The Edwards-Trinity aquifer system is in Lower Cretaceous rocks that underlie about 42,000 square miles of west-central Texas. From predominately terrigenous clastic sediments in the east and fluvial-deltaic (terrestrial) deposits in the west, the rocks of early Trinitian age grade upward into supratidal evaporitic and dolomitic strata, intertidal limestone and dolomite rock, and shallow- marine, open-shelf, and reefal strata of late Trinitian, Fredericksburgian, and Washitan age. The aquifers are the Edwards aquifer of the Balcones fault zone, the Trinity aquifer of the Balcones fault zone and Hill Country, and the Edwards- Trinity aquifer of the Edwards Plateau and Trans- Pecos. The Navarro-Del Rio confining unit overlies the subcrop of the Edwards aquifer; the Hammett con- fining unit is within the updip, basal part of the Trinity aquifer and a small southeastern fringe of the Edwards-Trinity aquifer. Transmissivity values average less than 10,000 feet squared per day over more than 90 percent of the study area because of widespread cementation, recrystallization, and mineral replacement. However, fractured and leached rocks in the Balcones fault zone cause transmissivity values to average about 750,000 feet squared per day in the Edwards aquifer, which occupies less than 10 percent of the study area.
Additional publication details
USGS Numbered Series
Geologic history and hydrogeologic setting of the Edwards-Trinity aquifer system, west-central Texas
Water-Resources Investigations Report
U.S. Geological Survey ;
Earth Science Information Center, Open-File Reports Section [distributor],
iv, 51 p. :ill. (some col.), maps (some col.) ;28 cm.