Significance of variations among ancient deltaic deposits in the Arkoma Basin, North-Central Arkansas

Abstract

The Arkoma Basin is one of several foreland basins formed in association with the Ouachita orogeny. The Arkoma Basin has been studied in depth with regard to stratigraphy, depositional environments, structure and its relationship to the Appalachian-Ouachita orogenic event. This study focuses on the variability of the deltaic deposits within the Arkoma Basin and the significance of the variables to both the delta complex and the overall tectonic setting. The specific characteristics to be investigated include variations in paleocurrent directions, bed thicknesses, bed geometries, organic contents, sand/shale ratios, mineral assemblages and fossil assemblages. In the case of the Arkoma deltaic deposits, bed thickness is a function of the duration and rate of the depositional event, assuming no scour has occurred. Bed geometry is controlled by the location of the deposit within the delta complex. The organic content, and thus trace fossil abundance, is controlled by the course of the river, as well as wave and tidal influences on the delta. The mineral assemblages are determined by the composition of the parent rock as well as the effects of weathering as the sediments are transported. Paleoflow in a deltaic system is controlled by the course of the river as well as specific branching of distributary channels. Traditional QFL data have been unable to resolve the conflict over source area. Two source areas have been proposed for this system: 1) a northern cratonic source and 2) an eastern Appalachian source. Detrital tourmaline chemistry provides an alternative method for determining provenance in this system. Tourmaline analysis suggests an eastern Appalachian source is more probable.