Distribution and Extent of Beds in Flysch Deposits, Ouachita Mountains, Arkansas and Oklahoma

Abstract

ABSTRACT The areal extent and distribution of individual beds in flysch are a matter of vigorous debate. The writers studied these problems by detailed investigation of lithologic variations in a stratigraphic interval between two tuffs in the lower Stanley Group of the Ouachita Mountains. A few key beds were recognized and compared in four stratigraphic sections; most individual layers are too discontinuous to be correlated over the area of approximately 20 by 40 km. The theoretical horizontal extent of sandstone and siltstone beds calculated from changes in their total and individual thickness between sections is limited to 20 to 60 km toward the north and east. A general northward decrease in the number and thickness of sandstone beds, in the sandstone to shale ratio, and in grain size in addition to the distribution of internal sedimentary structures and extent of tuff beds in the area studied indicate a southern, lateral source of sediment. The flysch beds probably were deposited in the form of a large fan. In addition to this regional pattern the vertical variation of proximal sandy facies and distal shaly facies was observed in each section. It is suggested that the sandy facies with granule conglomerate laminae, ripped-up pieces of shale, and plant debris was deposited in or near submarine channels, whereas the shaly facies with burrowed siltstone beds originated in a more quiet environment between channels. The migration of channels on a submarine fan may have been one factor influencing the distribution of these facies.