Abstract

The depositional and diagenetic history of the upper Madison to lower Amsden "sequence boundary beds" was investigated in a case study to reconstruct the environmental conditions during sea-level low-stand phases. Principally, this depositional interval is poorly recorded in upper platform positions and the diagenetic history of the boundary beds reveals valuable information concerning the long interval of shallowing and emergence of the platform. Emergence of the Madison platform in central Wyoming during the Meramecian coincides with diagenetic alteration of the late-highstand carbonate platform sediments, algal mat and stromatolite growth, and subsequent intense karstification. Carbonates reveal early diagenetic silicification with preference to organic structures on the surface. The silicification process is controlled by textural sediment properties. The source of silica is allogenic and reflects environmental change including weathering during this depositional interval. The infilling of the Darwin Sandstone occurs subsequent to silicification.