Marine Carbonate Embayment System in an Eolian Dune Terrain, Permian Upper Minnelusa Formation, Rozet Area, Powder River Basin, Wyoming: ABSTRACT

Abstract

The eolian origin for Minnelusa sandstones has been stressed in numerous published articles. However, the dolomites that are interbedded with the eolian sandstones have received little attention. Isopach mapping of one of the dolomite units (Dolomite I) reflects a marine embayment system whose individual embayments range from 1/2 to 1 mi in width and trend primarily in a northwest direction. Consistently the embayment dolomites pinch out against the flanks of reworked, low relief, broad, eolian dune ridges. So far, 108 mi/sup 2/ of the Dolomite I marine embayment system have been mapped, but the overall extent of the system is undoubtedly much greater. Dolomite I is rarely cored, but cores from stratigraphically higher embayment dolomites in the upper Minnelusa show that these dolomites display the following, shoaling-upward sequence: (1) subtidal, sparingly fossiliferous dolomite; (2) intertidal, algal-laminated or brecciated or mud-cracked dolomite; and (3) very thin, supratidal, nodular anhydrite. The embayments, therefore, became the sites of marine sabkhas located between eolian dunes. Two main conclusions emerge from this study: (1) the juxtaposition of eolian sandstones and marine dolomites in a tectonically stable area suggests that eustatic sea level changes and a very arid climate were responsible for the marked environmental andmore » lithologic changes observed in the upper Minnelusa, and (2) arid, coastal, evaporitic sabkhas bordered by eolian dunes are known from a number of modern and ancient cases, but marine carbonate embayments and associated evaporitic sabkhas that penetrate deeply into eolian sandstone terrains are rare.« less