dashed 

where inferred

Surface control point

on top of 

Gordo formation

Surface control point

on top of 

CoKer formation

Subsurface control point

on top of 

Coker formation

Surface control point

on top of 

Pottsville formation

« 

Subsurface control point

on top of 

Pottsville formation

Zone of probable 

faulting

STRUCTURE CONTOUR MAP OF PARTS OF FAYETTE AND LAMAR COUNTIES, ALABAMA