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San Miguel Formation

San Miguel Formation
StateTexas
NameSan Miguel Formation
Geologic agePhanerozoic | Mesozoic | Cretaceous-Late [Gulfian]
Original map labelKsm
CommentsSandstone, limestone, and clay; fossilif. sand, sandy ls., and unfossilif. clay superficially like the underlying Upson, clay increases in amount upward; fossils include Exogyra ponderosa and many other marine megafossils; thickness about 400 ft in Crystal City-Eagle Pass area, 800 ft in Del Rio area.
Primary rock typesandstone
Secondary rock typelimestone
Other rock typesclay or mud
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone (Bed)
Minor
Sedimentary > Carbonate > Limestone (Bed)
Unconsolidated > Fine-detrital > Clay (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, Crystal City-Eagle Pass Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1977, Del Rio Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Geographic coverageKinney - Maverick

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