Abstract

Steeply dipping beds of mud-rich, bioclastic limestone and interbedded, fossiliferous, siliciclastic mudstone occur within the lower 4 meters of the Redwater Shale Member of the Sundance Formation at Garret Ranch in east-central (Natrona County) Wyoming. Features, such as the abundance of mud not related to in-filtering; lack of grain orientation; absence of erosive contacts and high energy sedimentary structures; paleoecologic dominance of Gryphaeid oysters and stratigraphic relationships that indicate a mound-like morphology, favor a biohermal/biostromal interpretation for the Garret Ranch lithosome and discount channel or shoal depositional models. Fabrics observed in bioclastic limestone flank beds of this feature suggest storm-wave modification of original biohermal sediments resulting in differential induration of variably mud-rich and mud-poor lithologies to form pseudo-foreset stratification.