GEOLOGIC HISTORY AND HYDROGEOLOGIC SETTING OF THE EDWARDS-TRINITY AQUIFER SYSTEM, WESTCENTRAL TEXAS
- Permanent Link:
- GEOLOGIC HISTORY AND HYDROGEOLOGIC SETTING OF THE EDWARDS-TRINITY AQUIFER SYSTEM, WESTCENTRAL TEXAS
- Series Title:
- A. Barker, Rene
W. Bush, Peter
Baker Jr., E.T.
- Publication Date:
- Subjects / Keywords:
- Edwards-Trinity ( local )
Aquifer System ( local )
Pre-Cretaceous Rocks ( local )
- serial ( sobekcm )
- The Edwards-Trinity aquifer system underlies about 42,000 square miles of west-central
Texas. Nearly flat-lying, mostly Comanche
(Lower Cretaceous) strata of the aquifer system
thin northwestward atop massive pre-Cretaceous
rocks that are comparatively impermeable and
structurally complex. From predominately terrigenous clastic sediments in the east and fluvialdeltaic (terrestrial) deposits in the west, the rocks
of early Trinitian age grade upward into supratidal
evaporitic and dolomitic strata, intertidal limestone and dolostone, and shallow-marine, openshelf, and reefal strata of late Trinitian, Fredericksburgian, and Washitan age. A thick, downfaulted
remnant of mostly open-marine strata of Eaglefordian through Navarroan age composes a small,
southeastern part of the aquifer system.
The Trinity Group was deposited atop a rolling peneplain of pre-Cretaceous rocks during three
predominately transgressive cycles of sedimentation that encroached upon the Llano uplift. The
Fredericksburg and Washita Groups were deposited above the Trinity Group mostly in the lee of
the Stuart City reef trend, a shelf margin ridge that
sheltered depositional environments in the study
area. The Washita Group subsequently was covered with thick, mostly fine-grained Gulf strata.
During late Oligocene through early
Miocene time, large-scale normal faulting formed
the Balcones fault zone, where the Cretaceous
strata were downfaulted, intensively fractured, and
differentially rotated within a series of northeasttrending fault blocks. In addition to fracturing the
rocks in the fault zone and extending the depth
of freshwater diagenesis, the faulting vertically
displaced the terrain, which steepened hydraulic
gradients and maintained relatively high flow
velocities near the surface. A shallow regime of
dynamic ground-water flow evolved that promoted dissolution and enhanced the transmissivity
of the Edwards Group in the Balcones fault zone.
Cementation, recrystallization, and mineral
replacement caused by deeper, comparatively
- Original Version:
- USGS, Vol. 94-4039 (1994-01-01).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
- Rights Management:
- This object is protected by copyright, and is made available here for research and educational purposes. Permission to reuse, publish, or reproduce the object beyond the bounds of Fair Use or other exemptions to copyright law must be obtained from the copyright holder.
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