Abstract Middle Ordovician strata of the Arbuckle and Ouachita Mountains record markedly different depositional settings (Figs. 1, 2). Three localities in the Arbuckles and one in the Ouachitas demonstrate both the vertical sequences of Lithofacies within each area and the contrasts in Lithofacies and biofacies between the two areas. Localities 1 through 3 (Fig. 1) are in the Arbuckle Mountain region. Locality 1 (Fig. 3) is in the northeastern part of the Arbuckles. It consists of a roadcut exposure along the west side of Oklahoma 99, about 3.5 mi (5.6 km) south of Fittstown, SW¼Sec.12, T.1N., R.6E., Pontotoc County. It is readily accessible and requires no permission to visit. Locality 2 (Fig. 3) is a long roadcut along the west side of the southbound lanes of I-35 on the south flank of the Arbuckle Mountains. It is in the SW¼Sec.25, T.2S., R1E., Carter County, is readily accessible, and requires no permission to visit. Locality 3 (Fig. 3) is at the north end of Criner Hills. It is a small quarry situated in the SW¼SE¼- Sec.9, T.5S., R.1E., Carter County, readily accessible from I-35 and U.S. 70 by well-maintained gravel roads. The quarry is on private land. Permission for access can be obtained from the landowner, Ronald Burns of Ardmore, Oklahoma (405- 657-8262). Locality 4 (Figs. 1,3) is at the western edge of the Ouachita Mountains. It is the Stringtown Quarry at the north end of Black Knob Ridge, directly north of the town of Stringtown, and situated in the center of

Abstract A thick sequence of Paleozoic sedimentary and very low-grade metamorphic rocks of geosynclinal facies crops out in the Ouachita Mountains of eastern Oklahoma and western Arkansas. Similar rocks crop out also in the Marathon and Solitario Uplifts of Trans-Pecos Texas. Data obtained from numerous well borings indicate that these outcrops are merely exposed minor segments of a long sinuous geosynclincal structural belt that stretches from eastern Arkansas into Mexico and is now buried beneath younger sediments. The term ‘Ouachita facies’ is applied to both the rocks of the outcrop areas and the buried rocks of the structural belt. In periods of active downwarping of the geosyncline, when large amounts of elastic detritus were available, the typical deposits in the Ouachita geosyncline were poorly sorted subgraywacke sandstone and impure clay shale. During periods of relative quiescence, when little clastic material was being supplied to the geosyncline, the sedimentary deposits were largely argillaceous limestone, siliceous shale, siliceous limestone, bedded chert, and novaculite. In the Marathon Uplift the major siliceous units are the Fort Peña Chert (Ordovician), Maravillas Chert (Ordovician), and Caballos Novaculite (Devonian-Mississippian). In the Ouachita Mountains the major siliceous units are the Bigfork Chert (Ordovician) and the Arkansas Novaculite (Devonian-Mississippi.). It has been suggested by some authors that the high silica content of some of the cherts and novaculites is an epigenetic feature resulting from a combination of surface exposure and from alteration of originally non-cherty sediments during the orogeny in which the Ouachita geosyncline was compressed, deformed, and uplifted. However, the cherts and novaculities maintain similar lithologic and faunal characteristics in wells throughout the entire Ouachita structural belt, although most of these rocks never have been exposed at the surface. The majority of the silica in the cherts and novaculites of Ouachita facies probably was supplied by extrusive vulcanism and submarine vveathering of volcanic ash. There has been some epigenetic redistribution of silica in the cherts and novaculites which crop out in the Ouachita Mountains and Marathon Uplift, but this redistribution is considered to be relatively unimportant.

Abstract The Dimple limestone (Atokan) of the Marathon region represents a period of carbonate deposition which interrupted the deposition of a thick terrigenous flysch section in the Ouachita geosyncline. It consists of laterally adjacent “shelf,” slope, and basin facies from north to south. The “shelf” facies is characterized by cross-bedded fossil and oolith lime grainstones. The slope and basin facies consist of sequences of distinctive limestone turbidites. Paleocurrent analysis indicates a uniform paleoslope dipping southward, with no apparent slope break. A southern source with less contribution to the basin is also indicated based on paleocurrent evidence. Slope facies limestones (proximal turbidites) may be graded, partly graded, or nongraded. Many beds are nongraded in their lowest parts but grade rapidly in their upper parts. Basal portions are often conglomeratic, and lime mudstone upper portions are often absent. “Floating” pebbles are common, as are large-scale convolutions. Small-scale cross-bedding is rare, and occasional medium-scale (up to 3 feet thick) cross-bedding has been observed, which is interpreted as “dune” bed forms. Associated rocks are subaqueous slump conglomerates and spicular lime mudstones. The slope facies is 5 miles wide. Basin facies limestones (distal turbidites) are nearly always graded. Pebbles are rare; the coarsest size being generally sand or silt. Lime mudstone beds are well-developed, and were deposited from turbidity currents because (1) thick mudstone beds overlie thick graded beds, and (2) the normal pelagic sediment is radiolarian-bearing mudstone (marl) with a large terrigenous mud component. Convolutions are common, and small-scale cross-bedding is abundant. Associated rocks are black radiolarian-bearing shales and spicular cherts. The portion of the Ouachita geosyncline revealed in the Marathon region is believed, in Dimple time, to have been a basin about 40 miles wide and perhaps a few hundred feet deep. Turbidity currents moving down a gently-sloping bottom from the north deposited limestones on the slope as well as in the basin. These proximal and distal turbidites display distinctive characteristics, and an awareness of them may assist in reconstructing facies patterns elsewhere.

The Ouachita Mountains–Arkoma basin region of southeastern Oklahoma was a site of rapid subsidence and sedimentation in middle Carboniferous time. The Ouachita geosyncline was an abyssal, marginal trough to which turbidity currents delivered at least 25,000 ft. of alternating layers of sandstone and shale. This geosynclinal flysch sequence thins northward across the Carboniferous continental slope where it grades laterally into shallow-water shelf sediments of the Arkoma basin area. The trough of rapid subsidence migrated northward and in Pennsylvanian (Morrowan) time was located along the present southern margin of the Arkoma basin. However, the rate of sedimentation in that part of the area kept pace with that of subsidence; thus the shallow-water environment of deposition was maintained. The gradual northward encroachment of the Carboniferous sea onto the flanks of the Ozark uplift was temporarily interrupted on several occasions by static sea-level conditions, during which times deltas prograded basinward from the north and east.

The Carboniferous rocks of the Eastern Interior basin reach a maximum thickness of 5,700 ft., and the Mississippian and Pennsylvanian subdivisions are separated by a major widespread erosional unconformity. The major subdivisions of the Mississippian are the Kinderhook, Osage, Meramec, and Chester Series, and those of the Pennsylvanian are the McCormick, Kewanee, and McLeansboro Groups. These series and groups constitute the basic stratigraphic slices treated herein. More than 3,200 ft. of Mississippian sediments were deposited in the Eastern Interior basin while thinner deposits accumulated on adjacent arches and uplifts. Biologically and chemically derived sediments dominate the Meramecian rocks of the region, whereas the volume of terrigenous detritus is significant in Kinderhookian and Osagian rocks and constitutes the bulk of Chesterian rocks. The distal marine parts of southward-prograding deltas pulsed into the area during early Kinderhook time. As they waned, carbonate deposition spread from the west and southwest to the east, covering extensive areas by the end of Kinderhook time. The Borden Delta complex prograded into the basin and adjacent eastern areas during Osage time. Siliceous, cherty Osagian rocks accumulated in the southwestern part of the region. Carbonate sedimentation, which was initially restricted to the western areas, again spread eastward and northward as the deltas waned, and reached its maximum extent during the Meramec. Evaporite deposition during mid-Meramec time marked a widespread episode of restricted circulation. The carbonate environment retreated as major delta deposits prograded southward and dominated the central part of the Eastern Interior basin during Chester time. Although generally restricted to southern parts of the region, carbonate accumulation periodically extended over large areas in and beyond the basin during this time. Depositional environments throughout the Mississippian were mostly shallow marine over broad areas, but deeper marine environments were present in the southern parts of the region during the Osage and early Meramec. These shallow seas opened and deepened southward across a broad shelf and connected with the deepening Ouachita Trough. The terrigenous deltaic sediments were transported into the region by the large Michigan River system, which drained eastern parts of the Canadian Shield and northern extensions of the Appalachian Mountain belt. Broad regional uplift marked the close of Mississippian time when the littoral zone retreated southward out of the area. By Early Pennsylvanian time the region was a southwest-inclined coastal plain with a well-developed linear drainage pattern and river valleys as deep as 200 ft. With renewal of subsidence during Early Pennsylvanian, the littoral zone transgressed north toward the Eastern Interior basin resulting in the accumulation of thick sequences of alluvial sands and muds in the pre-existing valleys and in the eventual burial of the unconformity under an apron of alluvial and upper delta-plain sediments. Shallow-marine environments moved into the area, and the long period of southwestward progradation, abandonment, and progradation of a series of deltas began. This Pennsylvanian deltaic sedimentation resulted in deposition of as much as 2,500 ft. of dominantly terrigenous, clastic sediments on a slowly subsiding shallow-water cratonic platform. The Michigan River system passed through the Michigan basin region, depositing mostly fluviatile and upper delta-plain sediments there. The river system with its delta plain and widespread coal-swamp deposits repeatedly prograded into the shallow-marine environments of the Eastern Interior basin, where thin but widespread bioclastic carbonates were accumulating. The cyclothemic character of the Pennsylvanian rocks here is the result of this repeated southwestward regressive progradation of at least 51 delta and subdelta sequences. Erosion of the latest Pennsylvanian sediments prevents us from deducing precisely when Carboniferous deposition ceased. A gradual shift took place from deposition of orthoquartzite sandstones in Late Mississippian–Early Pennsylvanian rocks to subgraywacke sandstones in the Middle and Late Pennsylvanian rocks. The terrigenous sediments of the Eastern Interior basin were derived largely from the tectonic borderlands of the northern part of the Appalachian basin and were transported west and southwestward by the Michigan River system. Throughout Carboniferous time, the Eastern Interior basin was connected across the shallow-marine cratonic platform with the Appalachian geosyncline to the east, the midcontinent basin to the west, and the deepening Ouachita geosyncline to the south.