LATE QUATERNARY STRATIGRAPHIC EVOLUTION OF THE NORTHERN GULF OF MEXICO MARGIN

LATE QUATERNARY STRATIGRAPHIC
EVOLUTION OF THE NORTHERN
GULF OF MEXICO MARGIN
Edited by:
JOHN B. ANDERSON
Earth Sciences Department, Rice University, Houston, Texas 77251-1892, U.S.A.
AND
RICHARD H. FILLON
Earth Studies Associates, 3730 Rue Nichole, New Orleans, Louisiana 70131-5462, U.S.A.
Copyright 2004 by
SEPM (Society for Sedimentary Geology)
Laura J. Crossey, Editor of Special Publications
SEPM Special Publication Number 79
Tulsa, Oklahoma, U.S.A. April, 2004

ISBN 1-56576-088-3
© 2004 by
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Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin
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1LATE QUATERNARY STRATIGRAPHIC EVOLUTION, NORTHERN GULF OF MEXICO MARGIN: A SYNTHESIS
LATE QUATERNARY STRATIGRAPHIC EVOLUTION OF THE
NORTHERN GULF OF MEXICO MARGIN: A SYNTHESIS
JOHN B. ANDERSON
ANTONIO RODRIGUEZ
Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama 35487-0338, U.S.A.
KENNETH C. ABDULAH
Pioneer Natural Resources, 5205 N. O’Connor Blvd., Irving, Texas 75039-3746, U.S.A.
RICHARD H. FILLON
Earth Studies Associates, New Orleans, Louisiana 70131, U.S.A.
LAURA A. BANFIELD
BP, 501 Westlake Park Blvd., Houston, Texas 77210, U.S.A.
HEATHER A. MCKEOWN
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, U.S.A.
Present address: ExxonMobil Exploration Company, 233 Benmar, Houston, Texas 77060, U.S.A.
AND
JULIA S. WELLNER
Abstract: This volume presents results from several high-resolution stratigraphic investigations of late Quaternary strata of the northern
Gulf of Mexico, from the Apalachicola River to the Rio Grande. The studies characterize deposition and strata formation associated with
different fluvial and deltaic systems during the most recent glacioeustatic cycle (approximately 120 ka to present).
The Gulf margin region encompasses a variety of depositional settings characterized by different drainage-basin size, physiography,
fluvial morphology, and structural and diapiric activity. The papers presented in this volume focus on fluvial response to climate and
base-level change, variations in delta growth and evolution across the shelf, lowstand delta and fan evolution, the evolution of
transgressive deposits on the shelf, the preservation of these deposits, and the resulting differences in stratigraphic architecture. In this
paper we summarize the key observations made in those studies and compare the paleogeography and deposystem evolution of the
various study areas.
The integration of the chronologies developed with key regional seismic surfaces allows comparison of stratal geometries produced by
contemporaneous depositional systems operating under identical eustatic conditions. This synoptic comparison permits differentiation
between eustatic and other controls on sedimentation and testing of many of the assumptions made in sequence stratigraphy. A set of
paleogeographic maps and sequence and systems-tract models depict the major depositional systems of the Gulf margin during different
stages of the eustatic cycle. These summary diagrams highlight considerable variability in stratigraphic architecture along the margin. For
example, the relative proportion of highstand, lowstand, and transgressive strata differs between study areas. Thus, deposition and stratal
packaging are more complex than most sequence stratigraphic models predict. However, for any given fluvial, deltaic, and fan system, the
general style of deposition appears to repeat itself from one glacioeustatic cycle to the next. Thus, the results of this study can be used to
test and calibrate quantitative stratigraphic models and to predict reservoir occurrence within a sequence stratigraphic framework.
Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin
SEPM Special Publication No. 79, Copyright © 2004
SEPM (Society for Sedimentary Geology), ISBN 1-56576-088-3, p. 1–23.
INTRODUCTION
During the past two decades there has been a proliferation of
sequence stratigraphic models, including the popular “slug dia-
grams”.Thesemodelsrelateobservationsfromseismicdata,well
logs, and outcrop studies to the character and spatial and tempo-
ral distribution of depositional systems in the subsurface (e.g.,
Jervey, 1988; Posamentier et al., 1988; Christie-Blick and Driscoll,
1995; Miall, 1997). The underlying assumption in such models is
that there is some orderly stratigraphic motif for any given basin
setting whereby the general style of deposition repeats itself with
each eustatic cycle as long as other controlling factors (tectonics,
climate,sedimentsupply,shelfgradient,subsidence,etc.)remain
relatively constant. This seems like a reasonable assumption;
however, the principal role of eustasy in controlling stratigraphic
architecture is now being reevaluated (Galloway, 1989; Walker,
1990; Schumm, 1993; Wescott, 1993; Shanley and McCabe, 1994;
Christie-Blick and Driscoll, 1995; Miall, 1997; Ethridge et al.,
1998).
Many researchers have attempted to improve stratigraphic
models by using outcrop data (e.g., Van Wagoner, 1995). Geolo-
gists working on outcrops are forced to make important assump-
tionsaboutpaleogeography,base-levelchange,andclimaticinflu-
enceonsedimentsupply.Thereisalsoalackofchronostratigraphic
control needed for detailed outcrop correlation. These problems
typically lead to debate about stratigraphic interpretations (Van
Wagoner, 1995,1998;Yoshidaetal.,1996,1998).Anotherapproach
to stratigraphic modeling is that of using laboratory experimental
models to examine stratigraphic response to changing base level,
discharge, and subsidence (e.g., Wood et al., 1993; Koss et al., 1994;
Heller et al., 2001; Paola et al., 2001). The main criticism of this
approach concerns the scale of these models, although Koss et al.
(1994) argue that the concept of sequence stratigraphy is scale
independent. There has also been a proliferation of quantitative
models for generating different stratigraphic architecture by vary-
ing such parameters as sediment input, subsidence, and eustasy
(e.g., Thorne and Swift, 1991; Steckler et al., 1993; Harbaugh et al.,
1999). But, there is a paucity of data to test these models.

J.B. ANDERSON, A. RODRIGUEZ, K.C. ABDULAH, R.H. FILLON, L.A. BANFIELD, H.A. MCKEOWN, AND J.S. WELLNER2
Thus, the various approaches to stratigraphic modeling are
limited by different factors. What is needed to develop more
predictive stratigraphic models are experiments in which sedi-
mentation and strata formation can be related to known rates of
eustasy, subsidence, and sediment discharge. It is important that
these experiments be carried out in a broad range of depositional
settings if the results are to be widely applicable for stratigraphic
analysis. Factors that should be defined for each setting include:
(1) the size, climatic setting, fluvial geomorphology, topography,
and geology of fluvial drainage basins that supply sediment to
the shelf, (2) the shelf gradient and subsidence rates, (3) the
eustatic and climatic history of the basin, and (4) oceanographic
influences on sedimentation.
Previous studies have shown that depositional geometries
and stratal architecture of Quaternary strata do reflect, at least at
first approximation, sea-level changes (e.g., Suter and Berryhill,
1985; Coleman and Roberts, 1988a, 1988b; Boyd et al., 1989;
Farron and Moldonado, 1990; Tesson et al., 1990; Hernández-
Molina, 1994; Sydow and Roberts, 1994; Anderson et al., 1996).
Although these studies were often limited in their geographic
coverage and paucity of sediment cores needed for chrono-
stratigraphic analysis and verification of seismic facies interpre-
tations, they showed a variety of stratal responses to the same
eustatic fluctuations. The next logical step is to conduct similar
experiments in a much larger basinal setting where regional
variations in climate, sediment discharge, subsidence,
neotectonics, and margin physiography and their influence on
sedimentationandstrataformationcanbeexaminedandchrono-
logically matched.
This volume contains papers that present results from studies
of late Quaternary strata of the northern Gulf of Mexico basin.
Our objective is to compare and contrast deposition and strata
formation within different linked drainage systems and margin
depocentersthroughonecompleteglacioeustaticcycle.Thenorth-
ern Gulf of Mexico margin is divided into eight distinct deposi-
tionalsettingsbasedondifferencesinfluvial-drainage-basinsize,
geology and physiography, climate setting, and margin physiog-
raphy (Fig. 1, Table 1).
We focused on the last glacioeustatic cycle (120 ka) for a
number of reasons. First, this is the time for which sea-level
change is best documented. Second, the strata of this age occur at
shallow enough subsurface depths to be imaged using high-
resolution seismic methods and they can be sampled using
conventional coring and shallow drilling techniques. Lastly,
Nueces
R.
50-60
50-60
30-40
30-40
20-30
40-50
R
io
G
rande
R
.
Colorado R.
Brazos R.
PascagoulaR.
50-60
0 500
km
Average Annual Precipitation (in)
Bathymetry (m)
Gulf of Mexico
200m
300m
400m
1000m
500m
100m
60-80
Mississippi River
Drainage Basin
Sabine R.
Apalachicola
R.
TombigbeeR.
GuadalupeR.
Trinity
R.
Pearl R.
PerdidoR.
MobileR.
RG
CT
ET
WL MD
MEL
ALWF
APL
FIG. 1.—Map of fluvial drainage basins for the northern Gulf of Mexico margin. Also shown are margin bathymetry and values of
mean annual precipitation for the region. The Gulf margin is divided into eight distinct settings based on differences in (1)
drainage-basin size, geology, and climate, which control sediment flux; (2) margin physiography; and (3) subsidence rates. The
different margin segments are labeled as follows. RG = Rio Grande, CT = central Texas, ET = east Texas, WL = western Louisiana,
MD = Mississippi Delta, MEL = Mississippi–eastern Louisiana, ALWF = Alabama–west Florida, and APL = Apalachicola. The
Mississippi River drainage basin is shaded.

chronostratigraphic methods for the late Quaternary provide the
level of resolution necessary for direct correlation of depositional
systems in different regions.
It is important that stratigraphic studies of this type encom-
pass the full eustatic cycle so that the entire range of eustatically
controlled and climate-controlled influences on sediment dis-
charge and deposition can be examined. Results presented in this
volume show that the sediment discharge of modern rivers in the
northern Gulf of Mexico are a fraction of what they were in the
past, so the modern depositional setting is not a good analogue
for most of the eustatic cycle.
Why the Gulf of Mexico?
The northern Gulf of Mexico margin encompasses a broad
spectrum of depositional settings and is, in our opinion, un-
equaled as a natural laboratory for research aimed at improving
ourunderstandingofsedimentationandstrataformationonlow-
gradientcontinentalmargins.Thereareanumberofreasonswhy
the Gulf is particularly well suited for research of this kind.
1. The margin receives sediment from a number of fluvial sys-
temswithverydifferentsedimentdischarges,intermsoftotal
sediment flux and proportions of suspended and bedload
material (Fig. 1). These differences in sediment discharge are
relatedtodifferencesindrainage-basinsize,geology,climatic
setting, and fluvial geomorphology (stream gradient, sinuos-
ity, channel morphology, etc.). For example, the rivers of east
Texas have very extensive meanderbelts and floodplains
where vast quantities of sediment are sequestered (Wright
and Marriott, 1993). In contrast, the rivers of Alabama and
west Florida are incised into mostly Pleistocene strata and
have rather limited flood plains where sediment storage can
occur.
2. The northern Gulf of Mexico margin spans five major climatic
belts that run roughly NNW–SSE across the state
(Thornthwaite, 1948). From east to west, precipitation reflects
humid, moist subhumid, dry subhumid, and semiarid condi-
tions (Fig. 1). Wet and dry phases, linked to glacials and
interglacials, respectively, have a marked effect on the cli-
matic belts, fluvial discharge, and fluvial and deltaic deposi-
tion. Late Quaternary climatic conditions for the Gulf Coast
region have been summarized in review papers (e.g., DuBar
et al., 1991; Toomey, 1993). These studies are highly general-
ized,buttheyprovideafirstapproximationforclimatechange,
which can be related to variations in sediment flux with time.
The drainage basins of Texas rivers have experienced semi-
arid to humid climate shifts, although the magnitude and
timingofthesechangesundoubtedlyvariedacrosstheregion.
The potential impacts of these climate shifts on sediment flux
to the Gulf should be profound (Langbein and Schumm,
1958). The Louisiana, Mississippi, Alabama, and west Florida
climates are believed to have remained relatively humid
throughout the last glacioeustatic cycle. We can estimate
sediment flux using the volumes of depositional units and
their ages.
3. Subsidence and sediment supply are relatively high, particu-
larly offshore Louisiana and Texas, and are reasonably well
constrained(e.g.,Paine,1993).Thus,preservationpotentialof
all systems tracts (highstand, lowstand, and transgressive) is
Study Area
(River)
South Texas
(Rio Grande)
Central Texas
(Guadalupe)
East Texas
(Brazos,
Colorado)
East Texas
(Trinity,
Sabine)
Western
Louisiana
Lagniappe
(West Mobile,
Pascagoula)
Florida Alabama
(East Mobile,
Escambia)
West Florida
(Apalachicola)
Drainage Basin
size (km2
) 400,000 24,000
118,000 (Brazos)
110,000 (Colorado)
44,000 (Trinity)
13,000 (Sabine)
unknown
95,000 (Mobile)
95,000 (Mobile)
19,000 (Escambia) 60,000
climate semiarid semiarid semiarid
to subhumid
moist subhumid moist humid moist humid moist humid humid
Fluvial Morphology braided to
meandering
small coastal
plain and
piedmont rivers
broad, meandering narrow,
meandering
broad, meandering steep, incised steep, incised
(Mobile)
small coastal-plain
river (Escambia)
steep, incised
bedload/suspended
load
high (mixed) low (mixed) high (suspended-
Brazos
bedload Colorado)
moderate
(suspended)
high (mixed) high (bedload) low (bedload) moderate
(bedload)
modern discharge
(m3
/s-1
)
123 75 226 (Brazos)
81 (Colorado)
730 (Trinity)
510 (Sabine)
2200 2200 (Mobile)
250 (Escambia)
650
Coastal-plain gradient
width (km)
low low
150
low
150
low
150
low
170
low steep
< 20 km
steep
75
Shelf
morphology
shelf-slope ramp shelf-slope shelf-slope shelf-slope shelf-slope ramp ramp
gradient (m/km) 1.8–2.75 1.2 0.6 0.5 0.5 0.5–3.3 1.2 (west) to 2.7
(east)-6
1.3– 3.5
width (km) 90 80 100 160 180 140 100 (west)-35 (east) 75
storm/wave/fluvial
dominated
fluvial wave fluvial wave fluvial fluvial storm storm
lithology muddy muddy muddy muddy mixed sandy sandy sandy
structure growth faulting growth faulting salt and growth
faulting
salt and growth
faulting
salt and growth
faulting
minor diapirs
and large scale
growth faulting
undisturbed by salt
and faulting
undisturbed by
salt and faulting
subsidence (mm/yr) high (0.1–5.0) high (0.1–5.0) high (0.1–4.0) high (0.1–4.0) high (0.1–5.0) low low (0.5) low (0.5)
sediment flux
(metric tons/year)
20,000,000 16,000,000 (B)
1,900,000 (C)
750,000 (S) 170,000
TABLE 1.—Characteristics of the various study areas. The modern Mississippi River Delta is not included. Study area locations
are shown in Figure 1. The drainage basin of the western Louisiana area, which is part of the ancestral Mississippi River
drainage basin, has changed, and its modern configuration is therefore unknown. Likewise, the drainage basin
of the Lagniappe delta is uncertain, but it probably was nourished by both the Mobile and Pascagoula rivers.
Data on modern river discharge and sediment flux are from Milliman and Syvitski (1992).

high, and these strata are thicker than on most other continen-
tal margins. For example, detailed work on the New Jersey
continental margin has shown that strata formed during the
falling stage of sea level (120 ka to 22 ka) are poorly repre-
sentedontheshelfbecauseofreworkingduringthetransgres-
sion (Duncan et al., 2000).
4. Shelfwidthsvaryfrom30kmto180km;shelfandupper-slope
gradients are therefore highly variable as well. The Texas and
Louisiana shelves have distinct shelf breaks, with the excep-
tion of the central Texas margin, which lacks a distinct shelf
break. The western Florida margin is more of a steep ramp
setting.
5. Over 25,000 kilometers of high-resolution seismic data is
available (Fig. 2), and there are abundant oil-company plat-
form borings and long cores needed to test seismic facies
interpretationsandforchronostratigraphicanalysis.Theonly
area where long cores were not available at the time of these
studies was on the Alabama and west Florida shelves.
6. The northern Gulf of Mexico region has a long history of
sedimentological and paleontological research and has been
the location of significant pioneering discoveries (e.g., Fisk,
1944; LeBlanc and Hodgson, 1959; Curray, 1960; Kennett and
Huddlestun, 1972; Frazier, 1974; Berryhill et al., 1986; Kohl,
1986).Theseearlierstudieshaveprovidedanimportantframe-
work for this investigation.
Methods
The data set used for this study consists of over 25,000 kilome-
ters of high-resolution seismic data (Fig. 2), lithological descrip-
tions of hundreds of oil-company platform borings, and paleon-
tological, sedimentological, and geochronological data from sev-
eral hundred pneumatic hammer cores (up to 5 meters length)
and ten long (average 100 m) cores.
In all of the papers contained in this volume, classical seismic
stratigraphic methods were used to describe the external forms
andinternalstratalgeometriesofdepositionalunits(e.g.,Mitchum
et al., 1977; Vail et al., 1977a, 1977b; Vail et al., 1997c). The nature
of the bounding surfaces and the reflection configurations of the
units were then combined with the timing of their formation to
examine the relative roles of eustasy and other controlling factors
(e.g., sediment supply and tectonism) on deposition. An analysis
of this kind is necessary in order to understand the factors that
influence the evolution and distribution of lithofacies in space
and time.
An independent chronology was established for the northern
Gulf of Mexico through integration of biostratigraphy, tephro-
chronology, radiocarbon dating, and oxygen isotope stratigra-
phy. The chronology is linked to regionally extensive seismic
reflectorsbytheintersectionofthelocationsofthesedimentcores
with the seismic dataset. These ties create a robust chronostrati-
graphic framework from which to interpret the temporal and
spatial distribution of depositional environments on the shelf
over the past 120,000 years.
Seismic Stratigraphic Method and Terminology
Sequence stratigraphy has provided a valuable means of
subdividingstratigraphicpackages,buttheproliferationofterms
and new methodologies has resulted in much confusion. Part of
the problem stems from the attempts of researchers to link
systems tracts to specific well-defined segments on a sea-level
curve(e.g.,Haqetal.,1987),butitisunclearwhetherthiswasever
the intention of the Exxon workers who developed the terminol-
ogy (Van Wagoner et al., 1988).
FIG.2.—SeismicdataacquiredduringthepastnineyearsbytheRiceUniversitygroup(areas1,2,3,4,5,8,and9),theLSU–OilIndustry
consortium (area 6), and the University of Alabama (area 7). The corresponding area numbers and papers in this volume are as
follows. 1 = Banfield and Anderson; 2 = Eckles et al., 3 = Abdulah et al., 4, 5 = Wellner et al., 6 = Fillon et al., Roberts et al., and
Kohl et al.; 7 = Bartek et al., 8 = Bart and Anderson, and McBride et al.; and 9 = McKeown et al.
98 96 94 92 90 88 86
30
28
26
FlorAla
EastTexas
Trinity/
Sabine
Western
Louisiana
Central
Texas
South
Texas
Gulf of Mexico
.
Apalachicola
1
2
3
4 5 6
7
9
8
East Texas
Brazos/
Colorado

In the end, what is important is the adoption of a consistent
means of stratigraphic analysis. In this volume, because there is
a well-defined sea-level curve spanning the late Quaternary, the
authors have related systems tracts to specific periods on the sea-
level curve. Several authors then apply the Exxon terminology,
using the original tripartite scheme for the partitioning of uncon-
formity-bounded sequences (Vail et al., 1977a, 1977b) (e.g., Figs.
3, 4), and others leave this interpretation to the reader. By linking
systems-tract terminology and all discussions of stratigraphic
features directly to the sea-level curve, the relative roles other
allocyclic processes play (in particular, climate change and asso-
ciated sediment supply) in influencing stratal stacking patterns
can be examined, and that is our ultimate objective.
One of the most confusing terms is “highstand systems tract”.
Because the highstand systems tract, by definition, rests above
the maximum flooding surface and below the sequence bound-
ary (Posamentier and Vail, 1988), it usually spans the period of
falling sea level. Likewise, when defining systems tracts purely
by their internal geometries (descriptively as opposed to geneti-
cally),itisclearthatthelowstandsystemstractmayincludemuch
of the time interval when sea level is rising (Nystuen, 1998).
Plint and Nummedal (2000) have suggested a new systems
tract, the falling-stage systems tract (FSST), which lies above
and basinward of the highstand systems tract and below the
lowstand systems tract. The term falling-stage systems tract is
more intuitive than highstand systems tract when referring to
the time when sea level is actually falling. But, the term has not
been widely accepted. Plint and Nummedal (2000) point out
that the most diagnostic criteria of the FSST are the presence of
erosionally based shoreface sand bodies in nearshore areas.
The erosion results from wave scour during sea-level fall
(regressive surface of marine erosion). This approach stems
from outcrop studies where such associations may be evident.
When working with seismic data and core logs, however, it is
not always possible to trace the base of the falling-stage sys-
tems tract.
A lingering controversy in sequence stratigraphy concerns
which surfaces should be used to subdivide sequences and
how these surfaces are identified. The Exxon model (Vail et al.,
1977a, 1977b; Vail et al., 1977c) favors use of the sequence
boundary. This surface of subaerial exposure and fluvial ero-
sion forms during much of the time interval when sea level is
FIG. 3.—Composite oxygen isotope records (Labeyrie et al., 1987; Shackleton, 1987) calibrated with U–Th dates on corals (Bard et al.,
1990; Chappell et al., 1996) and the Stage 3 paleoshoreline position on the Texas shelf (Rodriguez et al., 2000) are integrated and
used as a sea-level proxy curve for the past 140,000 years. Curve A is the SPECMAP oxygen isotope curve that shows the last four
glacial cycles (from Imbrie et al., 1984). Curve B shows the isotope curve converted to sea level with sea-level datums noted.
OIS 1
HST (early)
230 Th age (kyr)
U/Th dates of
Barbados corals
(Bard et al., 1990)
OIS 2 OIS 3 OIS 5
e
c
a
OIS
6
OIS
4
b d
20
0
-20
-40
-60
-80
-100
-120
-140
0 20 40 60 80 100 120 140
sealevel(m)
U/Th dates of
Huon, New
Guinea corals
(Chappell et al.,
1996)
New Guinea
lowstand deposits
(Chappell et al.,
1996)
Rodriguez et al., 2000
2
3
4
5a
5b
5c
5d
5e
6
7
8
9
10
11
12
0 100 200 300 400
Years BP (x 1000)
Glacioeustasy(m)
0
-120
18O(0
/00PDB)
-2.0
-1.0
0
1.0
2.0
TST LST HST (Late)
5e MFS
3 MFS
Stage 3
A
B
Benthic δδδδδ18O curve,
Norwegian Sea
(Labeyrie et al., 1987)
Composite
benthic/planktic δδδδδ18O
curve, Pacific Ocean
(Shackleton, 1987)

FIG.4.—A)SeismiclinesG-300XandLineG-90Yareusedtoillustratethekeyseismicstratigraphicsurfacesandgeneralizedstratalstackingpatternsonthemargin.The
stage5emaximumfloodingsurface(mfs)andthestage3maximumfloodingsurfaceareprominentdownlapsurfacesrecognizedatthebaseofhighstanddeltasthat
progradedacrosstheshelf,inthiscasetheancestralBrazosDelta.Thestage2sequenceboundary(SB)isalowstanderosionalsurfacethatoverlieshighstanddeltas.
Thetransgressivesurface,whichseparatesthelowstandandtransgressivesystemstracts,mergeswiththesequenceboundaryontheinnershelf,sothattransgressive
depositsliedirectlyonhighstanddeposits.Thetwolinesrepresentaneast–westtonorth–southsectionsoastofollowthemaindepositionalaxisoftheBrazosdelta
(afterRodriguezetal.,2000).B)SeismiclineR93-51isastrike-orientedprofilethatextendsalongtheoutershelf.ItcrossesthelatehighstandandlowstandColorado
andBrazosdeltasandthelowstandTrinity–Sabine–Brazosdeltaandillustratesthedifferentagesoftheseshelf-margindeltas.
10kilometers
40
80
120
160
200
Two-wayTravelTime(ms)LineR93-51
multiple
seafloor
earlyStage3
ColoradoDelta
lateStage3
ColoradoDelta
Stage2
SB
Stage3
BrazosDelta
0
30
60
90
120
Depth(m)
LineG300X
240
Stage2-1
Trinity/
Sabine/
Brazos
Delta
100
200
300
400
SouthEast
kilometers
1230
Two-WayTravelTime(ms)
Stage2lowstand
deposits
Stage3late
highstanddelta
Stage5early
highstanddelta
Stage2SB
Stage5emfsStage3mfs
multiple
LineR93-51
LineG-300XLineG-90Y
Transgressive
surface
Stage2-1
Colorado
Delta
A
B
NorthWest
WestEast

falling as well as the lowstand (Posamentier et al., 1988;
Posamentieretal.,1992).Galloway(1989)hassuggestedthatthe
maximum flooding surface, a condensed section formed during
the maximum flooding of the shelf, is the more prominent and
less diachronous surface and therefore should be used for
division of sequences. Sydow and Roberts (1994) used maxi-
mum flooding surfaces to subdivide the stratigraphic package
of the Lagniappe Delta because those surfaces were easier to
recognize than sequence boundaries, both on the slope and on
the shelf. On the Texas shelf, the sequence boundary is the more
prominent surface. Without question, this investigation dem-
onstrates that it is at the maximum lowstand when the most
basinward subaerial exposure and sediment bypass of the shelf
occurs. This is also the time when maximum incision of fluvial
valleys takes place.
Sediments that are eroded on the shelf to form the sequence
boundary are deposited on the slope to create a conformable
section, which may be quite thick. Should the sequence bound-
ary be placed above or below this section? For the most part,
delta development across the northern Gulf of Mexico shelf
during the late Quaternary occurred throughout the falling
limb of the sea-level curve (Fig. 4). These deltas reached the
shelf margin at different times, depending on the sediment
supply of their fluvial feeders. Some (e.g., the Brazos Delta)
were active during the falling stage of sea level; others (e.g.,the
Rio Grande) were most active during the lowstand; and others
remained active during the transgression (Trinity/Sabine/
Brazos deltas). For the most part, these deltas downlap the
maximumfloodingsurfaceandliebeneaththesequencebound-
ary (Fig. 4).
During the fall in sea level, shelf accommodation decreases
and deposition on the shelf shifts seaward, with erosion of inner-
shelf strata contributing to the nourishment of outer-shelf strata.
Thisconcepthasbeenaroundformorethanacentury(Chamberlin,
1898), but sequence stratigraphers have redefined it as a forced
regression (Posamentier et al., 1992) and yet another systems
tract, the forced regressive systems tract, has emerged (Hunt and
Tucker, 1992). The lower boundary of the forced regressive
systems tract (FRST) is the basal surface of forced regressions
(HuntandTucker,1995),whichiswherePosamentieretal.(1992)
and Posamentier and Morris (2000) would place the sequence
boundary. It is easily confused with the maximum flooding
surface.
Along-strikevariabilityinlateQuaternarystratalarchitecture
across the northern Gulf of Mexico margin is the rule rather and
the exception. This variability results from differences in the
timing and extent of delta progradation across the shelf, which is
controlled by the long-term sediment discharge of rivers (Fig. 4).
Figure 4 illustrates the problem. At this location on the shelf, the
Brazos delta prograded across the shelf prior to progradation of
the Colorado delta. This example illustrates why it is difficult to
trace the base of the forced regression. Kolla et al. (2000),
Hernández-Molina et al. (2000), and Trincardi and Correggiari
(2000) also found that the forced regressive surface is difficult to
recognizeandmapregionally,evenwiththebesthigh-resolution
seismic data.
Chronostratigraphy
Inthestudyareas,thechronologicframeworkwasdeveloped
by integrating foraminiferal abundance variations, foraminiferal
extinctions, tephrochronology, oxygen isotope stratigraphy, and
radiocarbon dates. This integrated chronology builds on previ-
ous work in the Gulf of Mexico by industry and academic inves-
tigators.
Biostratigraphy.—
Planktonic foraminiferal assemblages have long been used
to identify cold-water and warm-water intervals and to deter-
mine the age of the intervals (Ericson and Wollin, 1968; Thunell,
1984; Kohl, 1986; Kohl et al., this volume). Fluctuations in the
occurrenceoftwospeciesofplanktonicforaminifera,Globorotalia
menardii and Globorotalia inflata, are used to define Ericson zones
(Ericson and Wollin, 1968). This zonation was later modified by
KennettandHuddlestun (1972),whoexaminedthequantitative
presence or absence of the Globorotalia menardii complex and
several other foraminifera species in piston cores from the Gulf.
This modified zonation was used only when sufficient numbers
of planktonic foraminifera were present (e.g., Banfield et al., this
volume) (Fig. 5). The extinction of Globorotalia menardii flexuosa,
interpreted as occurring near the oxygen isotope boundary
between stages 5a and 5b (approximately 85 ka) and the first-
appearancedatumofthecalcareousnannofossilEmilianiahuxleyi
in stage 8 (approximately 260 ka) provide other important
biostratigraphic benchmarks for this study (Kennett and
Huddlestun, 1972; Poag and Valentine, 1976; Kohl et al., this
volume).
On the east Texas and western Louisiana shelves, planktonic
foraminifera are generally restricted to those stratigraphic inter-
vals that record maximum flooding of the shelf. Benthic foramin-
ifera, however, are generally more abundant in cores from this
sector of the northern Gulf. Thus, detailed analyses of benthic
foraminifera were conducted on cores and the paleobathymetric
curves generated from these analyses used to refine our oxygen
isotope and seismic stratigraphic interpretations in areas west of
themodernMississippidelta(Abdulahetal.,thisvolume;Wellner
et al. this volume). In areas east of the Mississippi delta, particu-
larlyattheshelfedgeandontheupperslope,planktonicforamin-
ifera are more abundant and provide the basis for additional
oxygen isotope and biostratigraphic interpretation (Fillon et al.,
this volume; Kohl et al., this volume).
Radiocarbon Dating.—
Conventionalandacceleratormassspectrometerradiocarbon
datesprovidefurtherinformationforthelastglacioeustaticcycle.
The maximum age that can be determined using AMS radiocar-
bon methods depends on sample quality but is about 40 ka None
of the authors exclude any samples for which radiocarbon dates
were obtained. Out-of-order dates can provide important infor-
mation on flooding and erosion on the shelf (see discussion by
Fillon et al., this volume).
Oxygen Isotope Stratigraphy.—
In this project, the global oxygen isotope curve is used as a
proxy sea-level curve. In addition, oxygen isotope curves were
generated within some study areas as a chronostratigraphic
framework and for correlation between study areas (Abdulah et
al.,thisvolume;BanfieldandAnderson,thisvolume;Ecklesetal.,
this volume; Fillon et al., this volume).
Previous oxygen isotope stratigraphic studies have tended to
avoid the continental shelf. This was due to concerns about
incomplete stratigraphic section due to erosion, variable deposi-
tion rates, paucity of planktonic foraminifers, diagenetic alter-
ation, and fresh-water contamination overwhelming the isotopic
signal (see discussion in Fillon et al., this volume). Furthermore,
foraminifera are patchy in their down-core distribution on the
Texas and Louisiana outer shelf and planktonic foraminifera are
restricted to highstand deposits. In the ideal case, seismic strati-

graphic analyses could be used to locate optimal core locations
and compile the most complete stratigraphic section using care-
fully selected cores from the outer shelf. But, with the exception
of the Lagniappe delta study (Fillon et al. this volume; Roberts et
al. this volume; Kohl this volume), the authors did not have the
option of planning core locations.
Despitetheseproblems,theresultsofstudiescontainedinthis
volume indicate that a useful oxygen isotope record can be
extracted from continental-shelf cores, given a seismic strati-
graphic framework and results from paleontological and radio-
carbon analyses (Fig. 5). That framework provides information
on where within the section there are unconformities and yields
information about where deposition was occurring on the shelf
during a particular time interval.
The oxygen isotope curves generated for this project were
interpreted by comparing them with reference oxygen isotope
curves of Globogerinoides ruber from Gulf of Mexico and Carib-
bean cores. The two reference curves are from DSDP site 619 in
the Pigmy Basin offshore Louisiana (Williams and Kohl, 1986)
and the southwestern Gulf of Mexico (TR-126-23; Williams,
1984). The Caribbean reference curve is a stacked isotope record
assembled from several deep-sea piston cores (Emiliani, 1978).
In addition, to provide stratigraphic benchmarks, these oxygen
isotope records also record the influx of 16O-rich meltwater into
the northern Gulf during the retreat of the Laurentide ice sheet.
Meltwater that flowed down the Mississippi River between 14
ka and 12 ka (Leventer et al., 1982; Fillon and Williams, 1984;
Williams and Kohl, 1986; Brown and Kennett, 1998) created a
negative spike in the planktonic oxygen isotope records of the
Gulf of Mexico (Kennett and Shackleton, 1975; Leventer et al.,
1982). At about 12 ka the outflow of meltwater shifted to the
Atlantic Ocean, through the Champlain–Hudson Valley (Teller,
1987). Older meltwater spikes associated with stage 5 through
stage 3 glaciation also have been identified in the Gulf of Mexico
by Williams (1984), Trainer and Williams (1990), and Joyce et al.
(1993).
Our chronostratigraphic framework is generally not precise
enough to allow identification of individual meltwater pulses,
with the possible exception of the 14 ka to 12 ka meltwater event
(Abdulah et al., this volume; Banfield and Anderson, this vol-
ume; Fillon et al., this volume) and a 260 ka stage 12-stage 13
transition meltwater event (Fillon et al., this volume). All of the
isotope curves from the Texas shelf show that possible meltwa-
ter spikes occur within the stage 3 interval of the cores. In
general, the magnitude of oxygen isotope variations due to
meltwater influx decreases westward away from the Missis-
sippi River and is low east of the river. The possibility that these
meltwater events indicate ice-volume-related eustatic events is
discounted. This is based on the observation that none of the
stage 3 deltas studied show the kinds of backstepping and
prograding character that would have occurred if these deltas
had been subjected to eustatic changes of the magnitude indi-
cated (tens of meters) by the spikes.
Sea-Level Record
The relationship between the oxygen isotope record and
global ice volume (Shackleton and Opdyke, 1973) provides a
proxy for changes in global sea level (Shackleton, 1987) (Fig. 3).
The conversion of the isotope curve to sea level assumes that sea
0
10
20
30
40
50
60
70
80
90
100
110
0.0 -1.0 -2.0 -3.0 -4.0
Depth(m)
clay
fine sand
clay
iii: Possible 42,800 to 44,300 (Williams and Kohl, 1986)
ii: 45,210 980 yr. B.P. at 10.7 m from AMS age date
i: 4,490 70 yr. B.P. at 5.8 m from AMS age date
vi: 85,000 yr. B.P. extinction of G. menardi flexuosa
6
5e
5d
5c
5b
5a
3
1 Z
i
ii iii
vi
missing
section
missing
section
iv
v
iv: 45,140 1,300 yr. B.P. at 14.0 m from AMS age date
v: Possible 60,700 (Williams and Kohl, 1986)
core B-2
2sb-ts
3mfs
5c
5d
5emfs
W E
Line 5
Two-waytraveltime(ms)
250
200
150
0
20
40
60
80
100
Depth(m)
A
core B-2
X
Y
B δ18O
FIG. 5.—A) A segment of seismic Line 5 from the south Texas shelf showing the location of core B-2 and the key seismic stratigraphic
surfaces sampled by this core. B) Oxygen isotope curve for Core B-2, showing chronostratigraphic benchmarks for seismic
stratigraphic correlation of late Pleistocene strata on the shelf and upper slope (after Rodriguez et al., 2000). Also shown are
Ericson zones (X–Z) as described by Kohl et al. (this volume).

level was 6 m higher than today during the last interglacial and
120 m lower than the present level during the last glacial. A 10 m
sea-level change for every 0.1 per mil change in δ18O, after
Shackleton and Opdyke (1973), provides the basis for sea-level
curves used in this volume (e.g., Fig. 3).
The proxy sea-level curve in Figure 3 is constrained by U–Th
dated sea-level stands for the interval between stage 5e and early
stage 2 by in situcorals (Bard et al., 1996; Chappell et al., 1996) and
is more tightly constrained for the time interval between late
stage 2 (ca. 18 ka) to present by radiocarbon-dated shell and peat
samples (e.g., Bloom, 1983). The seismic stratigraphic results of
this study show reasonable agreement with the isotope curve,
with the exception of the amplitude of isotope stage 3. Data from
this study show a sea-level stand of -15 m to -20 m for the highest
sea-level position during isotope Stage 3 (Rodriguez et al., 2000).
This is consistent with earlier studies in the Gulf (Suter et al.,
1987), offshore New Jersey (Wellner et al., 1993), and offshore
southeastAustralia(Royetal.,1997)andwithpublishedsea-level
reconstructions (Matthews, 1990; Moore, 1982; Chappell et al.,
1996; Kaufmann, 1997) used in the Lagniappe delta study (Fillon
et al., this volume).
Despite its inaccuracies, the proxy sea-level curve, like that
shown in Figure 3, is the most precise sea-level record for all of
geological time. It is generally accurate to within ± 30 m for the
timeintervalbetween120kaand15ka,andtowithin ±5mforthe
past 15,000 years. Oxygen isotope curves also provide the most
accurate indication of the timing and frequency of glacioeustatic
change.
Subsidence Rates
In this volume we constrain tectonic subsidence rates on the
shelf using maps of the elevations of the stage 5e maximum
flooding surface (Fig. 4). The assumption made in these calcula-
tions is that the relative water depth at the shelf break was
approximately the same at the onset of stage 5 interglacial condi-
tions as it is today. Stage 5e deposits occur at about 6 m above sea
level on the modern coastal plain and are exposed or nearly
exposed a short distance from the coast. Thus, subsidence rates
are negligible along the coast. In general, all along the Gulf
margin, the thickness of strata resting above the 5e maximum
flooding surface increases more or less linearly across the shelf.
This implies that subsidence rates increase linearly in an offshore
direction. Measured rates of subsidence are highest on the Texas
and Louisiana shelves and decrease from west to east across the
Mississippi and Alabama–west Florida shelves (Table 1). A dis-
cussion of the processes contributing to subsidence on the outer
shelf is contained in the paper by Fillon et al. (this volume).
RESULTS
Dataandinterpretationspresentedinthisvolumeprovidethe
basis for reconstructing summary paleogeographic maps (Figs.
6–8) that display the major depositional systems (systems tracts)
on the shelf and upper slope during the intervals 120 ka to 22 ka,
22 ka to 16 ka, and 16 ka to 4 ka. We selected these periods of time
for our paleogeographic reconstructions because they represent
Deltas
Channels and valleys
30
26
?
Shoreface deposits
Shelf muds
Legend
kilometers
0 200
RGD
CD
BD WLD
WLD
LD
EMD
28
AD
94 88
Highstand Systems Tract (Stage 5e-3)
98 96 92 90 86
1
2 3
1
1
2
2
3
1
2
4
WFLAD
FIG. 6.—Paleogeographic map showing major depositional systems that existed on the shelf 120 ka to 22 ka (stages 5e–3 highstand;
Fig. 3). The different lobes of individual deltas are numbered in chronological order. RGD = Rio Grande Delta, CD = Colorado
Delta, BD = Brazos Delta, WLD = Western Louisiana Delta, LD = Lagniappe Delta, EMD = Eastern Mobile Delta, WFLAD = West
Florida–Alabama Delta, and AD = Apalachicola Delta.
East Texas
Trinity/
Sabine
Western
Louisiana
East Texas
Brazos/
Colorado
Central
Texas
South
Texas
FlorAla Apalachicola

keyepisodesofsea-levelchange(Fig.3).Theindividualpapersin
this volume provide more detailed paleogeographic informa-
tion.
Correlation of strata between study areas is accomplished
using three prominent stratigraphic surfaces (Fig. 4). The oldest
of these surfaces is the stage 5e maximum flooding surface
(condensed section), which precedes the last high sea-level stand
at approximately 120 ka (Fig. 3). The stage 5e maximum flooding
surface is a downlap surface in most of the region (Fig. 4). It is
recognized in outer-shelf and upper-slope cores by a sharp in-
crease in planktonic foraminifera, by the presence of Globorotalia
flexuosa, and by a characteristic oxygen isotope signature (Fig. 5).
The highstand systems tract (in the Exxon sense) occurs between
this flooding surface and the stage 2 sequence boundary (Fig. 4).
There is another prominent flooding surface associated with the
stage 3 sea-level rise, but no prominent erosional surface is
reported that records the stage 4 sea-level fall (Fig. 3). On many
parts of the shelf, a stage 3 flooding surface separates early
highstand (stage 5) strata, which are confined mostly to the inner
shelf, from stage 3 to stage 2 strata, which occur mostly on the
outer shelf and slope (Fig. 4).
The third prominent stratigraphic surface is the stage 2 se-
quence boundary. It is a prominent erosional surface, marked by
deep fluvial valleys and truncation of delta topset beds (Fig. 4).
This surface is manifested in cores and platform borings by an
abrupt change in lithology, a dramatic change in sediment shear
strength (indicating prolonged exposure), general reduction of
fossils, and a characteristic oxygen isotope signature (Fig. 5).
Preservation of lowstand deposits on the shelf above the se-
quence boundary is minimal, except in incised valleys. Deposits
of the lowstand systems tract are confined mostly to the outer
shelf and slope (Fig. 7). They are separated from transgressive
deposits by the transgressive surface. The transgressive surface
correlates up dip to the first marine incursion onto the shelf (Fig.
4A).Ontheinnershelf,depositsofthetransgressivesystemstract
often rest on a surface that is the composite sequence boundary–
transgressive surface.
120 ka to 70 ka (Early Highstand)
Approximately 120,000 years before present, sea level was at
its maximum highstand position, a few meters above present
sea level (Fig. 3). An ancestral beach-ridge complex, referred to
as the Ingleside paleoshoreline, marks the location of this maxi-
mum highstand (Graf, 1966). In Texas and Louisiana, the
Ingleside paleoshoreline is located several kilometers landward
ofthemodernshoreline.Thisisthemostextensivepaleoshoreline
deposit of the last eustatic cycle. Its preservation suggests that
it was never subjected to either transgressive or regressive
shoreface erosion. North of the Ingleside paleoshoreline in
Texas, the landscape is dominated by fluvial meanderbelts that
spantheentireglacialeustaticcycle.Southofthispaleoshoreline
the coastal plain is virtually flat. Older fluvial channels are
mostlyburiedbeneathHolocenecoastal-plaindeposits.Stacked
maximum highstand fluvial channels can be seen in the many
sandpits that occur in the old Brazos and Colorado valley
systems.
After the last interglacial the ice sheets in both hemispheres
began to expand, and sea level fell episodically. By the end of
Stage 5 the paleoshoreline was located on the middle shelf, at
FIG. 7.—Paleogeographic map showing the major depositional systems that existed on the shelf and upper slope during the 22 ka to
16 ka (stage 2) lowstand (Fig. 3). Lowstand incised valleys are labeled as follows. RGV = Rio Grande, CV = Colorado, BV = Brazos,
T/SV = Trinity–Sabine, WMV = west Mobile, and EMV = east Mobile. MC = Mississippi Canyon.
98 96 94 92 90 88 86
30
28
26
Incised valley
Delta or wedge
Slope deposit
Legend
FlorAla
East Texas
Trinity/
Sabine
Western
Louisiana
East Texas
Brazos/
Colorado
kilometers
0
RGV
CV
BV
T/SV
Apalachicola
Lowstand Systems Tract (Stage 2)
200
MC
WMV
EMV
South
Texas
Central
Texas

98 96 94 92 90 88 86
30
28
26
Incised valley
Delta or wedge
Legend
0 200
Kilometers
MAFLA
Texas mud
Sand banks
100m
Transgressive Systems Tract (Stage 1)
MFLA
TMB
Shelf muds
approximately 60 m below present sea level (Fig. 3). This interval
of time when the paleoshoreline moved across the inner shelf is
referred to as the early highstand. The early highstand saw
increased sediment supply to the basin, as a result of fluvial
incision,whichremovedsedimentsstoredinthelowerreachesof
the drainage basins. During the early highstand, deposition was
confined to the inner shelf where subsidence rates are low, hence
preservationwaslow.Forthisreason,earlyhighstandstratahave
a patchy distribution on the inner shelf of Texas and are generally
absent on the Alabama and west Florida inner shelves (Fig. 6).
Early highstand deposits are more extensive on the western
Louisiana shelf, where subsidence rates are high (Wellner et al.,
this volume).
During the Stage 5 interglacial high-sea-level episode, a sig-
nificant portion of the Mississippi River drainage was directed
toward the western Louisiana shelf. There, a large, sandy
highstand delta existed (Fig. 6; Coleman and Roberts, 1990;
Wellner et al., this volume). Likewise, highstand deltas were
associated with the ancestral Rio Grande, Colorado, and Brazos
Rivers in Texas (Banfield and Anderson, this volume; Abdulah et
al., this volume), and with rivers east of the modern Mississippi
delta (Fig. 6). As sea level fell during stage 5 (Fig. 3), these deltas
prograded basinward and their updip portions suffered consid-
erable erosion by rivers and streams and by waves (regressive
shoreface erosion). Again, the relatively low subsidence rates on
the inner shelf contributed to the poor preservation of the early
highstand deltas. Erosion of the upper portions of these deltas
removed the upper sand-prone fluvial and delta-front deposits,
leaving mostly muddy distal bar and prodelta deposits on the
inner shelf. The only exception to this was the western Louisiana
Delta, which includes widespread sandy facies on the inner shelf
(Coleman and Roberts, 1990).
Rivers with relatively low sediment fluxes, such as the Trinity
and Sabine, apparently did not construct large deltas on the
continental shelf during the early highstand. On the Alabama–
west Florida shelf, early highstand deposits are thin and patchy.
They may be the remnants of a once extensive braided sheet sand
thatformedonthesteepshelfassealevelfell(BartandAnderson,
this volume; McKeown et al., this volume).
On the central Texas shelf, where there are no large rivers,
depositionduringthisperiodwasdominatedbycoastalandshelf
processes (Eckles et al., this volume). These systems were fed by
sediment eroded from adjacent deltaic headlands and delivered
to the central Texas coast by longshore currents flowing from the
east and south. Prograded clastic shoreline and shoreface depos-
itsarepreservedontheinnershelf.Overthelongterm,accommo-
dationspacecreatedbysubsidencewasnotbeingfilled,resulting
in the narrow, steep shelf physiography of this region.
70 ka to 22 ka (Late Highstand “Falling Stage”)
Approximately 70 ka, during stage 4, sea level fell then rose
rapidly, culminating in the stage 3 flooding event (Fig. 3). At the
peak of the flooding the paleoshoreline was located on the inner
shelf, perhaps as high as -15 m (Rodriguez et al., 2000). Following
the flooding episode, falling sea level again shifted the
paleoshoreline to the outer shelf, causing incision of fluvial
channels during stage 2.
Deltas constructed during this period of falling sea level
generally contain more sediment than early highstand deltas,
FIG. 8.—Paleogeographic map showing the major depositional systems that existed on the shelf during the 16 ka to 4 ka (stages 2–1)
transgression (Fig. 3). TMB = Texas Mud Blanket; MAFLA = MAFLA sheet sand. The transgressive deltas of the Mississippi River
are taken from Frazier (1967).
East Texas
Brazos/
Colorado
East Texas
Trinity/
Sabine
Central
Texas
South
Texas
Western
Louisiana
FlorAla Apalachicola

deposited in the interval 120 ka to 70 ka, despite the fact that stage
3 was no longer in duration than stage 5. During stage 3, deposi-
tion was greatest on the outer shelf where subsidence rates, and
therefore preservation potential, are high (Fig. 4). Also, cannibal-
ization of stage 5 deposits by fluvial processes and regressive
shoreface erosion resulted in a large offshore flux of sediment,
and hence contributed to the volume of the stage 3 deposits (Fig.
4A). Large stage 3–stage 2 deltas were associated with the Rio
Grande, Colorado, Brazos, western Louisiana, west Mobile–
Pascagoula (Lagniappe delta), east Mobile, Perdido–Escambia,
and Apalachicola rivers (Fig. 6).
The Rio Grande, Colorado, Brazos, and western Louisiana
deltas of this age are characterized by clinoforms that dip at low
angles (less than 3°) and are composed mainly of prodelta muds
(Fig. 9A). The topset beds of these late highstand deltas do,
however, include extensive, sandy fluvial feeder channels and
distributary-mouth bars. Indeed, the sandy mouth bars of these
deltas cover vast areas on the outer shelf (Fig. 6; Abdulah et al.,
this volume; Banfield and Anderson, this volume; Wellner et al.,
this volume). The Lagniappe delta also contains thick and
extensive delta-front sand deposits (Sydow and Roberts, 1994;
Roberts et al., this volume). West Florida–Alabama late high-
stand deltas have relatively steep clinoforms (greater than 3°)
and little or no bottomset (prodelta) beds (Fig. 9B). These fea-
tures, in conjunction with seismic facies interpretation, indicate
that late highstand deltas on the ramp-like outer shelf are sand-
prone (Bart and Anderson, this volume; McKeown et al., this
volume). On this slowly subsiding part of the margin, accom-
modation space was minimal, so these deltas experienced large
lateral shifts.
The larger river deltas of the northern Gulf of Mexico shelf
experienced virtually continuous growth during the stage 3 sea-
levelfall(Figs.4A,6).Thesedeltasweresituatedinashelf-margin
position at the end of the late highstand (Fig. 4). However, the
times at which individual deltas reached the shelf margin vary
acrosstheregion,presumablyasaresultofthedifferentsediment
discharge of the rivers. The diachronous progradation of deltas
across the outer shelf is illustrated in seismic profile R93-51, a
strike-oriented profile collected across the outer shelf (Fig. 4B).
This profile shows that the younger late stage 2 Colorado and
Trinity–Sabine–Brazosshelf-margindeltasonlaptheolderstages
3–2 Brazos delta. The stage 3–early stage 2 Brazos delta progra-
dedacrosstheoutershelffirst,followedbytheotherdeltas.Thus,
noteveryshelf-margindeltaisinthelowstandsystemstract.This
is an important point because it is implicit that not every shelf-
margin delta is associated with a slope fan or basin-floor fan. It
also explains why shelf-margin deltas can be large, despite the
brief time span of the lowstand.
Line R93-51 (Fig. 4B) also illustrates how dip lines across the
shelf margin may image the superimposed clinoforms of tempo-
rally offset deltas. This results in different stratigraphic architec-
tures at different locations along the outer shelf and upper slope.
The diachronous response of deltas to sea-level rise along the
Gulf margin is similar to that observed in the Adriatic Basin by
Trincardi et al. (1994).
On the central Texas shelf, sandy prograding clastic shoreline
and shoreface deposits grade offshore into shelf muds; there are
no outer-shelf sand bodies in that area. Prograding shorelines
associated with the early fall in sea level were unable to keep pace
with the rapid fall that occurred during stage 4. This was largely
due to reduced sediment supply during this time (see discussion
inEcklesetal.,thisvolume).Bythelatehighstand,theRioGrande
and Colorado deltas, which had served as longshore sediment
sources for the central Texas shelf during the early highstand,
were not being eroded as extensively as they were during the
early highstand. Thus, sand deposition occurred in different
environments and at different times across the Texas shelf.
22 ka to 16 ka (Lowstand)
During the lowstand, streams and rivers cut their deepest
incised valleys, to produce the Stage 2 sequence boundary, and
significant volumes of sediment bypassed the shelf (Fig. 7). The
stage2sequenceboundaryisaprominentsurfacethroughoutthe
northern Gulf of Mexico and constitutes a definitive surface for
separating highstand and lowstand systems tracts. On the basis
of global sea-level curves (Fig. 3), the paleoshoreline in the
northern Gulf was situated at or near the shelf break (approxi-
mately -120 m water depth) during the last glacial maximum.
Thus, the shelf was subarially exposed. The exact age and dura-
tion of the stage 2 lowstand is still uncertain, but it spanned only
afewthousandyears.Prominentfeaturesofthelowstandinclude
incised fluvial valleys, lowstand deltas, slope fans, and other
sediment-gravity-flow deposits (Fig. 7).
Lowstand fluvial valleys of the northern Gulf of Mexico vary
considerably in their morphology. In general, the low-gradient
east Texas and western Louisiana shelves are characterized by
valleys that become broader and shallower in a seaward direc-
tion. On average, these valleys are 40 m deep at the present
shoreline, which is about the same depth of incision as during the
previous lowstand (Blum and Price, 1998). The similarity in
depths of incision of different rivers, which vary in terms of
discharge and gradient, indicates a similar response to base-level
fall regardless of these differences.
The Rio Grande and Colorado rivers remained relatively
fixed in their locations throughout the highstand, resulting in
broad channels that subsequently were incised during the maxi-
mum lowstand. These incised channels deepen offshore, cutting
into late highstand and lowstand deltas to produce sandy slope
fans. In contrast, the Brazos and western Louisiana rivers di-
verted from their late highstand channels into different locations
at the beginning of the lowstand, leaving their broad feeder
channels and associated highstand deltas isolated on the shelf.
There are no slope fans downdip of these features. The Trinity
and Sabine rivers have occupied the same valleys throughout the
eustatic cycle, and apparently during previous eustatic cycles.
Broad, terraced cross sections and a deep, U-shaped incision
characterize these channels and sediment bypass during re-
peated eustatic lowstands has nourished fans within slope
minibasins (Anderson and Rodriguez, 2000).
On the ramp-like central Texas shelf, distinct fluvial channels
are evident only on the inner shelf, a result of the fact that
gradients on the inner shelf were lower than river gradients and
outer-shelf gradients (Eckles et al., this volume). The steep ramp-
like west Florida shelf is characterized by extensive but shallow
braided channel complexes on the inner shelf and discrete late-
highstand to lowstand channels on the outer shelf (McKeown et
al., this volume). This difference between the central Texas and
westFloridafluvialgeomorphologiesreflects,inpart,differences
in substrate conditions on the shelf. West Florida rivers flowed
across sandy substrates so that they were laden with bedload
material. On the central Texas shelf, rivers cut into muddy
sediments and delivered little sand to the outer shelf and slope;
they were suspended load-dominated rivers.
Incised fluvial valleys vary widely in their morphology, de-
pending on when these valleys were cut within the overall
eustatic cycle, differences in relative fluvial and shelf profiles,
and substrate conditions (muddy versus sandy shelves). At-
tempts to characterize incised fluvial valleys based on a single
shelf setting (e.g., Posamantier, 2001), can therefore be mislead-

FIG.9.—SeismiclinesG-410andAPL19areusedtocontrastthestratigraphicarchitecturesoftheA)eastTexasandB)westFloridamargins,respectively.TheEastTexas
shelfischaracterizedbycontinuousdeltaprogradationduringthehighstandthroughtheearlytransgressionwithaprominentlowstanddeltaandslopefan.Theramp-
likewestFloridamarginischaracterizedbyprominenthighstanddeltasandapaucityoflowstandstrata.
0
100
200
NS
multiple
MFS-7
SB-6
1kilometer
v.e.~33x
MFS-5
-
TS
APL19
Delta
B
Upperslopemaximum
1km
V.E.=17x
fault
5eMFS
h
b
Two-WayTravelTime
(ms)
100
200
300
ravinementsurfaceSB2
WaterBottomMultiple
Sediment
gravityflow
5eMFS
a
b
G-410
Shelf-edgedelta
g
fedc
TS
A
APL19
SB-2
Two-WayTravelTime(ms)
Two-WayTravelTime
(ms)
A
B
V.E.~33x
0km1

ing.Furthermore,subdivisionofvalley-filldepositsintodifferent
systems tracts (e.g., Van Wagoner et al., 1990) offers serious
challenges (Blum, 1993; Blum and Valastro, 1994; Ethridge et al.,
1998).
The shelf-margin deltas of the northern Gulf margin show a
complex pattern of progradation and aggradation that varies
from one delta to the next. This complexity reflects the part of the
eustatic cycle over which these deltas were constructed. Some
deltas were active during the late highstand through the early
transgression, such as the Colorado, Rio Grande, and Lagniappe
deltas. Other deltas, such as the Trinity/Sabine/Brazos delta,
were nourished during the lowstand and a significant part of the
transgression (Fig. 4B).
16 ka to 4 ka (Transgression)
The final episode of sea-sea level change occurred between
approximately 16 ka and 4 ka During this period, melting ice
sheets contributed just over 100 m of sea-level rise to the oceans.
There are several different depositional systems associated with
the transgressive episode in the northern Gulf of Mexico (Fig. 8).
These include shelf-margin deltas, fluvial- and wave-dominated
deltas, thick shelf muds, incised-valley fills, sand banks and
ridges, and transgressive sheet sands.
Transgressive, backstepping deltas are associated with those
rivers with the largest sediment fluxes (Mississippi, Rio Grande,
Colorado, Brazos, and Apalachicola). The absolute age of these
deltas appears to differ, on the basis of their location on the shelf,
and their development appears to have been rapid and short-
lived. These deltas prograded across the shelf at a time when sea
level was rising rapidly (Fig. 3). Episodes of delta growth suggest
increased sediment supply, believed to have been caused by
climatic changes, which occurred at different times in the differ-
ent study areas (Abdulah et al., this volume; Banfield and Ander-
son, this volume).
Just as the morphology of incised fluvial valleys varies across
the northern Gulf of Mexico shelf, so do the types of sediments
that fill these valleys. Transgressive deposits in the Trinity–
Sabine areas are confined to the incised valleys or to areas
immediately adjacent to the incised valleys. In interfluve areas,
the transgressive ravinement surface is amalgamated with the
sequence boundary, as evidenced by a thin (< 1 m) marine mud
unit lying directly on Pleistocene (Stage 3) deposits. The Trinity–
Sabine incised-valley-fill facies architecture consists of discon-
tinuous, backstepping fluvial and estuarine (upper and lower
bay) facies separated by aggradational valley-fill deposits (Tho-
mas and Anderson, 1994). The estuarine facies include upper to
lower bay deposits as well as tidal-inlet sands. Flooding surfaces
often are manifested by an absence of one or more of the valley-
fill facies, and individual flooding events result in updip facies
shifts of many tens of kilometers (Thomas and Anderson, 1994).
On the Mississippi–eastern Louisiana shelf, cored transgressive
deposits range in thickness from 1 m to 9 m and comprise back-
stepping estuarine, sound, and neritic facies (Fillon et al., this
volume; Roberts et al., this volume). In that area, only the latter
part of the transgression appears to be represented. Radiocarbon
dates range from 12.4 ka to 8.24 ka (Fillon et al., this volume).
Underlying coarse fluvial sediments filling the late stage 2 inci-
sion surface are undated but are suspected to be of last glacial
maximum age (Roberts et al., this volume). Similar backstepping
fluvial/estuarine/marine facies characterize fluvial-valley suc-
cessions in western Louisiana (Nicol et al., 1994) and offshore
Alabama (Bartek et al., this volume).
The Brazos and Colorado rivers have larger sediment sup-
plies than the Trinity, Sabine, and probably Mobile rivers. The
BrazosandColoradoriversfilledtheirincisedvalleyswithfluvial
deposits and abandoned them to occupy more shallow valleys.
The result of these fluvial avulsion events has been the formation
of multiple transgressive fluvial channels on the shelf and the
sequestering of a significant volume of fluvial sediments in these
channels.Preservationofthesetransgressivechannelsvariesand
depends on their depth of incision, which in turn is controlled by
wheresealevelwaswhenavulsiontookplace.Olderchannelsare
incised more deeply and hence have better preservation. Trans-
gressive ravinement led to decapitation of fluvial channels and
mouth-bar facies and reworking of these facies into widespread
shelf sand bodies.
On the east Texas shelf, large banks lie adjacent to and above
the Trinity–Sabine incised valley. These banks have been inter-
pretedassubmergedpaleoshorelinescomposedofaback-barrier
estuarine unit at the base, a fore-barrier, lower shoreface and ebb
tidal delta unit above, and a storm-reworked unit at the top
(Nelson and Bray, 1970; Rodriguez et al., 1999). A transgressive
section cored in Main Pass Block 288 at the Lagniappe shelf edge
contains this same succession (Roberts et al., this volume).
Sand ridges characterize the south Texas inner shelf. These
isolated inner-shelf sand ridges formed in situ at present water
depths (Rodriguez et al. 2001). The different origins of east Texas
banks and south Texas ridges are attributed to variations in the
depth of shoreface ravinement (deeper in south Texas), shelf
gradient (steeper in south Texas), and accommodation space
(lower in south Texas) (Rodriguez et al., 2001).
An extensive (24,000 km2) transgressive-sand-ridge field
covers most of the Mississippi–Alabama–Florida shelf in the
northeastern Gulf of Mexico (the MAFLA sand sheet; McBride
et al., 1999; McBride et al., this volume). The MAFLA sand
sheet is bounded below by the transgressive ravinement sur-
face and above by the modern sea floor (the maximum flood-
ing surface) and is composed predominantly of reworked
polycyclic late-highstand and lowstand sand (McBride et al.,
1999).
On the central Texas shelf and south Texas outer shelf, the
youngest deposits of the transgressive systems tract consist of
widespread marine muds of the “Texas Mud Blanket” (Shideler,
1981; Eckles et al., this volume). The mud blanket is up to 45 m
thick in central and south Texas and is composed of sediment
from the Rio Grande to the south and from as far east as the
Mississippi River (Shideler, 1981).
4 ka to Present (Late Holocene Highstand)
Thepresent-daysedimentaryenvironmentrepresentsamaxi-
mum highstand, which is a unique part of the total glacioeustatic
cycle (Fig. 3). Currently, the shelf is flooded and extensive coastal
barriers exist. Onshore, broad meanderbelts occur on the low-
gradient coastal plain and provide storage for vast quantities of
sediment. These meanderbelts, however, are not nearly as exten-
sive as the broad alluvial plains that formed during the previous
maximum highstand (Stage 5e).
During the present highstand, the Mississippi River, with its
huge sediment supply, has prograded far onto the outer conti-
nental shelf. A significant amount of the fine-grained sediment
that is delivered to the Gulf by the Mississippi River is trans-
ported to the west in wind-driven surface currents influenced
by the Coriolis effect. These fine-grained sediments are depos-
ited on the central and south Texas shelves as the Texas Mud
Blanket. Elsewhere on the shelf, sedimentation is at a minimum
and the most important process occurring today is the forma-
tion of a condensed stratigraphic section (maximum flooding
surface).

DISCUSSION
Fluvial Response to Sea-Level (Base-Level) Change
Within the northern Gulf of Mexico Basin, there is a fairly
strong correlation between the long-term sediment supply of
rivers and the size of their drainage basins. Currently, bays
occupy the fluvial valleys of rivers with low sediment discharge,
such as the Trinity, Sabine, and Mobile rivers (Galveston Bay,
Sabine Lake, and Mobile Bay, respectively). Rivers with greater
sedimentdischarge,suchastheBrazosandColoradorivers,have
beguntoconstructprominentdeltaicheadlandsacrossthecoastal
plain (Fig. 8). These differences reflect the inability of smaller
rivers to fill their valleys as fast as sea level rose during the
postglacial transgression.
TheresponseofGulfCoastriverstoeustatic(base-level)change
during the past 120,000 years varied across the shelf. Highstand
fluvial channels are widespread on the shelf, particularly on the
low-gradient Louisiana and east Texas shelves (Berryhill et al.,
1986;Andersonetal.,1996).Ingeneral,channelsthatextendfarther
onto the shelf are deeper and narrower than channels that extend
only short distances across the shelf. This indicates that incision
occurs throughout the falling limb of sea level.
During the last highstand, several of the larger rivers of the
region formed large deltas as sea level first began to fall. The
sediment discharge of these rivers was significantly greater than
today. Estimates of sediment flux of the Rio Grande and Brazos
rivers during the last several highstands were in the range of 1.4
to 2.9 km3/yr and 0.3 to 3.2 km3/yr, respectively. However, this
increaseinsedimentfluxdidnotoccureverywhere.Apalachicola
River sediment flux rates appear to have varied little between the
previoushighstandandcurrenthighstand,averaging0.4km3/yr
and 0.5 km3/yr, respectively (McKeown et al., this volume).
Differences in modern and ancient sediment flux of the larger
Texas rivers versus the Apalachicola River are attributed to
differences in the sediment storage capacity of these rivers. Texas
rivers have much more extensive alluvial plains with significant
sediment storage capacity (Blum and Price, 1998). In contrast,
west Florida rivers, including the Apalachicola River, occupy
relativelyhigh-gradientchannelsthatareincisedintoPleistocene
strata. The coastal plain is narrow and flood plains are small,
hence their sediment storage capacity is relatively small.
Duringafallinsealevel,sedimentsstoredinalluvialdrainage
basins of Texas and Louisiana are eroded as rivers incise, their
tributaries branching out into the alluvial basins (Koss et al.,
1994). The result is a large increase in sediment flux during the
falling limb of the sea-level curve. In contrast, the sediment flux
of west Florida rivers remained relatively unchanged (McKeown
et al., this volume).
Incisedfluvialchannelsalsoexistinthetransgressivesystems
tract of the Louisiana and Texas shelves. In Texas, these channels
are associated with the ancestral Brazos and Colorado rivers.
Avulsion of these rivers during the transgression resulted in
channels being cut to shallower depths as sea level rose. The
younger channels have been deeply eroded by shoreface erosion
andextendoffshoreintomarinemuds.Oldertransgressivechan-
nels extend offshore into transgressive deltas (Abdulah et al., this
volume) and reflect times when sediment supply was greater.
Variationsinsedimentsupplyduringtransgressionswerecaused
by climatic changes.
Climate Control on Sediment Supply to the Basin
Climate variation is known to be a major controlling factor on
fluvial processes (Schumm, 1965, 1993; Hall, 1990; Ethridge et al.,
1998). Indeed, Blum (1993) and Ethridge et al. (1998) conclude
that, because the influence of sea-level (base-level) change on
fluvial morphology diminishes in a landward direction, the
climatic influence on sediment delivery to the basin may be
greater than that of eustasy.
The fluvial response to changes in climate can be very com-
plex. For example, the same river can show different responses
along its course because of changes in gradient and changes in
sedimentloadasitflowsthroughdifferentclimaticbelts(Schumm
and Brakenridge, 1987). In general, the sediment flux of fluvial
systems increases with increasing mean annual precipitation
(Schumm,1965).Butthemannerinwhichthesedimentdischarge
of rivers responds to climate change is more complex than this
simplerelationshipsuggests.Schumm(1965)arguedthatachange
from semiarid to arid conditions would result in a decrease in
sedimentdischarge.Incontrast,achangefromhumidtosemiarid
climates would result in an increase in sediment discharge be-
cause of a decrease in vegetation cover, particularly grasslands.
As previously noted, in the northern Gulf of Mexico basin
there is a fairly strong correlation between the long-term sedi-
ment flux of rivers (i.e., over a complete glacioeustaticcycle) and
the size of their drainage basins. This is in itself an important
finding because the sediment discharge of modern rivers shows
little correlation to drainage-basin size (Hovius, 1998), although
the correlation is stronger when the relief of the drainage basin
is considered (Milliman and Syvitski, 1992; Morehead and
Syvitski, 1999). The timing and volume of sediment influx to the
northern Gulf of Mexico margin during the last eustatic cycle
varied from one river to another. This diachronous influx of
sediment is undoubtedly a result of the different climate set-
tings of the rivers. Currently, climate varies from humid to
semiarid across the study area, with a nearly threefold differ-
ence in mean annual precipitation across the region (Fig. 1). It is
likely that the magnitude and timing of climate change differed
across the region during the last glacial–interglacial cycle (120
ka to present).
Perlmutter et al. (1998) generated computer models that illus-
trate how differences in the timing of sediment discharge during
a glacial-eustatic cycle result in differences in the volumes and
character of different systems tracts. Their work is based on
modern sediment yields, which are quite low compared to other
times in the last 120,000 years. Also, they do not take into account
effects of vegetation changes and rates of soil development and
erosion and the delayed response of these changes on sediment
yield. Their work did show, however, that sediment supply from
modern rivers varies by more than two orders of magnitude
during a single climate cycle and that variations in the timing of
sediment supply differ between climatic belts. Their work also
showed that the greatest changes in sediment yields occur in the
regions where climate varies from arid to subhumid, which
includes the Texas coastal plain.
In general, all of the larger Texas, Louisiana, and Mississippi
deltasexperiencedcontinuousgrowththroughoutthehighstand.
Climate changes did occur along the Gulf Coast as the ice sheets
tothenorthexpanded,butanyimpactoftheseclimatechangeson
sediment supply to the Gulf was overshadowed by the effects of
sea-level fall. Sea-level (base-level) fall was the driving force in
delivering sediment to the margin. Indeed, detailed work on the
ancestral Brazos delta has shown that growth of the delta during
the last highstand was strongly regulated by fifth-order eustatic
fluctuations (Anderson et al., 1996; Abdulah et al., this volume).
No sediment budgets for the lowstand have been obtained,
owing to bypass of the shelf during the lowstand. So, the impact
of climate change on sediment supply to the basin at this time is
unknown. However, sediment fluxes of the different rivers ap-

pear to have varied significantly during the transgression. This
difference is attributed to climatic influence on sediment supply
rather than eustasy.
BlumandPrice(1998)pointoutthat,withintheColoradoRiver
drainage basin, the postglacial sea-level rise was accompanied by
warmertemperaturesandincreasedtropical-stormfrequencyand
more flashy discharge regimes. The net effects of these climatic
changes were degradation of soils and general denudation of
upland landscapes within the drainage basin. Sediments removed
from the upland areas of the drainage basin were transported
basinward. Floods delivered some of this sediment into the exten-
siveflood-plainsettingsofthecoastalplain(Blumetal.,1994;Blum
and Valastro, 1994). There, these sediments are sequestered until
the next eustatic fall. But there was also a significant flux of
sediment to the Gulf, as recorded by the transgressive deltas
associated with the ancestral Brazos, Colorado, and Rio Grande
rivers (Abudlah et al., this volume; Banfield and Anderson, this
volume). The backstepping nature of these deltas suggests epi-
sodic sediment flux that is probably controlled by higher-fre-
quency climatic events. The most recent event occurred around 11
to9ka,whenboththeColoradoandRioGrandedeltasexperienced
significant phases of growth (Abdulah et al., this volume; Banfield
and Anderson, this volume). These periods of increased sediment
fluxtothebasinundoubtedlyresultedfromashifttodrierclimates
and associated reduction in the area of grasslands following the
Younger Dryas climatic event (Banfield, this volume; Snow, 1998).
On the Lagniappe shelf at this time the transgressive flooding
event continued unabated.
Stratigraphic Models
Differences in fluvial response to sea-level change and climate
have resulted in very different stratigraphic architectures across
the northern Gulf of Mexico margin. Similar along-strike variabil-
ityinsystemstractsareobservedonothercontinentalshelves(e.g.,
TrincardiandCorreggiari,2000;McMurrayandGawthorpe,2000).
It is possible to group the different study areas of the northern
Gulf of Mexico margin into seven type sections on the basis of
their gross stratigraphic architecture. These type sections are
illustrated using stratigraphic slug diagrams (Fig. 10). Table 1
provides key information about each area, and Table 2 summa-
rizestheimportantdepositionalfeaturesforeachareabysystems
tract. These models are generalized, but they serve to illustrate
the very different stratigraphic architectures that exist on the
margin and their relationship to the margin setting. Our general
models can be used to predict the distribution of reservoir-scale
sand bodies on the shelf and for stratigraphic correlation. We
hope that by providing well-documented case studies our results
will inspire other researchers to develop quantitative deposi-
tional and reservoir models for the shelf (e.g., van Heijst et al.,
2001). For greater details on these different areas, refer to the
individual papers in this volume.
A West Florida–Alabama Margin.—
A steep, ramp-like profile and slow subsidence rates charac-
terize the west Florida margin (Bart and Anderson, this volume;
McKeown et al., this volume). High-gradient, bedload-domi-
nated rivers and streams deliver sediment to the margin. The
currentclimateishumidandisunlikelytohavebeensignificantly
drier during glacial times.
There has been minimal preservation of early highstand
deposits on the west Florida shelf. Inner-shelf sediments were
eroded and transported seaward, where they are incorporated
into late-highstand deltas that prograded into relatively deep
water (up to 70 m water depth). A lowstand delta and fan
complex is lacking. During transgression, sandy delta tops were
erodedandthesandsspreadacrosstheshelfasanextensivesheet
sand (MAFLA Sheet Sand; McBride et al., this volume).
The Latium shelf of Italy is perhaps a good analogue to the
West Florida shelf. The largest sediment supplier to the shelf is
the Tiber River. It is narrow (30 km), has no abrupt shelf break,
and has a narrow coastal plain with several small rivers draining
highlands. Thus, the coastal plain is unable to stockpile large
amounts of sediment. As a result, changes in base level and
climate appear to have had a rapid influence on sediment supply
to the shelf (Chiocci, 2000). Also, there are no canyons dissecting
the margin and no basin-floor fans. Lowstand deposits were
supplied to the slope through gullies as a line source rather than
through canyons. This has resulted in a uniform thickness of
sediments on the upper slope, possibly also reflecting stronger
longshore transport during the lowstand.
B. Lagniappe (Mississippi–Eastern Louisiana Margin.—
During the late highstand and lowstand, sediments from the
Pascagoula and parts of the Mobile drainage system were depos-
ited offshore of Mississippi and western Louisiana to construct
the Lagniappe delta. The delta prograded across a relatively
broad, low-gradient shelf that experienced relatively low subsid-
ence. During the maximum lowstand, deposition shifted to the
east and constructed a shelf-margin delta (Roberts et al., this
volume). Progradation of this shelf-margin delta continued into
the initial transgression (Fillon et al., this volume; Kohl et al., this
volume). These deltas contain extensive delta-front sand bodies,
but no associated lowstand fan has been identified. Currently the
deltas are being buried beneath muds shed from the Mississippi
River.
C. Western Louisiana–Brazos Margins.—
Theseareasarecharacterizedbybroad,low-gradientmargins
that have experienced moderate to rapid rates of subsidence
(Abdulah et al., this volume; Wellner et al., this volume). Large,
suspended-load-dominated rivers deliver sediments to these
margins.
Early-highstand fluvial channels occur on the inner shelf, but
sandy delta topset beds (mouth bars) are mostly confined to the
outer shelf. Extensive delta-front sands are associated with late-
highstand deltas. These deltas were abandoned, because of flu-
vial avulsion, prior to the lowstand. Thus, there are no lowstand
deltasorfansonthesemargins.Transgressivedepositsaremostly
muds, with the exception of incised-fluvial-valley fills and iso-
lated sand banks.
D. East Texas—Trinity–Sabine Margin.—
The east Texas shelf is a broad, low-gradient shelf that has
been nourished with sediment from the mixed bedload/sus-
pended load-dominated Trinity and Sabine Rivers throughout
the eustatic cycle and by the Brazos River during the lowstand
(Abdulah et al., this volume).
Highstand deposits are thin and composed of mud. Shelf
bypass through the Trinity–Sabine–Brazos valley has resulted in
the development of a large lowstand delta and slope fan complex
whose distribution on the margin has been strongly regulated by
salt diapirs (Wellner et al., this volume). Transgressive deposits
are mostly confined to the incised fluvial valley and include
extensive fluvial sands and backstepping bayhead deltas and
tidal deltas (Thomas and Anderson, 1994). The only exceptions

¥ramp setting
¥bedload-dominated
rivers and streams
low subsidence
onlapping wedge
(hemipelagic mud)
TST-sheet sand
sand ridges
carbonate
mound
TS/SB
HST deltaMFS
A West Florida
¥broad, low-gradient shelf
¥moderate subsidence
¥large, mixed load river
MFS
HST delta
SB/TS
LST
delta
TST delta
incised valley
TS
LST-slope fan
E East Texas-Colorado
¥narrow, steep shelf
¥large, mixed load river
MFS
SB
LST delta fan
HST delta
TST delta
incised valley
TST marine mud
G South Texas-Rio Grande
SB
F Central Texas
¥narrow, steep shelf
¥small, bedload-dominated rivers
HST marine mud
HST shoreline/
shoreface deposits
marine muds
MFS
Transgressive
mud blanket
TST/LST mud
B Lagniappe
¥broad shelf, low gradient
¥low subsidence
¥rivers with moderate bedload
TST
(muds)
slumps
late highstand-
lowstand delta
(sandy mouth
bars)
onlapping
wedge
MFS
TS
¥broad, low-gradient shelf
¥small suspended load-dominated river
HST marine
mud LST turbidites
within minibasins
LST/early TST delta
SB/TS
TST-sand banks
SB
incised valley
D East Texas-Trinity/Sabine
MFS
TS
TST
early HS
TST
MFS
MFS
late HS
C Western Louisiana/Brazos
¥broad shelf, low-gradient
¥river with dominant
suspended load
FIG. 10.—Seven stratigraphic models (A–G) are used to illustrate the different stratal architectures of the northern Gulf of Mexico
margin. See text for discussion. Dots indicate sand-prone areas.

are isolated sand banks that occur adjacent to the incised valleys
(Rodriguez et al., 1999).
E. East Texas—Colorado Margin.—
West of the Trinity–Sabine incised fluvial valley, the margin
is supplied with sediments by the Colorado and Brazos rivers,
which have relatively high sediment flux rates and extensive
coastal-plain sediment storage capacities. The Colorado River
had a high bedload contribution to the margin relative to other
eastTexasrivers.Theareaexperiencedsignificantclimaticchanges
during the last glacial–interglacial cycle; specifically, it was drier
during interglacial times (Toomey, 1993). Subsidence rates are
relatively high (0.1 to 4.0 mm/yr).
Thin, sandy early highstand deltas on the inner shelf and
thick, sandy late highstand deltas on the outer shelf characterize
themargin(Abdulahetal.,thisvolume).Sedimentbypassduring
the lowstand resulted in a sandy Colorado lowstand delta and
slopefancomplex.Thetransgressivesystemstractincludeslarge,
sandy deltas and sand-filled incised fluvial valleys. The high
sedimentyieldoftheColoradoRiverduringtherecentglacial-to-
interglacial transition is credited with the increased sediment
supply that led to the formation of transgressive deltas on the
shelf.
F. Central Texas Margin.—
The central Texas margin has a relatively steep profile and
lacks a distinct shelf break. The margin experiences moderate
rates of subsidence (Eckles et al., this volume). Small, mixed
bedload/suspended load rivers deliver sediment to the region,
along with converging coastal currents that deliver sands from
adjacent east Texas and south Texas coasts. The climatic setting is
believed to have been more humid during glacial times than it is
today (Toomey, 1993).
Sand-prone deposits are mostly confined to the inner shelf
andconsistofearly-highstandprogradingshorelineandshoreface
deposits.Theoutershelfismud-dominated,therearenolowstand
deltas or fans, and a transgressive mud unit blankets the shelf.
G. South Texas—Rio Grande Margin.—
The south Texas margin has a broad, low-gradient shelf. The
Rio Grande River has been the principal supplier of sediment to
the margin during the late Quaternary and, for that matter,
throughout most of the Tertiary. Of the various study areas, it has
the most persistently dry climate.
Extensive highstand deltas with large delta-front sand bodies
occur on the shelf, including both wave- and fluvial-dominated
deltas(BanfieldandAnderson,thisvolume).Averythicklowstand
delta and fan complex occurs on the shelf margin and upper
slope,whichincludesthicksandunits.Thetransgressivesystems
tract includes incised fluvial valleys and transgressive deltas that
have been buried beneath a transgressive mud blanket.
CONCLUSIONS
1. Highly variable fluvial morphologies, drainage-basin size,
and climate settings characterize the northern Gulf Coast.
These differences result in rather different long-term sedi-
ment discharges of rivers. There are also major differences in
shelf physiography and subsidence across the margin. Paleo-
geographic maps for the highstand (falling sea level), low-
stand, and transgressive systems tracts, which are related to
South Texas
(Rio Grande)
Central Texas
(Guadalupe)
East Texas
(Brazos, Colorado)
East Texas
(Trinity, Sabine)
Lagniappe
(Mobile)
FLORALA
(Mobile, Escambia)
West Florida
(Apalachicola)
Systems-
Tract
Descriptions
Highstand (HS) • early HS preservation
• areally extensive
muddy deltas lobes
(extensive prodelta)
(< 0.5° angle) and
associated
distributaries
(aggrading sigmoidal
clinoforms at seaward
margin) (wave/fluvial
dominated)
• prograding
shoreline
(converging
longshore
currents)
• muddy deltas
(extensive prodelta)
with minimal delta
lobe switching
during early fall
• sandy deltas with
associated
distributary systems
during late fall
• minimal HS
preservation
outside incised
valleys
• minimal HS
preservation on
inner shelf
• preserved sandy
deltas with several
lobes (< 5° angle)
and associated
distributaries
(aggrading
sigmoidal clino-
forms at seaward
margin) (fluvial)
• preserved thick,
lobate silty to fine
sand deltas with
several lobes and
associated
distributaries
(aggrading
sigmoidal
clinoforms at
seaward margin)
• minimal HS
preservation on
inner shelf
• preserved sandy
deltas with
several lobes
(> 3° angle) and
associated
distributaries
(fluvial and
wave)
HS Sediment
Supply
(km3
/1000 yr)
1.4 to 2.9 0.1 to 1.2 0.3 to 3.2 1.0 0.4 (100 kyr)
0.9–3.0
Lowstand (LS) • incised fluvial valley
• shelf-edge deltas
(fluvial)
• slope fan
• shallow, narrow
incised channels
• no major cross-
shelf incised
fluvial valleys or
slope canyons
• no LS deltas
• incised fluvial
valleys
• muddy and sandy
shelf-margin delta
(Colorado only)
• muddy and sandy
slope fans
(Colorado only)
• single incised
fluvial valley
(point source)
• sandy shelf-
margin delta
• slope fans
• shallow, broad
fluvial system with
terraces
• no cross-shelf
incised fluvial
valleys or canyons
• no slope fans
• broad, shallow
incised fluvial braid
system (line source)
• no cross-shelf
incised fluvial
valleys or canyons
• no slope fans
• broad, shallow
incised fluvial
braid system with
terraces (line
source)
• no cross-shelf
incised fluvial
valleys or
canyons
• distributaries are
incised to shelf
break
• no LS fans
Transgressive (T) • deposition not
confined to incised
valleys
• localized sandy delta
lobes (fluvial/wave
dominated)
• LS wedge
(backstepped deltas)
• valley fill
• 40-m-thick mud
blanket
• reef trend
~ 60 m
• sandy and muddy
incised-valley fill
• deltas with lobe
switching
(fluvial/wave)
• sandy and muddy
incised valley fill
• sandy banks
preserved
adjacent to
incised valleys
• muddy shelf-
margin deltas
• incised-valley fill
• sand ridges
• two delta lobes
• carbonate mounds
• hemipelagics
• shoreline-parallel
shelf currents
• valley fill
• sand ridges
• carbonate mounds
• thin, laterally
extensive slope
wedges (shoreline-
parallel upper slope-
currents)
• valley fill
• sand ridges
• backstepped
delta lobes
• thin slope
wedges (not
extensive)
• hemipelagics
TABLE 2.—Summary of the depositional styles of systems tracts for the various study areas
in the northern margin of the Gulf of Mexico.

well known sea-level histories, serve to illustrate how depo-
sition varied across the continental margin. There is consider-
able variability in stratigraphic architecture across the mar-
gin,whichisillustratedusingsevenstratigraphicmodels.The
models can be used to predict the occurrence of reservoir-
scale sand bodies in continental-margin settings.
2. The current maximum highstand is characterized by signifi-
cant sediment storage in low-gradient alluvial plains and
minimal sediment discharge by rivers, the exception being
the Mississippi River. Sedimentation on the margin is mini-
mal, and the modern sea floor is a condensed stratigraphic
section (maximum flooding surface). The only exception is
the wave-dominated central Texas shelf, where a thick Ho-
locene mud blanket is accumulating. Thus, the modern
setting provides only a glimpse of how strata are formed on
the margin.
3. During the last falling limb of the sea-level curve, the larger
rivers of the Gulf Coast Region had sediment fluxes up to an
order of magnitude greater than their current sediment
fluxes. These rivers nourished large highstand deltas. In
general, sediment fluxes of rivers increased with falling sea
level. This was partly the result of cannibalization of early
highstand deltas by fluvial incision and regressive shoreface
erosion. If climate regulated sediment yields during this
time, the effects were overshadowed by sea-level change.
4. The central Texas shelf was wave-dominated during the last
highstandandwascharacterizedbyprogradingclasticshore-
line and shoreface deposits. Progradation of these deposits
across the shelf occurred only during the early highstand,
largely because erosion of the Colorado and Rio Grande
deltas nourished the central Texas deposits. Elsewhere along
the Gulf margin, coastal deposits are mostly confined to the
maximum updip limit of flooding surfaces.
5. Rivers with high sediment supplies are prone to avulsion,
during both falling and rising sea level. This results in a
significant amount of sediment delivered by these rivers
beingsequesteredontheshelf.Incontrast,riverswithsmaller
sediment supplies are more inclined to occupy the same
channels throughout the eustatic cycle. This results in greater
sedimentbypassoftheshelf,whichequatestoslopeandbasin
floor fan systems (Anderson and Rodriguez, 2000).
6. Abandonment of highstand shelf-margin deltas by some of
the larger rivers (Brazos and western Louisiana fluvial sys-
tems) prior to the Stage 2 lowstand resulted in an absence of
lowstand delta and slope fans in these regions.
7. Over the length of a glacioeustatic cycle, the overall sediment
flux of a river is determined by the size of its drainage basin.
The climate effects on sediment flux of different rivers are
more apparent during the transgression; however, the effect
of climate on sediment flux varied across the margin.
8. Geomorphology (width and cross-sectional geometry) alone
is not a suitable criterion for distinguishing highstand and
lowstand fluvial channels. Lowstand fluvial geomorphology
varies widely across the shelf. These differences are the result
of differences in shelf gradient, drainage-basin size and cli-
mate (which controls discharge), substrate conditions on the
shelf, and the interval of the eustatic cycle during which the
river occupied the channel.
9. Idealizedtripartiteincised-valley-fillsuccessions(e.g.,Wright
and Marriott, 1993; Zaitlin et al., 1994) are the exception rather
than the rule on the northern Gulf of Mexico shelf. Along the
margin, valley fills range from those that are dominantly
fluvial (e.g., the Brazos valley) to those that are dominantly
marine (e.g., central Texas valleys). This is due to the different
sediment supplies of these rivers and their capacity to keep
pace with the rate of sea-level rise during transgression.
10. Ourdatashowthatfifth-ordersea-levelfluctuationshavehad
a marked influence on sedimentation on the continental shelf.
11. The modern physiography of the margin is largely a product
of sediment supply. A broad shelf and distinct shelf break
characterize portions of the margin where sediment supply is
high, with the exception of the modern Mississippi delta.
Narrow, steep shelves with a less distinct shelf break charac-
terize areas with relatively low sediment supply.
12. The occurrence of sand bodies within deltas varies across the
shelf.Largeriverswithhighsuspendedloadsconstructmuddy
deltasinwhichsandsaremostlyconfinedtomouthbarsinthe
topset portions of the deltas and to the point bars of the
meandering rivers that nourished these deltas. Smaller,
bedload-dominatedrivers,suchasthoseofwestFlorida,have
constructed sandy deltas.
REFERENCES
ANDERSON, J.B., ABDULAH, K., SARZALEJO, S., SIRINGAN, F., AND THOMAS, M.A.,
1996, Late Quaternary sedimentation and high-resolution sequence
stratigraphy of the east Texas shelf, in De Batist, M., and Jacobs, P.,
eds., Geology of Siliciclastic Seas: Geological Society of America,
Special Publication 117, p. 95–124.
ANDERSON, J.B., AND RODRIGUEZ, A.B., 2000, Differences in late Quaternary
highstand, lowstand, and transgressive fluvial channels of the east
Texas shelf: implications for shelf-upper slope reservoir models: Gulf
Coast Association of Geological Societies, Transactions, v. 50, p. 343–
348.
BARD, E., HAMELIN, B., AND FAIRBANKS, R.G., 1990, U–Th ages obtained by
mass spectrometry in corals from Barbados: sea level during the past
130,000 years: Nature, v. 346, p. 456–458.
BARD, E., HAMELIN, B., ARNOLD, M., MONTAGGIONI, L., CABIOCH, G., FAURE, G.,
AND ROUGERIE, F., 1996, Deglacial sea-level record from Tahiti corals
and the timing of global meltwater discharge: Nature, v. 382, p. 241–
244.
BERRYHILL,H.L.,SUTER,J.R.,AND HARDIN,N.S.,1986,LateQuaternaryFacies
and Structure, Northern Gulf of Mexico: American Association of
Petroleum Geologists, Studies in Geology 23, 289 p.
BLOOM, A.L., 1983, Sea-level and coastal geomorphology of the United
States through the late Wisconsin glacial maximum, in Porter, S.C.,
ed., Late Quaternary Environments of the United States, Vol. 1:
University of Minnesota Press, p. 215–229.
BLUM,M.D.,1993,Genesisandarchitectureofincisedvalleyfillsequences:
a late Quaternary example from the Colorado River, Gulf Coastal
Plain of Texas, in Weimer, P., and Posamentier, H., Siliciclastic Se-
quenceStratigraphy:RecentDevelopmentsandApplications:Ameri-
can Association of Petroleum Geologists, Memoir 58, p. 259–283.
BLUM, M.D., TOOMEY, R.S.I., AND VALASTRO, S., JR., 1994, Fluvial response to
late Quaternary climatic and environmental change, Edwards Pla-
teau, Texas: Palaeogeography, Palaeoclimatology, Palaeoecology, v.
108, p. 1–21.
BLUM, M.D., AND VALASTRO, S., JR., 1994, Late Quaternary sedimentation,
lower Colorado River, Gulf Coastal Plain of Texas: Geological Society
of America, Bulletin, v. 106, p. 1002–1016.

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