Pen Formation

Pen Formation
State Texas
Name Pen Formation
Geologic age Late Cretaceous
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Claystone (Bed)
Incidental
Sedimentary > Clastic > Sandstone (Bed)
Comments Equivalent to upper part of Austin Chalk. mostly clay, gray, yellow, calcareous, and sandstone beds in upper part. lower 50 ft contains inch-thick chalk beds, concretions throughout, marine fossils throughout, Exogyra ponderosa common; 219-700 ft thick in Big Bend N.P., 1,000 ft thick in Terlingua area, mapped in south Brewster County.
References

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

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 Brewster - Presidio