ABSTRACT

The Mississippi River alluvial aquifer of eastern Morehouse Parish, Louisiana, and southern Chicot County, Arkansas, contains elevated salinity. Most of the salt present in the Mississippi River alluvial aquifer of southern Chicot County is derived from saline waters in underlying aquifers of Tertiary age and introduced into the Mississippi River alluvial aquifer by upward flow along the regional ground-water flow pattern. Salinity in underlying aquifers of Tertiary age is acquired by subsurface dissolution of halite and subsequent transport of solutes by regional ground-water flow. Once introduced into the Mississippi River alluvial aquifer of southern Chicot County, water with elevated salinity flows southwestward into Morehouse Parish along a buried fluvial channel eroded into the underlying Cockfield Formation.

Within an area of brackish alluvial water in southern Chicot County, Br/Cl ratios indicate that a small part (approximately 5 percent) of the solutes may be derived from brines within the deeply buried Smackover Formation of Jurassic age. The presence of this area of brackish water in conjunction with the reported location of the intersection of two regional wrench faults, one of which may penetrate into the Smackover Formation, supports the hypothesis that upward flow is channeled through the area of intersection of these faults.