Stratigraphy and Sedimentology of the Morrison Formation in the Western Panhandle of Oklahoma with Reference to the Historical Stovall Dinosaur Quarries

Abstract

New investigations of the Morrison Formation in the western Oklahoma panhandle reveal that the formation is approximately 60 m thick near Kenton, considerably less than historical measurements. We provide a new isopach map of the Morrison Formation at the basin margin and divide the formation into three new members based on geological, geochemical, petrographic, and paleontological characteristics. Each member is defined by unique depositional facies recording a variable climatic signal and the eventual progradation of the distributive fluvial system to the basin margin. Analogous depositional facies and lithologies of these units suggest they are lateral facies successions of the well-established members of the Colorado Plateau. The Cimarron Member is composed of numerous small, ephemeral, clastic lakes at the distal margin of the alluvial braid plain of the Tidwell Member. The Boise Member consists of numerous perennial limestone lakes at the distal edge of the Salt Wash Member distributive fluvial system. At the top of the member, the lake coalesced into a large lake, herein termed Lake Stovall. The Kenton Member records the progradation of the Brushy Basin Member distributive fluvial system to the basin margin in Oklahoma. Kenton Member fluvial deposition was by small, isolated, anastomosing fluvial channels and their associated splays. The gradual progradation of facies to the basin margin signifies that deposition in the foreland basin was geographically extensive and protracted. Dinosaur fossils excavated during the 1930s are placed into a stratigraphic framework. All quarries lie in the basal 6 m of the Kenton Member. Depositional facies and taphonomic data imply the dinosaurs died during a series of severe droughts. Bone dispersal and burial resulted from ephemeral flood splay events.