## LSU Historical Dissertations and Theses

1993

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

J. S. Hanor

#### Abstract

Solute source tracing using Br/Cl and $\rm\sp{87}Sr/\sp{86}Sr$ ratios indicate that the source of brackish water in the Mississippi River alluvial and Jasper aquifers of Concordia Parish, Louisiana are brines and saline waters from the Wilcox aquifer. The proximity of maximum concentrations of dissolved solids to the location of plugged and abandoned oil wells and test holes indicates that brines and saline waters have migrated upward through these oil wells and test holes. Br/Cl ratios in the Wilcox aquifer suggest dissolution of halite as a major source of dissolved solids. Apparent thermodynamic equilibrium exists between plagioclase and kaolinite, plagioclase and Na-smectite, microcline and albite, and illite and Ca-smectite. The presence of a (Ca,Mg,Sr)CO$\sb3$ solid solution may buffer concentrations of dissolved Mg and Sr. Values of $\delta\sp{18}$O may also be buffered by water-rock interaction. Values of $\rm\sp{87}Sr/\sp{86}Sr$ in conjunction with regional ground-water flow indicates that solutes in the upper unit of the Wilcox aquifer were derived from the North Louisiana Salt Dome Basin while solutes in the middle unit were derived from the Gulf Coast Salt Dome Basin. If so, solutes in both the upper and middle units have been transported over considerable lateral distances by ground-water flow to reach their current locations. The majority of brackish water in the Mississippi River alluvial aquifer in southeastern Arkansas is derived from saline waters in underlying Tertiary aquifers. Br/Cl ratios of brackish water indicate that a small part (approximately 5%) of the solutes within an area of anomalous salinity may be derived from brines of the Smackover Formation. The presence of the area of anomalous salinity in conjunction with the intersection of regional wrench faults also supports the idea that upward flow may be channeled through the area of intersection of these faults. Once present in the alluvial aquifer of southeastern Arkansas, Brackish water flows to the southwest along a fluvial channel at the base of the alluvial deposits. Estimated flow velocities indicate that significant southwestward movement of brackish water could occur on a human time scale.

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