QUATERNARY MAPPING NEAR THE WISCONSIN (MIS 2) AND ILLINOIS (MIS 6) EPISODE LIMITS, CENTRAL INDIANA, USA

Geologic mapping efforts near the limits of the Wisconsin (MIS 2) and Illinois (MIS 6) Episode glaciations in central Indiana (USA) over the last decade have focused on improving the chronologic and stratigraphic framework of glacial sediments. Focused wireline and direct push coring, combined with radiocarbon, luminescence (quartz and feldspar), and cosmogenic dating, have improved the correlation and differentiation of MIS 2 and MIS 6 tills and have enabled the creation of time-distance diagrams. In addition, LiDAR digital elevation models have greatly improved our ability to trace ice-margin positions and identify other subtle glacial features. Significant findings near the limit of MIS 2 glaciation include an improved chronology of deposition of two late Wisconsin tills (24.0 ka and 21.5 ka) and chronology of outwash aggradation and associated slackwater deposition within the West Fork White River valley and tributaries (ca. 27 to 21 ka). These data sets suggest that the Laurentide Ice Sheet advance to and retreat from the MIS 2 maximum limit averaged ca. 40 m/yr within the global last glacial maximum. The maximum extent and chronology of MIS 6 glaciation has been refined in several areas, including the Flatwoods region, the Beanblossom and Salt Creek drainage basins, and the glacial Lake Patoka basin. Deep wireline coring and outcrop sampling in these areas, coupled with quartz and feldspar luminescence dating, cosmogenic (¹⁰Be) depth profiles, and soil-stratigraphic data, have enabled the reconstruction of the MIS 6 ice advance to its maximum limit between ca. 140 and 160 ka. Passive seismic techniques (horizontal-to-vertical spectral ratio, HVSR) have supplemented coring and archive data to reconstruct the bedrock surface near the MIS 2 and MIS 6 glacial limits. Several bedrock paleovalleys (ca. 40 m deep) are present in the mapping area, and coring indicates the fill of these paleovalleys is variably composed of MIS 6 and MIS 2 till, outwash, and glaciolacustrine sediments. Determining the architecture of the Quaternary fill of these paleovalleys is important, as they can host aquifers in areas with limited water resources.