CARBONATE TEXTURES AND MICROORGANISMS OF OLIGOCENE FRESHWATER LIMESTONE IN BREWSTER COUNTY, TEXAS

Outcrops of freshwater limestones are exposed near Elephant Mountain and Sul Ross State University in Brewster County, Texas. Six separate outcrops were described along Texas state highway 118 south of Alpine, Texas and one other outcrop was described at the base of “Bar S R Bar” hill adjacent to the campus of Sul Ross. These outcrops of limestone, which lie stratigraphically between the Pruett Tuff and the Sheep Canyon Basalt, contain textures that include packstones of varying degrees from tightly to loosely packed. Some textures include peloidal to oolitic packstones where as some others were varying degrees of grainstones. The “Bar S R Bar” Hill outcrop, produced samples with carbonate textures which included wackestones with intermittent lenses of packstones, in which allochems were dominantly made up of fragmented mollusk shells. Thin sections have shown clasts that have been identified as reworked and recrystalized material that is commonly found in littoral zones. Bivalves, oncolites, ostracods, and Goniabasis sp. have also been identified in most of the described sections.