Facies Distribution of Hosston Sand, Central Texas--Implications to Low-Temperature Geothermal Waters: ABSTRACT

Abstract

Electric-log patterns indicate that the Hosston Formation of central Texas consists of four principal facies: (A) massive sandstones greater than 80 ft (24 m) thick, (B) distinct sandstones 10 to 80 ft (3 to 24 m) thick interbedded with sharply defined shale breaks, (C) sandstones less than 10 ft (3 m) thick intercalated with shale and siltstone beds, and (D) thin calcareous (dolomitic?) beds with interbedded shale and siltstone. Facies A shows characteristics of fluvial sands, B of either deltaic or strand associations, C of interdistributary and overbank mud and silt deposits, and D of shallow intertidal to supratidal low-energy environments. Cross sections show facies A and B to be concentrated on and north of the San Marcos platform, whereas facies D is present farther downdip. Distinctive sequences of facies B with superposed facies D occur between these two belts. Facies C is somewhat erratic in its distribution. Warm waters are currently being produced from the A and B facies. The nature and distribution of the C and D facies probably preclude their use as a geothermal resource. End_of_Article - Last_Page 1607------------