New Evidence for Dating Carboniferous Flysch Deposits of Ouachita Geosyncline, Arkansas and Oklahoma: ABSTRACT

Abstract

Ammonoids and other invertebrate fossils from the Stanley Shale, Jackfork Sandstone, and Johns Valley Shale provide new information on the ages and correlations of these three stratigraphic units. The Stanley Shale is Late Mississippian (Chesterian) in age through most of the Ouachita Mountains region, except for a basal part, approximately 75 ft thick, of probable Meramecian age. In Saline and Perry Counties, Arkansas, Pitkin Limestone fossils, most of them in reworked boulders, are present about 500 ft below the top of the Stanley. Near Little Rock, Arkansas, ammonoids in the upper part of the Stanley represent the Reticuloceras tiro zone of the lower Hale. The Jackfork Sandstone is of Early Pennsylvanian (Morrowan) age in Arkansas, but near Talihina, Oklahoma, its basal plant-bearing beds are of Late Mississippian (Chesterian) age. Cymoceras, an early Morrowan ammonoid genus, has been recognized in the lower part of the Jackfork near Amity, Arkansas. The Game Refuge Formation of Harlton at the top of the Jackfork has yielded Morrowan brachiopods and trilobites in Atoka County, Oklahoma. The Johns Valley Shale contains indigenous ammonoid assemblages representing the Branneroceras branneri, Axinolobus modulus, and Diaboloceras neumeieri zones. These three zones are present also in the type section of the Bloyd Shale, indicating a direct equivalence of the two formations. Masses of Caney Shale in the Johns Valley, some of them enormous, as well as boulders of Lower Ordovician to Lower Pennsylvanian rocks, were introduced largely by turbidity flow and gravity gliding. End_of_Article - Last_Page 719------------