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Washita and Fredericksburg Groups, undivided

Washita and Fredericksburg Groups, undivided
State Texas
Name Washita and Fredericksburg Groups, undivided
Geologic age Phanerozoic | Mesozoic | Cretaceous-Early [Comanchean]
Comments Washita Group--alternating thick clay units and thin limestone units; clay, calcar, commonly sandy, dk bluish gray and black; limestone in lower part hard, bluish gray to shtie, in upper part soft, thickbedded; marine megafossils; thickness 200 ft. Fredericksberg Group--Limestone,dolomite,chert, marl. Limestone nodular, aphanitic, marly, gray, yell, white, pink; dolomite, find grained, gray; chert, in thin layers and nodules; marl locally gypsiferous, gray. abundant Exogyra texana some beds made almost entirely of Gryphaea sp., exposed thickness 50 ft in Hobbs Sheet (1976).
Primary rock type clay or mud
Secondary rock type limestone
Other rock types dolostone (dolomite); chert
Lithologic constituents
Major
Unconsolidated > Fine-detrital > Clay (Bed)
Minor
Sedimentary > Carbonate > Limestone (Bed)
Incidental
Sedimentary > Carbonate > Dolostone (Bed)
Map references
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references
Bureau of Economic Geology, 1976, Hobbs Sheet, Geologic Atlas of Texas: University of Texas at Austin, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1966, Texarkana Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Counties Brewster - Pecos