Regional Lithostratigraphy of Permian Phosphoria Formation, Western Overthrust Belt: ABSTRACT

Abstract

A regional synthesis of the lithostratigraphic relationships for the Permian Phosphoria Formation illustrates the cyclic lithofacies types, carbonate reservoir, and potential organic facies for the western Overthrust belt of Wyoming, Idaho, and Utah. Palinspastically restored subsurface control sections (70) and measured outcrop sections (35) indicate a complex, intertonguing, transgressive-regressive sequence of shallow-water carbonates, clastics, and highly organic phosphatic mudstone deposited in a shallow marine shelf-margin environment. Distribution of facies types was affected by paleostructural growth of late Paleozoic structural elements including the Sublette basin of Utah and Bannock highs of western Wyoming-southeastern Idaho. These highs helped define the Wyom ng shelf-margin slope. Identification of paleostructural growth is based on interpretation of depositional environments and thickness patterns of the Permian deposits. The Phosphoria Formation and the equivalent beds of the Park City Formation are divisible into two main depositional cycles--the Meade Peak-Franson Members and the Retort-Ervay Members--based on the regional correlation network generated for the Overthrust belt. Carbonate deposition and reservoir development occurred during maximum transgressive stages, whereas deposition of phosphorite and organic shales occurred during maximum regressive stages. The reservoir facies is closely associated with early diagenetic dolomitization of carbonate shelf deposits concentrated along paleostructural high areas of the shelf-margin environment. End_of_Article - Last_Page 952------------