(GP/GT) for Additional Water Supply in the Lower Rio Grande

sediment deposited as discrete sequences of sand and mud, which
represent an orderly succession of lithologies reflecting
depositional environment.
Both deltaic progradation and deltaflank
aggradation characterize the Frio sediments in the area.
Thick sequences of shelf and upper-slope prodelta mUdstone and
delta-front sandstone are overlain by equally thick massive,
shoreface to coastal-barrier sandstone (Finley and others, 1989).
The massive clays deposited in deep water have low densities
compared to the superjacent sandstone bodies, and are also water
saturated.
The rapid deposition and sediment loading create
unstable conditions which initiate and sustain movement of faults,
slumps, and diapirs (Henry and Morton, 1982). Major growth faults
were formed contemporaneously with deposition which caused
substantial thickening of the sedimentary sequences.
These growth
faults form broadly arcuate zones parallel to the coast which
contain sediment sequences that increase in thickness toward the
faults, or away from the basin (Fig. 3).
Subsequently, with increased depth of burial, the sediments
were subjected to increased pressures and temperatures. Compaction
of the sediments resulted in pore waters being expelled from the
clays into the more porous and permeable sandstones. Diagenesis at
the clay-sandstone contacts resulted in permeability barriers which
prevented further movement of the pore waters. These fluids became
over-pressured by the weight of the compacting overlying sediments,
and acted as thermal barriers by reducing heat flow in the
sediments.
The sandstones were deposited in nearshore environments that
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