ABSTRACT

In the extreme southern Laramie Basin the Casper Formation contains thin, lenticular limestones along low-relief truncation surfaces within the sandstone units. These limestones are of small geographic extent and, to date, have yielded no macrofossils. There are angular fragments of limestone laterally adjacent to the limestone lenses, and rounded pebbles of limestone occur in the lower part of some of the overlying sandstones. The limestones are ostracodal, peloidal, microsparites with massive, laminated, and disrupted fabric. Sparry calcite filled desiccation cracks, fenestral gas cavities, and burrow cavities are common, and there has been extensive stylolitization.

The limestones were precipitated in small, shallow ponds in which environmental conditions were harsh because of fluctuations in water temperature, depth and salinity. This interpretation of depositional environment suggests that Casper sediments in the southernmost Laramie Basin were at least periodically exposed to subaerial conditions.