Strawn Group

Strawn Group
State Texas
Name Strawn Group
Geologic age Middle Pennsylvanian; Atoka and Des Moines Series
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Claystone (Bed)mostly mudstone with thin sandst. units and a few limest. lentils
Comments Unit redefined, renamed, or modified as described in at least 11 publications up to 1960 since orginally described by Dumble (1890) as alternating clays and shales and thin-bedded limestones, with fire clay and coal, overlying Richland-Gordon sandstones and underlying Brownwood-Ranger series. Mostly sh. and mudst., silty, greenish gray to red, mudcracks common, generally poorly exposed, underlies subdued topography, fossils include plants and marine magafossils locally; limestone beds generally impure and discontinuous, more abdt. near top; sandst. forms thin discontinuous sheets and small channel fills, fewer beds near top. Ricker Station Ls.(1-4 ft thick) and Capps Ls. (up to 20 ft thick) in upper part of Strawn GroupUpper part above Capps Ls. equivalent to Brownwood Shale (fr. Brownwood Sheet, 1976). Group 1300-1400 ft thick.
Stratigraphic units Mineral Wells Fm.(top), Garner Fm., and Millsap Lake Fm.(bse)(Sellards, 1933). (fr. Brownwood Sheet, 1976) Capps Limestone, Ricker Station Limestone, pre-Brazos River Fm undivided.
References

Cooper, G.A., and Grant, R.E, 1972, Permian brachipods of West Texas, I, in Smithsonian Contributions to Paleobiology no. 14.

Dumble, E.T., 1890, Texas Geological Survey 1st Annual Report, pl. 3, p. lxvi.

Plummer, F.B., and Moore, R.C., 1921, Stratigraphy of the Pennsylvanian formations of north-central Texas: University of Texas Bulletin 2132.

Bureau of Economic Geology, 1976, Brownwood sheet, Geologic Atlas of Texas, Bureau of Economic Geology, University of Texas at Austin, 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 Brown - Lampasas - McCulloch - Mills - San Saba