Sandstone-Carbonate Cycles in Tensleep Formation, Eastern Bighorn Basin and Western Powder River Basin, Wyoming: ABSTRACT

Abstract

Outcrop and core study of the Tensleep Formation in the eastern Bighorn basin and western Powder River basin has revealed cyclic deposits of eolian sandstone and marine carbonate. These cycles, several meters to tens of meters thick, represent the rise and fall of sea level on the Wyoming shelf during Pennsylvanian and Early Permian time. Falling sea level was marked by development of a sharp scour surface at the base of each cycle and progradation of eolian dunes over an exposed, shallow carbonate shelf. Subsequent sea level rise resulted in the reworking of eolian sand through wave activity and burrowing organisms. Subtidal carbonates overlies the reworked eolian sands and are sandy at the base, grading upward into fossiliferous dolomite mudstones to wackestones. The sharp scour surface, normally present directly on the subtidal carbonates, indicates that erosion eliminated any regressive marine deposits by deflation to the ground-water table during shoreline progradation or by deflation related to abrupt drop in sea level. Relative sea level changes on the low-relief Wyoming shelf affected large areas during Tensleep deposition. This resulted in widespread sandstone-carbonate cycles that provide the basis for regional correlations of the Tensleep Formation throughout the eastern Bighorn basin and western Powdermore » River basin.« less