INVESTIGATION OF AN UNSTABLE PLATFORM MARGIN AMIDST INCIPIENT FORELAND BASIN DEVELOPMENT: LATE MISSISSIPPIAN SLUMPING ALONG INHERITED STRUCTURES IN THE EASTERNMOST ARKOMA BASIN

Reactivation of inherited rift margin structures is often invoked to explain patterns of subsidence during foreland basin development. Furthermore, lateral variations in such reactivation can affect the distribution of depositional processes. The Arkoma Basin, which formed during the final phase of Pangean assembly, provides an opportunity to investigate how structural inheritance influences foreland basin depositional systems. From Early to Middle Pennsylvanian, previous research documents east to west migration of flexural extensional subsidence that reactivated inherited structures of the Neoproterozoic-Cambrian Reelfoot rift. Furthermore, previous authors have interpreted thickness changes in Late Mississippian rocks (e.g., the Fayetteville Shale) of the eastern Arkoma Basin to indicate syndepositional fault movement along inherited structures. We document a concentrated zone of slumping during Fayetteville Shale deposition that is along the eastern basin margin and is consistent with a record of early basin tectonic activity that reactivated ancient structures.

The zone of concentrated slumping within the Late Mississippian Fayetteville Shale occurred on the starved outer ramp of a carbonate-shale system. It is parallel to, and directly west of the NE-trending, Mississippi River embayment bounding structure of the Reelfoot rift. Although slope instability in outer ramp environments can be an autogenic process, the spatial distribution of this swath of instability and the sediment starved character of the Fayetteville Shale suggest syndepositional fault reactivation as a possible driver of slumping. We present a stratigraphic framework, primarily from well log data, that details predictable sequence stratigraphic correlations, stratal thickness trends, and facies relations inboard of the eastern basin margin. Conversely, along that margin, the Fayetteville Shale exhibits highly variable log character and interval thickness patterns. We explore the possible drivers of these Late Mississippian stratigraphic features within the incipient foreland basin in relation to inherited rifted margin structures, the approaching Ouachita orogenic belt to the south, and early southern Appalachian orogenesis to the southeast.