Tanyard Formation

Tanyard Formation
State Texas
Name Tanyard Formation
Geologic age Early Ordovician
Lithologic constituents
Major
Sedimentary > Carbonate > Dolostone (Bed)
Sedimentary > Carbonate > Limestone (Bed)
Comments (from Cloud and others, 1943) name given to rocks at base of Ellenburger Group exposed at the Tanyard, the section on east bank of Buchanan Lake aoopsite mouth of Jim John Crk., NW Burnet Co., TX on the Llano uplift. Consists of dolomite and limestone and is thickest at west side of uplift and thinnest on east side. Dolomite is gray, irreg. bedded, fine- to coarse-grained, vuggy to porous. Limestone is gray, sublithographic, thick- to thin-bedded, weathers rought or smoothlyirregular to pitted, craggy. Ls. is present mainly in upper and lower parts of the unit, whereas dolomite is mostly present in the middle. (from Llano Sheet of Geologic Atlas of Texas, 1981) Upper part, Staendebach Mbr--ls. and dolomite, thickly to thinly bedded, cherty; ls. aphantic, v. lt. gray; dolo. mostly fine- to medium-grained, lt.-gray to yellowish-gray and brownish-gray; gastropods, cephalopods, and trilobites preserved in chert. Lower part, Threadgill Mbr.--dolomite and ls., thickly to thinly bedded, sparingly cherty; is eastern area dolo. predominates, medium- to coarse-grained, lt-gray, locally greades laterally to massive, v. lt-gray ls., lower part is Cambrian in age; in western area mostly ls., aphanitic, lt-yellowish-gray, gastropods common. Thickness of Tanyard Fm. 525-660 ft, thins westward, locally missing by truncation in NW area.
Stratigraphic units Ellenburger Group, Tanyard Fm. divided into Threadgill and Staendebach Members
References

Bureau of Economic Geology, 1981, Llano sheet, Geologic Atlas of Texas, Bureau of Economic Geology, University of Texas at Austin, scale 1:250,000.

Cloud, P.E., Jr., Barnes, V.E., and Bridge, Josiah, 1946, Stratigraphy of the Ellenberger group in central Texas--a progress report, in Texas mineral resourses: University of Texas Publication 4301, p. 133-161, [1945].

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 Blanco - Burnet - Gillespie - Kimble - Lampasas - Llano - McCulloch - Mason - Menard - San Saba