DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY

fy uf Liou
2 d yp

‘GALVESTON

Big Constance Lake

BLANCHE BAY.

ATCHAFALAYA BAY

tower NOP

2 Timbolier Island

28°

©
856° : 1 or TNTEROR-GEOLOGICAL SURVEY, RESTON, VA—1990 90°
95° 94° 93° 92¢

Base from U.S. Geological Survey SCALE 1:1 000 000 Compiied in 1982-83

International Map of the World (IMW Series), 1955 a j # a % ] 195 SaphoeTERS 6. M. Richmond, coordinator

Mositied Polyconic Projection ————s

% f} % 50 MILES
CONTOURS IN METERS ABOVE MEAN SEA LEVEL
NATIONAL GEODETIC VERTICAL OATUM OF 1928
126° 120° wayne 102" 96° 0 ae 18° ne cM 36° 90° 92°

48°

va

a

28°

ae

Rar
Ora Neachreig
ATCHEWANIT wait
mes, i

rou, oz

mia
teoma | | wits

TORT
/ nd Non
jae DAKOTA)
Stedon UD Stone mt .
: 3 as] abs
e B
bar Thame TH DAKOTA
C OW Ey 2 Ke
{ ne fra Coo
‘ue [ay a
Cs Ora NEBRASKA
Any in COLORADO
wner | emit? an
ErOnn heme wen aed
tg) blued wer
Pes ARIZONA
She, VJ mam

—
Ue anezues me CW MEXICO ORTHO!
S A ve, wy
Sth te

\ rg a
ae: ms
ul \ st

INDEX TO INTERNATIONAL MAP OF THE WORLD 1:1,000,000
TOPOGRAPHIC SERIES
Showing location of the Quaternary Geologic Map of the White Lake
4° x 6° quadrangle in red [U.S. Geological Survey, Miscellaneous In-
vestigations Series Map I-1420 (NH-15)] and other published maps in
the Quaternary Geologic Atlas of the United States in yellow.

QUATERNARY GEOLOGIC MAP OF THE WHITE LAKE 4° x 6° QUADRANGLE, UNITED STATES

32° i

LOUISIANA.

\

D

vi S

Fe

ia GULF OF

28° L

MEXICO

30°

LOESS DISTRIBUTION AND THICKNESS, IN METERS

=i 2.5-50m
[EE 50-100m

[ED <r
[ln] 05-10

1.0-2.5m

David E. Pope, William A. Gilliland, and E. G. Wermund

29° |

Lake
Pontchartrain

GULF

“MEXICO

State compilations by

Edited and integrated by

ANCESTRAL AND PRESENT DELTAS OF THE MISSISSIPPI RIVER, LOUISIANA

(Modified from Frazier, 1967; Morton and Nummedal ,1982)
Atchafalaya—1973 to present
Plaquemines—450 to 1,100 years B.P.
Lafourche—700 to 1,900 years B.P.
St, Bernard—1,700 to 2,900 years B.P.
Teche—2,700 to 3,900 years B.P.
Maringouin—6,200 to 7,200 years B.P.

Gerald M. Richmond, David L. Weide, and David W. Moore

1990

QUATERNARY GEOLOGIC ATLAS OF THE UNITED STATES

wl

MEXICO

RESPONSIBILITY FOR STATE COMPILATIONS

(1) LOUISIANA GEOLOGICAL SURVEY
(2) MISSISSIPPI GEOLOGICAL SURVEY
(3) TEXAS BUREAU OF ECONOMIC GEOLOGY

PREPARED IN COOPERATION WITH THE

LOUISIANA GEOLOGICAL SURVEY

MISSISSIPPI GEOLOGICAL SURVEY
TEXAS BUREAU OF ECONOMIC GEOLOGY

LIST OF MAP UNITS

HOLOCENE
ALLUVIAL GRAVELLY SAND

ALLUVIAL CLAY

NATURAL LEVEE SILT AND CLAY
FRESHWATER-MARSH PEAT AND CLAY
SALINE-MARSH DEPOSIT

FRESHWATER-, BRACKISH-, AND SALINE-
MARSH SILT AND CLAY, UNDIFFER-
ENTIATED

BEACH SAND

BEACH SAND AND SHELL SAND

BEACH SHELL-FRAGMENT AND SHELL
SAND
BEACH MUD

LAGOON AND TIDAL-FLAT SILT AND CLAY

HOLOCENE AND LATE PLEISTOCENE
ALLUVIAL-FAN DEPOSIT

LATE PLEISTOCENE
ALLUVIAL CLAY AND SILT
ALLUVIAL GRAVELLY SAND
ALLUVIAL SAND AND SILT
ALLUVIAL SILT AND CLAY
DELTA DEPOSIT
DELTA SAND, SILT, AND GRAVEL
DELTA SILT AND CLAY
BEACH AND NEAR-SHORE MARINE SAND

LATE PLEISTOCENE AND MIDDLE
PLEISTOCENE

LOESS AND LOESSIAL COLLUVIUM AND
ALLUVIUM,

LATE PLEISTOCENE TO EARLY
PLEISTOCENE

ALLUVIAL CLAY, SILT, SAND, AND
GRAVEL, UNDIFFERENTIATED

COLLUVIAL AND ALLUVIAL GRAVEL,
SAND, SILT, AND CLAY

MIDDLE PLEISTOCENE
ALLUVIAL GRAVEL, SAND, AND SILT

ALLUVIAL SAND, SILT, AND CLAY
ALLUVIAL SILT AND CLAY

EARLY PLEISTOCENE TO PLIOCENE(?)
ALLUVIAL PEBBLE GRAVEL AND SAND

ALLUVIAL SAND, SILT, AND CLAY

QUATERNARY AND TERTIARY

LIMONITIC SANDY DECOMPOSITION RE-
SIDUUM

QUARTZ SAND DECOMPOSITION RESID-
UUM

CLAYEY FINE TO MEDIUM SAND AND
SANDY CLAY DECOMPOSITION RESID-
UUM

SANDY CLAY DECOMPOSITION RESIDUUM

FINE SILTY CLAY DECOMPOSITION RESID-
UUM

MASSIVE CLAY DECOMPOSITION RESID-
UUM

SILTY OR MICACEOUS SANDY CLAY DE-
COMPOSITION RESIDUUM

CONTACT

ARTIFICIAL FILL

FAULT—Bar and ball on downthrown side
BEACH AND DUNE RIDGE

TEPHRA LOCALITY—Pearlette family, undif-
ferentiated

Tell

NOTE: This map is the product of collaboration of State
geological surveys, universities, and the U.S. Geological
Survey, and is designed for both scientific and practical pur-
poses. It was prepared in two stages. First, separate maps and
map explanations of the parts of States included in the
quadrangle were prepared by the State compilers indicated
on the inset diagram, Areas of Responsibility. Second, these
maps were combined, integrated, locally supplemented, and
related to a uniform map symbol classification. The map unit
descriptions also were combined, supplemented, and coor-
dinated with those of other maps of this series so that individual
unit descriptions are applicable throughout both this map and
all other maps of the series. Diagrams accompanying the map
were prepared by the editors.

Differences in mapping or interpretation in different areas
were resolved by correspondence to the extent possible. Most
simply reflect differences in available information or differences
in philosophies of mapping. Such differences serve to en-
courage further investigation.

Less than forty percent of the surficial deposits of the
United States have been mapped and described. Traditionally,
mapping of surficial deposits has been focused on glacial,
alluvial, eolian, lacustrine, and marine deposits. Slope and
upland deposits have been mapped in detail only in restricted
areas. However, an enormous amount of engineering construc-
tion and many important problems of land use and land
management are associated with regions that have extensive
slope and upland deposits (colluvium, and residuum for ex-
ample). These materials have many different physical
characteristics. Therefore, an effort has been made to classify,
map, and describe there deposits, based in large part on un-
published interpretations of individuals, published and un-
published subsoil data, and the distribution of bedrock parent
materials. The classification is crude, but represents a first step
toward a more refined and useful product.

For scientific purposes, the map differentiates Quaternary
surficial deposits on the basis of a combination of criteria, such
as lithology, texture, genesis, stratigraphic relationships, and
age, as shown on the correlation diagram and indicated in the
map unit descriptions. Some geomorphic features, such as
dune ridge, are distinguished as map units. Erosional features,
such as stream terraces, are not distinguished, and differen-
tiation of sequences of alluvial deposits of different ages is rarely
possible at a scale of 1:1,000,000.

For practical purposes, the map is a surficial materials
map, on which materials are distinguished on the basis of tex-
ture, composition, and local specific characteristics such as
swelling clay. It is not a map of soils as soils are recognized
and classified in pedology or agronomy. Rather it is a generaliz-
ed map of soils as recognized in engineering geology, or of

. subsoils or parent materials from which pedologic and
agronomic soils are formed. As a materials map it serves as
a base from which a wide variety of derivative maps for use
in planning engineering, land use, or land management pro-
jects can be compiled.

ALLUVIAL DEPOSITS

PALUDAL
DEPOSITS

CORRELATION OF MAP UNITS

DELTA
EOLIAN AND LAGOONAL COLLUVIAL
DEPOSITS BEACH DEPOSITS DEPOSITS DEPOSITS

QUATERNARY GEOLOGIC ATLAS OF THE UNITED STATES

WHITE LAKE 4° x 6° QUADRANGLE
MISCELLANEOUS INVESTIGATIONS SERIES
MAP I-1420 (NH-15)

DECOMPOSITION RESIDUAL DEPOSITS

DESCRIPTION OF MAP UNITS

HOLOCENE

asa ALLUVIAL GRAVELLY SAND—Light-gray, yellowish- or brownish-gray,
locally reddish orange, coarse to fine sand and subangular to well-
rounded pebble gravel; poorly to well sorted, poorly to well stratified,
locally clayey. Deposit includes interbedded or admixed silt and clay,
especially in flood plains of major drainages. Gravel is chiefly chert
and (or) quartz; present in point-bar, stream-channel, and low ter-
race deposits. It is commonly derived from older gravel units.
Mapped areas include local natural levee deposits of silt and clay (fl),
organic muck, and swamp deposits on flood plains, and colluvium
along margins of valley floors. Thickness 3-30 m
aca ALLUVIAL CLAY —Light- to dark-gray, yellowish-gray, or brownish-gray
clay, silty clay, and organic clay. Includes abundant organic matter
as disseminated particles, peat layers, and large wood fragments. Also
includes minor thin layers of medium to fine quartz sand and, locally,
fine chert-pebble gravel. Deposit underlies abandoned meander chan-
nels and overbank flood areas adjacent to natural levees of Mississip-
pi River and other major rivers. Along lower valleys of Mississippi and
Atchafalaya Rivers, deposit is predominantly backswamp organic clay
and silt. Thickness 3-20 m; locally 30 m where deposit fills paleochan-
nels in underlying Pleistocene fluvial sand and gravel
cian NATURAL LEVEE SILT AND CLAY—Brown to grayish-brown, light-
to medium-gray silt and silty clay containing small amounts of fine
sand, chiefly quartz; parallel- and wavy-laminated clay and silt deposits
locally contain abundant plant fragments; climbing ripple cross-
laminations are common. Deposit forms broad natural levees 2-5 m
high along present and former courses and distributaries of the
Mississippi River and other major rivers. Levee deposits slope gently
away from river channel, merging imperceptibly with backswamp
deposits. Thickness 1-4 m; as much as 8 m along Mississippi River
west of New Orleans
hpe | FRESHWATER-MARSH PEAT AND CLAY —Gray to black herbaceous
peat and clay, intermixed and interbedded; color darkens as content
of organic matter increases. Includes interbedded freshwater and
brackish-water carbonaceous clays characterized by layers disrupted
by root casts and calcareous nodules. Widespread on the Mississippi
River delta plain and Louisiana chenier plain (Chabrek and Linscombe,
1978). Thickness 1-5 m
SALINE-MARSH DEPOSIT—Gray to black herbaceous peat and car-
bonaceous clay intermixed and interbedded. Color darkens as con-
tent of organic matter increases. Interbedded with soft clay, clayey
silt, and sandy silt; burrowed; shells locally abundant. Includes saline
and brackish-water deposits of the Mississippi River delta plain and
the Louisiana chenier plain (Chabrek and Linscombe, 1978).
Thickness 2-8 m
FRESHWATER-, BRACKISH-, AND SALINE-MARSH SILT AND
CLAY, UNDIFFERENTIATED—Gray to black, blue, or green her-
baceous silt and clay intermixed and interbedded; local thin sand
layers. Includes organic-rich deposits of freshwater-, brackish-, and
saline-marsh environments. Mapped only in Texas. Thickness 0.25-3
m
BEACH SAND— White to light-gray, well-sorted, fine sand, chiefly quartz.
Deposit occurs along seaward beaches of Timbalier Island and Isles
Dernieres where it overlies coastal saline-marsh deposits (hps). Deposit
is the wave-reworked part of a 20- to 30-m-thick layer of prograding
delta-front sand. Also forms outer margin of the present Atchafalaya
River delta. Mapped only in Louisiana. Thickness 0.5-3 m
[ » | BEACH SAND AND SHELL SAND— White to light-gray, well-sorted, fine
quartz sand; abundant shells and shell fragments. Deposit forms
beaches, spits, and barrier bars along Texas coast, and beaches along
seaward margin of saline-marsh deposits (hps) in western Louisiana.
Also forms beach and dune ridges on saline-marsh (hps) and
freshwater-marsh (hpc) deposits in western Louisiana. In Texas,
deposit commonly covered by locally active sand dunes. Thickness
of modern beach deposit 1-12 m. Thickness of landward beach- and
dune-ridge deposit 2-8 m
BEACH SHELL-FRAGMENT AND SHELL SAND—White to light-gray
shell-fragment and shell sand, including minor amounts of fine quartz
sand, silt, and clay. Occurs mostly along shore of Point Au Fer Island
at southwestern margin of Mississippi River delta in Louisiana.
Thickness 1-3 m

a BEACH MUD—Gray to black silt and clay; color darkens as amount of

organic matter increases. Deposit forms narrow beaches bordering
saline-marsh (hps) and freshwater-marsh (hpc) deposits, and Lake
Pontchartrain. Mapped only in Louisiana. Thickness 0.5-2 m

LAGOON AND TIDAL-FLAT SILT AND CLAY—Light- to dark-gray silt,
clay. and very fine sand intermixed and interbedded: includes marine
and local eolian deposits on tidal flats, tidal deltas, and washover
fans along inland margin of barrier beaches. Mapped only in Texas.
Thickness 0.5-2 m

HOLOCENE AND LATE PLEISTOCENE

ALLUVIAL-FAN DEPOSIT — Yellowish- to brownish-gray, locally reddish
orange gravel, coarse to medium sand, and minor silt and clay, in-
termixed and interbedded; structureless to poorly bedded. Pebbles
and sand chiefly chert and quartz, derived from Tertiary sediments.
Mapped only in Texas. Thickness 1-5 m

LATE PLEISTOCENE

acb ALLUVIAL CLAY AND SILT (Deposits of Deweyville terrace of Bernard,
(1950)—Light: to medium-gray clay and silty clay; poorly to well sorted,
poorly to well bedded. Locally includes some admixed or interbedded
fine quartz sand. Mapped only along Sabine and Calcasieu River
drainages in Louisiana. Thickness 3-5 m
ALLUVIAL GRAVELLY SAND (Deposits of “Braided stream terraces”
of Saucier, 1974)—White to gray or brown, poorly to well-sorted, fine
to coarse sand and gravel; chiefly quartz. Includes minor silt and clay.
Consists of both outwash and alluvium. Deposit present along west
side of Mississippi River flood plain in Louisiana. Thickness 3-8 m;
locally 10-40 m where deposit fills paleochannels that cut into underly-
ing Pleistocene fluvial sand and gravel deposits
ALLUVIAL SAND AND SILT (Sand-silt facies of Prairie terrace as
mapped by Saucier, 1974)—Light- to dark-brown, red, or reddish-
brown, fine to coarse silty sand, locally interbedded with silt and gravel.
Gravel is predominantly chert and quartzite, and is more abundant
than in deposits of Prairie terrace farther south. Mapped areas include
numerous abandoned channel and ox-bow lake deposits of silt, clay,
and organic matter, and remnants of natural levee ridges underlain
by oxidized sand and silt. Locally Prairie terrace is covered by a thin,
discontinuous veneer of loess. Thickness of alluvial sand and silt 2-5
m; locally 10 m where it fills paleochannels that cut into underlying
Pleistocene fluvial sand and gravel deposits
ALLUVIAL SILT AND CLAY (Silt-clay facies of Prairie terrace as
mapped by Saucier, 1974) Brown to red and dark-red clayey silt.
Surface of deposit marked by numerous, closely spaced, circular
depressions and small silty clay mounds. Depressions range from 3
to 150 m in diameter and are filled with light- to medium-gray silty
clay grading downward to red-brown silt containing abundant dark-
red iron-manganese “buckshot” pellets. Silt contains rare gravel lenses
and grades down through fine sand into coarse sand interbedded with
gravel lenses and clay lenses. Mapped only in Louisiana along margins
of Mississippi River flood plain. Thickness 1.5-7 m; locally 50 m where
it fills paleochannels cut into underlying Pleistocene fluvial sand and
gravel deposits
ae] DELTA DEPOSIT (Prairie Formation of Fisk, 1938, 1940, in Louisiana
and Mississippi) —Light-gray to brown, poorly to well-sorted sandy
clay, silt, and clay, intermixed and interbedded. Locally includes scat-

tered shell debris and thin, discontinuous lenses of peat. In places near
coast, may include estuarine and lagoonal silt and clay and delta-front
sand. Forms a delta plain that slopes seaward from about 18 m above
sea level to 1.5 m above sea level. Mapped areas include younger
swamp deposits and alluvial clay (aca). Thickness! 30-100 m
[ERB vex sand, sit, ano GRAVEL (Distributary channel facies of the
Beaumont Formation in Texas) —Yellowish- to brownish-gray, locally
reddish-orange sand, silt, and minor fine gravel, intermixed and in-
terbedded. Includes deposits of stream channels, point bars, crevasse
splays, and natural levee ridges characterized by poorly defined
meander belt ridges and pimple mounds aligned about normal to coast.
Near coast, may include marine deposits. Thickness! 3-10 m on
northern edge of outcrop; thickens southward to more than 100 m
in subsurface
DELTA SILT AND CLAY (Interdistributary mud facies of Beaumont For-
mation in Texas)—Light- to dark-gray clay and silt intermixed and
interbedded; contains layers and lenses of decayed organic matter.
Comprises fluvial-delta plain, coastal-marsh, and lagoonal deposits.
Includes plastic and compressible clay in depressions of former chan-
nels, inter-beach ridge swales, and coastal lagoons. Thickness!
5-10 m along north edge of outcrop; thickens southward to more
than 100 m in subsurface
[oma BEACH AND NEAR-SHORE MARINE SAND (Relict beach ridge and
associated sand facies of Beaumont Formation in Texas)—Light- to
dark-gray, light- to dark-brown well-sorted fine sand containing abun-
dant shells and shell fragments and minor amounts of silt and clay.
Interfingers with silt and clay in layers along inland margins. Includes
beach, beach ridge, spit, and fore-island dune deposits. Surface com-
monly is thinly mantled by clayey silt and characterized by widespread
pimple mounds. Locally it is mantled by sand dunes of Holocene age.
Thickness 3-10 m

LATE PLEISTOCENE AND MIDDLE PLEISTOCENE

[ee] LOESS AND LOESSIAL COLLUVIUM AND ALLUVIUM—Yellowish-
brown to reddish-brown and grayish-brown, massive silt mixed with
clay and fine sand; locally includes thin lenses of very fine to fine quartz
sand. Thickness ranges from a maximum of 30 m along the Mississippi
River to 3 m at eastern limit of map unit. To east, loess, mixed with
locally derived colluvium or alluvium, persists as a thin patchy deposit
for 30 or more kilometers. Bluffs of thick loess along Mississippi River
and other rivers are commonly deeply gullied. Locally, the loess com-
prises two units separated by a paleosol developed in the lower unit.
Deposit mapped only in Mississippi. Thickness 1 30 m

LATE PLEISTOCENE TO EARLY PLEISTOCENE

(=e) ALLUVIAL CLAY, SILT, SAND, AND GRAVEL, UNDIFFERENTIATED
(Alluvial terrace deposits of Deweyville, Beaumont, Lissie, and Willis
age in Texas) —Light-brown to reddish-brown, mottled pinkish-orange,
fine to coarse sand and silt. Includes lenses of yellowish-tan clay, and
well-rounded to subangular gravel composed of quartz, quartzite,
chert, silicified wood, and ironstone; clasts 1-4 cm in diameter.
Cemented by iron oxide in places. Locally includes colluvium and
sediments reworked from older terrace deposits. Thickness 3-20 m

[let] COLLUVIAL AND ALLUVIAL GRAVEL, SAND, SILT, AND CLAY—
Light-gray, yellowish-brown, or orange-brown, pebble to granule
gravel, sand, and minor sit intermixed and interbedded. Gravel chiefly
quartz, but also chert in minor amounts. Deposit mostly derived from
Willis Formation (agc) on adjacent uplands. Includes some sand
deposits of alluvial-fan origin, notably along southern edge of the
uplands. Thickness 0.5-5 m

MIDDLE PLEISTOCENE

ALLUVIAL GRAVEL, SAND, AND SILT (Coarse-grained channel facies
of Lissie Formation in Texas) —Light-gray, yellowish-brown, and tan,
fine gravel, sand, and minor silt and clay, intermixed and interbedded.
Clasts chiefly quartz and chert. Deposit locally cross-laminated, and
characterized by scour-and-fill and slump structures common to chan-
nels in headward sector of delta plain. Surface generally slightly higher
than adjacent terrain. Thickness 10-25 m

[ah | ALLUVIAL SAND, SILT, AND CLAY (Fine-grained channel facies of

Lissie Formation in Texas; Bentley and Montgomery Formations of
Fisk 1938, 1940, in Louisiana)—Light-gray to brown or orange-
brown, medium to fine sand, silt, and minor gravel and clay, inter-
mixed and interbedded. Locally characterized by channel-and-fill and
graded-bedding structures common to deposition in meander chan-
nels, point bars, and local braided channels on headward sector of
delta plain. Surface generally characterized by pimple mounds and
low dunes of Holocene age. Thickness 10-25 m, but more than 100
m in subsurface beneath younger seaward delta units

ALLUVIAL SILT AND CLAY (Fine-grained overbank facies of Lissie For-
mation in Texas)—Light-gray, tan, and yellowish-brown clay, silt,
sand, and very minor pebble to granule gravel intermixed and in-
terbedded, poorly to well sorted; locally contains calcium carbonate
and iron oxide concretions. Commonly displays thin, laminar stratifica-
tion and local crossbedding. In places, contains lenses rich in organic
matter. Upper part stained by iron and manganese oxides. Flat sur-
face characterized by abundant round shallow depressions and pim-
ple mounds. Texture, structure, and distribution between alluvial chan-
nel deposits (ash) indicate flood overbank deposition in flood basins,
backswamps, and lakes. Thickness 55-65 m

EARLY PLEISTOCENE TO PLIOCENE(?)

ALLUVIAL PEBBLE GRAVEL AND SAND (Citronelle or Williana For-
mation in Louisiana and Mississippi; channel facies of Willis Forma-
tion in Texas }Light-gray to orange-brown or reddish-orange, gravelly
coarse to fine sand containing lenses of moderate- to dark-red sandy
silt and white to light-gray clay. Clasts, commonly in an unconsolidated
coarse sand matrix, are subangular to subround granules to medium:
size pebbles, mostly chert, but a few of quartz in Mississippi and Loui-
siana; in Texas mostly quartz but a few of chert. In Texas, deposits
are characterized by structures indicating deposition in straight tor-
rential channels, braided channels, and coarse meander belts on
coalescing alluvial fans of moderate relief. In Louisiana and Missis-
sippi, the Citronelle Formation is considered of middle Pliocene to
possible early Pleistocene age on the basis of fossil leaves (Berry, 1916;
Stringfield and LaMoreauz, 1957; Doering, 1958). In Alabama, a
vertebrate fauna, collected from dark-gray clay beneath oxidized sand
typical of the Citronelle Formation, has been assigned a Hemphillian
(middle Pliocene) age by F. C. Whitmore (Isphording and Lamb, 1971).
Mapped areas include some locally derived gravelly sand, alluvium,
and colluvium. Thickness as much as 60 m; thickest at southern edge
of outcrop

Ly ALLUVIAL SAND, SILT, AND CLAY (Overbank facies of Willis Forma-
tion in Texas) —Light-brown, pale-yellow, orange, or orange-brown
fine sand, silt, and clay intermixed and interbedded; a broad, dissected,
gently sloping flood-plain and flood-overbank deposit; ferruginous
nodules common in the oxidized upper part. Thickness 5 to more
than 50 m along southern border of outcrop

QUATERNARY AND TERTIARY

a LIMONITIC SANDY DECOMPOSITION RESIDUUM?—Light-gray,
yellowish-brown, brown, or dark-reddish-brown clay to silty clay, and
fine to medium quartz sand; contains irregularly cemented to hard
limonitic clay and limonite veins and nodules. Deposit grades down
into sandstone, shale, and siltstone bedrock. Mapped areas include
locally derived colluvium and bedrock outcrops. Thickness 1-15 m

| QUARTZ SAND DECOMPOSITION RESIDUUM?—Pale-gray to
reddish-brown, locally muscovitic, coarse to medium quartz sand;
locally slightly clayey. Locally contains irregular, hard, limonite-

Holocene

Late Pleistocene

QUATERNARY
Middle Pleistocene
Early Pleistocene
PLIOCENE
AND OLDER

cemented masses, nodules, and veins. Mapped areas include younger
locally derived colluvium, bedrock outcrops, and,in Texas, broad low
sand dunes deflated from the residuum in late Pleistocene and
Holocene time. Thickness 2-10 m

(RBI) cuavev rine 10 MepiuM SAND AND SANDY CLAY DECOMPOSI-
TION RESIDUUM2—Gray, buff, orange, or brown, clayey, fine to
medium quartz sand and fine sandy sity clay. In places, contains
subrounded sandstone pebbles. Mapped areas include locally derived
younger colluvium and bedrock outcrops. Thickness 1-3 m; thinnest
where developed on tuff in Texas

[=| SANDY CLAY DECOMPOSITION RESIDUUM2—Pale-yellow, orange,
teddish-orange, of greenish-gray, mottled, fine sandy clay, locally
clayey fine sand or clay: in places includes medium to coarse pebbly
sand. Pebbles and sand chiefly quartz. Mapped areas include some
locally derived colluvium and bedrock outcrops. Thickness 1-2 m

(ERB ve sicty cray pecomposition RESIDUUM?—Black to dark.
gray or dark-brown silty clay; light brown to reddish brown where ox-
idized. Clay is strongly smectite; expands when wet, shrinks and forms
a crack structure, called gilgai, when dry. Mapped areas include some
locally derived colluvium and bedrock outcrops. Thickness 0.5-1 m,
locally as much as 2 m

MASSIVE CLAY DECOMPOSITION RESIDUUM?—Gray to dark-

brownish-gray, yellowish-brown to dark-brown, or mottled light-red
to orange clay, sandy clay, and fine quartz sand, commonly limonite
stained. Clay is smectitic; expands when wet, shrinks when dry. Lower
part of deposit may contain brown coal fragments. Mapped areas in-
clude some younger locally derived colluvium and bedrock outcrops.
Thickness 1-3 m

[EG sity on micaceous sanpy clay DECOMPOSITION
RESIDUUM?—Brown silty clay and micaceous, fine sandy clay,
commonly limonite cemented. Lower part may contain fragments of
lignite and petrified wood. Mapped areas include some younger locally
derived colluvium and bedrock outcrops. Thickness 1-2 m

1Thicknesses of delta deposits are approximate because (1) delta deposit thicknesses vary
greatly from area to area; (2) thickness data from outcrops and drill holes are limited; and (3)
itis difficult to ascertain the actual base of deposit. In practice, the base of a deposit is placed
at a buried soil, a change in prevalent grain size or bulk density, or other characteristic indicating
a significant change in depositional process. However, thickness of individual units may be
overstated where similar delta deposits are superposed and their contact is not recognized

DECOMPOSITION RESIDUUM, for purposes of this map, is defined as material derived
primarily by in-place chemical decay of clastic rock with no appreciable subsequent lateral
transport

SOURCES OF INFORMATION

LOUISIANA

Alford, J. J., Kolb, C. R., and Holmes, J. C., 1983, Terrace stratigraphy in the Tunica
Hills of Louisiana: Quaternary Research, v. 19, no. 1, p. 55-63.

Berry, E. W., 1916, The flora of the Citronelle Formation, in Shorter contributions
to general geology: U. S. Geological Survey Professional Paper 98-L, p. 193-208.

Chabrek, R. H., and Linscombe, Greg, 1978, Vegetative-type map of the Louisiana
coastal marshes: Louisiana Department of Wildlife and Fisheries, scale 1:250,000.

Deering, J. A., 1958, Citronelle age problem: American Association of Petroleum
Geologists Bulletin, v. 42, no. 4, p. 764-786.

Fisk, H. N., 1938, Geology of Grant and LaSalle Parishes, Louisiana: Louisiana
Geological Survey Bulletin 10, 246 p.

1940, Geology of Avoyelles and Rapides Parishes, Louisiana: Louisiana
Geological Survey Bulletin 18, 240 p.

Frazier, D. E., 1967, Recent deltaic deposits of the Mississippi River—Their develop-
ment and chronology, in Symposium on the geological history of the Gulf of Mex-
ico, Antillean-Caribbean region: Gulf Coast Association of Geological Societies
Transactions, v. 17, p. 287-315.

Isphording, W. C., and Lamb, G. M., 1971, Age and origin of the Citronelle Forma-
tion in Alabama: Geological Society of America Bulletin, v. 82, no. 3, p. 775-780.

Morton, R. A., and Nummedal, Dag, 1982, Regional geology of the N. W., Gulf Coastal
Plain, in Nummedal, Dag, editor, Sedimentary processes and environments along
the Louisiana-Texas coast: Geological Society of America Field Trip Guidebook,
1982, p. 3-25.

Stringfield, V. T., and LaMoreaux, P. E., 1957, Age of the Citronelle Formation in
the Gulf Coastal Plain: American Association of Petroleum Geologists Bulletin,
v. 41, no. 4, p. 742-746,

Woodward, T. P., and Gueno, A. J., Jr., 1941, The sand and gravel deposits of Loui-
siana: Louisiana Geological Survey Bulletin 19, 365 p.

MISSISSIPPI

Bicker, A. R., Jr., 1969, Geologic map of Mississippi: Mississippi Geological, Economic,
and Topographic Survey, scale 1:500,000.

Bicker, A. R., Jr., 1966, Claiborne County geology and mineral resources: Mississippi
Geologic, Economic, and Topographic Survey Bulletin 107, 174 p.

1969, Copiah County geology and mineral resources: Mississippi Geologic,
Economic, and Topographic Bulletin 110, p. 11-62.

Grim, R. E., 1936, The Eocene sediments of Mississippi: Mississippi Geological Survey
Bulletin 30, 240 p.

Saucier, R. T., 1967, Geological investigation of the Boeuf-Tensas Basin, lower
Mississippi Valley: U.S. Army Engineer Waterways Experiment Station Technical
Report No. 3-757.

1974, Quaternary geology of the lower Mississippi valley: Arkansas Ar-
chaeological Survey Research Series 6, 26 p.

Snowden, J. O.,Jr., and others, 1968, Loess investigations in Mississippi: Mississippi
Bureau of Geology Bulletin 111, 267 p.

Thomas, E. P., 1942, The Claiborne: Mississippi Bureau of Geology Bulletin 48, 96 p.

Vestal, F. E., and McCutcheon, T. E., 1942, Adams County mineral resources:
Mississippi Bureau of Geology Bulletin 47, 200 p.

TEXAS.

Bernard, H. A., 1950, Quaternary geology of southeast Texas: Baton Rouge, Loui-
siana State University Ph.D. dissertation, 164 p.

Bernard, H. A., Major, C. F., dr., Parrott, B. S., and LeBlanc, R. J., Sr., 1970, Re-
cent sediments of southeast Texas—A field guide to the Brazos alluvial and deltaic
plains and the Galveston barrier island complex: Texas Bureau of Economic
Geology Guidebook 11, 83 p.

Bernard, H. A., and LeBlanc, R. J., 1965, Résumé of the Quaternary geology of the
northwestern Gulf of Mexico province, in H. E. Wright, Jr., and D. G. Frey, editors,
The Quaternary of the United States: Princeton University Press, p. 137-185.

Eargle, D. H., 1968, Nomenclature of formations of Claiborne Group, middle Eocene,
coastal plain of Texas: U. S. Geological Survey Bulletin 1251-D, 25 p.

Fisher, W. L., McGowen, J. H., Brown, L. F., dr., and Groat, C. G., 1972, En-
vironmental geologic atlas of the Texas coastal zone, Galveston-Houston area:
Texas Bureau of Economic Geology, 91 p.

Ricoy, J. U., and Brown, L. F., Jr., 1977, Depositional systems in the Sparta Forma-
tion (Eocene), Gulf Coast basin of Texas: Gulf Coast Association of Geological
Societies Transactions, v. 27, p. 139-154.

Texas Bureau of Economic Geology, 1968, Geologic atlas of Texas, Beaumont sheet:
Texas Bureau of Economic Geology, scale 1:250,000.

1968, Geologic atlas of Texas, Palestine sheet: Texas Bureau of Economic
Geology, scale 1:250,000.

1975, Geologic atlas of Texas, Beeville-Bay City sheet: Texas Bureau of
Economic Geology, scale 1:250,000.

LOESS INDEX MAP

Thorp, James, and Smith, H.T.U., 1952, Pleistocene eolian deposits of the United
States, Alaska, and parts of Canada: National Research Council, Committee for
the Study of Eolian Deposits, Geological Society of America, scale 1:2,500,000.

For sale by US. Geological Survey Map Distribution,
Box 25286, Federal Center, Denver, CO 60225