Presidio Formation

Presidio Formation
State Texas
Name Presidio Formation
Geologic age Early Cretaceous; Aptian; Albian Series
Lithologic constituents
Major
Sedimentary > Clastic > Conglomerate (Bed)
Minor
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Comments Conglomerate, limestone, sandstone, and siltstone. A basal well indurated pebble to boulder conglomerate, 30-80 ft thick grades upward to sandstone and siltstone, overlain by impure carbonate rocks, calcar sandst, and siltstone. Thickness about 400 ft+-. Ross (1943, p. 66) mapped five subdivisions, from base up, 1) 50-90 ft of soft marl, clay, thin-bedded sandy ls., calcar sandst. and shell breccia (missing locally), 2) 90-120 ft conglo., sandy ls., calcar. sandst., and a few beds of shale and marl. 3) 'tripartite unit' massive ls., calcar sandst., thinbedded ls., thin beds of shall breccia (Ostrea), 4) shell-breccia unit of 110-165 ft of soft sandst. interbedded with thin beds of sandy ls., hard clacar sandst., marl, shale, and shell breccias, 5) resistent unit of 25-50 ft of hard sandy to pure ls., with some beds of calcar. sandst. Total thickness 436 ft measured.
References

Bureau of Economic Geology, 1979, Emory Peak--Presidio Sheet, Geologic Atlas of Texas, University of Texas at Austin.

Ross, C.P., 1943, Geology and ore deposits of the Shafter mining district, Presidio County, Texas: U.S. Geological Survey Bulletin 928-B, 125 p.

https://pubs.er.usgs.gov/publication/b928B

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 Presidio