Pennsylvanian-Early Permian Depositional Systems and Shelf

The American Association of Petroleum Geologists Bulletin
V.64, No. I (January 1980), P. 88-106, l9Figs., liable
Pennsylvanian-Early Permian Depositional Systems and Siieif-iMargin
Evolution, Paio Duro Basin, Texas^
C. ROBERTSON HANDFORD and SHIRLEY P. DUTTON^
Abstract The Palo Duro basin of the Texas Panhandle is filled primarily with Pennsylvanian, Permian, and
Triassic strata that record the depositional history of a
shallow cratonic basin. Regional deformation during
Early Pennsylvanian time across a belt encompassing
the southern Oklahoma and Delaware aulacogens resulted in the formation of the basin. Rapid basin subsidence and marine transgression dominated Pennsylvanian depositional history but was followed by marine
regression and rapid filling of deeper parts of the basin
during Early Permian (Wolfcampian) time. Pennsylvanian and Lower Permian strata consist of four major
fades assemblages or depositional systems. An extensive fan-delta system Is composed of arkosic sandstones eroded from Precambrlan highlands flanking
the basin and deposited by braided streams along the
margins of the basin. In the southeastern part of the
Palo Duro basin, westward prograding, high-constructive deltas dispersed sediment across a shelf environment and into basin and slope environments. A thick,
massive sequence of limestone accumulated seaward
of the deltas In a carbonate-shelf and shelf-margin system that encircled most of the basin. The slope and
basin system consists of terrigenous elastics that were
tunneled downslope into deep baslnal environments by
feeder channels that formed along shelf margins.
Interplay between basin subsidence and local sedimentological controls determined the depositional style
and resulting fades patterns. Rapid Pennsylvanian
subsidence combined with invasion and deposition of
terrigenous elastics across carbonate-bank environments caused parts of the northwestern shelf margin to
retreat westward toward shallow, clear water. During
Early Permian time subsidence rates slowed and sedimentologlc controls dominated basin evolution. Thick
slope wedges, which were fomned by deltas that prograded to shelf edges and debouched sediment into
the slope environment, created shallow foundations for
subsequent carbonate-bank development and progradatlon.
Porous shelf-margin dolomites, delta-front sandstones, and fan-delta arkoses are considered potential
reservoirs for oil and gas, Potential source rocks may
be present in adjacent, thick basinal and slope shales.
tion through time have been documented. As a
result, stratigraphic studies often ignore mechanisms by which basins are filled with shelf-margin
and related sediments over long periods. Analyses
of the genetic stratigraphy of sedimentary basins
and long-term history of shelf margins lead to a
more complete understanding of basic principles
of basin evolution. The common association of a
similar suite of depositional systems in other cratonic basins indicates that these principles have
general appUcability.
Pennsylvanian and Lower Permian (Wolfcampian) strata in the Texas Panhandle preserve important phases of the depositional history of the
Palo Duro basin. Across much of the basin two
opposing, east and west shelf margins are laterally separated by approximately 30 to 50 mi (48
to 80 km) of deeper basin facies. Thus, the evolution of coeval shelf margins may be compared
and contrasted. Such a comparison shows that
the development, relative positions, and migration of shelf margins in the Palo Duro basin were
strongly dependent upon intrabasinal controls
such as subsidence and the supply and transport
of terrigenous sediment to deeper parts of the basin.
The objective of this report is to develop a regional depositional model for the evolution of
Pennsylvanian and Early Permian shelf margins
in the Palo Duro basin. To do so requires (1)
identification of all major depositional systems,
(2) delineation of shelf-margin trends through
time, and (3) discussion of the interrelation
among depositional systems and their combined
INTRODUCTION
This report documents the evolution of shelf
margins in the Palo Duro basin. It begins with
original shelf-margin development and expansion
during the Pennsylvanian and continues through
a period of rapid progradation and southward migration of shelf margins into the Midland basin
during Permian time. Facies, morphology, and
depositional and diagenetic processes along
Pennsylvanian-Permian shelf margins have been
investigated (Newell et al, 1953; Dunham, 1969;
Malek-Aslani, 1970; Wilson, 1975; Babcock,
1977; Cys and MazzuUo, 1977; Yurewicz, 1977),
but few examples of regional shelf-margin evolu-
©Copyright 1980. The American Association of Petroleum
Geologists. All rights reserved.
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'Manuscript received, February 20, 1979; accepted, July 9.
1979. Published with permission of the Director, Bureau of
Economic Geology, The University of Texas at Austin, Austin,
Texas 78712.
^Bureau of Economic Geology, The University of Texas at
Austin, Austin, Texas 78712.
Article Identification NumlKr
0149- 1423/80/BOO l-0004$03.00/0
88
Palo Duro Basin, Texas
impact upon shelf-margin evolution.
More than 400 geophysical and sample logs
served as the data base from which this report
was prepared, but for a basin measuring approximately 20,000 sq mi ( > 50,000 sq km), this represents only a moderate drilling density. Numerous
stratigraphic cross sections were constructed, using the highest quality logs available, to determine the framework of Pennsylvanian and
Lower Permian facies. Integration of sample logs
and core descriptions with geophysical logs enhanced the capability to interpret lithology and
construct lithofacies maps.
REGIONAL GEOLOGIC SETTING
The Palo Duro basin in the Texas Panhandle is
a shallow cratonic basin surrounded by positive
tectonic elements (Fig. 1). It is bordered on the
north by the Amarillo uplift, a fault-bounded,
granitic and gabbroic Precambrian block that
separates the Palo Duro and Anadarko basins.
Block-faulted basement rocks of the Matador
arch form the basin's southern boundary with the
Midland basin. The Palo Duro basin is asymmetrical, with the deepest part, approximately 10,000
ft (3,000 m), just north of the Matador arch. The
western rim of the basin is the Bravo dome and
Sierra Grande uplift; the basin's eastern border is
a north-south trending basement high that separates it from the Hardeman basin. Most workers,
however, consider the Hardeman basin to be an
eastern extension of the Palo Duro.
Basement structure delineates several folds that
89
strike southeast from the Amarillo uplift (Fig. 1).
Nicholson (1960) suggested that these are secondary folds which formed in response to shear
movement along the Amarillo uplift. Wickham
(1978) described similarly oriented folds in the
Southern Oklahoma aulacogen which includes
the Amarillo-Wichita uplifts and Anadarko basin, thus flanking the northeastern boundary of
the Palo Duro basin. Wickham indicated that
these folds were created by major strike-slip
movement during Pennsylvanian compression
and deformation of the aulacogen and the Ouachita system. South of the Palo Duro basin, the
Delaware aulacogen (Walper, 1977) was deformed at the same time. Deformation of the two
aulacogens directly resulted in the formation of
the Anadarko and Ardmore basins. Midland and
Delaware basins, the Arbuckle, Amarillo-Wichita
uplifts, and the Central Basin platform. Proximity
of the Palo Duro basin to all of those features and
their similar geologic history indicate that the
Palo Duro basin also formed as a result of deformation of the two aulacogens.
The Palo Duro basin is filled mostly with Pennsylvanian, Permian, and Triassic sedimentary
rocks (Fig. 2). The pre-Pennsylvanian section
System
Series
Group
Quaternary
General lithology
and depositional setting
Fluvial and
lacustrine elastics
Tertiary
Cretaceous
Nearshore marine elastics
Dockum
Fluvial-deltaic
and lacustrine elastics
Artesia
Sabkha salt,
a n h y d r i t e , red beds,
and peritidal d o l o m i t e
Ochoa
Triassic
Guadalupe
Pease River
Leonard
Clear Fork
Wichita
Permian
Wolfcamp
Shelf-margin carbonates,
basin shale,
and deltaic sandstones
Pennsylvanian
Mississippian
Shelf limestone and chert
Ordovician
Ellenburger
Shallow/-marine{?)
sandstone
Cambrian
*rocambrian
FIG. 1—Regional geologic structure (after Nicholson,
1960) and location of study area and cross sections.
Shelf d o l o m i t e
Igneous and m e t a m o r p h i c
FIG. 2—Schematic stratigraphic chart of Palo Diiro basin. Few formal stratigraphic units are recognized except in Leonardian-Ochoan Series (after Nicholson,
1960; Johnson, 1976).
C. Robertson Handford and Shirley P. Dutton
90
^
FAN-DELTA SYSTEM
(PROXIMAL)
LITHOLOGY
I '/, ] Do!omi1e
P = P l Limestone
FAN-DELTA SYSTEM
(DISTAL)
WM
Sandstone
^ ^
Granite wash
I
I Shale
t-.'-VrJ Precambrian
granite
SLOPE SYSTEM
BASIN SYSTEM
SHELF-MARGIN
SYSTEM
DELTA SYSTEM
FIG. 3—Typical spontaneous potential and resistivity (SP and Res) log patterns of facies composing each depositional system. Depths are in feet.
DEAF SMITH
I
DONLEY
5
EXPLANATION
I Dolomite ^S
I
I Shale
I
Aggrodotional Shelf Margin
|i'>.v'j Precombrion Bosement
T Progradationol Shelf Margin
IOI5l(m
100
Dolomite and Doiomltic Limestone [ p ^ Limestone p ^ ^ Sondstone
1 ^ Gronlte Wash
ICOlLINGSWORTHi WHEELER
200
300 m
} Transgresslve Shelf Margin
FIG. 4—East-west cross section showing stratigraphic framework and depositional systems of PennsylvanianLower Pennian strata. Datum is top of WoUcampian Series. GR, gamma ray logs; other logs are SP and Res.
Depths are in feet. See Figure 1 for location.
I
EXPLANATION
I Staple
b?<^Gronite Wosh
| Sandstone
FIG. 5—East-west cross section. Datum is top of Wolfcampian Series. See Figure 1 for location. Depths are in feet.
Progrodationo! Stieif Margin
t'/'^-ilP^ecambrian Basement
] Dolomite ^ ^ Dolomite and Dolomitic Limestone ^ ^ 3 Limestone [
I00d^300m
200
I I Aggradational Shelf Margin
N. MEX
ROOSEVELT
ORDOVICIAN'
•D
<o
ai
w
CD
X
01
O
O
92
C. Robertson Handford and Shirley P. Dutton
consists of a thin basal sandstone (Cambrian) and
shallow-shelf carbonate rocks (Ordovician and
Mississippian) up to several hundred feet thick.
These rocks are present as erosional relicts across
the basin, testifying to the regional tectonism and
erosion during Late Mississippian to earliest
Pennsylvanin time. The Pennsylvanian and Permian section is roughly divisible into evaporite and
nonevaporite facies. Shallow-marine carbonate
rocks, basinal shale, and deltaic sedimentary deposits comprise most of the Pennsylvanian and
Lower Permian, whereas thickly bedded salt,
anhydrite, and red beds of various sabkha and
tidal-flat environments make up the middle to
Upper Permian section. Triassic fluvial-deltaic
and lacustrine facies (McGowen et al, 1977) form
most of the remaining basin fill.
,m
CM IN.
0 0
2-- I
6 2
3
PENNSYLVANIAN-EARLY PERMIAN
DEPOSmONAL SYSTEMS
Pennsylvanian and Lower Permian (Wolfcampian) strata in the Palo Duro basin have never
been satisfactorily or formally divided into formations or members although several informal
names have long been used. No attempt to establish formal nomenclature is made here. Instead
the basin fill is discussed in terms of genetic
stratigraphic units or depositional systems. The
concept of a depositional system as an informal
stratigraphic unit was introduced by Fisher and
McGowen (1967) to facilitate subdivision of a basin fill into process-related suites of sedimentary
facies. A depositional system is composed of assemblages of facies which are genetically hnked
by inferred depositional environments and associated processes (Brown and Fisher, 1977). Examples are meander-belt fluvial systems, delta systems, and submarine-fan systems.
Four depositional systems or combinations of
systems have been recognized in the Pennsylvanian-Lower Permian of the Palo Duro basin.
They are: (1) fan-delta system, (2) high-constructive delta, (3) carbonate-shelf and shelf-margin,
and (4) slope and basin. Because of the relatively
low density of well control in the Palo Duro basin
facies, resolution and mappable separation of systems is limited; hence shelf, shelf margin, slope,
and basin were combined into two systems for
convenience. Each depositional system is characterized by distinctive facies assemblages, vertical
sequences, spatial distribution, and geophysicallog signature (Figs. 3-5).
Fan-Delta System
Pennsylvanian and Early Permian sedimentation patterns were strongly influenced by blockfaulted Precambrian basement highlands surrounding the basin. The highlands shed large
quantities of terrigenous, arkosic ("granite wash")
sediment and, by forming topographically high
boundaries around the basin, they largely controlled the positions and orientation of shelf margins. Major sediment-source areas included the
Amarillo-Wichita uplifts on the north and east,
and the Bravo dome and Sierra Grande uphft on
the northwest. The Matador arch fault blocks
were smaller, more local sources of terrigenous
sediment during Early Pennsylvanian time only.
Arkosic sand and gravel were carried by highFIG. 6—Core of Wolfcampian distributary braided- gradient, braided streams to alluvial fans and fan
channel sequence showing several small fining-upward
cycles. Pebbly sandstone and laminated sandstone are deltas that fringed uplifts and prograded into mainterpreted as channel and braided-bar crest, respective- rine environments. Fan-delta deposits include arly. Sequence is capped by overbank or channel-plug kosic sandstones which were deposited in braidmuddy sandstone. Core is from Potter County, Texas, ed-channel, delta-plain, and destructional-bar
Standard Bivens 7, 3,606 to 3,618 ft (1,099 to 1,103 m). environments (Figs. 5-7). Interbedded limestone
Palo Duro Basin, Texas
and sandstone in distal-fan environments indicate
local marine transgression across abandoned delta lobes.
Fan-delta granite wash deposits are thicker and
of greater areal extent in the Lower Pennsylvanian section than in younger strata. Thick wedges
of Lower Pennsylvanian granite wash up to 400 ft
(120 m) thick abut against the Amarillo uplift and
thin to the southwest (Fig. 8). Lobes of sandstone
extend to the southern margin of the basin. Another wedge of granite wash sandstone extends
from the Bravo dome southeastward across the
basin. In contrast, the general limit of influence
of the Amarillo uphft was reduced in Permian
time because Lower Permian granite wash is restricted to the northern half of the basin just adjacent to Precambrian granite highlands (Fig. 9).
By Late Pennsylvanian and Early Permian time,
movement along most fault systems in the uplifts
had stopped, but highlands continued to supply
coarse-grained sediment to major fan-delta systems until they were worn down by erosion. Near
the end of Early Permian (Wolfcampian) time
most of the uplifts were blanketed by shallowmarine carbonate deposits.
High-Constructive Delta System
Prominent elongate and lobate sandstone isol-
93
ith patterns parallel with paleoslope in the southeastern Palo Duro basin delineate a system of
westward-prograding, high-constructive deltas
(Fig. 9). Most of the clastic sediment comprising
deltaic sequences was probably derived from the
Wichita Mountains in Oklahoma or highlands
along the Ouachita system in Texas. Upper Pennsylvanian elastics entering the Palo Duro basin
generally were deposited on the shelf but, in the
southeastern part of the basin, high-constructive
deltas dumped large quantities of terrigenous sediment into deep-water environments (Fig. 5). Several thick sandstone bodies in the deep basin have
geometries and log patterns similar to bar-finger
deposits (Fisk, 1961; Frazier, 1967; Galloway,
1968). Associated with Pennsylvanian to Permian
bar-finger sandstones are crevasse-splay sandstones, interdistributary-bay mudstone, prodelta
mudstone, and destructional-phase or transgressive limestone (Fig. 10).
Delta sequences became thinner through Early
Permian time, implying that water depths in prodelta environments decreased through time.
Through the Pennsylvanian and Permian transition interval delta-front sandstones are up to 400
ft (120 m) thick, but the same genetic sandstones
in the middle Wolfcampian section are generally
less than 30 ft (10 m) thick. Similarly, Galloway
CM IN.
OTO
2".I
^••2
6-
^-5
FIG. 7—Cores of Wolfcampian fan-delta environments. A, crevasse-splay sandstone and shale with load casts and
burrows; B, distal delta-plain facies displaying soft-sediment faulting; C, laminated slighdy fossiliferous arkose of
destructional bar. A is from Potter County, Texas, Standard Bivens 7, 3,659 ft (1,115 m); B, C are from Hartley
County, Texas, Standard Bivens 12, at 3,673 and 3,688 ft (1,120 and 1,124 m), respectively.
94
C. Robertson Handford and Shirley P. Dutton
EXPLANATION
Inferred sediment dispersoi routes
J
> 200 ft 160 ml granite wash
["ijl'Jl Precombrian highlonds
Faults
• Well control
Contour interval = 100 ft (30 ml
mii*0':%M0'S'"
FIG. 8—Sandstone isolith map of Lower Pennsylvanian section.
Palo Duro Basin, Texas
FIG. 9—Sandstone isolith map of Lower Permian section.
95
C. Robertson Handford and Shirley P. Dutton
96
and Brown (1972) suggested that thin progradational facies of the Cisco fluvial-deltaic system in
north-central Texas are due to deposition on a
stable, shallow shelf. In contrast, thick delta-front
and prodelta sequences of the Mississippi delta
are thought to be related to active basin subsidence in conjunction with depositional loading of
thick prodelta and slope muds, and progradation
into water up to 300 ft (90 m; Fisk, 1961). The
change in thickness of Permian progradational
delta sequences indicates an overall shallowingupward history of prodelta water depths which
may be related to slower rates of subsidence in
the Palo Duro basin.
Carbonate-Shelf and Shelf-Margin System
Seaward of the deltaic facies are Pennsylvanian-Permian carbonate-shelf and shelf-margin
complexes that together form up to 2,800 ft (850
m) of limestone and dolomite. During the early
stages of basin formation in earliest Pennsylvanian time the Palo Duro basin was covered by
shallow seas. Later, as the basin deepened, isolated carbonate buildups began forming across the
shelf. These buildups rapidly coalesced around
the basin and developed into prominent shelf
margins that probably stood several hundred feet
above the basin floor during Late Pennsylvanian
time (Figs. 4, 5).
As Pennsylvanian transgression and basin subsidence continued, shelf margins were forced
either to aggrade or retreat. Along the eastern and
southwestern sides of the basin the position of the
shelf margin was stationary through Late Pennsylvanian time. Shelf-margin carbonate banks
simply built up vertically and kept pace with subsidence and/or transgression. However, two different shelf margins are recognized in the north-
South
North
-24 miles0 -rO
feet
-
100-
meters
50
FIG. 10—Cross section of Pennsylvanian-Permian deltaic sandstones and associated facies. Top of bar-finger
sandstone and destructional-phase limestone were used as stratigraphic datum planes. Pennsylvanian-Permian
boundary is unknown. Depths are in feet.
97
Palo Duro Basin, Texas
EXPLANATION
I
I 400-800 ft 1122-244 ml net limestone
>
800 ft (244 m) net limestone
V.^jPrecQmbngn highlands
^
Inferred fan-delta
sediment dispersal
routes
Contour interval = 200 ft (60 m)
Faults
• Well control
Pennsylvanian shelf margin
Retreat position of ^ * ">- — ^
Pennsylvanian shelf margin
w5JS ,M S/r'^o^p^^v'^';^^^^^^
FIG. 11—Upper Pennsylvanian limestone isolith map.
98
C. Robertson Handford and Shirley P. Dutton
EXPLANATION
I
I > 7 0 % carbonote
— —
Lower Wolfcampian shelf margin
— ^
Middle Wolfcampian shelf margin
•^•^
Upper Wolfcampian shelf margin
•
Well control
Contour interval = 1 0 %
FIG. 12—Map showing percentage of carbonate in Lower Permian strata.
N
Palo Duro Basin, Texas
ern part of the western shelf (Figs. 4, 11). The
younger shelf margin retreated as much as 18 mi
(30 km) west, or landward, of the older shelf margin. The two shelf margins merge in central
Swisher County to form a single, massive sequence of limestone more than 1,000 ft ( > 300 m)
thick.
Conversely, vertical sequences of Lower Permian facies and relative positions of shelf margins
reflect an overall marine regression. During earUest Permian time shelf margins were widely separated in the southern part of the basin, but narrowed northward (Fig. 12). Concomitantly, water
depths decreased northward; on the basis of the
thickness of individual shelf-margin sequences,
99
maximum water depths are inferred to have been
200 to 300 ft (60 to 90 m). In the northern part,
the basin was probably less than 100 ft (30 m)
deep. Through the remainder of Early Permian
(Wolfcampian) time, the basin rapidly closed as
shelf margins prograded toward the basin axis
and southward into the Midland basin. Rates of
p^gradation varied across the Palo Duro basin.
Relative positions of Lower Permian shelf margins through time show that the western margin
prograded shorter distances than did eastern and
northern shelf margins (Fig. 12).
Although no core is available for examination
and sample-log descriptions are inconclusive,
Pennsylvanian and Lower Permian shelf margins
C'
DONLEY
BRISCOE
MOTLEY
EXPLANATION
^ ^
LIMESTONE AND DOLOMITE
[
I SANDSTONE
I
I SHALE
[23
EEEDER CHANNEL
0
5 kilometers
100200 feet -
-50 meters
FIG. 13—Cross section showing massive shelf-margin carbonate deposits (Permian) and lenticular pods of feederchannel fill. See Figure 1 for location. Depths are in feet. Datum is top of Tubb formation (Leonardian).
100
C. Robertson Handford and Shirley P. Dutton
EXPLANATION
f 1 > SO t w t (16 m) CarbonalB
H^ S«<llmont DlgpffrMl
• Well Control
Because dense well control is lacking, stratigraphic correlations in the vicinity of channels
are very difficult and hinder accurate determination of the nature of the contact between channelfill and contiguous shelf-margin strata. However,
massive shelf-margin strata break up into thin
units which are intercalated with interpreted overbank and channel-fill shale along the channel
margins (Fig. 13). This suggests that the contact is
not completely erosional, and that these channels
may be combination erosional and aggradational
types. Active depositional valleys (as opposed to
incised, erosional channels) are known in the upper parts of some modern submarine fans (Normark, 1978). Furthermore, canyons may have
been deepened by upbuilding of shelf margins as
FIG. 14—Isopach map of Lower Permian feeder-channel-fill sequence and distribution of stratigraphically
equivalent limestone. Contours suggest dispersal of sediment from east to west. Contour interval, 10 ft (3 m).
were probably composed of carbonate banks inhabited by crinoids, brachiopods, bryozoans, fusulinids, and sponge-phylloid algal bioherms
(Wilson, 1975). The organisms were not rigid
frame builders but encrusting and sediment-baffling forms. Dominant organisms must have been
fairly tolerant of terrigenous mud because carbonate and deltaic environments were juxtaposed.
Slope and Basin System
Beyond the shelf break a series of broadly coalescing slope wedges of terrigenous elastics and
areas of "deep" basin sedimentation can be recognized. Sediments include black shale, dark micritic limestones, and thin sandstones, all of
which were probably deposited by gravity-induced processes in fan-head feeder channels
(Walker, 1978) of small submarine fans and a basin-plain environment. Slope systems are lenticular in strike section, wedge-shaped in dip section,
and thicken basinward (Figs. 4, 5). The updip
limit of a slope wedge is defined by its termination against massive carbonate facies of the shelf
margin or extreme thinning where it passes between two superposed shelf-margin sequences.
Slope facies grade downdip into basinal facies.
Sediment comprising slope wedges was probably introduced through passes between carbonate buildups on the shelf margin and carried
downslope in feeder channels. Several offset, superposed feeder channels have been recognized in
the Lower Permian section along the eastern shelf
margin (Figs. 13, 14). Channel sites coincide with
the progradational limits of major delta lobes and
are mostly filled with dark mudstone or shale.
CM IN.
OTO
2
6-
L3
FIG. 15—Core of matrix-supported, graded, subaqueous, debris-flow deposit of Pennsylvanian age. Lime
mudstone clasts are supported by terrigenous mudstone
matrix. Core is from Swisher County, Standard Johnson
1 at 7,824 ft (2,385 m).
Palo Duro Basin, Texas
EARLY
PENNSYLVANIAN
FIG. 16—Paleogeographic evolution of Palo Duro basin in Pennsylvanian-Early Permian time.
101
102
C. Robertson Handford and Shirley P. Dutton
well as periodic incision by currents (Von der
Borch, 1969). Upbuilding of adjacent carbonateshelf margins and slopes relative to canyon cutting may have been favored because of biogenic
carbonate production, trapping and binding of
sediment by organisms, and possibly syngenetic
cementation. These processes would have allowed
shelf margins to maintain steeper slopes and higher profiles than intervening channels. Thus we believe that erosional processes may not have been
so significant in the formation of these channels
as were adjacent shelf-margin upbuilding and
concomitant channel aggradation.
Shelf margins were sources of carbonate debris
carried into the basins by feeder channels. Carbonate deposits produced in shallow water at the
shelf-edge were locally carried downslope by debris flows and turbidity currents. Matrix-supported conglomerates (Fig. 15) were probably deposited by debris flows in the heads of feeder
FIG. 17—Two-phase evolutionary model of Permian
shelf-margin progradation. Phase I, progradation of delta to shelf margin and deposition of delta-derived sediments in slope environment. Phase II, delta abandonment, resumption of carbonate bank upbuilding, and
progradation across platform of slope-wedge sediments.
Model assumes relatively constant sea level and steady
subsidence.
channels or in upper fans, and skeletal grainstones probably represent braided-channel deposits in suprafan lobes (Walker, 1978).
SHELF-MARGIN RETREAT AND
PROGRADATION
Throughout Pennsylvanian basin subsidence
and marine transgression the eastern and southwestern shelf margins remained stationary. The
rate of carbonate deposition was equal to basin
subsidence, so thick carbonate sequences built up
vertically. Along the northwestern shelf, however,
two shelf margins developed (Figs. 4, 11), the
younger margin having retreated landward approximately 18 mi (30 km). Retreat of this part of
the shelf margin may have been caused by interaction between subsidence and clastic sedimentation.
During the Pennsylvanian the Palo Duro basin
was surrounded by block-faulted highlands which
shed detritus to the basin. Seaward from the highlands and associated fan deltas, carbonate banks
were constructed along the shelf margin (Fig. 16).
During Late Pennsylvanian time carbonate productivity and hence bank development may have
been severely hampered by periodic influxes of
terrigenous sediment to the shelf. As a major fandelta lobe prograded southward into the basin between the northeastern and northwestern shelf
margins (Figs. 8, II), plumes of turbid water advanced ahead of the delta and deposited mud in
the bank environment. Although many of the
shelf-margin bank organisms were fairly tolerant
of muddy waters, carbonate productivity probably decreased significantly where turbid plumes
intruded frequently. Shelf-margin development
slowed so much that along the basin axis it could
not keep pace with basin subsidence. As a result
parts of the shelf margin drowned and were blanketed by prodelta mud. Shelf-margin banks were
forced to reestablish up to 18 mi (30 km) westward in shallow, clear water that was not frequently invaded by muddy water. Although
northeastern margin banks were similarly bathed
by muddy water, the shelf margin was constructed on a basement high that apparently did not
subside so rapidly as the western shelf, and it remained stationary. Galloway et al (1977) have
shown that deposition of terrigenous elastics can
control progradation of shelf margins, but this example from the Palo Duro basin indicates that
under certain conditions deposition of terrigenous sediment can influence shelf-margin retreat
as well. Subsidence and shelf-margin retreat continued until early Wolfcampian time. The eastern
shelf margin retreated 15 to 20 mi (24 to 32 km),
and the western shelf retreated another 30 mi (48
Palo Duro Basin, Texas
103
EXPLANATION
OKLAHOMA
TEXAS> 5 0 f t 115 m) porous carbonate
~^~"
N
Pennsylvanian shelf margin
Retreat position of Pennsylvanian stielf margin
• Well control
Contour interval variable (in feet)
FIG. 18—Isopach map showing distribution and thickness of porous dolomitized strata of Pennsylvanian age. Map
is based upon semiquantitative information gathered from sample logs. Absolute values of porosity are not represented.
C. Robertson Handford and Shirley P. Dutton
104
OKLAHOMA
I DALLAM
TEXAS'
EXPLANATION
> 200 feet porous corbonote
—
Lower Wolfcampian shelf morgin
Middle Wolfcompion shelf rrxirgin
Upper Wolfcompion shelf morgin
Well control
Contour interval variable .-
FIG. 19—Isopach map of porous, dolomitic strata of Early Permian age. Data were gathered from sample logs,
hence absolute values of porosity are not represented.
Palo Duro Basin, Texas
km) landward from Late Pennsylvanian to Early
Permian time.
Two different evolutionary paths of sedimentation are recognized in the Early Permian shelfmargin stratigraphic record. Highly progradational carbonate sequences tend to be present along
the eastern and northern shelf-margin trends, but
the western shelf margin exhibits limited basinward progradation (Figs. 5, 12). Through early to
middle Wolfcampian time the eastern shelf margin prograded westward 10 to 30 mi (16 to 48 km)
while parts of the western margin remained stationary (Fig. 16). During this time the shallow
northern half of the basin filled rapidly, resulting
in a southward shift of the deeper basin. By the
end of Wolfcampian time the shelf margin had
prograded to the northern edge of the Midland
basin and the Palo Duro basin was transformed
into a wide, flat peri tidal shelf (Fig. 16).
The coincidence of delta lobes, progradational
shelf-margin systems, and slope feeder channels
in the southeastern Palo Duro basin suggests that
their development is genetically related. Highly
progradational shelf-margin sequences are best
developed marginal to major clastic sources and
in front of delta systems. In contrast, superposed,
nonprogradational sequences formed in areas
that received smaller quantities of clastic sediment. In general, carbonate productivity along
shelf margins was not great enough to provide
sufficient sediment to sustain significant progradation.
Permian shelf-margin progradation occurred
repeatedly by a two-phase process (Fig. 17). During the first phase, high-constructive deltas prograded across the shelf and terminated near the
shelf margin. Increased deposition of terrigenous
clastic sediment and freshwater discharge probably led to a sharp decline of carbonate deposition near active distributaries. Fine-grained clastic sediment was carried across the shelf margin
and downslope through feeder channels and deposited in slope and basinal environments. Continued deposition on the slope formed thick, progradational wedges of sediment. During the
second phase, following delta-lobe switching or
abandonment, clear water conditions returned
and carbonate-producing organisms reestablished
on a shallow platform composed of slope-wedge
sediment. Soon afterward carbonate banks coalesced, accreted basinward over the clastic foundation, and formed a new shelf margin.
PETROLEUM POTENTIAL
Potential hydrocarbon reservoirs are present in
the Palo Duro basin-in shelf-margin dolomite,
delta-front sandstone, and fan-delta arkose (Ta-
105
Table 1. Potential Pennsylvanian-Permian
Stratigraphic Traps in Palo Duro Basin
Porosity
Reservoir
(%)
Seal
Shelf-margin
carbonate
rocks
> 10
Delta-front
sandstones
15
Shale
Fan-delta
arkose
18
Shale and
basement
Shale and
dolomite
Producing
Field
Analog
Empire-Abo,
N. Mex.
Kemnitz,
N. Mex.
Morris-Buie,
Tex.
Blaco, Tex.
Mobeetie,
Tex.
ble 1). Pennsylvanian and Lower Permian dolomite is present in a band 10 to 30 mi (16 to 48 km)
wide along and just behind the shelf margins
(Figs. 18, 19). Zones of porous ( > 10%) dolomite
may be sealed by contiguous slope and basinal
shale and relatively nonporous shelf Umestone, a
configuration similar to productive Lower Permian shelf-margin trends in New Mexico.
Delta-front sandstone similar in age and facies
to producing deltaic sandstones of the MorrisBuie and Blaco fields in Shackleford County,
north-central Texas, have log-computed porosities of approximately 15%. Porous (18%) fan-delta sandstones along the south flank of the Amarillo uplift and around the Bravo dome may form
reservoirs similar to that of the Mobeetie field in
Wheeler County, Texas, on the north side of the
Amarillo uplift. Pennsylvanian and Permian carbonate and clastic rocks produce hydrocarbons in
the southeastern part of the Palo Duro basin
(Cottle and Motley Counties). A recent discovery
in Oldham County (Baker and Taylor Drilling
Co. Taylor 1-B) reportedly has production from
Pennsylvanian or Lower Permian fan-delta arkose.
CONCLUSIONS AND SUMMARY
In this study intrabasinal, local tectonic, and
sedimentologic controls have been considered to
account for regional facies patterns and depositional styles. No evidence was seen to indicate
eustatic sea-level changes of great magnitude.
However, tectonics undoubtedly were responsible
for providing a source of terrigenous sediment
and influencing the initial position and orientation of the Pennsylvanian shelf margins. In addition tectonics, in combination with fan-delta progradation, seem to have played a significant role
in controlling Pennsylvanian shelf-margin retreat.
106
C. Robertson Handford and Shirley P. Dutton
Fisher, W. L., and J. H. McGowen, 1967, Depositional
systems in the Wilcox Group of Texas and their relationship to occurrence of oil and gas: Gulf Coast Assoc. Geol. Socs. Trans., v. 17, p. 105-125.
Fisk, H. N., 1961, Bar-finger sands of Mississippi delta,
in Geometry of sandstone bodies: AAPG, p. 29-52.
Frazier, D. E., 1967, Recent deltaic deposits of Mississippi River; their development and chronology: Gulf
Coast Assoc. Geol. Socs. Trans., v. 17, p. 287-315.
Galloway, W. E., 1968, Depositional systems of the lower Wilcox Group, north-central Gulf Coast basin:
Gulf Coast Assoc. Geol. Socs. Trans., v. 18, p. 275289.
and L. F. Brown, Jr., 1972, Depositional systems
and shelf-slope relationships in Upper Pennsylvanian
rocks, north-central Texas: Univ. Texas Bur. Econ.
Geology Rept. Inv. 75, 62 p.
- M. S. Yancey, and A. P. Whipple, 1977, Seismic
stratigraphic model of depositional platform margin,
eastern Anadarko basin, Oklahoma: AAPG Bull., v.
61, p. 1437-1447.
Johnson, K. S., 1976, Evaluation of Permian salt deposits in the Texas Panhandle and western Oklahoma for
underground storage of radioactive wastes: Oak
Ridge, Tennessee, Union Carbide Corp., Oak Ridge
Natl. Lab., Rept., 73 p.
The task of documenting regional Pennsylva- Malek-Aslani, M., 1970, Lower Wolfcampian reef in
Kemnitz field. Lea County, New Mexico: AAPG
nian and Permian depositional history of the Palo
Bull., V. 54, p. 2317-2335.
Duro basin was made easier by the lack of formal
stratigraphic units because few Uthologic units are McGowen, J. H., G. E. Granata, and S. J. Seni, 1977,
Depositional framework of the lower Dockum Group
laterally persistent enough for regional correla(Triassic), Texas Panhandle (abs.): Gulf Coast Assoc.
tion through the basin. Hence our task was unenGeol. Socs. Trans., v. 27, p. 246.
cumbered by what otherwise could have been a Newell, N. D., et al, 1953, The Permian reef complex of
column consisting of locally estabUshed stratithe Guadalu]>e Mountains region, Texas and New
graphic units that offered little utility toward unMexico: San Francisco,W. H. Freeman and Co.,236p.
raveling the depositional history of the basin.
Nicholson, J. H., I960, Geology of the Texas Panhandle, in Aspects of the geology of Texas: Univ. Texas
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139-181.
Through deposition of large quantities of terrigenous deltaic sediment in the rapidly subsiding basin, shelf margins were forced either to aggrade or
retreat shoreward. Subsidence rates decreased by
Permian time so that sedimentologic controls became more important in controlling shelf-margin
development. Most importantly, they largely controlled the episodic supply of terrigenous sediment to shifting centers of deposition in the basin,
thus determining whether the shelf margin aggraded or prograded. As a result. Lower Permian
facies patterns reflect a complex interplay between (1) episodes of delta progradation accompanied by submarine-fan feeder channel development along shelf margins and deposition of
slope wedges versus (2) delta abandonment or
switching and carbonate-bank upbuilding and
progradation across slope-wedge platforms. The
Palo Duro basin filled with discontinuous wedges
of carbonate and terrigenous sediment in a manner nearly identical to that by which the Eastern
shelf in north-central Texas was constructed
(Galloway and Brown, 1972).