Pecan Gap Chalk

Pecan Gap Chalk
State Texas
Name Pecan Gap Chalk
Geologic age Late Cretaceous; Gulfian Series
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Carbonate (Bed)chalk
Minor
Sedimentary > Clastic > Sandstone (Bed)limesand
Sedimentary > Clastic > Mudstone > Claystone (Bed)
Comments In East Texas and Gulf Coast to Rio Grande- Sherman Sheet (1967) in Collin County, upper 45 ft limest. in alternating intervals of soft, light to med. olive-gray limesand and hard, granular, dk bluish-gray limest., glauconitic with most of it in limesand, phosphate pebbles throughout, thin to v thin beds, limesand minutely cross-bedded; marine megafossils abdt; southward limesand replaced by calcar, silty clay; grades east in Hunt Co. and beyond to chalk. Thickness 50-70 ft. In Texarkana Sheet (1966) unit is chalk, in part clayey and sandy, sl. bituminous, glauconitic, phasphatic at base; thickness 120 ft. On Waco Sheet (1970) unit is chalk in lower part grading up to chalky marl; thickness 215 ft. In north, central, and south Texas including Quaternary for all of west Texas- chalk and chalky marl, v. lt. yell to yell-brn, Exogyra ponderosa common; thickness 100-400 ft thick on San Antonio Sheet (1974).
References

Bureau of Economic Geology, 1967, Sherman 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.

Bureau of Economic Geology, 1970, Waco Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.

Bureau of Economic Geology, 1974, San Antonio Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.

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.

NGMDB product
Counties Bell - Bexar - Caldwell - Collin - Comal - Delta - Falls - Fannin - Guadalupe - Hays - Hill - Hunt - Lamar - Limestone - McLennan - Medina - Milam - Red River - Rockwall - Travis - Williamson