Alluvium in Rio Grande, subdivided into areas predominantly of clay (TXQac;0)

State	Texas
Name	Alluvium in Rio Grande, subdivided into areas predominantly of clay
Geologic age	Phanerozoic \| Cenozoic \| Quaternary \| Holocene
Original map label	Qac
Comments	Flood-plain and backswamp silt and clay--dark-gray to dark-brown or brownish-gray silt, clay, and silty clay. Contains minor amounts of medium to fine quartz sand. Interdistributary fine sediment of the Rio Grande delta. Mostly inactive; deposition occurs during floods that accompany large, relatively infrequent tropical storms. Unit burrowed by animals; locally very organic with abundant plant fragments. Extensively cultivated. Overlies older distributary sand deposits (Moore and Wermund, 1993b).
Primary rock type	silt
Secondary rock type	clay or mud
Other rock types
Lithologic constituents	Major Unconsolidated > Fine-detrital > Clay (Bed) Unconsolidated > Fine-detrital > Silt (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., 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)]
Geographic coverage	Cameron - Hidalgo