ASSESSING THE AQUITARD INTEGRITY OF THE ZILPHA CLAY INTERVAL OF THE MIDDLE CLAIBORNE AQUIFER, NORTHERN MISSISSIPPI EMBAYMENT

Recent studies have identified numerous naturally occurring breaches, or leakage pathways, in the protective confining layer overlying the Middle Claiborne aquifer in the northern Mississippi Embayment. Consequently, a deeper understanding of the Middle Claiborne Strata (Sparta-Memphis Sand) has become a priority. Middle Claiborne strata were deposited during the Eocene and includes fluvial, deltaic, and shallow marine deposits. Its fluvial-marine transitional nature contributes to significant heterogeneity and time-transgressive characteristics, complicating its hydrostratigraphy. A key heterogeneous unit within the Middle Claiborne is the Zilpha Clay interval, which holds formation status in Mississippi but is discontinuous further north; it is part of the Cane River formation in southeastern Arkansas and Louisiana. To evaluate the Zilpha clay interval as a potential interbedded aquitard within the Sparta-Memphis aquifer, analyses were conducted on sediments recovered from boreholes located in Shelby County, TN (AEM-1, MSA-1, and EPA-1). The methodology included sedimentologic core descriptions, inductively coupled plasma mass spectrometry (ICP-MS), total organic carbon (TOC) analysis, and X-ray diffraction (XRD). Sedimentological investigations revealed grey to light grey, fine to coarse-grained mudstone with ripples, cross and parallel laminations, and high organic matter content, sparsely distributed in AEM-1 but abundant with leaf impressions in MSA-1. The sparse glauconitic contentindicates deposition in a delta plain environment influenced by a river-dominated delta. Chemostratigraphic analyses provided major and minor elemental concentrations, reflecting depositional conditions such as detrital input, primary productivity, and oxidation rates. ICP-MS results indicated significant continental input with elevated oxidation, primary productivity, and detrital influx. Future work will focus on biostratigraphic analysis of pollen assemblages, as well as measuring hydraulic conductivity at depth using triaxial testing. This will help determine groundwater mixing ratios concerning hydraulic conductivity (K), thickness (B), and transmissivity, (T = KB) within the aquifer.