Abstract During Pennsylvanian time, the Ardmore basin was the site of almost continuous deposition in long, narrow, and oftendeep basins lying in close proximity to structurally and topographically high islands. These islands and sea-mount archipelagoes formed and were rejuvenated during the several orogenic pulsations that mark the Pennsylvanian Period in southern Oklahoma as one of extreme unrest. As the islands were upfolded, they were truncated, and some of them buried—partly in their own detritus. The base of the Pennsylvanian is drawn at the base of the Rod Club sand. The underlying Goddard shale, which was formerly included in the Springeran Series, is now considered to be Chesterian in age. The Springeran Series as defined herein is apparently restricted to the Ardmore-Anadarko basin with only a very thin wedge, if any, within the western McAlester basin. It consists of shales with sandstone members, in many places oil bearing, which are “regionally persistent but locally very erratic” (phrase from Hubbard and Thompson, 1926, p. 457). The Morrowan Series began with a very widespread “transgression” of marine sands that covered the peneplained surface of most of Oklahoma north of the Wichita Mountains-Criner Hills axis, and extended northwest into southwestern Kansas and the Texas Panhandle. This was followed by marine shales and then limestones. Local uplifting (Wichita orogeny) began in the Criner Hills and elsewhere, possibly during late Springeran time, and increased in magnitude inthe Morrowan Epoch, producing coarse conglomerates east of the Criner Hills. It culminated in early Atokan time in intricate folding and faulting. These folds lie en echelon , with their axes about 10° from the major tectonic trend. Many of the upfolded insular structures that now contain vast amounts of oil were first formed duringthis period of unrest. Concomitant erosion of these islands stripped as much as 8,000-13,000 feet of sediments from many of them before their burial in late Desmoinesian time. The Atokan Series began with the deposition of thick conglomerates in the vicinity of the Criner Hills. Marine shales, sands, and some limestones make up the rest of the unit. Near the end of the epoch the Ouachita orogeny intensely compressed the Ouachita geosyncline to the east, raising the Ouachita Mountains into fairly high relief. The Desmoinesian rocks of the Ardmore basin tell the erosional story of that land mass. Great wedges of chert conglomerates, sands, and deltaic sediments extend northwestward into the Ardmore basin, where they intertongue with swamp and marine strata. The marine sands contain tremendous quantities of oil, in structurally high positions. Around the island uplifts a considerable accumulation of locally derived detritus was deposited. The presently exposed Arbuckle Mountains were strongly uplifted in late Desmoniesian time (first major phase of the Arbuckle orogeny), shedding detritus into adjacent submerged areas. An interval without severe tectonism resulted in slow subsidence of most of the region in Missourian time, with an influx of transgressive marine shales, sands, and limestones, interbedded with a few tongues of continental sediments.Bythe end of Missourian time most of the structural islands were completely buried. The end of this epoch was marked by the culmination of the Arbuckle orogeny, with great uplift in the Arbuckle Mountain area and intense compression ofthe Ardmore basin, continuing into Virgilian time. Close folding accompanied by major faulting occurred at this time. The Virgilian Series consists largely of terrestrial and shallow-water conglomerates and red shales that were deposited in the low areas surrounding the eroding mountain ranges that were formed during the Arbuckle orogeny. By the endofVirgilian time, both the erosional and the depositional surfaces were nearly flat.

Abstract During Pennsylvanian time, the Ardmore basin was the site of almost continuous deposition in long, narrow, and often deep basins lying in close proximity to structurally and topographically high islands. These islands and sea-mount archipelagoes formed and were rejuvenated during the several orogenic pulsations that mark the Pennsylvanian Period in southern Oklahoma as one of extreme unrest. As the islands were upfolded, they were truncated, and some of them buried—partly in their own detritus. The base of the Pennsylvanian is drawn at the base of the Rod Club sand. The underlying Goddard shale, which was formerly included in the Springeran Series, is now considered to be Chesterian in age. The Springeran Series as defined herein is apparently restricted to the Ardmore-Anadarko basin with only a very thin wedge, if any, within the western McAlester basin. It consists of shales with sandstone members, in many places oil bearing, which are “regionally persistent but locally very erratic” (phrase from Hubbard and Thompson, 1926, p. 457). The Morrowan Series began with a very widespread “transgression” of marine sands that covered the peneplained surface of most of Oklahoma north of the Wichita Mountains-Criner Hills axis, and extended northwest into southwestern Kansas and the Texas Panhandle. This was followed by marine shales and then limestones. Local uplifting (Wichita orogeny) began in the Criner Hills and elsewhere, possibly during late Springeran time, and increased in magnitude in the Morrowan Epoch, producing coarse conglomerates east of the Criner Hills, It culminated in early Atokan time in intricate folding and faulting. These folds lie en echelon , with their axes about 10° from the major tectonic trend. Many of the upfolded insular structures that now contain vast amounts of oil were first formed during this period of unrest. Concomitant erosion of these islands stripped as much as 8,000-13,000 feet of sediments from many of them before their burial in late Desmoinesian time. The Atokan Series began with the deposition of thick conglomerates in the vicinity of the Criner Hills. Marine shales, sands, and some limestones make up the rest of the unit. Near the end of the epoch the Ouachita orogeny intensely compressed the Ouachita geosyncline to the east, raising the Ouachita Mountains into fairly high relief. The Desmoinesian rocks of the Ardmore basin tell the erosional story of that land mass. Great wedges of chert conglomerates, sands, and deltaic sediments extend northwestward into the Ardmore basin, where they intertongue with swamp and marine strata. The marine sands contain tremendous quantities of oil, in structurally high positions. Around the island uplifts a considerable accumulation of locally derived detritus was deposited. The presently exposed Arbuckle Mountains were strongly uplifted in late Desmoinesian time (first major phase of the Arbuckle orogeny), shedding detritus into adjacent submerged areas. An interval without severe tectonism resulted in slow subsidence of most of the region in Missourian time, with an influx of transgressive marine shales, sands, and limestones, interbedded with a few tongues of continental sediments. By the end of Missourian time most of the structural islands were completely buried. The end of this epoch was marked by the culmination of the Arbuckle orogeny, with great uplift in the Arbuckle Mountain area and intense compression of the Ardmore basin, continuing into Virgilian time. Close folding accompanied by major faulting occurred at this time. The Virgilian Series consists largely of terrestrial and shallow-water conglomerates and red shales that were deposited in the low areas surrounding the eroding mountain ranges that were formed during the Arbuckle orogeny. By the end of Virgilian time, both the erosional and the depositional surfaces were nearly flat.

Abstract Grayson County is located in the eastern part of north-central Texas, adjacent to the Red River. Sherman,, the county seat, is about 70 miles north of Dallas. Although occasional wildcat wells had been drilled in the county since early in the century, the first commercial oil pool, the Handy field, was not discovered until 1946. Development has been active since that time, particularly since the discovery of Oil Creek production in the Sandusky field in 1950. As a result, 15 oil fields with about 65 different pay zones have been discovered. The main regional geological features are—Muenster arch, Marietta basin and associated Gordonville trough, and Ouachita facies of the eastern portion of the county. The Gordonville trough in the northwest portion of the county extends in a northwest-southeast direction parallelling the Muenster arch, and conforming generally to the structural grain established by the Wichita and Arbuckle orogenies in southern Oklahoma. The Sandusky platform, on which a substantial portion of the production in Grayson County is located, borders the Gordonville trough on the southwest, and owes its existence to a series of tremendous faults stepping down into the trough. In the southwestern quarter of Grayson County the Ordovician (Ellenburger) beds dip northeastward away from the crest of the Muenster arch, which lies further south-westward in northern Denton and southern Cooke counties. The geologic structure of the area is strongly influenced by faults, the major ones associated with subsidence of the Marietta basin and the minor ones connected with more local adjustments. The Sherman anticline is the largest anticlinal feature in the county, being about 12 miles long and having approximately 2,000 feet of closure. The stratigraphic column includes beds from Gulf and Comanchean rocks at the surface down to probable Cambrian—possibly as much as 35,000 feet of sediments in the Gordonville trough. Cretaceous rocks rest on Pennsylvanian from Virgilian to Morrowan with great angular unconformity. Pennsylvanian from Deese down to lower Dornick Hills (or possibly Springer) rests with great angular and erosional unconformity on Mississippian (Woodford) down to Ordovician Ellenburger. Most of the oil is found in sands of Desmoinesian age—Deese (Strawn)—upper Dornick Hills; Atokan—middle Dornick Hills; and Simpson (Ordovician)—Oil Creek sand. Four oil fields, Handy, Sandusky, Big Mineral, and Sherman, are briefly described as examples of structure, stratigraphy, accumulation, and character of the production in the area.

Abstract The post-Hunton unconformity in southern Oklahoma is evidenced by the age of the rocks encountered at the base of the Woodford shale. A pre-Woodford distribution study illustrates the magnitude of pre-Mississipian folding, and suggests a tectonic framework for delineating pre-Woodford structural trends. An isopachous study of the Hunton suggests that the first pronounced structure building in southern Oklahoma occurred during middle Hunton time, at the close of the Silurian Period. The Hunton exhibits radical variations in thickness as a result of truncation at the basal Woodford unconformity and also the unconformities and fades changes within the Hunton group. Woodford rests unconformably on rocks ranging in age from Arbuckle, in the HoIIis basin in southwest Oklahoma, to upper Hunton, in south-central Oklahoma. A unique carbonate sequence attaining a maximum thickness of 115 feet in the subsurface occurs at the base of the Woodford shale, and rests unconformably on beds as old as Viola along the Mannsville-Aylesworth anticlinal trend in south-central Oklahoma. This carbonate occurrence, its lithologic description, and its possible relationship with the outcrop are briefly discussed.

Abstract The pre-Atokan rocks were investigated by determining the geology of the surface of the large pre-Atokan unconformity, including the areal distribution of formations at this surface, and the present structural position of this unconformity. A pre-Atokan paleogeologic map, a structure map on the pre-Atokan unconformity, and cross sections drawn to true scale were constructed by using data from well samples and electric-log correlations. In the construction of the paleogeologic map an attempt was made to project the contacts of the surface rock units, which are exposed in the Criner Hills, into the subsurface. As established by earlier investigations, the original pre-Atokan surface was developed during the Wichita orogeny in early Pennsylvanian time; and the present subsurface structure of the area was developed both then and during the Arbuckle orogeny in late Pennsylvanian. The constructed paleogeologic map (PI. 1) definitely shows that the structural trends of the Criner Hills, formed during the Wichita orogeny, extend to the northwest and southeast, in the subsurface. The map contoured on the pre-Atokan unconformity (PI. 2) shows evidence that during the Arbuckle orogeny the area was again folded and faulted along the former tectonic trends, and some completely new structures were formed. In some cases faulting during the Arbuckle orogeny was along the planes of earlier established faults, but the movement was in the opposite direction.

Abstract The area of investigation in southwestern Oklahoma extends from the Cement field, Tps. 5-6 N., Rs. 9-10 W., northwestward along the north flank of the Wichita Mountains to the Oklahoma-Texas boundary. A study of Pennsylvanian sediments in this area reveals conspicuous facies changes both laterally and normal to the mountain flank. The lateral facies changes show a close relationship to the provenance from which the sediments were derived. Correlation difficulties are amplified because of these facies changes. Fusulinids provide reliable age determinations where present. The Pennsylvanian rocks are dominantly elastics; the principal facies near the mountain front is granite wash, a coarse clastic sediment composed primarily of igneous rock fragments with variable amounts of detrital carbonates and chert; subordinate facies are arkosic sandstones, arenaceous, silty shales, and thin, argillaceous limestones. These continental and transitional facies interfinger basinward with normal marine sandstones, shales, and limestones. The study reveals that regionally the reservoir characteristics are largely controlled by the source areas of clastic sediments. The best reservoir development is found in the western part of the area where the provenance is predominantly granitic rocks.

Abstract In the Ardmore basin the Sycamore formation occupies the stratigraphic interval between the Caney (Meramecian) and Woodford (uppermost part = Kinderhookian) formations. The Sycamore is divisible into two members, herein named the Cornell Ranch (lower), and Worthey (upper). The Cornell Ranch comprises up to 80 feet of silty to sandy, clayey, cherty limestones, dolomitic claystones, and dark gray, calcareous, clayey shales; with a soft, green shale, locally pyritic and glauconitic at the base, lying with apparent conformity upon the Woodford. The Worthey member comprises approximately 310 feet of compact, tough, blocky, slate blue, silty to sandy limestone, massive at the base, thick bedded near the middle, and thin bedded toward the top; eastward from the type locality, the upper portion gives way to the lower Caney shale. The massive portion of the Worthey forms the prominent Sycamore hogback. Faunal evidence is lacking for a definite determination of the age of the Sycamore, and for many years it has been arbitrarily assigned to the Osagean. No attempt is made in this paper to clarify the age relationships.

Abstract The Altus field, Jackson county, Oklahoma, is about 3.75 mi. long, and averages 1.5 mi. in width. The field was discovered in 1934. The cumulative production to February 1, 1956, was 3 > 773 > I 8o barrels of oil. The daily average production in February 1956, was 349 barrels of oil from 197 wells. The average gravity of the oil is 48°. Production is obtained from four main granite wash units of the Pontotoc group (Wolfcampian) encountered between the depths of 1,200 and 1,600 feet. A fault terminates the field at the east side. The Altus structure was a positive element until Hennessey (Clear Fork) time.

Abstract The small but prolific West Frederick field is situated on an anticlinal trend which extends from the Frederick area in Tillman County, Oklahoma, to the Fargo producing area of Wilbarger County, Texas. Accumulation resulted from entrapment by anticlinal closure, although minor faulting exists. Oil is produced from the Canyon limestone and from Arbuckle dolomite. In each of these carbonate reservoirs the porosity and permeability have been increased by weathering at an unconformity.

Abstract The South Palacine field, located in Sees. 16, 21, 22, 23, 26, 27, 28, and 34, T. 2 S., R. 6 W., Stephens County, Oklahoma, was discovered in May 1049. Principal production comes from several sandstone zones in the Hoxbar sequence of upper Pennsylvanian age. Structurally the field is associated with the Wichita Mountains-Criner Hills trend of folding. The Hoxbar group of the Pennsylvanian System rests upon an eroded pre-Pennsylvanian surface, underlain by rocks of Ordovician age and older. Cumulative production to December 1956 was 9,104,605 barrels of oil, with daily production at that time averaging about 1,600 barrels.

Abstract The Carter-Knox oil field, located in the southeastern end of the Anadarko basin in southeastern Grady County and northeastern Stephens County, Oklahoma, covers an area of approximately 16.5 square miles, 1.5 miles wide and 11 miles long. The structure is a very steeply dipping, faulted anticline, which was first mapped on the surface in 1916. It produces from the rocks of the Permian System, and the Hoxbar, Deese, Springer, and Simpson groups. The first oil well was completed in 1923. Since the discovery of oil in the Permian, the field has undergone several drilling cycles, the latest being the development of gas-condensate production in the Simpson group which began with a Bromide sand discovery in 1956. As of January 1958, the Carter-Knox field had produced a total of 33,581,015 barrels of oil; and on the same date was producing 3,370 barrels of oil per day from 407 wells, from all zones.

Abstract Discovered in 1017, the Milroy field comprises 2,650 currently productive acres lying in the central-eastern portion of T. 2 S., R. 4 W., and extending into T. 2 S., R. 3 W. The Milroy structure is only slightly closed on the surface, but attains more than 2,500 feet of closure in the subsurface pre-Pennsylvanian strata. Its N. 65 ° W. axis parallels the Wichita-Criner Hills anticlinorium. Production is derived from several horizons from the Permian down to the Ordovician, but the bulk of the 9,187,735 cumulative barrels of oil has been recovered from Pennsylvanian sandstones of Desmoinesian and Atokan age.

Abstract Correlation of the several sandstone members of the Springer section has been done by use of the self-potential and resistance curves of the electric logs of the wells of the field. Examination of well cuttings has been useful in correlating the upper members of the Humphreys sandstone. Delineation of these curves in thirteen west-east cross sections shows local uniformity in the several sandstones of the Springer which can be considered due to consistent sedimentation; and also local variations and disappearance of the beds due to interrupted or variable sedimentation or to folding and faulting. These last two possibilities must depend upon the interpretation of the data in accordance with the general principles of sedimentary and structural geology. The northwest-southeast trending synclinal area between the major Milroy uplift to the southwest and the relatively minor Camp uplift to the northeast has on its southwest flank an involved series of serpentine folds in the supposedly incompetent Humphreys sandstone beds which are shown to be continuous unless there is clear evidence of faulting. This is done to simplify the picture and does not assume that minor faulting and folding are not present. The usefulness of this paper depends upon the wealth of data which deep drilling on 10-acre spacing has made available.

Abstract The West Brock field, in southern Carter County, Oklahoma, was discovered by H. F. Gibson in February, 1947. To date practically all production has been from Pennsylvanian horizons. Oil is trapped in several closures against the south side of east-west trending normal faults. Oil is also found in lenticular sandstones at various positions on these structures.

Abstract The Southwest Ardmore field is a north-south elongate anticline that plunges to the north and south. It is adjacent to, and on the east flank of, the Criner Hills and separated by a fault on the southwest which defines production. There is more than 1,400 feet of structural relief, not including the faulted side of the field. The oil accumulation is probably due to a combination of structure and reservoir characteristics. Surface outcrops are confined to rocks of the Deese group and Viola limestone. The field produces from sandstones and limestones in the Bromide, Tulip Creek, and McLish formations at depths of 600 to 2,600 feet.

Abstract The North Madill field is located in Sees. 9, 10, 14, 15, 16, 22, and 23, T. 5 S., R. 5 E., Marshall County, Oklahoma. Production is from the First, Second, and Third Bromide sands and the basal McLish sand of the Simpson group. The structure is a thrust-faulted anticline with the production on the northeast or upthrow block. The date of this faulting and structural formation cannot be determined within narrow limits, but it is believed to be of Pennsylvanian age. The Comanchean beds on the surface rest unconformably on rock of lower Morrowan age and very slightly reflect the underlying structure. The discovery well was started in August 1954, and completed in December 1954, producing from the basal McLish sand. As of October 1, 1957, the field covered approximately 1,340 acres with 69 producing wells. Total cumulative production to October 1, 1957, was about 1,680,000 barrels. Development is continuing to the northwest, northeast, and southeast.

Abstract The Jackfork formation was found to consist of about 5,800 feet of tan and gray sandstones interbedded with minor amounts of dark clay shale. Mapping was done on the basis of thin, persistent siliceous shales, the Maroon shale member of the Jackfork, and the Morrow faunal zone described by Honess from McCurtain County (Honess, 1924). More than 6,000 feet of Atoka is exposed, but the top of this formation is not in evidence. The trace of the Boktukola fault as seen on the state geologic map was corrected. A new large thrust fault, the Cloudy fault, was mapped and named. The southeast half of the area consists essentially of a compressed syncline between these two faults. The northwest half forms the undisturbed south flank of the Big One anticline.

Abstract The Ardmore district displays a thick Paleozoic section, essentially complete from Upper Cambrian to lower Permian, with some older and younger rocks, all exposed in a small area of varied structure and remarkable orogenic history; though of modest topographic relief. For any geologist wishing a good general picture of North American geology, it is one of the indispensable areas for him to see. Because of its exposures of scores of strata which produce oil within a few miles of these outcrops, it is an especially classic area for petroleum geologists. It is also much used by college classes for an introduction to field problems.