GEOLOGIC MAPPING OF THE TOCOWA 7.5-MINUTE QUADRANGLE, TALLAHATCHIE AND PANOLA COUNTIES, NORTHWESTERN MISSISSIPPI: GEOLOGIC FRAMEWORK CHARACTERIZATIONS OF MISSISSIPPI VALLEY ALLUVIAL FANS AND THEIR POTENTIAL FOR AQUIFER RECHARGE

The Mississippi River Valley Alluvial Aquifer (MRVA) within the Mississippi Embayment is a crucial freshwater resource in the southern United States, supporting agricultural, municipal, and industrial demands. Excessive groundwater extraction, however, has led to significant declines in water levels across the region. The surficial expressions of most Mississippi Valley wall alluvial fans indicate they overlay the MRVA and are composed of coarse-grained sediments, indicating substantial potential for groundwater recharge. Despite this, the subsurface connectivity and sedimentary architecture of these fans remain poorly understood due to the absence of subsurface exploration and detailed geological maps for the area. This study focuses on the Tocowa quadrangle in northwestern Mississippi, encompassing parts of Panola and Tallahatchie counties. A detailed geologic map at a scale of 1:24,000 was prepared, integrating field mapping, interpretations of existing borehole data, and shallow coring. Remote sensing and LiDAR Digital Elevation Models (DEMs) were used to create a geologic map.

Detailed mapping revealed the presence of Eocene Zilpha and Kosciusko formations from the Claiborne Group, succeeded by Quaternary Upland Complex terrace deposits, loess deposits, and alluvium. The alluvial fans subsurface architecture and connectivity with the MRVA was carried out through geophysical surveys including electrical resistivity tomography and ground penetrating radar. The mapping identified and characterized six alluvial fans emanating from the valley walls that are modified by the Yocona and Little Tallahatchie Rivers. These fans consist primarily of poorly sorted gravelly sand with alternating lenses of coarse-grained sand, silt, and clay. Borehole data indicated that these alluvial fans extend to depths of up to 45 meters, interfacing with Tertiary sediments and contributing significantly to the Upper Claiborne aquifer. Results indicate the alluvial fans significantly contribute to groundwater recharge. Further research that includes more drilling, geophysics, and measurements of infiltration rates over broader areas within the Mississippi Embayment is needed to refine groundwater models and improve management and sustainably strategies for this vital freshwater resource.