Eaglebine play of the
southwestern East Texas basin:
Stratigraphic and depositional
framework of the Upper
Cretaceous (Cenomanian–
Turonian) Woodbine and
Eagle Ford Groups
Tucker F. Hentz, William A. Ambrose, and
David C. Smith
The Woodbine and Eagle Ford Groups of the southwestern East
Texas basin compose an emerging play, which has generated considerable interest because of its potential for new hydrocarbon
production from both sandstone and mudrock reservoirs.
However, the play’s stratigraphic and depositional relations are
complex and directly relate to the play’s exploration challenges.
Productive Woodbine and Eagle Ford (sub-Clarksville) sandstones intertongue with a poorly defined, subregional mudrockdominated interval that thins southwestward toward the
San Marcos arch. We propose dividing this succession into two
intervals: (1) the Lower unit, a high-gamma-ray unit at the base
of this mudrock succession that is inferred to be equivalent to
the Maness Shale of the Washita Group and to part of the lower
Eagle Ford Group on the San Marcos arch, and (2) an Upper unit,
a basinward-thickening zone of consistently lower gamma-ray-log
facies inferred to be equivalent to the Woodbine Group, Pepper
Shale, and the Eagle Ford Group of the East Texas basin.
Because the Cenomanian–Turonian boundary occurs within the
Eagle Ford Group of the East Texas basin and the lower Eagle
Ford section of the San Marcos arch, most of the Manessthrough-Eagle Ford succession exists as a much-thinned section
on the arch.
Copyright ©2014. The American Association of Petroleum Geologists. All rights reserved.
Manuscript received December 31, 2013; provisional acceptance April 01, 2013; revised manuscript
received June 03, 2014; final acceptance July 07, 2014.
DOI: 10.1306/07071413232
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Tucker F. Hentz ∼ Bureau of Economic
Geology, The University of Texas at Austin,
University Station, Box X, Austin, Texas
78713-8924; tucker.hentz@beg.utexas.edu
Tucker F. Hentz is a research scientist
associate at the Bureau of Economic
Geology, Jackson School of Geosciences at
The University of Texas at Austin. His areas
of interest include sequence-stratigraphic
analysis and siliciclastic depositional
systems. Hentz received his B.A. and M.S.
degrees in geology from Franklin & Marshall
College and The University of Kansas,
respectively.
William A. Ambrose ∼ Bureau of Economic
Geology, The University of Texas at Austin,
University Station, Box X, Austin, Texas
78713-8924; william.ambrose@
beg.utexas.edu
ABSTRACT
AAPG Bulletin, v. 98, no. 12 (December 2014), pp. 2551–2580
AUTHORS
2551
William A. Ambrose is a research scientist at
the Bureau of Economic Geology, Jackson
School of Geosciences at The University of
Texas at Austin. His areas of interest include
unconventional energy minerals, siliciclastic
depositional systems, and stratigraphy.
Ambrose holds B.S. and M.A. degrees in
geosciences from The University of Texas at
Austin.
David C. Smith ∼ Bureau of Economic
Geology, The University of Texas at Austin,
University Station, Box X, Austin, Texas
78713-8924; david.carr@beg.utexas.edu
David Smith is a research scientist associate
and database analyst at the Bureau of
Economic Geology, Jackson School of
Geosciences at The University of Texas at
Austin. Smith received his B.S. degree in
geosciences from The University of Texas at
San Antonio.
ACKNOWLEDGEMENTS
This study was funded by the State of Texas
Advanced Resource Recovery (STARR)
project. The author thanks Sun Resources NL
for access to its well-log data set. Stewart
Bayford of Sun Resources generously shared
his knowledge of Woodbine geology and
reservoirs. We also extend our appreciation
to Eric Potter for his insights into Eagle Ford
and Woodbine production, Steve Ruppel for
input on regional Eagle Ford stratigraphic
issues, and John Snedden for discussions
regarding finer details of basin-scale
sequence stratigraphy. Special thanks go to
Gene Powell for allowing us to reproduce
Eaglebine production statistics published in
his digest. The manuscript benefited from
the reviews of Rick Abegg, Art Donovan,
Ryan Grimm, and Mihaela Ryer. Jason
Suarez prepared the illustrations under the
direction of Cathy Brown, Manager, Media
Information Technology. Publication
authorized by the Director, Bureau of
Economic Geology.
The AAPG Editor thanks the following
reviewers for their work on this paper: Rick
Abegg, Arthur D. Donovan, Ryan Grimm,
and Mihaela S. Ryer.
Basinwide integration of the Woodbine sequencestratigraphic framework shows that the number of fourth-order
sequences in the unit decreases westward from 14 in the basin axis
to no more than 9 in the most active part of the Eaglebine play
because of their systematic depositional pinch out approaching
the western basin margin. The Eagle Ford Group consists of three
fourth-order sequences capped by the sub-Clarksville sandstones
that accumulated after the major late Cenomanian–early
Turonian flooding event recorded by a basinwide transgressive
systems tract (TST) at the base of the unit.
Depositional systems of the Woodbine Group vary within
the study area, even between stratigraphically adjacent systems.
On-shelf siliciclastic systems include fluvial-dominateddelta; incised-valley-fill fluvial and nearshore-marine; and wavedominated-delta deposits.
INTRODUCTION
The Eaglebine play of east-central Texas stratigraphically comprises primarily siliciclastic facies of an outer-shelf depositional
environment of the lower Upper Cretaceous (Cenomanian)
Maness Shale and Woodbine Group and the upper Cenomanian
and Turonian Eagle Ford Group (Figure 1). Areally, the play is
defined primarily by the subsurface distribution of Woodbine
Group and Eagle Ford sandstones (hence, the informal term
“Eaglebine”) and equivalent mudrock facies extending from the
northeast flank of the San Marcos arch into the southern part of
the East Texas basin to the Texas–Louisiana state boundary
(Figure 1). The entire on-shelf interval is vertically constrained
by the Buda Limestone of the Washita Group at the base and the
Austin Chalk at the top. The downdip part of the play extends
southeast of the Edwards reef trend, which marks the approximate
Woodbine shelf margin (Wu et al., 1990) (Figure 2), where localized shelf-edge deltaic deposits (Ambrose and Hentz, 2012) and
upper- and lower-slope Woodbine sandstones are interpreted to
exist along at least parts of the shelf-edge and slope trends
(Siemers, 1978; Foss, 1979; Stricklin, 2002). However, most
exploration activity currently exists within a zone about 20 mi
(32 km) northeast of the shelf margin across the southern part of
the East Texas basin (Figure 2). The shelf-edge and deeper slope
Woodbine- and potential Eagle Ford-equivalent sandstone facies
are being scrutinized (e.g., Bunge, 2011), and the productive area
of the play may well expand into the slope region.
Although historically productive sub-Clarksville fluvialdeltaic sandstones occur within the upper part of the Eagle Ford
Group in the southwest part of the East Texas basin in the play
2552
Eaglebine Play of the Southwestern East Texas Basin
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A
Stage
A'
Maverick
Basin
San Marcos
Arch
East Texas
Basin
Stage
Coniacian
Eagle Ford
Group
Austin Chalk
Turonian
?
Woodbine
Group
er
pp
Pe
N
Cenomanian
San Marcos
Arch
Upper
Eagle Ford
Group
Cenomanian
M
an
es
sS
Fo
rd
es
to
Gr
ne
ou
p
r
we
Lo
A'
ha
le
A
e
gl
Ea
Eaglebine
play
m
Turonian
ale
Sh
Coniacian
da
Bu
Li
Laminated, calcareous,
organic-rich mudrock
Interbedded, burrowed,
laminated, calcareous mudrock
Organic-poor, clay-rich,
siliceous mudrock
Fluvial–deltaic
sandstone
Deep-platform
lime mudstone
Shallow-platform
lime mudstone
ft
200
0
m
60
0
Figure 1. Schematic southwest–northeast cross section AA′ illustrating regional lithostratigraphic and lithofacies relationships across
the Eagle Ford Group (southwest of San Marcos arch) and Eaglebine play areas. Approximate location of stage boundaries from
Donovan et al. (2012) (Maverick basin) and Pessagno (1969), Hancock et al. (1994), and Hancock and Walaszczyk (2004) (East Texas
basin). Modified from Hentz and Ruppel (2010, their figure 9).
area (Barton, 1982; Surles, 1987), most recent exploration efforts in the play have targeted Woodbine
sandstone facies. Exploration in the Eaglebine play
is driven primarily by recent advances in horizontaldrilling and multistage hydraulic-fracturing methods
to maximize hydrocarbon production primarily from
subregional stratigraphic traps in complex sandstone
successions at the southwestern fringe of the
Woodbine complex and in other areas of the southern
East Texas basin. Many historic Woodbine fields with
structural and combination traps are associated with
salt structures in the East Texas basin (Jackson and
Seni, 1984; Wescott and Hood, 1994). However,
stratigraphic traps formed either by facies pinch out
or diagenetic barriers in mostly thin (<25 ft [8 m]),
locally fractured sandstone beds characterize the
developed parts of the play not associated with salt
structures (Siemers, 1978; Foss, 1979).
Lease acquisition and exploration is quite active
in the play; however, little is known about
Woodbine depositional facies, areal and vertical distribution of sandstone facies, and their sequencestratigraphic context either at the play or field scale.
The few studies of stratigraphic and depositional
aspects of the subsurface Woodbine Group are either
broadly regional and based on sparsely distributed
well data (Oliver, 1971) or focus on the unit in the
central, northeastern, and eastern parts of the East
Texas basin (Ambrose et al., 2009). The area of greatest exploration activity in the play is currently in the
southwest part of the East Texas basin, where
Woodbine fluvial-deltaic sandstones are regionally
HENTZ ET AL.
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2553
97°
94°
106°
100°
94°
36°
Oklahoma
Woodbine outcrop
Arkansas
32°
Texas
Louisiana
33°
ne
28°
East Texas
field
–T
alco
Fault
Zo
exico
of M
ulf
G
Mexico
0
N
0
200 mi
400 km
Sabine
Uplift
Mex
ia
East Texas
Basin
Study area
Houston
Basin axis
Leon
Play area
(most active)
Robertson
ertson
31°
Madison
Grimes
G
Burleson
Ed
ds
wa r
trend
reef
0
40 mi
0
60 km
Brazos
Figure 2. Map of the study area and major structural features within the Eaglebine play area, highlighting the currently most active
area of the play in Leon, Madison, Brazos, Burleson, Grimes, and Robertson counties.
discontinuous and thinner than those of the axial part
of the basin to the east (Figure 2). In this area, most
current Eaglebine wells target upper Woodbine sandstones just below the base of the Eagle Ford Group
(Powell Shale Digest, 2013), although production
exits from thin sandstones throughout the Woodbine
succession near the southwestern margin of the main
Woodbine depocenter.
This study has several objectives: (1) clarify fundamental issues of the lithostratigraphy within the
area of most active Eaglebine exploration (Figure 2);
(2) discuss possible chronostratigraphic relations of
the Maness, Woodbine, and Eagle Ford intervals
and the mudrock-dominated succession into which
these units all grade at this margin of the East Texas
basin; (3) define the sequence-stratigraphic framework of the Woodbine and Eagle Ford Groups in the
area; and (4) identify the depositional systems and
2554
trends of potential reservoir sandstones of the
Woodbine Group in a focused part of this active area
(Leon, eastern Robertson, Madison, and western
Houston counties).
DATABASE AND METHODS
The database used in this study includes (1) welllog suites for about 510 wells in the 3350‐mi2
ð8680‐km2 Þ study area of Leon, Madison, and
western Houston counties used (Figure 2); (2) about
1100 additional well logs distributed throughout
the play area from the San Marcos arch to the
Sabine uplift and the central East Texas basin; and
(3) 39 ft (12 m) of one publicly available whole
core from the study area to corroborate Woodbine
depositional-systems identification and stratal-stacking
Eaglebine Play of the Southwestern East Texas Basin
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patterns interpreted from well logs of one of the
mapped sandstone units. Five publicly available
whole cores from five wells in the study exist, but
well logs could not be acquired for two of them.
One core is from the same sandstone zone as that in
a close offset well and is thus largely redundant, and
one other core is from a sequence that depositionally
pinches out along the eastern edge of the study area.
No seismic data were available for the study. The
regional set of well logs was used for regional
sequence-stratigraphic correlation and delineation
of the areal distribution of the gross Eagle Ford
and Woodbine lithofacies to provide a play-scale context for the varying rock successions. The denser
well-log data set of the study area enabled sequencestratigraphic correlation and gross-sandstone
mapping to create a focused view of the Eaglebine
lithofacies relations, sandstone trends, and depositional systems within the most active area of
exploration.
For sequence-stratigraphic correlation within the
study area, primarily gamma-ray logs were used to
ensure consistent and accurate representation and
interpretation of sandstone and mudstone intervals
within the study interval. Because of varying
gamma-ray scales on logs of differing age and the
typical slight downhole drifting of the gamma-ray
curve, we used a relative gamma-ray cutoff value to
best calculate gross-sandstone values. A cutoff value
of one-half the length from the shale base line to the
lowest gamma-ray value (sandstone) within 200 ft
(61 m) of the measured interval was used. Only
gamma-ray curves were used for systems-tract interpretation because they most accurately represent siliciclastic grain-size stacking patterns.
Techniques used for interpreting sequence stratigraphy from wireline logs are discussed by Van
Wagoner et al. (1990) and Mitchum et al. (1993).
Sequence-stratigraphic surfaces, including sequence
boundaries (SB), transgressive surfaces of erosion
(TS), and maximum flooding surfaces (MFS) were
inferred primarily from the logs’ gamma-ray signatures, supported by whole-core data from the study
area. The correlated surfaces (SB, TS, and MFS) are
numbered in consecutive order of increasing age in
increments of 10 (for example, SB 10, SB 20, …,
SB 100). The sequence boundary at the base of an
incised-valley fill (IVF) of a lowstand systems tract
(LST) was correlated with that at the top of an adjacent upward-coarsening cycle that represents a younger highstand systems tract (HST) into which the
valley fill was cut. Transgressive surfaces of erosion
define the top of the aggradational valley fill and
coincide with sequence boundaries atop the HST.
Maximum flooding surfaces cap upward-fining successions, the transgressive systems tracts (TSTs), at
gamma-ray maxima above the lowstand IVF and
highstand successions. Because Woodbine sandstones tend to be discontinuous in the southwest part
of the East Texas basin, we used these regionally correlated MFSs to more rigorously define the succession’s systems tracts.
REGIONAL GEOLOGIC SETTING
The East Texas basin, a structural embayment of the
Gulf Coast Basin, is bounded on the north and west
by the Mexia–Talco fault zone and on the east by
the Sabine uplift (Figure 2). In its deepest part, the
basin is filled with more than 13,000 ft (>3960 m)
of Mesozoic and Cenozoic strata (Wood and
Guevara, 1981), which were structurally modified
by mobilization of the Middle Jurassic Louann Salt,
most commonly as diapirs, throughout Cretaceous
and early Cenozoic basin sedimentation (Seni and
Jackson, 1984). Salt mobilization and concurrent
rapid accumulation of voluminous Woodbine siliciclastic sediments were the principal mechanisms for
Late Cretaceous (Cenomanian) subsidence and creation of accommodation in the East Texas basin (Seni
and Jackson, 1984; Ambrose et al., 2009). The
Sabine uplift is a low-relief regional anticlinorium
lying astride the Texas–Louisiana border between
the East Texas basin and north Louisiana diapir province (Ewing, 1991a). The uplift was gradually rising
during deposition of the Woodbine Group, which
greatly affected its sequence distribution and framework within the adjacent basin (Ambrose et al.,
2009). The southwestern part of the East Texas basin
merges into the northeast flank of the San Marcos
arch (Figure 1), a broad southeast-trending area of
lesser subsidence between the Maverick basin of
South Texas and the East Texas basin. Laubach and
HENTZ ET AL.
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2555
Jackson (1990) inferred it to be a basement uplift
related to late Mesozoic to Cenozoic foreland or intraplate folding.
The Woodbine Group represents the dominant,
most widespread episode of coarse siliciclastic deposition during the Late Cretaceous in the East Texas
basin (Oliver, 1971; Ambrose et al., 2009). This
basin-scale fluvial-deltaic complex reaches a maximum thickness of approximately 1090 ft (∼330 m)
in the basin axis and thins eastward toward the
Sabine uplift, westward toward the outcrop belt
(Figure 2), and southwestward toward the San
Marcos arch. Within the study area, the Woodbine
interval thins toward the west from about 920 ft
(∼280 m) in southern Houston County to about
560 ft (∼170 m) in western Leon County (Figure 3).
The Edwards reef trend coincides with the
approximate location of the Woodbine depositional
shelf edge (Wu et al., 1990, their figure 2A)
(Figure 2).
LITHOSTRATIGRAPHY AND
CHRONOSTRATIGRAPHY
Regional subsurface lithostratigraphic relations
between the lower Upper Cretaceous succession
(Buda Limestone to Austin Chalk) in the prolific
Eagle Ford Group play area southwest of the
San Marcos arch and the same interval northeast of
the arch in the East Texas basin are complex
(Figures 1, 4–6). This complicated stratigraphic and
regional lithofacies framework has a direct bearing
on the exploration challenges of the Eaglebine section
Figure 3. Isochore map
of Woodbine Group of
the central and southern
parts of the East Texas
basin, including the study
area.
94°58'
32°35'
Isochore (ft)
1000–1100
900–1000
800–900
700–800
600–700
500–600
400–500
Basin axis
Contour interval = 100 ft
Study area
Anderson
600
500
Freestone
80
0
0
Houston
90
0
70
Leon
N
Madison
30°50'
96°50'
2556
0
10 mi
0
15 km
Eaglebine Play of the Southwestern East Texas Basin
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Mancini and
Puckett (2005)
Barton (1982)
Nichols (1964)
Austin Chalk
Austin
Chalk
Austin
Chalk
Austin
Chalk
Austin
Chalk
Coker Sand
Dexter
Formation
Lewisville
Formation
Harris Sand
Maness
Shale
Woodbine Group
Eagle Ford
Group
Subclarksville
Sand
Buda
Limestone
Harris
Formation
Lewisville
Formation
Woodbine Group
Lewisville
Formation
Woodbine
Formation
Maness
(Pepper)
Buda
Limestone
Buda Limestone
Buda
Limestone
Maness Shale
Woodbine Group
Harris
Delta
Lower unit
Dexter
Formation
Pepper
Shale
Buda
Limestone
Cenomanian
Woodbine
Group
Maness
Shale
Upper
unit
S.C.*
Coker
Dexter
Formation
Eagle Ford Group
Turonian
Upper Cretaceous
Eagle Ford
Subclarksville
Sub-Clarksville sandstones
Eagle Ford
Group
Adams and
Carr (2010)
Coniacian
to Campanian
Eagle Ford
Group
Stage
Series
This study
*Subclarksville Sand
Figure 4. Schematic diagram summarizing proposed subsurface stratigraphic framework of this study and subsurface nomenclature
of selected earlier studies.
in the currently most active area of the play
(Figure 2). Hentz and Ruppel (2010) discussed some
of the subsurface stratigraphic intricacies in this
region. After correlating more densely spaced well
logs over a larger area in this region, we can now
present a clearer picture of gross lithofacies correlations to guide explorationists and researchers. Until
detailed paleontologic study from cores is conducted,
we cannot prove precise age correlations among the
described subsurface intervals. However, sequencestratigraphic analysis provides a reasonable chronostratigraphic proxy for biostratigraphic study.
Eagle Ford Group (Maverick Basin)
Southwest of the San Marcos arch in South Texas,
only the Eagle Ford Group occurs between the Buda
Limestone and Austin Chalk (Childs et al., 1988),
both of which extend from the Texas–Mexico border
to the Sabine uplift on the eastern margin of the East
Texas basin (Sohl et al., 1991) (Figure 1). The
organic-rich lower Eagle Ford Group, the primary target interval for drilling and completion, greatly thins
(but is continuous) over the San Marcos arch (Hentz
and Ruppel, 2010). However, the upper Eagle Ford
Group is restricted to the Maverick basin area of
South Texas (Hentz and Ruppel, 2010; Tian et al.,
2012) (Figure 6A). The northern subsurface limit of
the lower Eagle Ford Group occurs about 50 mi
(∼80 km) northeast of the arch axis (Figure 5). In this
southwestern part of the East Texas basin (eastern
Milam, Burleson, and Washington counties and
western Robertson County), the Buda Limestone-toAustin Chalk interval extends into the basin as a
HENTZ ET AL.
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2557
Figure 5. Areal subsurface distribution of the lower Eagle Ford Group, Pepper Shale, Lower unit, Upper unit, and Woodbine Group
in the Eaglebine play area. Refer to Figure 6B for cross-sectional interpretation of depicted lithostratigraphic zones. Locations of
Mexia–Talco fault zone and Edwards and Sligo shelf margins from Ewing (1990).
mudrock-dominated succession consisting of two
informal divisions herein defined by contrasting
gamma-ray-log facies: Lower unit and Upper unit
(Figure 6B). The Lower unit is the northeastward
(basinward) continuation of the uniformly highgamma-ray log facies of the lower Eagle Ford Group
(Figure 6B, wells 1, 2), and it is characterized by a
nearly isopachous (100–145 ft [30–44 m]) interval of
similarly high-gamma-ray log facies (wells 3–7).
In contrast, the Upper unit comprises a basinwardthickening (<200 ft [<60 m] to ∼525 ft [∼160 m]),
consistently lower gamma-ray-log facies. The
“transition” zone depicted in Figure 5 delineates the
general areal extent of the change from lower Eagle
Ford log facies to those of the Lower and Upper units.
2558
Eagle Ford Group (East Texas Basin)
This entire two-unit mudrock succession thickens
markedly toward the northeast into the basin from
25 ft (8 m) or less along the axis of the San Marcos
arch (Figure 6B, well 1) to greater than 650 ft
(>200 m) near the southwesternmost occurrence of
prominent Woodbine sandstone facies (Figure 6B,
well 6). In western Limestone, southeastern Falls,
Robertson, western Leon, Brazos, southern Grimes,
eastern Burleson, and eastern Washington counties,
part of the Upper unit is inferred to be chronostratigraphically equivalent to the Eagle Ford Group
(Figure 6B, wells 6, 7). Note that in the East Texas
basin, the Eagle Ford Group only occurs as a
Eaglebine Play of the Southwestern East Texas Basin
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separate, definable lithostratigraphic unit where
Woodbine sandstone facies underlie it and define
its base (Figure 4). That part of the Upper unit that
is likely time equivalent to the Eagle Ford Group
probably progressively thins southwestward
because of both regional depositional thinning near
the edge of the East Texas basin and to erosional
truncation at the base-of-Austin Chalk unconformity. The unconformity is present throughout the
East Texas basin, with rocks of late Turonian and
early Coniacian age missing through truncation
and possibly nondeposition (Surles, 1987; Ambrose
et al., 2009), and it is present in outcrop along
the crest of the San Marcos arch (Young and
Woodruff, 1985).
Biostratigraphic studies by Moreman (1942),
Kennedy (1988), and Hancock et al. (1994) establish that the Cenomanian–Turonian boundary occurs
in outcrops of the lower part of the Eagle Ford
Group and, by correlation, in the East Texas basin
subsurface (Surles, 1987) (Figure 1). Moreover, biostratigraphic analysis of the subsurface Woodbine
and Eagle Ford sections in the Kurten field of
northeastern Brazos County by Turner and Conger
(1981, their p. 214) shows that the boundary lies
within the Eagle Ford section. Fossil evidence of
the Cenomanian–Turonian boundary within Eagle
Ford Group outcrops (Jiang, 1989) and in a nearsurface Eagle Ford core (Corbett and Watkins,
2013) immediately north of the San Marcos arch in
the Austin, Texas, area indicates that strata that are
time equivalent to at least a portion of the East
Texas basin’s Eagle Ford Group occur on the northeast flank of the arch and likely on the arch axis.
Based on paleontology-supported, sequencestratigraphic correlation northeastward from Eagle
Ford (Boquillas) outcrops in West Texas into the
subsurface, Donovan et al. (2012) extrapolated
Turonian Eagle Ford strata to the southwest flank
of the arch. Therefore, the Cenomanian–Turonian
boundary and at least part of the Eagle Ford section
of the East Texas basin extend across the San
Marcos arch into the Eagle Ford Shale play area of
South Texas (Figure 6), although the much-thinned
upper part of the Eagle Ford Group has probably
been locally removed by erosion at the base-ofAustin Chalk unconformity northeast of the arch.
Pepper Shale
The Pepper Shale is defined in the subsurface as that
portion of the mudrock-dominated succession
between the Buda Limestone of the Washita Group
and Austin Chalk that is equivalent only to the
Woodbine section (Adkins and Lozo, 1951; Childs
et al., 1988; Dawson et al., 1993) (Figure 4). The
Pepper section consists of mostly distal deltaic and
prodeltaic facies that accumulated on the fringe of
the sandstone-rich fluvial-deltaic Woodbine Group.
It can be most clearly distinguished as a distinct unit
closest to the area of Woodbine sandstone terminations in eastern Limestone, western Leon, western
Madison, and central Grimes counties (Figure 5).
This area also coincides with the southwestwardmost
occurrence of the formally defined Eagle Ford Group
in the East Texas basin. Therefore, the Pepper Shale
is areally restricted to this general area where the
Woodbine and Eagle Ford Groups no longer exist as
stratigraphically definable units. Immediately to the
southwest, only the Upper and Lower units of the
mudrock-dominated Buda Limestone-to-Austin
Chalk interval can be defined, and the basinward part
of the Upper unit grades into the Pepper Shale
(Figure 6B). Generally thin (≥10 ft [3 m]) sandstone
beds, which extend southwestward from the fringe
of the Woodbine fluvial-deltaic complex into the
Pepper succession, form stratigraphic and diagenetic
traps that are among the prime drilling targets for
Eaglebine explorationists. Established sandstone reservoirs in Kurten field along the Woodbine-complex
margin (Figure 5) of northeastern Brazos County
(Turner and Conger, 1981) and in nearby Iola field
in northwestern Grimes County (Barton, 1982) are
representative of these targets using current drilling
and completion technology. The depositional and
sequence-stratigraphic context of these sandstone
units within the Woodbine and Pepper successions
are discussed in the sections “Sequence Stratigraphy”
and “Woodbine Depositional Facies.”
Maness Shale of Washita Group
The middle Cenomanian Maness Shale is a mudrock
interval that is defined only in the subsurface of the
East Texas basin between the top of the Buda
HENTZ ET AL.
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2559
B
50 mi
80 km
0
B
0
-100°54'51"
29°41'39"
Austin
Chalk
RES
GR
RES
ENRE
1 Lopez
Approximate
Cenomanian-Turonian
Cenomanian-Turon
nian
boundary
GR
PEDECO
1 Mallard
1
2
3 5
GR
4
6
7
8
RES
BRENT
7 Austin Chalk
9
10
B'
m
75
T
Texas
N
31°10'47"
-93°45'26"
No horizontal scale
0 0
200
ft
Figure 6. Regional southwest-to-northeast cross section BB′ illustrating the lithostratigraphic framework of the Buda Limestone–to–Austin Chalk interval in South and East Texas. (A)
Southwestern segment of cross section extending from the Maverick basin (left) to the San Marcos arch (right). Approximate position of the Cenomanian–Turonian (C–T) stage boundary in the Maverick basin from Donovan et al. (2012). Boundary location near the axis of the San Marcos arch from Jiang (1989) and Corbett and Watkins (2013). Interpretation of the
regional facies transition from the upper Eagle Ford Group to the lower Eagle Ford Group is largely based on the presumed extension of the C–T boundary through both units.
See Figure 5 for definition of dot patterns depicted in index map. Modified from Hentz and Ruppel (2010). (B) Northeastern segment of cross section extending from the San
Marcos arch to the eastern part of the East Texas basin. The divisions “Lower unit” and “Upper unit” apply only to the dominantly mudrock succession between the Buda
Limestone and Austin Chalk in wells 3–6 (and Lower unit in well 7), southwest of the primary Woodbine depocenter and geographic area of Eagle Ford Group occurrence. Datum
is the base of the Austin Chalk, a regional unconformity. GR = gamma-ray; RES = deep resistivity.
Georgetown
g
Limestone
Buda
Limestone
Lower
Eagle
Ford
p
Group
Upper
Eagle
Ford
Group
Datum
RES
GR
GR
RES
RISA
2 Bartlett Est.
TRANSTEXAS
A-1 Chittim Ranch
Base of
Austin Chalk
(A)
3300
3400
3500
35
500
3600
3700
3800
800
3900
4500
4600
4700
4800
4900
5000
5100
5200
530
5300
5400
4000
00
4100
4200
4300
4400
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4500
Eaglebine Play of the Southwestern East Texas Basin
5500
5200
530
5300
5400
5500
5600
5700
5800
5900
5700
5800
5900
6000
00
6900
7000
7100
7200
7300
2560
HENTZ ET AL.
GR
ft
No horizontal scale
0 0
75
m
Lower
Eagle
Ford
Group
200
RES
Figure 6. Continued.
Georgetown
Limestone
Buda
Limestone
Base of
Austin Chalk
GR
RES
GR
GR
GR
Austin
Chalk
Lower
unit
Upper
unit
RES
Approximate
Cenomanian-Turonian
boundary
RES
Buda
Ls.
RES
Datum
GR
Pepper
Shale
RES
GR
RES
Eagle
Ford
Group
GR
GR
Maness
Shale
Woodbine
Group
RES
RES
GR
RES
MOBIL
1 Sara Ann Unit
TEXAKOMA
1 Coleman
EURATEX
1 Trinity
CASHCO
1 Sanders
EASTERN
2 Morgan
NORTH CENTRAL
1 Putz
GEODYNAMICS
1 Vyhopen
HOUSTON
1 Coffield-Sante
KELPETRO
1 Bingham
BRENT
7 Austin Chalk
B'
10
9
8
7
6
5
4
3
2
1
6900
7000
7100
7200
7300
6400
6500
6600
6700
6800
6900
5400
5500
5600
5700
5800
5900
8300
8400
8500
8600
8700
(B)
8500
8600
8800
8900
7700
7800
7900
8000
8100
8200
8300
9400
9500
9600
9700
9800
9900
10,000
10,100
10,200
10,300
10,400
9000
9100
9200
9300
9400
9500
9600
9700
9800
9900
10,000
10,100
8400
8500
8600
8700
8800
8900
9000
9100
9200
9300
9400
9500
9500
7700
7800
7900
8000
8100
8200
8300
8400
8500
8600
8700
8800
8900
8000
8100
8200
8300
8400
8500
8600
8700
8800
8900
9000
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2561
Limestone and the base of Woodbine sandstone
facies (Bailey et al., 1945) (Figures 1, 4, 6B).
Because the base of the Woodbine sandstone section
is locally and regionally irregular, thickness of the
Maness Shale (as a lithostratigraphic unit) within the
basin varies considerably from less than 90 ft
(<27 m) to greater than 210 ft (>65 m). It extends
continuously throughout the East Texas basin only
where the Woodbine Group exists. Explorationists
are examining the Maness interval for hydrocarbon
potential, but we are not aware that it is currently an
active target within the Eaglebine play. However,
the proposed equivalent mudrocks of the Lower unit
(Figures 6B, 7), which have high-gamma-ray and
sporadically high-resistivity-log expression (presumed to record organic-rich strata), are currently
being scrutinized by operators for their thermal
C
maturity and organic content to determine their
prospectivity.
Based on regional well-log (gamma-ray) correlation, Hentz and Ruppel (2010) proposed that the
Maness Shale is probably time-equivalent to at
least part of the lower Eagle Ford Group of the
San Marcos arch and Maverick basin areas.
Definition of the Lower unit as a stratigraphic link
between the lower Eagle Ford and Maness successions (Figure 6B) and sequence-stratigraphic interpretation support this contention. The contact
between the Buda Limestone and the Maness Shale
is a regional mid-Cenomanian unconformity and
sequence boundary that formed during a lowering of
relative sea level after Buda and before Maness and
Woodbine deposition that affected the entire Gulf
Coast Basin (Salvador, 1991; Mancini and Puckett,
C'
2
4
6
7
9
KELPETRO
1 Bingham
GEODYNAMICS
1 Vyhopen
EASTERN
2 Morgan
CASHCO
1 Sanders
TEXAKOMA
1 Coleman
9900
MFS 10
RES
8600
GR
8700
RES
9800
10,100
Datum
8900
8800
8700
6500
6800
6700
6600
Base of
Austin Chalk
GR
RES
SB 10
8800
GR
10,000
RES
10,200
GR
10,300
RES
8600
GR
Maness Shale
and
Lower unit
Buda Limestone
Grayson Shale
Georgetown
Limestone
Systems tract
Highstand
Transgressive
Figure 7. Cross section CC′ derived from well logs shown in Figure 6B, illustrating the laterally consistent transgressive–regressive
gamma-ray-log pattern of the Maness Shale and Lower unit. The pattern occurs basinwide in the Maness interval and represents a
third-order transgressive systems tract, lower part of the initial Woodbine highstand systems tract, and intervening third-order maximum
flooding surface (MFS 10), all deposited above the regional third-order sequence boundary SB 10—the well-documented midCenomanian unconformity of the northern Gulf Coast Basin. Well numbers at tops of wells coincide with those shown in Figure 6B.
Along and near the axis of the San Marcos arch, the characteristic retrogradational–progradational log pattern of the Lower unit and
Maness Shale is not apparent (well 2). This much-thinned section on the arch represents much of the upper Cenomanian and part of
the Turonian succession of the East Texas basin. The overall lower gamma-ray-log signature of the Maness Shale in well 9 relative to that
of the equivalent Lower unit in the other wells is interpreted to be a result of higher silt content associated with sedimentation within the
basin’s regional Woodbine depocenter (Figure 6B). GR = gamma-ray; RES = deep resistivity.
2562
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
2005; Mancini and Scott, 2006). Throughout the
study area and the basin, the top-Buda unconformity
records a surface of exposure and hiatus but exhibits
no clear evidence of erosional truncation on well
logs. However, locally in the Austin, Texas, area the
uppermost Buda interval is highly brecciated and is
interpreted by Fairbanks (2012) to record karsting.
The Maness interval consistently comprises a
lower, upward-fining (retrogradational) section and
an upper, upward-coarsening (progradational) unit
(Figure 7) throughout the East Texas basin. The retrogradational part of the Maness succession, uniformly
about 60 ft (∼18 m) thick in most of the basin, represents a third-order TST that formed after lowstand conditions recorded by the interbasinal unconformity at
the underlying top-of-Buda sequence boundary
(Ambrose et al., 2009). The upper, progradational
Maness interval records initial highstand conditions
of earliest Woodbine sedimentation. A third-order
maximum flooding surface (MFS 10 [Figure 7])
occurs at the boundary between the two Maness
systems tracts. Sequence boundary SB 10 (midCenomanian unconformity [Figure 7]), which occurs
near the top of the Buda Limestone basinwide, is a
regional chronostratigraphic marker defining the start
of both Maness deposition in the East Texas basin
and lower Eagle Ford deposition in the Maverick basin
and San Marcos arch areas. Toward the southwest
within the study area, the Maness retrogradational–
progradational log-facies profile is continuous with
that of the Lower unit (Figures 6B [wells 3–7], 7), indicating correlation of the mid-Maness maximum flooding surface (MFS 10) into the lower Eagle Ford Shale
succession of the northwest flank of the San Marcos
arch and, therefore, recording the time equivalency of
the Lower unit with at least part of the lower Eagle
Ford interval. The retrogradational–progradational
Lower unit (with MFS 10) cannot be resolved in wells
close to the axis of the arch because of the pronounced
thinning of the Buda Limestone-to-Austin Chalk interval (Figure 6B, wells 1, 2). The much-thinned section
between the mid-Cenomanian unconformity (SB 10)
and the base of the Austin Chalk above the
Cenomanian–Turonian boundary on and near the arch
represents the combined duration of Maness Shale,
Woodbine Group, and part of Eagle Ford Group deposition in the East Texas basin (Figures 6B, 7 [well 2]).
The section likely contains multiple disconformities
(representing hiatuses) that coincide with some of the
sequence boundaries defined in this study primarily
within the Woodbine Group and possibly the sequence
boundaries documented by Donovan et al. (2012)
in complete Eagle Ford Group outcrops in distant
West Texas.
Woodbine Group
Details regarding the sandstone and mudrock facies,
sandstone trends, and the sequence framework of the
Woodbine succession are discussed in the following
sections. However, one aspect of the unit’s lithostratigraphy needs mention here. Researchers of the
Woodbine Group commonly use the terms Dexter
and Lewisville to define the lower and upper formations of the unit, respectively. In our experience, the
divisions cannot be clearly defined in the subsurface
of the Eaglebine play area using well-log data.
The formation names were first defined by Sellards
et al. (1932) from outcrop study only. Because of this,
they are inappropriate subsurface stratigraphic terms
for the Eaglebine play area and most of the deep
East Texas basin in which lithofacies vary considerably from those of the outcrop.
SEQUENCE STRATIGRAPHY
East Texas Basin
Ambrose et al. (2009) documented that the greater
Woodbine succession (top of Buda Limestone to
lowermost Eagle Ford Group) consists of a maximum
of 14 fourth-order sequences in a broad area covering
the central and northeastern parts of the East Texas
basin and Sabine uplift. The number of sequences
systematically decreases from 14 to 3 toward the
uplift because of gradual depositional pinch out on
the western flank of this contemporaneous topographic high and extensive erosional truncation at
the pronounced base-of-Austin Chalk unconformity
on the uplift (Figure 8). The maximum number of
sequences (and maximum thickness) exists along the
basin axis (Figure 2). We extended our sequence correlations from our previous study (Ambrose et al.,
HENTZ ET AL.
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2563
Basin axis
D
SKLAR
3 Hill
PACIFIC
1 Hartley
INEXCO
1 Swift
ENCANA
A1 Carr
SABINE
1 Limerick
TEXAS CRUDE
1 Doyle
D'
SW
1 Ryan
TEXAS CRUDE
1 Chapman
Sabine Uplift
McMURREY
1 Bland
WORLDWIDE
5 Denman
Austin Chalk
NOE
1 Wilson
ft
200
m
60
Eagle Ford Group
MFS 150
0
0
Mu
d
fac rock
ies
No horizontal
scale
SB 70
Woodbine Group
96°
95°
N
D'
Sequence boundary
Maness Shale
fau
32°
10
East Texas
Basin
M-T
SB
lt zo
ne
Sabine
Uplift
Buda Limestone
0
40 mi
0
60 km
Depositional pinch-out
Erosional truncation
Base-of-Austin unconformity
D
31°
Figure 8. Cross section DD′. Schematic rendering of the sequence-stratigraphic framework of the Woodbine Group across the East
Texas basin and Eaglebine study area (far western part of cross section). Eastern half of cross section modified from Ambrose et al.
(2009; their figure 5B). Datum is third-order maximum flooding surface MFS 150 that occurs in the lower part of the Eagle Ford
Group throughout the East Texas basin. “Mudrock facies” of the west part of the cross section include the Pepper Shale, Lower unit,
and Upper unit (Figures 4, 6B). General upsection thinning of fourth-order sequences is characteristic of the Woodbine succession.
Regional thickness variation of the Eagle Ford Group is partly because of erosion at the base-of-Austin Chalk unconformity. SW = SW
Operating, Inc.; NOE = T.C. Noe Oil Account.
2009) into the Eaglebine study area by additional
regional well-log correlation to characterize the
systems-tract framework on the western side of the
basin where the greater Woodbine succession also
thins (Figure 3).
Although the early Late Cretaceous (Cenomanian
and Turonian Stages) was a period of consistently
high eustatic, “greenhouse” conditions (Haq et al.,
1988), salt mobilization in the East Texas basin
during Woodbine deposition (Seni and Jackson,
1984) created basin accommodation during the
Cenomanian that was enhanced by the influx of abundant coarse sediment from the north margin of the
Gulf Coast Basin (Sohl et al., 1991), also termed the
2564
southern Arkansas uplift of the Ouachita system
(Ewing, 1991a, b). We infer that these conditions provided the mechanism for relative-sea-level fluctuations of sufficient magnitude to result in periodic
incision of and coarse-sediment aggradation in lowstand incised valleys during Woodbine sedimentation
(Ambrose et al., 2009). Such accommodation creation also enabled preservation of Woodbine IVFs.
Similar tectonic conditions, high sedimentation
rates, and preservation of thick incised-valley
fills (16–131 ft [5–40 m]) dominated by fluvial facies
also characterized deposition of the Woodbineequivalent lower Tuscaloosa Formation of the North
Louisiana Salt basin and the Mississippi Salt Basin,
Eaglebine Play of the Southwestern East Texas Basin
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the former located just east of the Sabine uplift
(Woolf, 2012).
The contact between the Woodbine Group and
Eagle Ford Group is unconformable throughout the
East Texas basin, but it is not a single, regional unconformity. Instead, it comprises depositional pinch outs
of several fourth-order sequences at the top of the
Woodbine Group (Figures 8, 9). Considering these
stratal relationships in a broader basin-scale context,
we interpret these depositional pinch outs to record
what Vail (1987) termed “apparent truncation.” Vail
defined apparent truncation as parallel seismic reflectors within a low-order TST that systematically terminate basinward below the associated low-order
marine condensed section and MFS. We propose that
the Woodbine interval above about fourth-order SB
70 is a third-order TST in which the pinch outs represent apparent truncation of fourth-order sequences
below third-order MFS 150 (Figure 8). Although Vail
(1987) depicts apparent truncation in the basinward
direction, the same features would be expected to exist
near basin margins where accommodation also
deceases (Figure 8). Upsection thinning of the
Woodbine fourth-order sequences is consistent with a
decrease in sediment supply and accommodation during a low-order, basin-wide transgressive depositional
phase. The succession of sequences between SB 10
and about SB 70 (Figure 8) likely represents a thirdorder LST because of the occurrence of multiple
coarse-sandstone- and gravel-bearing fourth-order
IVFs in the lower Woodbine Group shelf succession
in the eastern part of the East Texas basin (Ambrose
et al., 2009). However, until lowstand slope and
basin-floor deposits equivalent to this sequence set
can be identified in seismic profiles and well logs, we
cannot confirm this interpretation.
Eaglebine Study Area
Primary aspects of the sequence stratigraphy of the
Buda Limestone-to-Austin Chalk shelf succession
are consistent across the southern two-thirds of
the basin, with the documented thinning of the
Woodbine Group at the eastern basin margin also
occurring at the western margin. The number of
fourth-order sequences systematically decreases
westward from 14 in the basin axis to no more than
9 because of their gradual depositional pinch out near
the western basin margin (Figures 8, 9). In the
northeastern part of the study area, three of those
sequences pinch out within a zone of approximately
20 mi (∼32 km) (Figure 9). Additional stratal thinning caused by regional sequence pinch out within
the Pepper Shale facies probably exists; however,
the absence of clearly discernable sandstone-bearing
depositional cycles (systems tracts) on the well logs
precludes their definition.
Nine highstand-dominated, fourth-order sequences (S1–S9) ranging from 30 to 105 ft (9–32 m) thick
characterize the greater Woodbine succession within
most of the study area (Figure 9). The HSTs within
the nine sequences range considerably from 32 to
110 ft (10–33 m) thick. Underlying TSTs vary from
10 to 40 ft (3–12 m) thick, but most are no more than
about 15 ft (∼6 m) thick. The HSTs typically thin
toward the southwest, whereas the TSTs are nearly
isopachous across the study area (Figure 9). Percentsandstone content within Woodbine sequences generally increases upward from S1 to S6 and again from
S7 to S12 (Figure 9), whereas sequence thickness
within the same two successions decreases upward.
However, in this off-axis area near the margin of the
main Woodbine fluvial-deltaic complex, percentsandstone content of any one sequence is quite variable, and thus the vertical trend of percent-sandstone
also varies. These generally sandstone-bearing but
mudrock-dominated progradational and retrogradational successions are similar to those described by
Phillips (1987) as transgressive and regressive shelf
facies composing high-order sequences in the region
at the margin of the main Woodbine depocenter in
Leon, Madison, Brazos, and Grimes counties.
Generally thin (5–40 ft [1.5–12 m]) and commonly discontinuous sandstone units capping the
sequences in the study area are primary completion
targets for hydrocarbon producers. In contrast to
these relatively sandstone-poor sequences, some
Woodbine sequences in the northeastern part of the
study area close to the basin axis are distinguished
by the occurrence of thicker sandstone units (as much
as 80 ft [24 m]), some of which are inferred to be lowstand IVFs and are expressed as blocky to blockyserrate gamma-ray-log signatures. Whole cores from
East Texas field (Figure 2) demonstrate that these
HENTZ ET AL.
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2565
E
E'
6500
6700
S17
S16
6800
Datum
S10
SB 70
7200
7300
7300
6400
7400
6500
7400
30
6600
6700
0
95°41'
31°44'
Systems tract
E'
Transgressive
Lowstand:
incised-valley fill
Leon Co.
Houston
Co.
E
30°59'
96°16'
Madison Co.
6800
Highstand
20 km
Woodbine
Group
SB 2
7500
7600
SB
7600
7300
S2
SB 60
SB 40
S1
0
S12
S11
SB 50
7500
7100
7200
S4
S3
20 mi
MFS 150
S6
S5
0
Eagle Ford
Group
SB 130
6100
SB 80
SB
SB 1 120
10
6200
0
6900
SB 10
SB 180
7000
7100
6900
S7
Austin
Chalk
RES
S15
SB 90
S8
7000
Pepper
Shale
SB 160
GR
7100
6800
S9
7000
6800
6900
6700
No horizontal
scale
7200
0
6600
6700
6500
SB 170
6600
0
RES
5600
GR
5700
Sonic
5800
GR
200 ft
TEXAS CRUDE
1 Doyle
5900
RES
INEXCO
1 Swift
6300
GR
60 m
SKLAR
3 Hill
6000
ENCANA
A1 Carr
Depositional pinch-out
Base-of-Austin unconformity
Fourth
order
MFS 10
SB 10
Maness
Shale
Buda
Limestone
Maximum flooding surface
Transgressive surface
Sequence boundary
SB 180 Third-order surface
S9
Fourth-order sequence
Figure 9. Details of sequence-stratigraphic and systems-tract framework of Woodbine Group in the southwestern East Texas basin.
Wells coincide with the western four wells in Figure 8. Datum is third-order maximum flooding surface MFS 150 near the base of the
Eagle Ford Group. sub-Clarksville sandstones occur between MFS 150 and the base-of-Austin Chalk unconformity. Particularly salient
features include (1) depositional pinch out of 3 of the maximum 14 fourth-order sequences of the greater Woodbine succession,
(2) occurrence of three fourth-order sequences in the Eagle Ford Group, and (3) westerly gradation to progressively sandstone-poor
Woodbine strata and the Pepper Shale facies. Woodbine sequences S13 and S14 (associated with SB 140 and SB 150, respectively) depositionally pinch out east of the study area (Figure 8). GR = gamma-ray; RES = deep resistivity; SB = sequence boundary.
2566
Eaglebine Play of the Southwestern East Texas Basin
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log facies in the lower Woodbine Group are characterized by coarse, granular fluvial sandstones and
chert-clast conglomerates (Ambrose et al., 2009).
Gross-sandstone mapping also supports this IVF
interpretation of an upper Woodbine sequence in the
study area (described in the following section,
“Woodbine Depositional Facies”).
Third-order sequence boundaries SB 10
(mid-Cenomanian unconformity) and SB 180 (baseof-Austin Chalk unconformity) bracket the study succession. Similarly, MFS 10 and MFS 150 record its
major, low-order flooding events, which are associated with its thickest TSTs immediately below and
above the Woodbine Group, respectively (Figure 9).
Three additional progradational intervals as much
as 100 ft (30 m) thick, each overlain by thinner retrogradational units (10–15 ft [3–5 m] thick), occur
within the overlying Eagle Ford Group in the study
area. These progradational and retrogradational units
progressively thicken toward the basin axis to as
much as 150 ft (46 m) and 32 ft (10 m), respectively
(Figure 8). They are inferred to record HSTs and
TSTs, respectively, of three fourth-order sequences
likely forming a progradational sequence set that
accumulated after the major late Cenomanian–early
Turonian flooding event recorded by MFS 150 and
its associated TST (Figure 9). The upper beds of
these highstand successions are the productive
fluvial-deltaic sub-Clarksville sandstones. Because
Woodbine sequences S13 and S14 (associated with
SB 140 and SB 150, respectively) depositionally
pinch out east of the study area (Figure 8), the three
fourth-order Eagle Ford sequences are designated
S15, S16, and S17 (associated with SB 160 and SB
170, respectively) (Figure 9). Only SB 160 and SB
170 occur in the East Texas basin; uppermost Eagle
Ford sequence S17 is preserved subregionally and is
consistently truncated by SB 180 (base-of-Austin
Chalk unconformity). Underlying sequence S16 is
also subregionally truncated by SB 180, reflecting
erosional relief of as much as 80 ft (24 m) outside
the Sabine uplift area (Figures 8, 9). Basinward thickening of these sequences indicate that sediment supply during Eagle Ford deposition kept pace with
accommodation creation in a basin that subsided
most along its axis and less at its margins. The thickening also records that the period of subsidence
continued uninterrupted from Woodbine through
Eagle Ford deposition.
WOODBINE DEPOSITIONAL FACIES
To characterize the depositional systems and delineate trends of potential reservoir sandstones of the
Woodbine Group in the Eaglebine study area, we
constructed gross-sandstone maps of the six uppermost sequences (S5 through S10) in the main study
area (Figure 9). Sandstone attributes of three of these
sequences (S5, S7 and S8, and S9) represent the variety of inferred depositional environments; therefore,
only maps of these sequences are herein presented.
Interpretations of S5 are supported by descriptions
of one whole core (Basin 1 Maude).
Sequence 5
Description
Two parallel, northwest-to-southeast-oriented primary sandstone trends exist within S5 in the study
area (Figure 10). The eastern trend displays downdip
bifurcation and a subregional, southwestwarddeviating sandstone pathway. The two trends themselves bifurcate from a 19-mi- (31-km-) wide primary
trunk in the north, but they narrow toward the southeast (down depositional dip) from a maximum width
of about 7 mi (11 km) to less than about 2 mi
(∼3 km). Sandstone values of the western trend
gradually decrease to 0 ft in northern Madison
County, whereas sandstones of the eastern trend
probably extend farther to the southeast outside the
area of well control. The main area of sandstone
occurrence is mostly surrounded by areas of dominantly mudrock (zero gross sandstone), defining the
lobate shape of the sandstone fairway. Gross sandstone was not calculated along most of the eastern
edge of the study area beyond the limit of well control. Thickness of S5 ranges from about 55 to 80 ft
(∼17–24 m); sequence thickness is generally greatest
in the northern part of the study area. Grosssandstone thickness within the sequence varies from
0 to 50 ft (0–15 m), with highest values occurring in
the northwestern edge of the mapped area in southern
Freestone and northern Leon counties. However,
HENTZ ET AL.
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by King Fahd University of Petroleum & Minerals user
2567
95°41'17"
N
31°40'56"
.
SON CO
ANDER
O.
EC
Gross sandstone (ft)
ON
ST
NE
TO
ES .
LIM CO
EE
30
FR
20–30
10–20
Distributary
channel
0–10
0
F
Core
Basin 1 Maude
Crevasse
splay
Interdistributary
bay
F'
Delta
front
.
CO O.
C
ON
IS
ON
LE
.
D
MA
ON
ST
CO
U
HO
30°56'10"
96°21'18"
0
5 mi
0
8 km
Figure 10. Gross-sandstone map of sequence S5 within the Eaglebine study area.
most gross-sandstone thicknesses within the two
principal trends are 10 to 35 ft (3–11 m).
Vertical expression of lithofacies varies within
S5 and is recorded in the gamma-ray logs of the study
wells (Figure 11). Principal log facies include
(1) blocky-serrate to upward-fining, both with planar
bases, and (2) overall upward-coarsening and serrate.
Facies 1 is characterized by a single sandstone unit
2568
approximately 20 to 35 ft (6–11 m) thick that locally
occurs at the top of upward-coarsening (progradational) mudrock-rich successions, whereas facies 2
comprises thin sandstone and siltstone beds (<10 ft
[3 m]) in the upper half of the upward-coarsening
intervals. This is the only mapped sequence described
in this paper that is supported by a publicly available
whole core.
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
F
F'
EP
3 Donahoe
RES
GR
WISENBAKER
2 Robert A Trust
RES
GR
RES
INEXCO
1 Lundy
GR
RES
6800
GR
MACHIN
1 Cook
MFS 60
SB 60
Interdistributary
bay facies
S5
MFS 50
SB 50
7000
8200
7200
6400
6900
8100
Datum
7100
6300
MFS 70
SB 70
Systems tract
Transgressive
Highstand
Distributary channel
Figure 11. Northwest-to-southeast-oriented cross section FF′ illustrating systems tracts and depositional facies of sequence S5.
Line of section shown in Figure 10. GR = gamma-ray; RES = deep resistivity; MFS = maximum flooding surface; SB = sequence boundary.
The Basin 1 Maude core documents sedimentary
characteristics of facies 2. The lower 13-ft (4.0-m)
section of the core is slightly upward coarsening,
ranging from sandy mudstone at the base to very fine
to fine-grained sandstone at the top, where it is truncated by planar-stratified, fine-grained sandstone at
7871 ft (2399.7 m) (Figure 12A). This lower section
contains abundant siderite and abundant organic fragments. Stratification consists of multiple, low-angle
scour surfaces and ripples (Figure 12B), although
these are poorly preserved because of pervasive softsediment deformation. The core’s middle section of
planar-stratified, fine-grained sandstone from 7860
to 7871 ft (2396.3 to 2399.7 m) is erosion-based
(single erosion surface) and exhibits little grain-size
variation, although the upper 2 ft (0.6 m) grades
upward into muddy siltstone. Accessory features
include clay clasts, organic fragments, minor softsediment deformation, and a 2-ft (0.6-m) zone of oil
staining in the upper part of the section. The dominant bedding type is horizontal, planar stratification
(Figure 12C). The upper 15-ft- (4.5-m-) thick section
comprises 2- to 3.5-ft- (0.6- to 1.1-m-) thick beds of
very fine and fine-grained sandstone interbedded
with silty mudstone and contains multiple zones
of soft-sediment deformation and microfaults
(Figure 12A, D). The grain-size profile of the upper
section is variable, and individual sandstone beds
range from 0.5 to 2.5 ft (0.2 to 0.7 m) thick. The dominant stratification type is ripples and small-scale ripple scours. Organic fragments and millimeter-scale
sideritic layers (Figure 12D) are common in the
section.
Interpretation
Deposits of S5 in the study area represent a highstand river-dominated deltaic system. Because it is
largely areally constrained by a peripheral zone of
zero gross sandstone, the mapped area probably
depicts most of single lobe of a larger delta system
within the HST. Log facies 1 records distributary
channels that traversed the S5 delta plain. The primary evidence for this interpretation is their slightly
sinuous and downdip bifurcating gross-sandstone
HENTZ ET AL.
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by King Fahd University of Petroleum & Minerals user
2569
7800
7840
Mud
Silt
V. fine
Fine
Medium
Comments
Coarse
Depth
(ft)
Gravel
Res
V. coarse
Grain Size and Sedimentary Structures
GR
CO3 CMT (%)
Oil stain (%)
(A)
Rock
type
Basin 1
Maude
SB 60
7850
Fine-grained
organics,
sideritic ripples
sd
7900
Cored
interval
sd
sd
e
e
7860
Well-sorted/planar
stratification
Very fine to fine-grained
sandstone
Mudstone
Planar stratification
e
7870
Slump
Siderite
Upward fining
Clay clasts
Upward coarsening
(B)
e
sd
sd
Fault
sd
7880
Bedded siltstone
Siltstone and
mudstone
Soft-sediment
deformation
Sharp
microfaults
Erosional contact
Sandstone
Ripples
sd
Plant fragments
ssd
sd
7890
(C)
1 in.
(D)
1 in.
1 in.
Figure 12. Description of the Basin 1 Maude core, southeastern Leon County. (A) Well log and descriptive profile from 7845 to
7884 ft (2391.8 to 2403.7 m). (B) Organic-rich, very fine-grained sandstone with scour surfaces in lower-crevasse-splay facies at
7873.0 ft (2400.3 m). (C). Fine-grained sandstone with planar stratification in splay-channel facies at 7862.3 ft (2397.0 m). (D) Very
fine-grained sandstone with microfaults and soft-sediment deformation in splay-platform facies at 7848.0 ft (2392.7). Cored well is
located in Figure 10. No clear evidence of a transgressive surface of erosion exists in the cored section; therefore, SB 60 is inferred to
occur atop the sandstone unit just above the cored interval. Gamma-ray expression of a retrogradational unit (TST) above SB 60 is
absent. However, surrounding wells in the S5 zone, such as the nearby Wisenbaker 2 Robert A Trust well (Figure 11), exhibit
well-defined transgressive systems tract. GR = gamma-ray; Res = deep resistivity; SB = sequence boundary.
2570
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
patterns (Figure 10), features that are characteristic
of modern river-dominated deltaic systems (Fisk,
1961; Galloway, 1975). Moreover, their gammaray log facies consistently exhibit aggradational to
upward-fining sandstone bodies with flat, erosional
bases overlying delta-plain deposits, similar to
those described by Fisher (1969) and Brown et al.
(1973). These localized, linear, and erosion-based
units record channelized systems truncating
mudrock-dominated facies 2 that is interpreted to
record interdistributary deposits of the riverdominated deltaic system.
The Basin 1 Maude core comprises facies 2 and
records the interdistributary setting of the S5 riverdominated deltaic system. Interdistributary deposits
are typically characterized by sandstone-poor sediments with thin, organic-rich overbank and splay
sandstones that flank distributary-channel fills (e.g.,
Coleman and Prior, 1982; Bhattacharya and
Walker, 1991). The cored well is located at the
downdip margin of a large crevasse splay branching
off from the eastern distributary channel of the S5
delta (Figure 10). The lower 13 ft (4 m) of the core
contain predominantly levee-overbank deposits representing the early stages of crevasse-splay development, including overbank flooding associated with
early-stage breach of the distributary channel and
sheet-flow of sediment-laden water. These deposits
record repetitive deposition of thin, erosion-based
sand beds associated with scouring from traction
currents that alternate with silty mud beds, which
reflect suspension sedimentation. The dominant
stratification type in these levee facies is lamination,
although it is commonly destroyed by bioturbation
and sediment compaction (Elliott, 1974a, 1975).
The sandstone-dominated middle section consists
of splay-channel deposits indicating maximum
depositional energy within the splay complex. Such
crevasse-channel-fill sediments commonly comprise
unidirectional trough crossbeds or planar-stratified
beds indicating high-energy deposition from flood
currents (Coleman et al., 1964). The upper heterolithic section of the core is composed of upper-splay
and crevasse-platform facies that were deposited
over the splay-channel complex. These facies are
characterized by thin sandstones interbedded with
organic-rich, silty mudstones (Elliott, 1974b).
Sequence boundary SB 60 occurs at the tops of
both the localized distributary-channel fills and the
progradational interdistributary successions of the
S5 HST. Both are consistently overlain by thin
(7–10 ft [2–3 m]) retrogradational TSTs throughout
the study area (Figure 11).
Sequences 7 and 8
Description
Sequences S7 and S8 are depicted in a single map
(Figure 13) because they occur as laterally adjacent
units between the regionally correlated MFSs above
SB 70 and SB 80 (Figure 9). However, the grosssandstone map and log facies of the two units reveal
that they comprise dissimilar geologic attributes.
The gross-sandstone map of the S7 interval in the
southwestern part of study area displays characteristics that are similar to those of S5 succession: generally parallel, northwest-to-southeast-oriented,
slightly sinuous sandstone trends (∼5 mi [8 km] to
<1 mi [<2 km] wide) that bifurcate and become narrower down depositional dip (southwestward).
Gamma-ray log facies of the S7 interval are characteristically serrate to upward coarsening (Figure 14),
with gross-sandstone values varying from <5 to
47 ft (<2–14 m), comparable to those of S5. Log
facies with planar-based, blocky-serrate to upwardfining sandstones also locally characterize the interval within the main elongate sandstone trends.
Sequence S7 thickens progressively from approximately 70 to 160 ft (∼21–49 m) toward the
southeastern part of the study area.
At the northeast margin of the study area, S8
occurs as thick (29–101 ft [9–31 m]), flat-based
blocky to blocky-serrate intervals on gamma-ray logs
in the upper part of the MFS 70-to-MFS 80 succession (Figure 14). Overall thickness of the MFS
70-to-MFS 80 succession in the study area does not
change significantly with thickness variation of these
blocky-sandstone zones, and the lateral change from
the S7 to S8 facies is abrupt. A sharp boundary
divides the areal distribution of S7 and S8 facies
(Figure 13), with the boundary locally occurring
between closely spaced wells. However, the grosssandstone trend of the S8 zone indicates that
sand transport occurred from the northwest to
HENTZ ET AL.
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2571
Net sandstone (ft)
Valley-fill margin
Incised-valley fill facies
> 70
N
60–70
50–60
40–50
30–50
Deltaic facies
> 40
30–40
95°41'17"
20–30
31°40'56"
10–20
0–10
Contour interval = 20 ft
Incised-valley
fill
.
SON CO
ANDER
N
TO
ES .
LIM CO
O.
EC
ON
ST
EE
E
FR
Distributary
channel
G'
G
.
CO .
O
LE N C
O
IS
AD
ON
.
ON
ST
Interdistributary
bay
CO
U
HO
M
0
5 mi
0
8 km
30°50'3"
96°15'35"
Figure 13. Gross-sandstone map of sequences S7 (southwest) and S8 (northeast) within the Eaglebine study area. The boundary
dividing the S7 and S8 facies (margin of incised valley) is sharp, occurring in some areas between closely spaced wells.
2572
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
G
G'
MOORE
1 Lundy
RES
GR
PALMER
A-1 Bromberg
DEN
GR
TEXAKOMA
1 Coleman
RES
GR
RES
MFS 80
7900
8100
Datum
7800
7700
GR
LASMO
1 Edwards
TS 80
8200
7900
8000
S7
7900
7800
S8
SB 80
8300
8000
MFS 70
SB 70
Systems tract
Lowstand:
incised-valley fill
Transgressive
Highstand
Figure 14. West-to-east-oriented cross section GG′ illustrating systems tracts of sequences S7 and S8. Line of section shown in
Figure 13. GR = gamma-ray; RES = deep resistivity; MFS = maximum flooding surface; TS = transgressive surface; SB = sequence
boundary.
southeast, generally similar to that of the S7 (and S5)
deposits.
Interpretation
Like those of S5, the strata of S7 in the study area
represent a highstand river-dominated deltaic system. We conclude this based on the presence of
the same map and log-facies attributes documented
and discussed for the S5 system. Our gross-sandstone map of S6 (not documented in this article)
displays the same sandstone-distribution and logfacies patterns, indicating that this deltaic depositional system persisted in the study area through
at least three consecutive fourth-order sequences
(a period of roughly 300–400 k.y. calculated based
on the average Woodbine fourth-order-sequence
duration of approximately 110 k.y. [Ambrose
et al., 2009]).
Sequence S8 records regional incision of the S7
deltaic sediments by a lowstand IVF system, deposits of which also occur in the lower Woodbine
Group (Ambrose et al., 2009). The gross-sandstone
pattern of the IVF, albeit in an area with sparser well
control than that of the S7 delta, records multiple
episodes of fluvial and possibly estuarine deposition
in the S8 valley. The abrupt areal boundary of the
IVF; its wide, generally continuous geographic distribution; its flat, erosional base; and its consistency
in thickness within the sequence support the occurrence of a significant event of regional incision.
The presence of a preserved remnant of S7 deltaic
strata within the IVF in northern Houston County
HENTZ ET AL.
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by King Fahd University of Petroleum & Minerals user
2573
(Figure 13) documents the variation of depth of incision within the valley system. Similar incision of a
river-dominated delta by a lowstand valley system
is documented by Hentz and Zeng (2003) and Zeng
and Hentz (2004) in their study of the Miocene siliciclastic strata of the ancestral Mississippi River
depocenter, offshore Louisiana. Both well-log correlation and stratal slices from a three-dimensional
seismic volume document lowstand incision by the
same fluvial feeder system of the older protoMississippi delta platform. A comparable setting is
envisaged in the study area during S7 and S8
deposition.
Sequence 9
Description
The mapped sandstone distribution of S9 strata in
the study area contrasts with that of S5, S7, and S8.
Most prominently, sandstone occurs over a smaller
total portion of the study area, with much of it
concentrated as a generally massive accumulation
in a localized area near the junction of Leon,
Madison, and Houston counties (Figure 15). A large
portion of the mapped area is bordered by a zone of
zero gross sandstone—to the east where transition
to the Pepper Shale occurs but also to the northwest, an area of abundant sandstone in S5, S7,
and S8 (Figures 10, 11, 13). Narrow (<1–4 mi
[<2–6 km]) northwest-to-southeast- and northeast-to-southwest-oriented bands of 20–40 ft
(6–12 m) gross sandstone extend into the area of
thickest sandstone. Sandstones that define these
bands uniformly occur in the upper half of S9, typically as two to three distinct units (each about
8–16 ft [∼2–5 m] thick) with blocky-serrate and
upward-fining gamma-ray-log profiles (Figure 16,
Mitchell 1 Gresham). The lowest of these sandstones
commonly have flat, erosional bases. Most of the map
area is marked by low gross sandstone (>0–20 ft
[>0–6 m]), with serrate log profiles (Figure 16,
Hilcorp 3 Leathers). The southern, massive sandstone
accumulation is characterized by a third distinctive
gamma-ray-log motif: blocky but slightly upward
coarsening and thick, with deposits ranging from
approximately 40 ft (12 m) in the northern part of
the accumulation to a maximum of 85 ft (26 m) in
2574
the southern part (Figure 16). These deposits contrast
with the S8 IVF facies in the study area (Figure 14)
by (1) their progradational stacking pattern and gradational base with underlying mudrocks and
(2) increase in thickness of these blocky-sandstone
zones with increasing total thickness of the sequence.
Like S7, S9 thickens progressively from about 40 to
115 ft (∼12–35 m) toward the southeastern part of
the study area.
Interpretation
Deposits of S9 in the study area represent a sand-rich,
wave-dominated deltaic system that accumulated during highstand conditions. Because the S9 system is
largely rimmed by a zone of mudrock-rich strata, the
mapped area probably depicts most of the areal extent
of this delta system. Small stable river systems,
expressed as multiple thin fluvial-channel-fill episodes within the same primary channel trends, traversed a sand-poor stream plain, similar to those that
occur in Cenozoic Gulf Coast units (Galloway,
1981). The fluvial systems stratigraphically transition
to much thicker, sand-rich strand plain deposits that
aggraded in the nearshore area of the delta system.
Stratigraphic and areal aspects are similar to those of
the Nayarit delta and strandplain system of the west
coast of Mexico (Curray et al., 1967) and the São
Francisco delta and strandplain of coastal Brazil
(Coleman and Wright, 1975; Dominguez, 1996), suggesting that like the Nayarit and São Francisco deltas,
deposition of the S9 system was most influenced
by wave, and only minimally by tide and fluvial,
processes. The consistent sandstone-rich log expression of the S9 strand-plain facies (Figure 16) supports
the comparison.
PRODUCTION OVERVIEW OF THE
EAGLEBINE PLAY
Because of complex stratigraphic relations in
the most active part of the Eaglebine play area
(Figure 2), compilation of the play’s productionrelated statistics is limited by the ability to accurately
identify which stratigraphic zone is productive. We
have found that even at the field scale, identification
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
95°41'17"
31°40'56"
.
SON CO
ANDER
.
O
EC
ON
ST
E
RE
N
F
NE
TO
ES .
LIM CO
Net sandstone (ft)
80
60–80
40–60
Stream plain
20–40
0–20
0
Contour interval = 20 ft
H
Strand plain
H'
.
N
EO
L
CO
.
CO
S
DI
MA
ON
0
5 mi
0
8 km
.
ON
ST
CO
U
HO
30°56'10"
96°21'18"
Figure 15. Gross-sandstone map of sequence S9 within the Eaglebine study area.
of the producing stratigraphic zone can be inconsistent with that of both nearby and distant fields.
Therefore, it is a challenge to compile meaningful
play-wide production statistics. For example,
Giddings field in northwest Fayette, southern
Lee, and southern Burleson counties has produced
1.3 million barrels of oil from the “Eagleford” as
of February 2014 (DrillingInfo.com, 2014). Studies
of the field, such as Horstmann (1987), show that
the reservoir zone is an equivalent of the Eagle
Ford Group (East Texas basin). However, this unit
exists only as a definable lithostratigraphic unit
starting ∼25 mi (∼40 km) northeast of the field
(Figure 5). Our Lower unit, inferred to be equivalent
to the Maness Shale and stratigraphically lower
than the Eagle Ford Group (Figures 6B, 7), composes the reservoir zone in at least the northern half
of the field.
HENTZ ET AL.
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2575
H'
PATRIOT
44 Seven J Farm
GR
RES
MAJESTIC
2 Cooper
MFS 150
HILCORP
3 Leathers
H
GR
RES
SB 110
7700
7800
RES
7800
GR
GR
RES
8100
MITCHELL
1 Gresham
Datum
MFS 100
SB 100
Stream plain
facies
S9
MFS 90
SB 90
MFS 80
SB 80
Systems tract
Transgressive
Highstand
Strand plain facies
Figure 16. Northwest-to-southeast-oriented cross section HH′ illustrating systems tracts and depositional facies of sequence S9. Line
of section shown in Figure 15. Note depositional pinch out of sequence S10 (SB 100 to SB 110) below the basinwide third-order transgressive systems tract capped by MFS 150. Figure 9 provides a more regional perspective of this S10 termination and pinch out of
fourth-order sequences S11 and S12. GR = gamma-ray; RES = deep resistivity; MFS = maximum flooding surface; SB = sequence
boundary.
However, certain general statements regarding
production in the play can be made. Welldeveloped, albeit low-permeability, sandstone units
within the mudrock-rich Woodbine and Eagle Ford
(sub-Clarksville) successions characterize reservoirs
in the northeastern part of the play area (most of
Leon, Madison, and western Houston counties
[Figures 2, 5]). In the Eaglebine play’s mudrockdominated southwestern half (western Leon,
Robertson, Brazos, central and southern Grimes,
and Burleson counties [Figures 2, 5]), operators
target thin (<25 ft [8 m]), low-permeability,
2576
subregionally discontinuous sandstone beds extending from the primary Woodbine fluvial-deltaic complex. Powell Shale Digest (2013) reports that within
these areas a total of 199 wells, completed using
horizontal-drilling and multistage hydraulic-fracturing methods, are producing oil and gas. These wells
were drilled by 27 different operators. Peak-month
daily average oil production averages 314 barrels
in the counties listed above, with a range between
238 (Robertson County) and 417 (Madison
County) barrels. Peak-month daily average gas production averages 288 thousand cubic feet (Mcf) but
Eaglebine Play of the Southwestern East Texas Basin
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by King Fahd University of Petroleum & Minerals user
ranges widely from 73 (Robertson County) to 548
(Grimes County) Mcf.
•
CONCLUSIONS
•
•
The mudrock-dominated succession between
the Buda Limestone and Austin Chalk constitutes much of the currently most active part of
the Eaglebine play in the southwestern part of
the East Texas basin. Based on regionally consistent differences in well-log facies, the succession is divided into two informal intervals, the
Lower and Upper units. Most of the Maness
Shale is inferred to be time equivalent to the
Lower unit and at least part of the lower Eagle
Ford Group of the San Marcos arch area.
Moreover, the Cenomanian–Turonian boundary
exists within the Eagle Ford Group of the East
Texas basin, the lower Eagle Ford section of
San Marcos arch, and by interpolation, the
Upper unit. Therefore, the lower Eagle Ford
section of the San Marcos arch represents a
time-condensed unit equivalent to most of the
top-Buda Limestone-to-base-Austin Chalk
interval in the East Texas basin.
This study, integrated with that of Ambrose
et al. (2009), presents a basinwide chronostratigraphic framework for the Woodbine Group.
Similar to that which occurs at the basin’s
eastern margin, the number of fourth-order
sequences in the Woodbine Group systematically decreases westward—from 14 in the basin
axis to no more than 9 in the most active part of
the Eaglebine play—because of their gradual
depositional pinch out at the top of the
Woodbine section near the western basin margin. The upper Woodbine Group above about
fourth-order SB 70 is inferred to compose a
third-order TST in which these pinch outs
represent apparent truncations (Vail, 1987) of
fourth-order sequences below the third-order
MFS (MFS 150) in the lower Eagle Ford
Group. Therefore, the contact between the
Woodbine Group and Eagle Ford Group is
unconformable throughout the East Texas
basin, but rather than a single, regional unconformity, it comprises systematic pinch out of
fourth-order sequences at the top of the
Woodbine Group. The lower Woodbine succession likely represents a third-order LST.
•
In the play area, the Eagle Ford Group consists
of three fourth-order sequences that accumulated after the major late Cenomanian–early
Turonian flooding event recorded by a basinwide TST at the base of the unit. The topset
beds of highstand successions are the productive fluvial-deltaic sub-Clarksville sandstones.
Depositional systems represented in the sandiest upper half of the overall-progradational
Woodbine Group vary within the study area,
even between stratigraphically adjacent sequences. Northwest-to-southeast-oriented, on-shelf
siliciclastic systems include fluvial-dominateddelta; incised-valley-fill fluvial and nearshoremarine; and wave-dominated-delta deposits.
Potential sandstone reservoirs comprise discontinuous distributary-channel, crevasse-splay,
delta-front, incised-fluvial, stream-plain, and
strand-plain facies.
REFERENCES CITED
Adams, R. L., and J. P. Carr, 2010, Regional depositional systems
of the Woodbine, Eagle Ford, and Tuscaloosa of the U.S.
Gulf Coast: Gulf Coast Association of Geological Societies
Transactions, v. 60, p. 3–27.
Adkins, W. S., and F. E. Lozo, 1951, Stratigraphy of the
Woodbine and Eagle Ford, Waco area, Texas, in F. E.
Lozo, ed., The Woodbine and adjacent strata of the Waco
area of Central Texas, a symposium: Dallas, Texas,
Southern Methodist University Press, Fondren Science
Series 4, p. 105–164.
Ambrose, W. A., and T. F. Hentz, 2012, Shelf-edge deltaic depositional system in the upper Woodbine succession, Double A
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