Facies architecture of an arid depositional system within the El Reno group (Permian) of Western Oklahoma

Abstract

Deposits of the El Reno Group (Permian) of central Oklahoma are represented by the Flowerpot Shale, Blaine Formation, Dog Creek Shale, and Duncan Formation. These deposits were studied through geological mapping, measuring section, and analyzing thin sections and XRD data. The Duncan Formation represents proximal deposits that grade into distal deposits of the Flowerpot Shale, Blaine Formation, and Dog Creek Shale. The classic flooding sequence for the Blaine Formation is represented by: 1) inundation with lacustrine or possibly marine water resulting in the deposition of carbonate (dolomites), 2) evaporation of water to the point of gypsum deposition, and 3) mudstone deposition during periods of no water. Six facies were identified within the Duncan Formation: 1) mudstone conglomerate; 2) clay layers; 3) ripple-cross laminated very fine-grained sandstone; 4) fine to medium sandstone with large-scale low-angle trough cross beds; 5) clean fine-grained sandstone with high-angle trough cross beds and root casts; and 6) shale-mudstone. Analogs can be drawn between the El Reno Group and facies described in the Douglas Creek terminal splay of central Australia and other sabkha systems. This comparison supports an interpretation that the Duncan Formation was deposited on the edge of an intracontinental basin as a terminal splay complex and the other units of the El Reno Group represent deposits from a continental sabkha-like system. An arid-land depositional environment may provide a better analogue when trying to interpret the Red Beds of the North American mid-continent than traditional depositional models.