barrier ridge and barrier flat deposts (TXQbr;0)

State	Texas
Name	barrier ridge and barrier flat deposts
Geologic age	Phanerozoic \| Cenozoic \| Quaternary \| Holocene
Original map label	Qbr
Comments	(from Beeville-Bay City Sheet (1975)): sand, silt, and clay; mostly sand, well sorted, fine grained, abdt shells and shell frags.; interfingers with silt and clay in landward direction; includes beach ridge, spit, tidal channel, tidal flats, washover fian, and sand dune deposits. (from Moore and Wermund, 1993a, 1993b): beach sand and shell sand--white to lt-gray, v. well sorted, angular, fine to v. fine quartz sand, shell sand, and shells with subordinate feldspar, rock fragments, and heavy minerals. Shell frags. form lag concentrations in places, for example on Padre Island near lat 27-deg 12 min where opposing longshore drift currents converge; on Little Shell Beach shells of the surf clam Donax (0.5-2 cm) are abundant; on Big Shell Beach, abraded shells of clams (1-4 cm), moslty Eontia, Mercenaria, and Echinochama, are as much as 80 percent of the sediment. Unit underlies beaches, spits, and barrier bars along coast. Upper shoreface commonly burrowed by the shrimp Callianassa; lower shoreface has very low angle crossbedding. On Matagorda Island, fore-island dunes are well developed immediately landward of beach and 308 m above it. Heavy minerals (0.1-1 percent of sand) form dark-colored laminae; silt and clay content 4 percent or less. Bedding is subhorizontal planar, low-angle cross-laminated, or massive. Unit includes vegetated sand of back-barrier flats and back-island dune fields. Thickness typically 6-12 m; fore-island dunes on Matagorda Island 1-8 m thick.
Primary rock type	sand
Secondary rock type	silt
Other rock types	clay or mud
Lithologic constituents	Major Unconsolidated > Coarse-detrital > Sand (Bed) Minor Unconsolidated > Fine-detrital > Silt (Bed) Unconsolidated > Fine-detrital > Clay (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	Moore, D.W. and Wermund, E.G., Jr., 1993a, Quaternary geologic map of the Austin 4 x 6 degree quadrangle, United States: U.S. Geological Survey Miscellaneous Investigations Series Map I-1420 (NH-14), scale 1:1,000,000. [http://pubs.er.usgs.gov/publication/i1420(NH14)] Moore, D.W. and Wermund, E.G., Jr., 1993b, Quaternary geologic map of the Monterrey 4 x 6 degree quadrangle, United States: U.S. Geological Survey Miscellaneous Investigations Series Map I-1420 (NG-14), scale 1:1,000,000. [http://pubs.er.usgs.gov/publication/i1420(NG14)] Bureau of Economic Geology, 1975, Corpus Christi Sheet, Geologic Atlas of Texas, Bureau of Economic Geology, University of Texas at Austin, scale 1:250,000. Bureau of Economic Geology, 1976, McAllen-Brownsville Sheet, Geologic Atlas of Texas, Bureau of Economic Geology, University of Texas at Austin, scale 1:250,000.
Geographic coverage	Aransas - Brazoria - Calhoun - Cameron - Chambers - Galveston - Jefferson - Kenedy - Kleberg - Matagorda - Nueces - Willacy