ABSTRACT

A 90-foot interval in six stratigraphic sections in the Big Goose and Little Tongue Members of the Mission Canyon Limestone contains 11 microfacies grouped into three facies associations: supratidal; intertidal, subdivided into upper and lower zones; and lagoonal, subdivided into inner and outer zones. Lime mud-rich, generally mud-supported, facies represent deposition in the supratidal, intertidal and inner lagoonal environments and are the dominant lithologies in all sections except at West Stillwater River where deposits of the outer lagoon are more common. Laminated, peloidal, intraclastic and skeletal lime mudstones and wackestones, and crystalline dolomites reflect the relatively restricted conditions of the shallow Osagean shelf sea. Many of these facies contain a sparse biota, cryptalgal structures and pseudomorphs after evaporite minerals. Three skeletal and ooid grainstone facies are deposits of small sand shoals in the outer lagoon. Several shallowing-upward sequences are superimposed upon the apparent major transgression onto the Wyoming shelf.