SURFACE AND SUBSURFACE LITHOSTRATIGRAPHY OF DEVONIAN SUCCESSIONS, NORTHERN ARKOMA BASIN, OKLAHOMA AND ARKANSAS

The Devonian System is represented in the northern Arkoma Basin of Arkansas and immediately adjacent Oklahoma by three unconformity-bounded units designated the Penters Chert, Clifty Formation and Chattanooga Shale in ascending order. In Arkansas, these units are assigned Lower, Middle and Upper Devonian/Lower Mississippian ages respectively, although biostratigraphic data are meager. Subsurface analysis of the units indicates that the Penters Chert is developed pervasively as a blanket deposit of penecontemporaneous chert and calcisiltites reflecting transgression of an outer shelf-lower ramp setting. Thickening-thinning relationships do not seem to reflect depositional topography by instead are related to post-Penters erosion. Chert lithology mirrors that of the lower Boone Formation suggesting a volcanic source of the silica, and deposition below the sediment-water interface while the calcisiltites were still poorly indurated. Initiation of basin formation following Penters deposition tilted what was to become the north limb of the Arkoma Basin and turncated its presumed shallow water equivalents, and devloped a karsted surface on the Penters and older strata. Thin orthoquartzitic sandstones and associated shallow water, dolomitic, carbonate mudstones of the Clifty Formation were deposited on the karsted surface at the top of the Lower Devionian section. Their distribution is unpredictable, and most knowledge of the interval is based on widely scattered outcrop exposures. The well-known Upper Devonian transgression across the southern midcontient is marked by black shale deposition of the Chattanooga Shale, and its thin, basal, phosphatic quartz sandstone Sylamore Member. Subsurface distribution of the Chattanooga also develops a predictable blanket geometry similar to the Penters, but in the outcrop belt, pronounced thickening-thinning relationships reflect the maturely karsted surface developed on the Penters and older strata across the northern Arkoma Basin.