STRATIGRAPHIC EVIDENCE INDICATING SYNDEPOSITIONAL FAULTING ALONG THE CASS FAULT SYSTEM IN THE SOUTHERN OZARKS, NORTHWESTERN ARKANSAS

The Cass Fault system of north-central Arkansas is composed of monoclines and normal faults that strike in an east-west direction. This complex structural system forms a transitional boundary between the North Arkansas Structural Platform (NASP) to the north and the Arkoma basin to the south. Paleozoic strata of the structural platform are essentially horizontal. The Arkoma basin south of the Cass system is characterized by south-dipping normal faults that extend into the Precambrian basement. During the late Pennsylvanian Period, tectonic activity associated with the Ouachita orogeny created four main structural and physiographic areas: the Ouachita Fold Belt, Arkoma Basin, NASP, and Ozark Uplift.

Due to the tectonic activity of the Cass system at the northern margin of the Arkoma basin, variable structural orientations are visible at land surface and influence the Cass present-day appearance. Previous investigations have provided insight regarding the depositional history, activity and geology of the Ouachita Fold Belt, Arkoma Basin, NASP, and Ozark Uplift. However, with regards to the Cass system, aside from its stratigraphy, there is a dearth of information available to the precise age of system.

This research based primarily on the construction of structural maps, structural calculations, example regional dip determination and borehole log interpretation provides a morprecise timeframe regarding the depositional and structural history of the Cass system. It was determined that erosion on the uplifted side of faults within the Cass and the deposition of coarse material immediately adjacent to the faults on the down dropped side occurred. Consequently, the orientation and variations of Morrowan strata thickness indicative of down-to-the-south faulting within the Cass system during the late Mississippian and early Pennsylvanian periods provided evidence corroborating syn-depositional normal faulting along the Cass fault system.