Tesnus Formation (TXPAMt;0)

State	Texas
Name	Tesnus Formation
Geologic age	Phanerozoic \| Paleozoic \| Carboniferous Mississippian-Late Pennsylvanian-Early
Original map label	IPMt
Comments	Exposed most extensively in Marathon region, Brewster Co., and in the 5-mi-diameter Solitario Uplift on Presidio-Brewster Co. line. (fr. Ft. Stockton Sheet, 1982) In SE (Marathon area) upper 5,000 ft, deep-water sediments, thin to thick bedded ss. and sh., with massive white quartzite intervals in upper part; lower 2,000 ft sh. In NW (Marathon area) nearly all blk sh. with few ss. beds, about 300 ft thick; thickness of formation 300-7,000 ft. (fr. Emory Peak-Presidio Sheet, 1979) Ss. and sh., sandst. fine grained, in part quartzitic, thin bedded, greenish brn. weathers rusty brn to olive gray; shale hard fissile, chloritic, green red, brn., blk; some arkose, chert, basal conglo., turbidity current boulder beds; thickness several thousand ft. crops out in Solitario Uplift, base of Santiago and Cochran Mtns. and at intervals eastward to headwaters of San Francisco Creek. (fr. Udden and others, 1916) at base of unit is Rough Creek Shale mbr. (obsol.) 865 ft thick of hard compact, brittle, dk-green occasionally blk shale. Above are ss., sh., chert, and a few lenticular layers of conglomerate. The ss. are soft to highly indurated, thin bedded to massive. Dense blk to brnish blk chert in thin layers.
Primary rock type	medium-grained mixed clastic
Secondary rock type	fine-grained mixed clastic
Other rock types	chert; arkose; conglomerate
Lithologic constituents	Major Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed) Sedimentary > Clastic > Sandstone (Bed) Sedimentary > Clastic > Mixed-clastic > Sandstone-Mudstone (Bed)some conglomerate, arkose, chert
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, 1982, Fort Stockton Sheet, Geologic Atlas of Texas, University of Texas at Austin, scale 1:250,000. Bureau of Economic Geology, 1979, Emory Peak--Presidio Sheet, Geologic Atlas of Texas, University of Texas at Austin. Udden, J.A., Baker, C.L., and Bose, E., 1916, Review of the geology of Texas: Bulletin of the Unviersity of Texas, no. 44.
Geographic coverage	Brewster - Pecos - Presidio