BASINAL SUBSIDENCE AND SEDIMENT SOURCE AS REFLECTED IN MORROWAN (EARLY PENNSYLVANIAN) STRATA: ARKOMA BASIN, ARKANSAS

The Arkoma basin is a Paleozoic structural feature in the Ouachita foreland that extends from central Arkansas and westward into southeastern Oklahoma. The basin fill is asymmetric with Paleozoic strata approaching 7000 meters in thickness at the southern margin. Northward, the section thins dramatically onto the Ozark uplift. Carbonate rocks ranging from Cambrian to Middle Mississippian in age, accumulated on a stable platform that that extended southward from the Ozark uplift through central Arkansas and beyond, prior to basin formation. Ouachita orogenic activity induced a pattern of basin subsidence from south to north along east trending down-to-the south normal faults that were syndepositional in the central and northern part of the basin and influenced sedimentological effects in rocks of Morrowan age. These effects were contemporaneous with east to west changes in sedimentary facies related to sediment source and volume.

Cross sections based upon wire line logs and surface data were used to construct a series of north to south cross sections, as well as along strike west to east cross sections. Calcareous sandstone and sandy limestone beds within the Hale and Bloyd formations (Morrowan) pass eastward along strike into non- calcareous sandstone and shale. The section thickens reflecting an eastern source dominated by terrigenous sediment. North to south cross sections display thickening on the downthrown side of normal faults, particularly with sandstone and shale units. Morrowan strata document the initiation of Arkoma basin subsidence during early Pennsylvanian time and reflect an eastern source of terrigenous sediment to the Arkoma shelf.