Wolfcampian Time Research Articles

Petroleum Geology of Pennsylvanian and Lower Permian Strata, Tucumcari Basin, East-Central New Mexico: ABSTRACT

The Tucumcari basin of east-central New Mexico is a structural depression that existed as a depositional basin from Strawn (Middle Pennsylvanian) until late Wolfcampian (Early Permian) time. Depth to Precambrian ranges from 6500 ft to more than 9000 ft. High-angle faults form the north, east, and west edges of the basin. No major structural discontinuities separate the basin from a shallow shelf to the south. Faults cut Pennsylvanian and Wolfcampain strata but generally do not offset post-Wolfcampian strata. Faults and regional structure control facies and thickness patterns within the Pennsylvanian and Wolfcampian. Coarse arkosic sands in the Pennsylvanian and Wolfcampian are good reservoirs. Those sands were deposited in northern and western parts of the basin and were derived from highlands of Precambrian granitic rocks that formed the northern and western margins of the basin. High-energy limestones are possible reservoirs in the southern part of the basin. Porous Wolfcampian dolostones cover the Frio uplift on the east side of the basin. Pennsylvanian and Wolfcampian marine shales and micritic limestones are source rocks within the Tucumcari basin. Post-Wolfcampian strata are thermally immature. Two presently noncommercial pools of oil and gas, the Latigo Ranch pool and the T-4 Ranch pool, have been discoveredmore » in Strawn sands in the northern part of the Tucumcari basin. Oil generated in the upper Paleozoic has migrated vertically into the Triassic; two oil accumulations, the Santa Rosa tar sands and the Newkirk oil pool, are in Triassic sandstones and have combined reserves of 153 million bbls of oil.« less

Preliminary Basin Analysis of Late Pennsylvanian-Permian Wood River Basin, South-Central Idaho: ABSTRACT

Stratigraphic correlation of partly coeval tectonostratigraphic units in the Smoky and Boulder Mountains, west and north (respectively) of Ketchum, Idaho, allows for reconstruction of the Late Pennsylvanian-Early Permian Wood River basin. These tectonostratigraphic units contain calcareous sandstones, silty limestones, and carbonaceous siltites and shales of the Wood River Formation (units 6 and 7 - Virgilian-Wolfcampian), Grand Prize Formation (Wolfcampian(.)), and Dollarhide Formation (Wolfcampian). Interpretation of sedimentary facies, petrologic characteristics, and structural relations suggests contiguous deposition of these units in a westward deepening basin in shallow shelf, outer shelf to upper slope, and lower slope to basin environments, respectively. In the Wood River basin, vertical facies changes within each formation are similar to lateral facies changes progressively westward between formations, as suggested by palinspastic reconstructions. Upsection and to the west, thick sequences of calcareous sands give way to fine-grained carbonaceous sediments, suggesting a deepening of depositional environments through time. Regional sea level rise, basin subsidence, or both, during Virgilian to early Wolfcampian time, is suggested by deepening-upward facies transitions in rocks of both the Wood River basin of central Utah and Oquirrh basin of northern Utah. Both basins evolved from shallow to moderate depth shelf-and-slope environments to more restricted, deeper watermore » environments. Paleogeography and basin development are relatively well constrained in the Oquirrh basin, but is more tentative in the Wood River basin where a lack of biostratigraphic control and structural complexities permit only tentative paleogeographic reconstruction.« less

Sedimentology and tectonic significance of Wolfcampian (Lower Permian) conglomerates in the Pedregosa basin: Southeastern Arizona, southwestern New Mexico, and northern Mexico

A single interval of red chert-clast conglomerate and associated strata (RCC/CRCC interval) occurs within the Earp Formation (Pennsylvanian-Lower Permian) at many localities in southeastern Arizona, southwestern New Mexico, and northern Mexico; this interval records a middle Wolfcampian erosional event in the northern Pedregosa basin and adjacent shelf. The RCC and CRCC intervals are probably proximal and distal braided-stream deposits, respectively, consisting of conglomeratic longitudinal and transverse bar deposits; fluvial-channel sandstone; and interfluvial fine-grained sandstone, siltstone, and shale, and they are interstratified within a much thicker sequence of shallow-marine deposits. The RCC/CRCC interval is uniformly thin (average 5 m thick), yet it is characterized by sheet-like lateral continuity, indicating that deposition occurred on an extensive, low-lying surface on which fluvial channel migration and channel switching were important processes. Paleoflow directions were generally southeastward. Biostratigraphic evidence suggests that middle and lower Wolfcampian strata below the RCC/CRCC interval were beveled northward. Much clastic material of the RCC/CRCC interval may be composed of reworked residuum of the beveled strata, with additional contributions possibly from regions north and northwest of the Pedregosa shelf. Middle Wolfcampian emergence of the northern Pedregosa basin and shelf and accompanying deposition of the RCC/CRCC interval were probably caused by tectonics. Other less important factors, such as eustatic sea-level fluctuations, may have amplified the regression. Evidence favoring a tectonic cause of regression are synchronous timing of tectonism and synorogenic sedimentation throughout a wide area in the Ouachita foreland. The RCC/CRCC interval was probably deposited on a forebulge peripheral to the Pedregosa foreland basin. Stratigraphic evidence indicates that the southern Pedregosa basin evolved rapidly from a slowly subsiding platform to a deep foreland basin during early or middle Wolfcampian time. Subsidence of the Pedregosa foreland basin was presumably caused by downflexure under northward-verging thrust sheets in the Chihuahua region during the Ouachita orogeny. Downflexure of the Pedregosa foreland basin evidently caused flexural forebulging and subaerial exposure of large areas cratonward. Flexural models predicting deflection of lithosphere under isostatic thrust and sediment loads agree satisfactorily with the forebulge concept for the origin of the RCC/CRCC interval.

Paleozoic Paleotectonics and Sedimentation in Southern Rocky Mountain Region: ABSTRACT

During the Paleozoic, the southern Rocky Mountain region included most of New Mexico and Arizona and at least the northern parts of adjacent Chihuahua and Sonora. It was particularly stable part of the North American craton during the Cambrian through Middle Devonian. Slow End_Page 863------------------------------ deposition of shelf clastics and dolomitic carbonates was interrupted by several long erosional hiatuses. Major recognizable tectonism first appeared in the Devonian with at least one depositional basin formed west of the Defiance-Zuni uplift. Thin Early Mississippian shelf carbonates and evaporites covered nearly the entire region. The most significant tectonic activities started in the late Chesterian and extended with increasing magnitude until the end of Wolfcampian time. Local basins and uplifts date from this interval and occurred in two belts. One belt was about 80 mi (130 km) wide along the western sides of the Hueco and Pedernal uplifts and along both sides of the Uncompahgre uplift. Another belt extended northwest from the Pedregosa basin into southeastern Arizona. Major tectonic events initiated the Morrowan, Atokan, and Missourian Epochs and occurred twice within the Wolfcampian Epoch. Leonardian, Guadalupian, and Ochoan Epochs were times of tectonic stability. During the Leonardian, sediments from the Uncompaghre uplift gradually covered all the other uplifts. The timing of these Paleozoic tectonic events suggests a cause-effect relationship with plate-tectonic histories that brought North American and northern Europe together in the Late Devonian (Acadian orogeny) and Euramerica and northwestern Gondwana together in the Late Mississippian through Early Permian (Appalachian orogeny). End_of_Article - Last_Page 864------------

Tectonic History and Influence on Sedimentation of Rhomb Horsts and Grabens Associated with Amarillo Uplift, Texas Panhandle: ABSTRACT

The Amarillo uplift consists of an en echelon series of fault blocks separating the Anadarko basin from the Palo Duro basin. The uplift is part of a northwest-southeast zone of basement weakness that extends from the Wichita Mountains in Oklahoma to southeastern Colorado. Initial faulting, related to the opening of the southern Oklahoma aulacogen, took place from late Precambrian through Middle Cambrian time. Renewed movement in the Late Mississippian or Early Pennsylvanian, probably of a left-lateral transcurrent nature, broke the Amarillo uplift into a series of rhomb grabens and rhomb horsts. The Lefors basin, for example, in Gray County is a small rhomb graben 4 mi (6.4 km) by 8 mi (12.8 km) that contains in excess of 4,000 ft (1,200 m) of Pennsylvanian and Wolfcampian arkose (granite wash). The Amarillo uplift continued to subtly affect depositional patterns following its burial in Wolfcampian time. Salt beds in the Clear Fork Formation (Leonardian) are purer and thicker in grabens where salt deposition proceeded at a faster rate relative to horsts. Recurrent motion on the Potter County fault in northern Potter and northeastern Oldham County produced cumulative displacements of 1,600 ft (488 m) on top of the Pennsylvanian, 800 ft (244 m) on Wolfcampian strata, 600 ft (183 m) on top of the Clear Fork Formation, and 450 ft (137 m) on the Dockum Group (Triassic). Post-Permian displacements are the result of both salt dissolution and minor structural movement. There is no direct evidence for Quaternary faulting, although the uplift is seismically active. End_of_Article - Last_Page 511------------

Carbonate-Clastic Facies Changes, Pennsylvanian-Early Permian, Northwest Arizona-Southern Nevada: ABSTRACT

Successive facies changes in Chesterian through Wolfcampian strata illustrate five distinct carbonate to clastic transitions. These result from differing combinations of depositional environment, climate, sea level changes, and differential subsidence. Comparative stratigraphy of successive facies change across the craton-miogeosyncline boundary, combined with analysis of sedimentary structures and lithology, enhances interpretation of the causes of these facies changes. A Chesterian to Morrowan transgressive facies change illustrates a carbonate to clastic transition resulting from shallow marine to subaerial environments, wherein the climate was tropical and marine current energy was low. A Morrowan to Atokan regressive facies change closely resembled the underlying transgressive facies change and results from similar circumstances, except that this transition has the addition of eolian quartz silt units and diagenetic overprints resulting from periodic emergence during the regression. A subsequent Atokan transgression illustrates a contrasting facies change. Sandstones change to carbonates more gradually. Rocks containing equal amounts of carbonate and quartz sand occur commonly. Fewer varieties of carbonate texture and fossil species occur in corresponding facies than in the Morrowan transition. Cross-bedding of similar style occurs in sandstones as well as in carbonates. The facies change results from a broad shallow marine environment in which there was an eastern detrital source in the eastern Grand Canyon region. These environments existed in conditions resulting from more open marine conditions and/or greater aridity than during the Morrowan sequence. The distribution of Desmoinesian strata is more easily explained by reciprocal sedimentation rather than by facies. Virgilian facies appear to result from a combination of the factors involved in the Morrowan and Atokan strata. Beginning in Wolfcampian time faulting and attendant differential subsidence control the distribution of clastic and carbonate facies. Carbonate buildups along the upthrown side of faults serve as clastic sediment traps. Also erosion may occur on the upthrown side of faults. Both of these result in abrupt facies changes in Wolfcampian sequences. End_of_Article - Last_Page 534------------

Climatic and Structural Controls of Stacked Algal Lime Mud Mound Development in Oquirrh Group (Pennsylvanian and Permian), Deep Creek Mountains, Southeastern Idaho: ABSTRACT

Oquirrh Group rocks comprise the uppermost of a series of allochthons exposed in southern Idaho. The basal unit of the Oquirrh Group, the West Canyon Limestone (Atokan), is composed largely of lime mudstone and fossiliferous lime wackestone with the exception of a coarse qaurtzarenite and lime mudstone clast debris flow that originated from syndepositional faulting. Overlying this unit are unnamed cyclic back-mound siltstones, sandstones, cherts, and fossiliferous wackestones and packstones that thicken southward from 270 to an estimated 1,000 m of noncyclic strata of similar lithologies. Cyclic, thinly stacked algal lime mud mounds are inferred to have developed in Desmoinesian time. In Virgilian time, syndepositional faulting controlled the development of thickly stacke (700 m) algal, lime-mud mounds. To the north and west, cyclic back-mound lithofacies consist of siltstone, sandstone, chert, lime mudstone, and fossiliferous wackestone and packstone. Similar but noncyclic fore-mound lithofacies are greatly thickened southward suggesting that syndepositional faulting controlled sedimentation. In Wolfcampian time, cyclic, stacked bryozoan algal lime mud mounds (300 m thick) developed. Thin tabular lime mud mounds developed in cyclic back-mound lithofacies. Similar fore-mound lithofacies thickened in a southerly direction. As many as 50 cycles developed in Middle Pennsylvanian to Lower Permian rocks. Eustatic sea level changes caused by late Paleozoic glaciation controlled cyclic sedimentation. Syndepositional faulting in Atokan, Desmoinesian, and Virgilian times also had the effect of keeping the northern and eastern parts of the study area in the marine photic zone. This area may have constituted a paleohorst within the Oquirrh basin in Pennsylvanian and Permian times. End_of_Article - Last_Page 914------------

Pennsylvanian-Early Permian Depositional Systems and Shelf-Margin Evolution, Palo Duro Basin, Texas

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 facies assemblages or depositional systems. An extensive fan-delta system is composed of arkosic sandstones eroded from Precambrian highlands flanking the bas n 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 clastics that were funneled downslope into deep basinal environments by feeder channels that formed along shelf margins. Interplay between basin subsidence and local sedimentological controls determined the depositional style and resulting facies patterns. Rapid Pennsylvanian subsidence combined with invasion and deposition of terrigenous clastics 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 sedimentologic controls dominated basin evolution. Thick slope wedges, which were formed by deltas that prograded to shelf edges and debouched sediment into the slope environment, created shallow foundations for subsequent carbonate-bank development and progradation. 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.

Depositional History of High-Constructive Delta Systems (Wolfcampian), Southeastern Palo Duro Basin, Texas: ABSTRACT

End_Page 2116------------------------------In Late Pennsylvanian and Early Permian time the Palo Duro basin was part of a relatively deep seaway that extended northward from the Midland basin into the Mid-Continent. Deep, central-basin areas were surrounded by massive, carbonate-shelf margins and shallow-shelf terrane. In the southeastern Palo Duro basin, high-constructive, elongate delta systems deposited quartzose sand derived from eastern sources (Wichita Mountains). Late Pennsylvanian and early Wolfcampian delta-front sandstones (> 200 ft or 60 m thick) are present on the basinward side of the shelf margin, suggesting that deltas prograded beyond the shelf margin and into deep water. Later, as terrigenous sediment supply was sharply reduced, the shelf margin prograded basinward over deep-water delta facies. During middle Wolfcampian time, clastic input was increased and high-constructive deltas once again prograded into the southeastern Palo Duro basin. However, progradation was not so extensive as earlier episodes and most delta-front sands were deposited in shallow-shelf environments. Conse uently shallow-water conditions precluded formation of thick delta-front sequences in shelf environments. Upper Pennsylvanian-Lower Permian deltaic sandstones in the southeastern Palo Duro basin are subarkoses. Porosity ranges from 0 to 13% and averages 4.8%. Both primary and secondary (leached feldspars) porosity are present. Cementation began with clay coats, followed by quartz overgrowths. Iron-rich dolomite replaced margins of framework grains and filled most remaining pores. Timing of feldspar leaching and kaolinite cement is unknown. End_of_Article - Last_Page 2117------------

Depositional Systems and Petroleum Potential of Lower Permian Strata, Palo Duro Basin, Texas: ABSTRACT

Lower Permian (Wolfcampian) strata of the Palo Duro basin consist of thick, terrigenous clastic and carbonate facies which were deposited in (1) fan-delta, (2) high-constructional delta, (3) carbonate-shelf and shelf-margin, and (4) slope and basinal systems. Lateral and vertical facies sequences across the basin indicate that these strata are regressive deposits and they document the first episodes of Permian marine retreat from the Texas Panhandle. Terrigenous clastic sediment was derived from highlands which surrounded part of the Palo Duro basin. Exposed Precambrian granite in the Amarillo uplift, Sierra Grande uplift, and Bravo dome yielded large quantities of arkosic sand (granite wash) to fan-delta systems which emptied into shallow-marine environments in the northern part of the basin. Along the basin's southeastern margin, high-constructive deltas prograded westward from the Wichita Mountains, depositing quartz-rich sand and mud across the shelf. Seaward of the clastic facies belt, a carbonate-shelf-margin complex, averaging 1,000 to 1,200 ft (300 to 365 m) in thickness and facing south toward the Midland basin, dominated Wolfcampian deposition in the Palo Duro basin. The western shelf margin consists of a superposed sequence of carbonate strata exhibiting limited basinward progradation. Contrarily, the eastern shelf margin is composed of several superposed, progradational carbonate sequences, individually averaging several hundred feet in thickness. During early to middle Wolfcampian time, the eastern shelf margin prograded westward 10 to 30 mi (16 to 48 m) while the western margin remained stationary. Shelf margins shifted in response to deposition of slope sediments in front of the shelf and in feeder channels, creating a f undation for subsequent carbonate buildups. Potential hydrocarbon reservoirs are thick zones of shelf-margin dolomites, delta-front sandstones, and fan-delta arkoses. Porosity figures in those facies are as high as 10 to 20%. Each potential reservoir facies is juxtaposed with potential source beds and nonporous sealing beds. End_of_Article - Last_Page 1426------------

Exploration Potential of Pennsylvanian-Permian Carbonate-Shelf Margins and Deltaic Sandstones, Palo Duro Basin, Texas: ABSTRACT

Potential hydrocarbon reservoirs occur in Pennsylvanian and Lower Permian (Wolfcampian) carbonate-shelf margins, fan-delta arkosic sandstones, and deltaic sandstones in the Palo Duro basin. Thick basinal shales, which are stratigraphically equivalent to shelf carbonate rocks and sandstones, may have served as hydrocarbon source beds, although present thermal gradients are inadequate for liquid hydrocarbon generation. During the Pennsylvanian, a carbonate-shelf-margin complex with 200 to 400 ft (60 to 120 m) of depositional relief developed around a narrow embayment that opened southward into the Midland basin. The position of local shelf margins shifted through time. Following initial construction, shelf margins retreated shelfward throughout Pennsylvanian and earliest Permian time. During later Wolfcampian, shelves prograded westward and southward into the basin, filling it by late Wolfcampian time. Potential hydrocarbon reservoirs are thick zones of secondary porous dolomite within the shelf-margin complex. Dolomite porosity is commonly greater than 10%. The distribution of porous dolomite along shelf margins may indicate dolomitization was related to (1) early postdepositional, mixing-zone diagenesis in islands present along the shelf margin, or (2) dewatering of basinal shale, leading to montmorillonite-illite conversion and release of magnesium during burial diagenesis. Pennsylvanian and Permian fan-delta deposits of arkosic sandstone (granite wash) shed off the Amarillo uplift are potential clastic reservoirs. Production occurs from stratigraphically equivalent, granite wash deposits on the northern side of the uplift in the Anadarko basin. Porosity in granite wash sandstones averages 15%. Pennsylvanian quartzose sandstones are also interbedded with thick sequences of basinal shale, suggesting that the sand entered the basin through passes in the shelf margin. Geometry of sandstone bodies suggests deposition as distributary-mouth-bar fingers of high-constructive elongate deltas. Porosity in these sandstones reaches 18%. End_of_Article - Last_Page 461------------

Lower Permian Facies Tracts and Evolution of Carbonate-Shelf Margins, Palo Duro Basin, Texas Panhandle: ABSTRACT

Lower Permian (Wolfcampian) strata of the Palo Duro basin consist of 1,000 to 2,000 ft (300 to 600 m) of terrigenous clastic and carbonate sediments which were deposited in basin, slope, shelf-margin, shelf, and deltaic environments. Lateral and vertical sequences of facies throughout the basin indicate that these strata are regressive and document the first episodes of Permian marine retreat from the Panhandle region of Texas. Terrigenous clastic sediment was derived from highlands which surrounded part of the Palo Duro basin. Exposed Precambrian granite in the Amarillo uplift, Sierra Grande uplift, and Bravo dome yielded large quantities of arkosic sand (granite wash) to fan-delta systems which emptied into shallow-marine environments in the northern part of the basin. Along the basin's southeastern margin, high-constructive deltas prograded westward from the Wichita Mountains depositing quartz-rich sand and mud across the shelf. Seaward of the clastic-facies belt, an arcuate, carbonate-shelf-margin complex, averaging 1,000 to 1,200 ft (300 to 360 m) in thickness and facing south toward the Midland basin, dominated Wolfcampian deposition. The western shelf margin consists of a superposed sequence of carbonate strata exhibiting limited basinward progradation. In contrast, the eastern shelf margin is composed of several superposed, progradational carbonate sequences, individually averaging several hundred feet in thickness. During early to middle Wolfcampian time, the eastern shelf margin prograded westward 10 to 30 mi (16 to 48 km) but the western margin remained stationary. Shelf margins shifted in response to deposition of slope sediments in front of the shelf, creating a foundation for subsequent carbonate b ildups. Slope deposits consist of (1) hemipelagic mud, (2) fine-grained clastic sediments transported downslope End_Page 461------------------------------ through submarine canyons incised in the shelf margin, and (3) redeposited carbonate sediment derived from shelf-margin buildups. End_of_Article - Last_Page 462------------

Petrology and Stratigraphy of Earp Formation, Pima and Cochise Counties, Arizona: ABSTRACT

Stratigraphic and petrologic studies show that the Earp Formation of Pennsylvanian and Permian ages in southeastern Arizona and southwestern New Mexico consists of fluvial clastic rocks that interfinger with supratidal, intertidal, and subtidal marine carbonate rocks. The clastics encroached initially from the northwest into the shallow Earp sea during Missourian time and continued migrating eastward during Virgilian and Wolfcampian time. Clastic-ratio and isopach maps, a convex-upward geometry shown by a thinning of the overlying Colina Limestone, and primary sedimentary structures indicate that the clastic-dominated part of the Earp Formation was deposited as a delta. In the carbonate lithologies, 3 environments of deposition are recognizable: supratidal, intertidal, and subtidal. The supratidal environment is characterized by pelmicrites filled with sparry calcite surrounded by a micrite envelope; desiccated, interlaminated carbonates of algal origin (biomicrites); the absence of fossils; evidence of dedolomitization; and bird's-eye structure (dismicrite). The intertidal environment is composed of pelmicrites, biomicrites, micrites, and biosparites. Fusulinid biomicrites and biomicrites that have delicate tests preserved are characteristic of the subtidal environment. End_of_Article - Last_Page 349------------

Slide-Block Geology, Coyanosa and Adjacent Areas, Pecos and Reeves Counties, Texas: ABSTRACT

A large-scale submarine slide occurred in early Wolfcampian (Permian) time in the Coyanosa and adjacent areas of the southeastern Delaware basin of West Texas. The slide, which bisects the Coyanosa field, comprises all rocks above the Upper Devonian Woodford Shale, the surface of detachment. Maximum dimensions were 16 mi from east to west, 9 mi north to south, and 2,000 ft thick. Lateral displacement from east to west was about 7 mi. Wildcat and development drilling in the area has revealed many paradoxical structural and stratigraphic conditions in the Mississippian through Wolfcamp interval. These sequences include repeated sections, exotic blocks, displaced facies, and abrupt stratigraphic hiatuses. The sole of the allochthonous plate was a thick, competent Mississippian limestone. Thick Permo-Pennsylvanian conglomerates shed from the rising Central Basin platform on the eastern side of Coyanosa, coupled with steepening of the flexure on the western and southwestern flank of Coyanosa, triggered the slide. End_Page 340------------------------------ The slide was along the bedding plane in the eastern two thirds of the area. In the western third of the area the arcuate leading edge cut up section along the western and southwestern flank of Coyanosa and continued along the sea floor to just beyond Rojo Caballos. Rapid emplacement is implicit from the westerly thinning wedge of detritus which was churned up by the toe of the slide as it traversed the sea floor. Alternate interpretations to submarine sliding require almost inexplicable faulting and erosion to account for the observed phenomena. End_of_Article - Last_Page 341------------

Oil and Gas Possibilities in Pedregosa Basin: ABSTRACT

Oil and gas have been found in the Pedregosa basin area, but it is not known if they are in commercial quantities. Geologists such as Kottlowski, Wengerd, Foster, and Zeller have suggested the oil potential of various zones. Analogies have been drawn between environmental and structural similarities of the Pedregosa basin and nearby oil-producing basins. Shows of oil have been reported from shallow water wells in southwestern New Mexico, southeastern Arizona, and the northern part of the state of Chihuahua. Zeller reported oil shows in the Big Hatchet Mountains in the Cretaceous strata and good petroliferous odor from Paleozoic rocks. The Hachita Dome well drilled in 1953 near the town of Hachita reported shows of oil from lower Paleozoic limestones. Humble Oil and Refini g Company's B. A. State, drilled south of the Big Hatchet Mountains, recovered gas on a drill-stem test from Permian rocks. The Humble well was reentered a few years ago by a group of independent oil men in an attempt to make a commercial gas well. They reported gas flow at the rate of 0.5 MMcf/d, but lost the hole when attempting to acid frac the gas zone. Oil shows were reported in the Cockrell well drilled north of Coyote Hills. Sample shows have been reported in the Pemex well drilled at Los Chinos in northern Chihuahua, Mexico. Oil shows in the surface exposure of the Mississippian near Bavispe, Chihuahua, were noted by Pemex surface geologists. Porosity in the middle sandstone member of the Cambrian Bliss Sandstone is present in the exposures at Big Hatchet Mountains. Cambrian sandstones produce on anticlines on the Eastern shelf of the Midland basin of West Texas. The 800 ft of porous Silurian Fusselman Dolomite, present in the Franklin Mountains, was eroded after Middle Devonian uplift in the Big Hatchet Mountains area. The eroded scarp is covered by sapropelic shale and dark chert of the Upper Devonian. Similar conditions on the Eastern shelf and Central Basin platform of the Permian basin of West Texas and southeastern New Mexico produce oil from structural and stratigraphic traps. Ordovician El Paso-Ellenburger dolomite is present and should be covered by the Devonian shale west of the Fusselman subcrop. The Ellenburger is an excellent producer on structure in the Permian basin of West Texas and southern New Mexico. Bioherms of Mississippian crinoids are present in the Sacramento and San Andres Mountains and very massive End_Page 536------------------------------ limestone cliffs up to 500 ft thick are present in southwestern New Mexico and southeastern Arizona. Horquilla reefs, 1,200 ft thick, were described and photographed by Zeller in the Big Hatchet Mountains. The reef started growing in Desmoinesian time and grew into early Wolfcampian time. Numerous reefs in West Texas and southeastern New Mexico grew at the same time and have produced billions of barrels of oil. Porous Epitaph Dolomite is visible in the Big Hatchet Mountains, reefs are present in the Mustang Mountains, and lagoonal evaporites are present in the Whetstone Mountains of Cochise County, Arizona. Presence of backreef evaporites up to 200 ft thick lends evidence that the Leonardian-age Epitaph Dolomite could be analogous to the prolific Abo production of southeastern New Mexico. Lower Cretaceous beds contain rudistid, coralline, algal, bioclastic banks up to 500 ft thick in the Big Hatchet Mountains and 200 ft thick in the Mule Mountains of southeastern Arizona. The large Pedregosa basin contains more than 25,000 ft of sedimentary rocks. For most of Paleozoic time, the basin had a history of environment and structural evolution similar to the Permian basin of West Texas and southeastern New Mexico. Billions of barrels of oil and tens of trillions of cubic feet of gas have been produced in the Permian basin. I believe a like amount will be found in the Pedregosa basin. End_of_Article - Last_Page 537------------

Early Permian Sedimentation and Paleogeography in East-Central Alaska Range, and Regional Implications: ABSTRACT

A detailed study of the Early Permian strata in part of the east-central Alaska Range strongly supports the hypothesis that a volcanic island archipelago, possibly similar to modern island arcs of the circum-Pacific type, existed in the eastern Alaska Range during the late Paleozoic. The depositional history of Early Permian strata in the study area further suggests that the geologic history of the inferred island arc system was responsible for the nature of upper Paleozoic stratigraphic successions throughout the eastern Alaska Range. The study area of approximately 80 sq mi is near Gulkana Glacier in the east-central Alaska Range east of the Richardson Highway, 170 mi south of Fairbanks, Alaska. The Permian strata are divided into 2 formations, informally named the Phelan Creek formation, of early Wolfcampian age, and the Gulkana Glacier formation, of middle Wolfcampian age. The units are separated by an erosional unconformity of small magnitude. The Phelan Creek formation, approximately 4,000 ft thick, is composed of interstratified pyroclastics, graded volcaniclastics, pebbly mudstone, and lenticular, fossiliferous limestone. The formation was deposited in a neritic basin below wave base. Subaqueous gravity processes deposited the pebbly mudstone, volcaniclastics, and many of the limestone and pyroclastic units. In contrast, the Gulkana Glacier formation, approximately, 1,000 ft thick, is composed of interbedded fossiliferous limestone and black shale and was deposited, mostly, above wave base by tractive currents. Thickness and grain size changes in the pyroclastic units of the Phelan Creek formation indicate that during early Wolfcampian time a group of volcanoes was a few miles west of the study area. The volcanoes probably were the source of all pyroclastic and volcaniclastic deposits in the formation. By middle Wolfcampian time the volcanoes were no longer active and began to subside producing an extensive shallow-water platform. The carbonate rocks and black shales of the Gulkana Glacier formation were deposited on top of this subsiding platform. Upper Paleozoic strata exposed elsewhere in the eastern Alaska Range can be divided similarly into a lower sequence containing mostly volcanic and volcanic-derived deposits and an upper sequence containing limestone and black shale. The thickness of these 2 sequences varies, but usually is more than 1,000 ft. Preliminary study of these strata suggests that these deposits also record the growth, extinction, and burial of volcanic islands. The sequence of depositional and tectonic events suggested by the vertical change from volcanics to limestone and black shale in the upper Paleozoic deposits of the eastern Alaska Range is strikingly similar to the Tertiary and Holocene history of some modern island arc systems. For example, Guam and Saipan of the Marianas group and the Windward Islands in the Caribbean consist of a complex succession of mostly End_Page 2470------------------------------ volcanics and volcanic derived rocks that closely resemble the strata of the Phelan Creek formation. These modern volcanic islands are mostly inactive and have subsided. Thick limestone-black shale caps are now being formed on top of the subsiding volcanic platforms. The resulting stratigraphic succession is nearly identical with the stratigraphic sequence that characterizes upper Paleozoic deposits throughout the eastern Alaska Range. End_of_Article - Last_Page 2471------------

Realms of Permian Tectonism and Sedimentation in Western Utah and Eastern Nevada

Realms of sedimentation of Permian rocks include basins, troughs, platforms, and shelves within or adjacent to the Cordilleran miogeosyncline. Peripheral tectonic uplands (Antler and Sonoma orogenic belts on the west, Utah-Wyoming and other shelves on the east), as well as intrageosynclinal positive areas (Northeast Nevada high, Western Utah high, Southern Nevada high, Emery uplift, and others), varied in degrees of tectonism and thus provided different types of detritus and material removed in solution to accumulate in the several depocenters. Oquirrh, Wood River, Bird Spring, Ely, Hamilton-Elko, Ferguson, Pequop-Diamond Creek, Montello-Sublett, Ruby, and Park City basins are the more negative parts of the geosyncline, whereas several shelves and the Riepe Spring, Callvi le, Pakoon, and Kaibab platforms identify the less negative repositories. Starved basins of relatively short geologic duration were present locally. The study area, embracing western Utah, eastern Nevada, and a part of southern Idaho, is about 300 mi (483 km) wide in an east-west direction and about 525 mi (845 km) long north-south. The Permian includes slightly more than 17,000 ft (5,182 m) of sedimentary rocks in northwestern Utah, but thins to featheredges toward the orogenic belts on the west and the craton on the east. Most basinal accumulations exceed 5,000 ft (1,524 m), and many aggregate 6,000-10,000 ft (1,829-3,048 m). Rocks include a vast spectrum of limestone, dolostone, orthoquartzite, siltstone, sandstone, mudstone, gypstone, redbeds, and minor shale. They are of Wolfcampian, Leonardian, and Guadalupian ages. Fusulinids and some corals are abundant and are excellent guide fossils in Wolfcampian and Leonardian rocks, w ereas mollusks (including some ammonoids), brachiopods, sponges, and conodonts have stratigraphic value in younger sedimentary rocks. Conodonts in particular are of index and correlation value in Guadalupian rocks. During Wolfcampian time a thick sequence of orthoquartzite and shelly limestone accumulated in the Oquirrh, Wood River, and Hamilton-Elko basins, whereas bituminous carbonate rocks formed in the Ferguson basin. Clean carbonate sediments and various arenites typified the shelves and platforms. The Leonardian was a time of diversification into deeply subsiding troughs, basins, and areally extensive shelves and platforms; orthoquartzite, limestone, dolostone, some evaporites, redbeds, and related sediments formed. During Guadalupian time basinal carbonate rocks accumulated locally. Very cherty mudstone and carbonate sediment formed in other depocenters, whereas patch reefs, redbeds, sandstone, and evaporites were deposited in other depositional realms. Ochoan rocks, as identified elsewhe e by certain ammonoids and advanced fusulinaceans, are not recognized in the eastern Great Basin, but it cannot be stated with assurance that they are absent. Lower Triassic nonmarine (and marine) rocks disconformably overlie Permian rocks in several places within the study area. Oil is produced in limited quantity from Permian rocks within the study area in Utah, and hydrocarbon shows in wells have been very common. This vast area, however, has not been tested adequately. It is a structurally complex area, and exploration for oil and gas will be hazardous and costly.

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------------

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------------

Permian System of Southern Rocky Mountains and Surrounding Provinces: ABSTRACT

The Permian Period lasted approximately 50 m.y., beginning 275 m.y. ago. The sedimentary rocks of this system have been divided into four series in the western United States. Despite the scarcity of datable fossils, series correlations generally are reliable except in the piedmont and intermontane redbed facies. The basal Wolfcamp Series is more extensive and thicker, on the average, than any of the other series. The Ochoa Series, the youngest, essentially is confined to the Permian basin, the Anadarko-Hugoton area and the Great Basin. The Guadalupe Series extends well beyond the erosional limits of the underlying Leonard Series in the northern Great Plains but is absent on much of the Colorado Plateau where the Leonard is well preserved. A regional unconformity, usually of low angle, separates Permian rocks from the Pennsylvanian System, even where the Virgil Series of Late Pennsylvanian age underlies the Wolfcamp. It is believed that late Virgilian-early Wolfcampian time is not represented in most of the region. The Triassic System also is separated from the Permian by a regional low-angle unconformity. Rocks of Early Triassic age are missing by nondeposition or erosion in part all of the southern structural provinces where the Ochoa is present. Detailed studies also indicate the presence of interseries unconformities of regional extent. Lower Leonard, lower Guadalupe, and lower Ochoa rocks have limited areal distribution. Permian depositional environments ranged from terrestrial-piedmont to deep-marine-basinal. Shelf-marine carbonates generally decrease in importance upward through the system whereas evaporite deposits, including halite, are more common and more widespread. Permian rocks are the source of considerable mineral wealth including, in addition to petroleum, potash, phosphate, sulfur, and helium. Carbonate and sandstone reservoir rocks of Guadalupian, Leonardian, and Wolfcampian ages have yielded vast quantities of oil and gas, especially in the central Rockies, Great Plains, and Permian basin. Permian source shales in western Wyoming and in the Permian basin were major oil contributors. End_of_Article - Last_Page 1904------------