Tanyard Formation (TXOt;0)

State	Texas
Name	Tanyard Formation
Geologic age	Phanerozoic \| Paleozoic \| Ordovician-Early
Original map label	Ot
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.
Primary rock type	limestone
Secondary rock type	dolostone (dolomite)
Other rock types
Lithologic constituents	Major Sedimentary > Carbonate > Dolostone (Bed) Sedimentary > Carbonate > Limestone (Bed)
Map references	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
Unit 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.
Geographic coverage	Blanco - Burnet - Gillespie - Kimble - Lampasas - Llano - McCulloch - Mason - Menard - San Saba