Abstract

The Siluro-Devonian rocks that crop out in the Ouachita folded belt in westcentral Arkansas were deposited during a period of tectonic inactivity. It is thought that the early phase of geosynclinal development is characterized by deposition of quartzose sandstones and carbonates, followed by a series of black carbonaceous shales, with associated bedded cherts. This latter portion of the sequence has been termed the euxinic facies, and this entire early phase is considered tectonically stable. The Siluro-Devonian rocks represented in this phase are the Blaylock Sandstone, the Missouri Mountain Slate, and the Arkansas Novaculite. The bedded siliceous sediments of this sequence are thought to be primary deposits, at least partly biochemical in origin, which probably were deposited in relatively shallow-water. The Siluro-Devonian rocks may be thought of as comprising an integral portion of the core of the Ouachitas.