Diablo Platform Research Articles

Seismic features of the Permian Basin Region from receiver function analysis

We used receiver function (RF) analysis to derive new seismic models of Moho depth, crustal Vp/Vs ratio, depth of sedimentary velocity discontinuity, and corresponding sedimentary Vp/Vs ratio in the Permian Basin region from the seismic waveform data of 260 moment magnitude (Mw) ≥ 6 teleseismic events. We obtained the optimal models by searching one- and two-layer models and comparing similarity between the synthetic and observed RFs. We find the first-order velocity discontinuity in sedimentary basins is shallower than the basin basement. The Delaware Basin (DB) exhibits a bowl-shaped sedimentary velocity discontinuity, with depths ranging from 1.7 km to 5.8 km, whereas the Central Basin Platform (CBP) has a shallow sedimentary velocity discontinuity, with 0.2 km to 2.7 km depths. Moho depth ranges from 36 km to 46 km in the Permian Basin region. The median Vp/Vs ratios of the crust are 1.75, 1.79, and 1.78 in the DB, CBP, and the Diablo Platform (DP), respectively. Our interpretation of the different Vp/Vs ratio in the three subregions is that the crust in the DB includes more low-Vp/Vs-ratio felsic rocks, and the crust in the CBP and DP contains more high-Vp/Vs-ratio gabbroic and basaltic rocks from the Proterozoic and Phanerozoic mafic intrusion.

97/02243 Physical modeling of coal-fired power plant stack flows

This chapter is concerned with the southern portion of the craton, the southern craton margin, and its geological relationship with the Ouachita Orogeny. The southern continental margin was shaped by extensional and transform faulting, during the breakup of Rodinia, and includes the Oklahoma Basin, a basin formed by transtensional faulting. Carbonate reef systems flourished along the entire continental margin from Texas to Newfoundland during the Early Paleozoic. Shallow-water, carbonate, and siliciclastic sedimentation continued in the Oklahoma Basin from Middle Ordovician through Earliest Mississippian time. The ocean that lay south of the North American Plate through much of the Paleozoic was closed by collision with Gondwana, starting in the Mid-Mississippian. Northwesterly directed contractional stress generated a regionally distinctive style of transpressive fault and block-uplift deformation across the Southwestern United States. Mild warping of the Texas–Oklahoma area during this period accentuated existing differentiation of the continent into a series of basins (including the Delaware and Midland basins) and intervening uplifts (Diablo Platform, Central Basin Platform, Eastern Shelf, Llano Uplift, Ozark Uplift). That portion of this basin and uplift system located within Texas now constitutes the classic Permian Basin. The carbonate platform and basin configuration of the Permian Basin is similar in topography and scale to that of the Cretaceous to modern Bahamas Platform. The basin is probably best known for the distinctive “clinoform” stratigraphy of the Capitan Reef, one of the first places where the lateral facies transition from back reef, through reef crest, foreef slope to basin floor was mapped and described in detail, based on superb outcrops in the Guadalupe Mountains.Sediments of the Absaroka Sequence (Uppermost Mississippian to Lower Jurassic) are widely distributed across the continental interior. For much of the Carboniferous to Permian, the Earth was under the influence of repeated, high frequency glacioeustatic sea-level changes. These caused transgressions and regressions that shifted shorelines and depositional systems back and forth hundreds to thousands of kilometers across low-relief continental interiors. The classic Pennsylvanian cyclothems of the southern US Midcontinent are the most characteristic and well-known products of this process.Crustal loading of the continental margin by colliding Gondwana terranes commencing in the Mid-Pennsylvanian generated typical foreland-type basins which now constitute the Ouachita system, and including such foreland basins as the Forth Worth, Arkoma, and Black Warrior basins. In the Ouachita Mountains of Oklahoma and Arkansas some 3,500 m of structurally disturbed Late Cambrian to Mississippian pre-orogenic strata have been mapped. They consist mainly of shales and sandstones, the latter representing a variety of sediment-gravity flow mechanisms.

Late Paleozoic Tectonic Evolution of the Eastern Margin of the Diablo Platform, West Texas: ABSTRACT

The Diablo platform is a long-lived positive tectonic feature that forms the western and southwestern margin of the Delaware basin of west Texas and New Mexico. The platform is known to have been episodically active from at least the early Paleozoic to the Holocene. Although the western margin of the platform is well exposed in fault blocks formed during Tertiary Basin-and-Range-style deformation, the eastern margin is largely concealed beneath Cretaceous to Holocene sediments and Tertiary volcanics. Well control along the eastern margin of the Diablo platform is sparse, averaging less than one sub-Permian penetration per 128 km[sup 2] (50 mi[sup 2]). This study is part of a larger effort to utilize newly acquired seismic data, reprocessed older seismic data, and subsurface well control to formulate a structural interpretation of the Delaware basin and its margins. Early 1970s-age Delaware basin group-shoot seismic data were reprocessed to image parts of the eastern margin of the Diablo platform. Data were reprocessed with a high-performance interactive computer workstation and commercially available software. Improved seismic imaging is obtained by detailed velocity analysis and residual statics. Results show that part of the eastern margin of the Diablo platform is bounded by west-dipping reverse faults having upmore » to 1000 m (3300 ft) of vertical displacement. High-angle normal (oblique ) faults having as much as 2000 m (6600 ft) or vertical displacement are, in part, younger than the reverse faults, cutting beds as young as Permian (Ochoan) age (Rustler Formation). These features are interpreted to reflect Pennsylvanian-aged northeast-southwest-oriented compression followed by Middle to Late Permian differential subsidence of the Delaware basin relative to the Diablo platform. Analogy with the basin-bounding margin adjacent to the Central Basin platform suggests that undiscovered compressional structures may exist along the eastern margin of the Diablo platform.« less

Impact of Late Cenozoic Extension on Laramide Overthrust Belt and Diablo Platform Margins, Northwestern Trans-Pecos Texas: ABSTRACT

Late Cenozoic basins and normal faults were superimposed upon preexisting Tertiary, Mesozoic and older structures of northwestern Trans-Pecos Texas. We analyzed the structural and stratigraphic framework of the region using borehole, seismic, outcrop, and aerial-photograph interpretations; regional cross sections were prepared to record Mesozoic and Cenozoic structural attributes. Laramide thrusting displaced Cretaceous rocks northeastward and produced northwest-trending thrust faults and related normal faults, folds, and monoclines. Cenozoic extension caused normal faulting that produced northwest- and north-northwest-trending, 3 to 30 mile-wide fault-bounded basins and adjacent mountain ranges. Tectonism continues to the present. The pre-late Cenozoic structural grain has at least partly controlled geometries of the late Cenozoic basins and associated faults. The deepest Cenozoic basin of this area developed along the leading edge of the Laramide thrust belt and the southwest margin of the Diablo Plateau, and has as much as 9800 ft of Cenozoic basin fill. The most active Quaternary faults vertically displace middle Pleistocene deposits by about 33 to 105 ft. The 56-mi-long Red Light Bolson, containing more than a 2000 ft of Cenozoic deposits, also formed near the leading edge of the older thrust belt. A northwest-striking Quaternary fault zone bounds this basin on its east margin. Twomore » series of Cenozoic basins also have formed northeast of the overthrust belt. The 50-mi-long Eagle Flat-Green River basin system consists of three basins that contain 900 to more than 2000 ft of basin fill. Late Tertiary-Quaternary tectonism has not been as active there as in the other large basins. The 124-mi-long Salt Basin graben system comprises five basins and marks the east edge of Quaternary faulting in this region. Cenozoic fill is more than 2000 ft thick, and the most active Quaternary faults vertically displace middle Pleistocene deposits by at least 13 to 36 ft.« less

The Origin of High-Frequency Platform Carbonate Cycles and Third-Order Sequences (Lower Ordovician El Paso Gp, West Texas): Constraints from Outcrop Data and Stratigraphic Modeling

ABSTRACT The passive-margin succession of the Diablo Platform (Lower Ordovician, west Texas) is represented by the second-order Sauk C supersequence set, consisting of a basal transgressive clastic unit (The Bliss Sandstone) above the breakup unconformity, marking the second-order basal lowstand transgressive phase), overlain by 750 m of drift-related, shallow-marine platform carbonates (the El Paso Group) recording the second-order highstand. Due to late Paleozoic structuring of the Gondwanan passive margin, present exposures in Texas are in an updip shelf position and lack internal stratal geometries across depositional strike, so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher-frequency, fifth-order cycles. Accommodation plots (Fischer plots) of high-frequency cycles gauge systematic shifts in third-order accommodation of two complete third-order sequences, each about 2 m.y. long and 60-140 m thick, within the El Paso Group. This is expressed in the vertical succession of types, systematic changes in thickness, and variations in subfacies as revealed by histograms of subfacies types tied to Fischer plots. A complete El Paso shelf sequence contains a thin lowstand systems tract of quartz arenite, a thick transgressive systems tract dominated by upward-thickening, thrombolitic subtidal cycles, and a highstand systems tract marked by dolomitic, thinning-upward peritidal cycles containing quartz sand. The El Paso third-order depositional sequences have been correlated by biostrat graphy and stacking pattern from the Franklin Mountains southeast to the Diablo Arch, northeast into the Ardmore Basin, and thence to the Appalachian Basin. Hence, the third-order sequences appear to be eustatic, based on biostratigraphic correlation of accommodation plots around the periphery of Gondwana. Time-series analyses suggest that a strict allocyclic, Milankovitch-driven, glacio-eustatic mechanism alone is insufficient to account for the higher-frequency fifth-order and lower-frequency third-order accommodation cycles. We used a two-dimensional forward computer simulation to compare allocyclic and autocyclic models for high-frequency cycles. The allocyclic simulation superimposes a deterministic, Milankovitch glacio-eustatic driver on a lower-frequency, third-order accommodation and generates a two-dimensional synthetic cross section composed of high-frequency peritidal and subtidal cycles stacked into third-order sequences. The autocyclic simulation is generated by a Ginsburg autocyclic mechanism for high-frequency cyclicity triggered by third-order accommodation changes The autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth-order development linked to onshore sediment transport and seaward progradation of tidal flats. The two-dimensional internal facies architecture of a third-order sequence and the high-frequency stacking patterns are simulated in both scenarios. Important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the Diablo platform cycles and sequences. As an alternative or a supplement to autocyclicity or Milankovitch-forced glacio-eustasy, we have studied stochastic models for driving high-frequency changes in relative sea level. These intriguing results maintain essentially all the features observed in the rock record. Our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized.

Early Permian (Middle-Late Wolfcampian) phylloid algal/Tubiphytes bioherms and associated facies along the margin of the Orogrande Basin, Hueco Mountains, west Texas

Middle-Late Wolfcampian phylloid algal/Tubiphytes biohermal complexes have been found exposed in western outliers of the Hueco Mountains of far west Texas. Paleogeographically, the bioherms are located along the fault-controlled shelf margin between the Late Paleozoic Diablo Platform and Orogrande Basin. Although Virgilian and Early Wolfcampian phylloid algal mounds are well-known from the Hueco and Sacramento Mountains, outcropping Middle-Late Wolfcampian bioherms have not been described previously from the Orogrande Basin area.The biohermal complexes are exposed in three large outliers that lie about 3 miles west of the main Hueco Mountains and extend for about 12 miles in a north-south direction. The shelf margin complexes are in the Hueco Canyon Formation and correlate to well-bedded shelf facies in the main Hueco Mountains based on fusulinid biostratigraphy.The phylloid algal/Tubiphytes shelf margin bioherms contain an upward shallowing facies succession, which consists of, in ascending order: (1) phylloid algal wackestone-bafflestone, (2) phylloid algal bafflestone-packstone, (3) phylloid algal-fusulinid bafflestone-packstone, and (4) Tubiphytes boundstones and Tubiphytes-fusulinid-phylloid algal packstones and grainstones. Unlike some previously described Wolfcampian phylloid algal buildups, the phylloid algal mound facies in these buildups contain only rare calcisponges, heliosponges, and marine radial fibrous cements. On the crest of the southern outlier there occurs a rather different type of bioherm, which contains nodular boundstones that are composed of encrusting red algae and bryozoans, and in which calcisponges are common. That bioherm is thought to be slightly younger in age than the phylloid algal/Tubiphytes bioherms, and it might also have been formed in a deeper-water setting.Bordering the phylloid algal/Tubiphytes bioherms on the seaward side are overlapping tongues and channels of lithoclastic-skeletal debris and skeletal grainstones and packstones. Some of these forereef units extend seaward into slope facies, which consist of dark-gray cherty limestones that generally lack skeletal fossils, but contain a rich ichnofossil assemblage in the shallower upper slope beds. Backreef facies consist mainly of skeletal-peloidal packstones and wackstones.The Hueco Mountains outlier exposures are significant because: (1) they establish the presence of a Middle-Late Wolfcampian shelf margin with distinct topographic relief in the southern Orogrande Basin, and (2) they provide an easily accessible field laboratory to study Middle-Late Wolfcampian shelf-to-basin facies relationships and shelf margin bioherms. Middle-Late Wolfcampian shelf margin bioherms are of particular interest because they represent an important transitional stage in the evolutionary history of Late Paleozoic reef communities, and because they form important petroleum reservoirs just to the east in the Delaware and Midland Basins.

Structural Constraints for Proposed Fort Hancock Low-Level Radioactive Waste Disposal Site (NTP-S34), Southern Hudspeth County, Texas: ABSTRACT

Structural complexities reduce the homogeneity necessary for a site characterization model to an unacceptable level for performance assessment for radioactive waste disposal sites. The proposed site lies between the northern, stable Diablo platform and the southern, mobile Mesozoic Chihuahua tectonic belt. Structural movement along this interface has been active for the past 14,000 years. In addition, the area lies along the northern margin of the Permian Marfa basin and the northeastern margin of the deeply faulted Hueco bolson segment of the late Cenozoic Rio Grande rift system. Recent seismic activity with extensive surface rupture in Quitman Canyon (30 mi southeast of the site) is also documented from the 1931 Valentine, Texas, earthquake (6.4 Richter scale). The site is underlain by either a thrust fault or the complex terminus of a Mesozoic thrust fault. This fault is a segment of the continuous thrust sheet extending from exposures in the Sierra Blanc area, 30 mi east (Devil Ridge fault), to the El Paso area west (Rio Grande fault). This segment of the Devil Ridge-Rio Grande thrust is documented by the Haymond Krupp No. 1 Thaxton wildcat drilled at Campogrande Mountain immediately south of the site. The recent rift fault scarp (Campo Grande)more » immediately south of the Thaxton well has a 17-mi surface trace and is, no doubt, related to the subsurface Clint fault to the west in the El Paso area. An additional complexity is the presence of a monoclinal flexure with a minimum of 900 ft of surface relief (2 mi northeast of NTP-S34). A 4.5-mi, east-west, down-to-the-south normal fault occurs near the top of the monocline with a small associated graben. These complexities seriously compromise the proposed Fort Hancock site.« less

Reconnaissance Geophysical Study of Diablo Platform, Texas: ABSTRACT

Reconnaissance Geophysical Study of Diablo Platform, Texas: ABSTRACT

Paleozoic evolution of southern margin of Permian basin

Prior to Late Pennsylvanian time, the Permian basin of West Texas was a part of the southern margin of the North American craton and was the site of shallow, warm-water carbonate deposition. As the South American margin of Gondwana gradually moved northwestward during late Paleozoic time, the oceanic floor deposits and overlying turbidite fan deposits between North America and South America became parts of large accretionary wedges of semiconsolidated sediments. In a series of steps, these wedges were folded and thrust toward the northwest against, then finally onto, the southern margin of North America. These compressive steps caused the repeated piling up of the accretionary wedges to form rapidly eroding highlands on the cratonic margins. Repeated loading on the North American margin formed a series of elongate, deep-water, depositional troughs (fore-deeps) immediately north and west of the accretionary wedges, and these received thick accumulations of turbidites. The youngest of these deep basins include the northwestern part of the Val Verde basin to the north and the Marfa basin to the west which received basinal deposits from within Desmoinesian into early Late Permian time. Loading of the cratonic margin also resulted in renewed faulting along generally northwest- to north-trending older zones of weakness. These zones are apparently of Precambrian age. On the craton, the late Paleozoic faults mainly had high-angle to vertical fault planes and commonly had large components of horizontal displacement. This fault system outlines the major uplifts and basins in the Permian basin region. The joining together of Gondwana and Euramerica across the Marathon salient of the orogenic belt was essentially completed by mid-Wolfcampian time. After that time, the southern margin of the Permian basin, represented by the Dugout and Marathon allochthons and the Diablo Platform, became a relatively stable tectonic area. The Glass Mountains expose a series of north- and northwest-dipping cuestas of Permian carbonate shelf and shelf-edge deposits that accumulated on a platform constructed from these two allochthonous accretionary wedges. These Permian deposits prograded north and northwestward into the narrow Hovey Channel, which connected the Marfa basin with the southern end of the Delaware basin. Carbonate-reef growth finally restricted the inflow of marine water into the Delaware basin near the end of late Guadalupian time.

Geophysical Review of Trans-Pecos Area of West Texas: ABSTRACT

The Trans-Pecos has intrigued and baffled the oil industry, and all exploratory efforts so far have remained fruitless. Our geophysical findings along with other geologic information allow us to analyze the overall hydrocarbon potential for this area. Gravity and magnetic data were helpful in regional mapping but were unreliable for localized information owing to numerous extrusive and intrusive rocks. Seismic mapping shows many undrilled structures. However, the success ratio for the structures already drilled is disappointing (e.g., on the Diablo platform, out of 22 structural leads, 11 have been drilled and all were dry, and in the Marfa basin 17 out of 41 leads were drilled without success). Results were similar in Salt-Flat graben. Many of these wells had good hydrocarbon shows and almost all yielded fresh water. Tectonically the area has undergone several periods of orogeny, the result of the latest being numerous Basin and Range faults. The area is still seismically active and shows appreciable geodetic movement. It is suggested that the traps were destroyed with subsequent leakage of hydrocarbon and repeated induction of fresh water. Trap destruction is apparently beyond the scope of seismic detection. The Chihuahua trough (United States), in spite of many discouraging facts, such as high heat flow, thermal waters, etc, shows some promise because seismic data reveal large thrust anticlines in the lower Paleozoic rocks (approximately 15,000 ft) that are yet to be adequately tested. Other smaller undamaged stratigraphic traps (reefs, truncations, pinch-outs, etc) are possibly present and could be targets for future exploration. End_of_Article - Last_Page 233------------

Marfa Basin of West Texas: Foreland Basin Subsidence and Depocenter Migration: ABSTRACT

The Marfa basin, encompassing approximately 6,000 mi2 (15,539 km2) of Presidio and Brewster Counties in west Texas, is a foreland basin that formed in the late Paleozoic in response to the encroaching Ouachita-Marathon thrust belt. The basin is one of several, including the Arkoma, Fort Worth, and Val Verde basins, that developed along the southern margin of the North American craton during convergence of North America and Africa-South America in Pennsylvanian to Permian time. We present a model of the formation of the Marfa basin in which basin subsidence is effected by compression from plate convergence and by loading owing to the emplacement of the Marathon fold-thrust complex. A model of foreland basin evolution by thrust loading as applied to the Idaho-Wyoming thrust belt can be applied with some modification to the Marfa foreland basin. Preexisting northwest-trending faults in the Marfa region were reactivated by the Marathon thrust belt as the latter advanced onto the continental margin toward the craton. Subsidence owing to compression and thrust loading first formed the Tesnus basin, a Pennsylvanian basin now buried beneath the Marathon overthrust. In the later stage of thrust-sheet emplacement, the depocenter split into two prongs, and the Marfa and Val Verde basins collected thick sections of Wolfcamp sediments. Preexisting northwest trends, which result from a Precambrian rifting event and the late Precambrian to Cambrian development of the Delaware aulacogen, controlled the location of subsidence in front of the thrust sheet. The fragmented craton was composed of northwest-trending high and low areas including the Diablo platform and the Delaware basin. These fragments behaved much like piano keys, subsiding first in a central region to form the Tesnus basin and later in adjacent regions forming the Marfa and Val Verde basins. The model is supported with data from 63 well logs that indicate the position of the depocenters through time and that suggest the differential elevation of crustal slices controlling the formation and location of the three Pennsylvanian-Permian foreland basins. End_of_Article - Last_Page 117------------

Tectonic Evolution of Trans-Pecos, Texas: ABSTRACT

Southern Trans-Pecos Texas contains parts of two of the major overthrust belts of North America, the older Ouachita and the younger Cordilleran. In addition, this area has been deformed by two other major tectonic episodes. As early as 1,000 m.y. ago, the Van Horn mobile belt was formed by the closure of an inner arc basin during the formation of a proto-Pangea. This mobile belt provided the base upon which the Diablo platform formed. Recent petrologic evidence suggests that the Van horn mobile belt continues southward into Mexico and underlies the Coahuila platform. During Late Pennsylvanian to Early Permian time, this platform, a continental promontory, impeded the northward movement of the overriding Ouachita orogenic thrust sheets, bending them southwestward at the in ersection of this thrust complex. During the late Mesozoic, the Diablo platform acted as a stable buttress, against which sediments of the Chihuahua trough were deformed and thrust. These folds and thrusts comprise the Chihuahua tectonic belt, which forms part of the Cordilleran thrust belt of North America. East of this platform, faulted monoclines may represent the southern limit of the fault-bounded, basement-cored uplifts of the front ranges. Finally, western Trans-Pecos Texas was overprinted by extensional basin and range faulting during the Cenozoic, with concomitant igneous intrusive and extrusive activity. The igneous intrusions occur in a belt trending roughly north-northwest, following the trend of the basin and range faulting. These intrusions are scattered through most of Trans-Pecos except for an area to the south where the four tectonic belts intersect. Here, extensive crustal fracturing and extension have resulted in the emplacement of a greater density of igneous material into the overlying crust. End_of_Article - Last_Page 1437------------

Structural Evolution of Chihuahua Tectonic Belt: ABSTRACT

The Chihuahua tectonic belt is a Laramide foreland fold and thrust belt that is in the initial phase of exploration. It can be compared to the Southern Overthrust belt prior to the Pineview discovery in 1975. The part within the United States is approximately 300 mi (483 km) long and extends from southeast of El Paso to Presidio, Texas. The frontal thrusts of the belt lie against the Diablo platform. The stratigraphic sequence involved in thrusting is Permian to Lower Cretaceous. Thrusting has been accomplished by decollement of Jurassic and Permian evaporates. The Malone Formation (Jurassic) is the proximal part of a fan-delta complex and contains marine, subtidal, intertidal, and supratidal facies. Two distinctive locally derived conglomerate facies are present: (1) clast-supported, bimodal, dolomite-pebble conglomerate (sheet-flood facies); and (2) a matrix-supported, dolomite-pebble conglomerate that lacks sorting (debris-flow facies). Probable correlatives of the Malone Formation occur at Sierra del Kilo and Sierra de la Alcaparra in Chihuahua 60 mi (97 km) to the southwest. By using new surface-mapping and surface-sampling plus interpretation of seismic and gravity data, a sequence of tectonic events can be inferred: (1) Late Triassic(?) faulting and formation of the Chihuahua trough; (2) Laramide folding and thrusting; (3) late Laramide en echelon left-lateral strike-slip folding; and (4) basin-and-range faulting. End_of_Article - Last_Page 548------------

Paleoenvironments of Upper Albian Stage (Cretaceous) of Western Trans-Pecos, Texas: ABSTRACT

Upper Albian (Cretaceous) rocks of western Trans-Pecos Texas crop out in an east-west trend along the northeastern margin of the ancient Chihuahua trough and adjacent Diablo platform. These rocks represent an alternating terrigenous-carbonate sequence within an overall transgressive phase. Twelve lithofacies and six biofacies were recognized from thin section point-count analysis and empirical outcrop data. Environmental parameters derived from lithofacies and biofacies, the interrelationships of facies, and comparison with several carbonate depositional models provide the basis for the establishment of depositional environments represented by upper Albian strata. A time-stratigraphic framework consisting of ammonite interval zones was used to trace the movement of environments through time and space. Distribution of these environments indicates initial transgression came from the south and proceeded northeastward across Trans-Pecos Texas. Upper Albian deposition was concluded with the onset of a major regressive phase marking the beginning of the Cenomanian Stage. End_of_Article - Last_Page 562------------

Depositional Environments, History, and Biostratigraphy of Upper Albian Rocks, Trans-Pecos Texas: ABSTRACT

Upper Albian rocks in Brewster, Presidio, Jeff Davis, Reeves, and Pecos Counties, Texas, between the Adkinsites brazoensis and Pleisioturrilites brazoensis zones are divided into 10 lithofacies and associated depositional environments. These lithofacies represent deposition in environments ranging from nearshore high-energy carbonate and quartz sands, to offshore high-energy carbonate shoals and rudistid banks, to medium- to low-energy offshore shales and biomicrites, to deeper water low-energy micrites. All or parts of the Benevides, Loma Plata, Sue Peaks, Santa Elena, Boracho, Fort Terrett and Fort Lancaster Formations are included in this study. The wide variety of lithofacies present reflects variations in local source areas, depositional slope, source area and basin stability, and paleogeography. Distribution and thickness of lithofacies during the late Albian indicate that the Glass Mountains area and Diablo platform were structural highs separated by a shelf basin which occupied the position of the Paleozoic Hovey channel. The northern part of the area was a gently sloping shallow-water shelf; the southern part was the northern edge of the Chihuahua trough. The use of ammonite zones to trace lithofacies and depositional environments through space and time shows an initial transgressive followed by a lesser regressive sequence. The overall effect of late Albian deposition was transgressive. End_of_Article - Last_Page 759------------

Lower Permian Limestones of Southern New Mexico and West Texas: ABSTRACT

Detailed petrographic and stratigraphic analyses of samples from the Lower Permian (Wolfcampian) of southern New Mexico and West Texas demonstrate the effects of major tectonic elements on redbed and carbonate sedimentation. Regional correlations are based on 3 informal stages (upper, middle, and lower Wolfcampian), as determined by fusulinid zonation. Uplifted areas, such as the Pedernal landmass, Diablo platform, and the Florida islands, display unconformable surfaces, limestone and chert conglomerates, and shallow-water carbonates facies consisting of foraminiferal-algal packstones and grainstones (shoal water), algal plate wackestones (bioherm), and ostracod-molluscan packstones and wackestones (lagoon). These highs were flanked by carbonate shelf deposits of normal marine wackestones and packstones which rim the Orogrande and Pedregosa basins. The former was a shallow water intracratonic basin in which about 2,000 ft of Wolfcampian sediments accumulated. The latter basin is less understood, but had a well-defined shelf margin and received at least 4,000 ft of Wolfcampian sediments. Distant uplifts on the north of the Orogrande basin shed thick redbed deposits which intertongued with carbonates on the south. Generally, this resulted in 3 major sedimentary phases (2 carbonate phases separated by a redbed phase) which correspond to the original threefold division of the type Hueco Limestone. This interpretation together with fusulinid zonation permits correlation of stratigraphic units of southeastern Arizona with those of West Texas and New Mexico: youngest Horquilla Limestone with Hueco Canyon Formation, Earp Formation with Abo Redbeds and Cerro Alto Limestone, and Colina Limestone with Alacran Mountain Formation. End_of_Article - Last_Page 631------------

Permian Patch Reefs in Finlay Mountains, West Texas

The two patch reefs investigated are within Leonardian (Middle Permian) strata in the northwestern part of the Finlay Mountains, about 16 mi (25.8 km) northwest of Sierra Blanca, Texas. The Leonard Series in these mountains was deposited on the southwestern margin of the Diablo platform bordering the Marfa basin and consists largely of marlstones, with smaller amounts of calcirudites and bioclastic limestones. The environment of deposition was one of relatively shallow, quiet waters that periodically sustained many benthonic calcareous organisms. Fragments of the skeletons of this fauna were deposited as bioclastic limestones on which patch reefs could become established. In the two patch reefs studied in detail, four facies are readily recognizable: subreef, reef flank, eef core, and suprareef. The principal reef-building organism in the reef-core facies is the algal genus Tubiphytes Maslov. Other organisms include calcareous sponges, fenestrate bryozoans, brachiopods, and rugose corals. Abundant crinoid stems and fusulinids are found in the associated bioclastic rocks. These reefs are similar to, but smaller than, the oil producing reefs of the same age on the platform edges around the Delaware and Midland basins on the east, but this is the first account of such reefs in the Finlay Mountains.

Late Paleozoic Sediments Derived From Pedernal Uplift: ABSTRACT

The Pedernal uplift, elongated northward from southern Otero County, New Mexico, to the present-day position of Pedernal Hills, was a late Paleozoic feature 40-75 mi wide and about 225 mi long; at the time of maximum development, the uplift connected southward with the Diablo platform and northeastward with Sierra Grande arch and Amarillo-Wichita uplift. This is Hill's (1958) Pedernal-Sacramento-Otero uplift, Adams' (1962) Pedernal arch, and Meyer's (1966) Pedernal uplift, but differs from Galley's (1958) Pedernal massif which he extended northeastward to encompass the southern Sierra Grande arch. The southern Pedernal area was beneath pre-Pennsylvanian seas, which derived their minor detritus from Penasco dome of northern New Mexico and southern Colorado. The Pedernal uplift emerged during Early Pennsylvanian time. Sediments which became sandstone, dark shale, and silty limestone were deposited westward in Orogrande and Estancia basins and eastward in Delaware basin. During Desmoinesian time, there was wide expansion of shallow seas; the Pedernal barely was awash, and provided only silt and clay for the limestone-choked seas, except for some deltaic subgraywacke in the Orogrande basin. Uplift of the northern part of the Pedernal uplift during late Desmoinesian time supplied arkose northeastward to the Rowe-Mora basin and westward to the Joyita-Los Pinos area and Estancia basin Beginning in late Missourian, the uplift took on the aspect of a tilted fault block, with the western edge higher (especially near Ruidoso) and providing more detritus westward into the Orogrande and Estancia basins, whereas only minor amounts of fine-grained materials swept eastward into the Delaware basin. These conditions continued into Virgilian time, culminating during the late Virgilian and early Wolfcampian with the westward dumping of a thick sequence of subgraywacke, arkose, and red to dark shale. Early Wolfcampian sediments derived from the west side of the Pedernal uplift range from quartzite and granite-cobble conglomerate to red shale, but by middle Wolfcampian the major detritus source was the Uncompahgre highland of north-central New Mexico and southwestern Colorado. Reddish clastics from this highland flooded Wolfcampian seas southeastward where Abo redbeds intertongue with Hueco Limestone. By late Wolfcampian time, most of the Pedernal uplift was buried beneath redbeds; only locally, as at the present-day Pedernal Hills and Pajarita Mountain, did remnant Precambrian-rock monadnocks rise above the red clastic flood. Higher remnants supplied minor detritus to lagoonal seas during Leonardian time. End_of_Article - Last_Page 537------------

Sedimentational Influence of Pedernal Uplift: ABSTRACT

Depositional and erosional features outline the late Paleozoic Pedernal uplift as a narrow northward-elongated landmass, connected southward with the Diablo platform and northeastward with the Sierra Grand arch and Amarillo-Wichita uplift. During pre-Pennsylvanian Paleozoic time, north-central and central New Mexico was periodically uplifted epeirogenically, but this bears little resemblance to late Paleozoic Pedernal uplift. Pedernal should not be applied to the massif in east-central New Mexico (southern part of Sierra Grande arch). Ordovician, Silurian, and Mississippian strata probably were deposited in most of New Mexico and adjoining areas, and Devonian beds in most of southern and western New Mexico, but were removed from large areas during subsequent erosion periods. Early Ordovician El Paso-Manitou was eroded in Middle Ordovician time; later Ordovician Cable Canyon-Harding and Montoya-Fremont as well as Silurian Fusselman Dolomite were partly removed during Late Silurian-Early Devonian time; and only a remnant of Mississippian was left in central New Mexico by erosion during Late Mississippian-Early Pennsylvanian time. Erosional and sedimentational patterns trend east-west for earlier Paleozoic strata, with a positive-trending feature in north-central New Mexico, contrasting with Pennsylvanian and early Pe mian northward trends related to the Pedernal uplift and its adjoining basins, Orogrande and Estancia on the west, and Delaware on the southeast. The northern New Mexico massif supplied some Cambrian sands, some Middle Ordovician Simpson sand and silt, and Late Devonian and Early Mississippian silt and clay. The Pedernal uplift area in south-central New Mexico was covered by early and middle Paleozoic seas, and did not become a detritus-source upland until Early Pennsylvanian time. During Pennsylvanian and early Wolfcampian time it provided much sediment to flanking basins; most of the uplift was worn down and was buried by floods of northern redbed material during late Wolfcampian time. Only remnant hills remained in the sandy seas of Leonardian time. End_of_Article - Last_Page 197------------

Delaware Basin Drilling

Abstract Many operators are now very active on drilling operations to reachPennsylvanian and older formations in the Delaware basin of West Texas. Deepdrilling in the basin has been sporadic since 1937 but larger rigs, improvedmud programs, better bits, stronger tubular goods, designed cementing programs, specialized tools and drilling programs to utilize these advanced materials andother techniques have permitted more economical drilling in recent years. Concentrated development drilling in certain areas has encouraged furtheradvances in technique and has decreased costs. Further drilling-cost reductions will be helpful in encouraging explorationand development of the unexplored areas and depths of the basin. Introduction Discovery of commercially productive quantities of gas from deep, largereservoirs in the older formations of the Delaware basin has causedconsiderable new drilling activity in several areas of the basin. Followingyears of disappointment and lack of commercial production, the basin hasrecently proved the Wolfcamp, Pennsylvanian, Devonian and Ellenburgerformations as sources. With increasing development and growing gas marketsencouraging each other, the result has been one of the largest West Texasdrilling campaigns in terms of dollar costs. The oil industry is now encouragedenough to invest more than $50 million in wells and facilities to find anddevelop the deeper reservoirs. Considerable time and effort are now being spenton the improvement of drilling programs to provide the most economicalexpenditure of drilling dollars available. Practices and techniques areimproving as a result of these efforts, but continued work will be needed asnew areas are drilled and new problems encountered. The Delaware basin offers alarge, varied assortment of problems and the industry is acquiring theexperience to put its technical knowledge to effective solutions. Geology Ancient seas laid down thick beds in the Permian Basin areas. Subsequentuplift of the Central basin platform divided the Delaware basin and Midlandbasin portions of the Permian Basin and provided conditions of similarity anddissimilarity between them. The Delaware basin portion characterized itself bythe presence of the Delaware Mountain group of sands and limes. In most cases, the Delaware basin also afforded deeper and thicker amounts of equivalentformation than the Midland basin. Movements during Pennsylvanian time of thesubsurface have furnished uplifting for extensive structuring and faultingwhich formed many traps for possible hydrocarbon accumulation. The basin is contained within the general area shown in Fig. 1. Bounded onthe east by the Central basin platform, on the west by Diablo platform, on thenorth in New Mexico by the Capitan Reef and on the south by the Marathon Thrustbelt, the Delaware basin is a general area with well-defined boundaries. Thebasin deepens from all sides toward the east center with the sharpest changefrom the east side. Development of the Basin Drilling wells to the Pennsylvanian formation or 10,000 ft and deeperstarted in the late 1930's. With very little encouragement in the way ofproduction, 51 such wells were drilled before 1960. These wells included thedeepest and the fastest ever drilled, but failed to find commercial quantitiesof oil or gas. All of the areas in the basin were touched by this drilling whichcontributed mostly information. This information affected later drillingprograms and drilling equipment could be used to advantage.