Water history of Cretaceous aquifers, East Texas Basin

Abstract

Circumstantial evidence of the history of water in five Cretaceous aquifers is supplied by water analyses comparisons and a study of the ratios of the major ions, Ca 2+, Mg 2+, Na +, Cl −, SO 2− 4 and HCO − 3. Water from each aquifer has distinctive characteristics, but there are interconnections between aquifers, especially near the Mexic-Talco fault zone and at an unconformity that extends across the Sabine uplift. Some piercement salt domes modify formation waters, but most salt domes have little or no noticeable effect. Apparently clay sheaths protect the salt columns from solution. Town water supplies on the north Texas shelf are affected by invasion of hot brine from the Tyler Basin, moving from east to west through the Woodbine Sandstone. This hydrodynamic flow in part accounts for the existence of the giant east Texas field to the west of the Sabine uplift, while similar updip truncated sandstones on the east side of the Sabine uplift are generally barren of oil, even though they occupy the same stratigraphic position as the Woodbine. Ion ratio comparisons show that water in the older, more deeply buried aquifers have been modified more (compared with presentday sea water) than that in younger, less deeply buried aquifers. Although this is generally true, there are explainable exceptions, where surface water has had opportunity to invade certain aquifers. Ion ratio maps show the effect of time and rock compositions upon the relative kind and amount of dissolved solids in the water, due to reactions with minerals and organic material in the rocks.