Marine grass banks, a possible explanation for carbonate lenses, Tepee Zone, Pierre Shale (Cretaceous), Colorado

Massive carbonate lenses surrounded by shale comprise the Tepee Zone of the Pierre Shale (Cretaceous) in Pueblo and El Paso counties, Colorado. The limestone bodies, occurring as fields of "tepee buttes," are recrystallized pellet lime mudstones and wackestones characterized by Nymphalucina occidentalis and ammonites. Shale facies fauna is typically ammonites and Inoceramus sp., both of which also occur as minor components of the limestone. Sedimentary relations and faunal zonation of the two lithofacies indicate synchronous deposition. The limestone bodies are interpreted to represent lagoonal grass beds that supported a distinct biotic community. Holocene grass-stabilized carbonate mounds, accumulating in terrigenous dominated, shallow marine environments, appear analogous to these limestone bodies.