USGS - science for a changing world

Mineral Resources On-Line Spatial Data

Mineral Resources > Online Spatial Data > Geology > by state > Texas

Wilberns Formation showing Point Peak, Morgan Creek Limestone, and Welge Sandstone Members, undivided

Wilberns Formation showing Point Peak, Morgan Creek Limestone, and Welge Sandstone Members, undivided
StateTexas
NameWilberns Formation showing Point Peak, Morgan Creek Limestone, and Welge Sandstone Members, undivided
Geologic agePhanerozoic | Paleozoic | Cambrian-Furongian
Original map labelCpw
CommentsFrom the top down, this map unit (excluding the uppermost stratigraphic member of the Wilberns Fm., the San Saba Member) includes the Point Peak Member, Morgan Creek Mbr., and Welge Sandstone Mbr. (descriptions that follow are from the Llano Sheet of Geologic Atlas of Texas (1981). Point Peak Mbr. is siltstone, limestone, and shale. Chiefly siltstone containing abdt. authigenic feldspar,mostly laminated, lower part lacks bioturbation; ls. consists of aphanitic stromatolitic bioherms, beds of introformational conglo., and granular ls. beds, one of which conains silicified Plectotrophia and alate Billingsella; shale mostly silty, grayish-green; thickness 25 to about 200 ft. thins SE-ward, also thin in the west area where stromatolitic biohersms included in the San Saba Mbr. probably started growth in the upper of the Point Peak Mbr. Morgan Creek Limestone Mbr.-- thickly to thinly bedded, granular, glauconitic, pink to redish-brown in basal part, upward gray to greenish-gray and brownish-gray with a recurrence of reddish-brown in the upper few feet in the northeast area; a few beds of stromatolites and some siltstone in the upper part, trilobites throughout and calcareous brachiopods in the upper part; thickness about 115 to 145 ft. Welge Sandstone Mbr.--thickly bedded, nonglauconitic to sparingly glauconitic in the eastern area, medium-grained, brownish-yellow; grades upward into Morgan Creek Limestone; forms a low scarp; thickness 20 to 25 ft.
Primary rock typelimestone
Secondary rock typemedium-grained mixed clastic
Other rock typesconglomerate; siltstone
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)ls. consists of stromatolitic bioherms, beds of intraformational conglo., and granular ls. beds
Minor
Sedimentary > Clastic > Sandstone (Bed)Thickly bedded, medium-grained sandstone chiefly in Welge Sandstone Member of Wilberns Fm.
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Siltstone (Bed)Point Peak Mbr. chiefly siltstone containing authigenic feldspar
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.
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 coverageBlanco - Burnet - Gillespie - Llano - McCulloch - Mason - San Saba

Show this information as [XML] - [JSON]

AccessibilityFOIAPrivacyPolicies and Notices

Take Pride in America logoUSA.gov logoU.S. Department of the Interior | U.S. Geological Survey
URL: http://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=TXCApw;0
Page Contact Information: Peter Schweitzer