Stratigraphic and environmental study of Chispa Summit Formation Upper Cretaceous

Rocks of Cenomanian and Turonian age in the northern Tierra Vieja Mountains, West Texas, consist of thick shale and flaggy limestone and sandstone interbeds. Evidence obtained through the study of microfossils and ammonites indicates that the lower portion of the Gulfian section, the Chispa Summit Formation, is equivalent to the Boquillas Formation of the Big Bend and Kent-Davis Mountain areas.