Geology of the Mercury Quadrangle, McCulloch County, Texas

Abstract

A new map showing detailed geology of the Mercury quadrangle, and 18 detailed, newly measured and described stratigraphic sections within the quadrangle are the main part of this paper. Lower Ordovician, Mississippian, Pennsylvanian, Cretaceous, and quaternary strata are exposed. Pennsylvanian beds unconformably overlap older Paleozoic formations, and Cretaceous formations truncate Pennsylvanian strata. Sandstone and conglomerate channel deposits, occurring at many levels in the Pennsylvanian sequence, are interpreted as indicators of repeated uplift and erosion of nearby land areas. These irregular deposits complicate accurate correlation of marker beds. Limestone reefs are found in three zones in the upper Canyon series. Interpretation of these limestone masses as reefs permits clarification of several correlation problems. The development of reefs, one above another along northeast southwest trends, suggests shallow, warm, clear water conditions of deposition. The nomenclature of the Canyon series is simplified by elevating former member names to formational rank. The Corn Creek limestone member of the Placid formation is the only new name proposed. Lower Paleozoic beds are folded broadly into the Hall uplift in the southwestern part of the quadrangle. Strawn, Canyon, and Cisco beds, covering 60 percent of the quadrangle, dip northwestward 60 feet per mile, and Cretaceous strata in the southwestern part of the area dip southward 10 feet per mile.