ICE-SHEET AQUIFER INTERACTIONS WITHIN THE ILLINOIS BASIN

Groundwater salinity, radiocarbon and stable isotope data support the hypothesis that late Pleistocene glaciation profoundly altered the groundwater hydrology of the Illinois Basin. Plumes of low salinity waters have been observed at depth in the Silurian-Devonian and Cambrian-Ordovician aquifer systems across the northern and western margins of the basin, and seem to correspond to the location of Laurentide Ice Sheet lobes. These dilute waters have low oxygen isotope values (<-12 per mil) compared to modern mean annual and Late Pleistocene precipitation in the region, and are likely a mixture of ice sheet meltwaters, modern and paleo precipitation and Paleozoic brines. Surprisingly, some of the most isotopically-depleted ground water is found within the basal Cambrian-Ordovician aquifers in the southwestern portion of the Illinois Basin, a significant distance from the where the aquifers crop out to the north. Here, we present a series of cross-sectional models that assess the degree to which glacial meltwaters beneath the Laurentide Ice Sheet infiltrated into saline Paleozoic reservoirs along structural arches and sub-vertical fault zones. Our parallel code solves equations for fluid motion, heat, multi-species (salinity, stable/radiometric isotope) solute transport, permafrost formation, and lithosphere flexure. We calibrated our model adjusting sediment and fault permeability. Our analysis assesses whether or not glacial meltwaters accessed deep Paleozoic reservoirs via recharge at the basin margins and/or along fault zones within the Illinois Basin.