The Lower Cretaceous Draney Limestone, a lenticular carbonate sequence well exposed throughout the Overthrust belt in western Wyoming and southeastern Idaho, records deposition in an extensive, shallow, low-salinity lacustrine system that minimally covered 30,000 sq km. The predominant lithologies of calcareous mudstone, micrite, intramicrite, and biomicrite contain a lacustrine biota composed predominantly of ostracods and the calcareous alga Chara, with less common bivalves and gastropods. The continuity of the Draney throughout the area indicates that this lake was a more or less continuous body of water throughout deposition. Individual units within the Draney, however, cannot be correlated over large distances; this fact suggests significant local chemical and/or phy ical variations within the lake basin during carbonate deposition.

The lake appears to have been relatively shallow throughout its extent, as evidenced by the presence of winnowed sandy biomicrite and the ubiquitous Chara, which in modern systems is restricted to shallow photic zones. Limonitic calcareous mudstones which exhibit well-developed calcite boxwork fabrics and vugs filled with calcite spar indicate infrequent subaerial exposure and alteration of lake sediments. Modern playa systems do not serve as a satisfactory analog to the Draney lake because features indicative of (1) frequent subaerial exposure, (2) deposition in exceedingly shallow water, or (3) coprecipitation of more evaporitic minerals have not been observed in the Cretaceous sections. On the contrary, lithologic, faunal, and floral features of Draney strata are more nearly identi al to those of marl deposits in modern, temperate-region, hardwater lakes. Therefore, Cretaceous carbonate deposition under somewhat similar conditions is suggested.

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