MIS 6 Ice-marginal Sediments in the Buried Bedrock Valley of the East Fork White River near Jasper, Indiana Report

Abstract

Quaternary glaciations left a permanent geomorphic imprint on large areas of the northern hemisphere interior continental regions. The interaction of ice and meltwater with existing landscapes altered the geomorphology, created new sedimentary archives, rerouted drainages, and left a palimpsest of landforms. During Marine Isotope Stage 6 (MIS 6; ca. 185,000–130,000 years ago), several ice-marginal lakes developed in south-central Indiana. Glacial Lake Patoka (GLP) developed along the lower course of the valley of the ancestral East Fork White River (EFWR) due to blockage by glacial ice. The GLP record comprises a > ~150-ft- (> ~50-m-) thick package of glaciodeltaic, glaciolacustrine, and eolian sediments that were studied using sedimentological, stratigraphic, and geochronological methods. The pre-MIS 6 bedrock valley traversed the basin approximately 6 miles (10 km) south of its modern course. During MIS 6 ice advance, the basin rapidly infilled, developing a delta inset in a larger lake that reached beyond the current boundaries of the flat landscape west of the city of Jasper. New bedrock outlets were excavated to release water to the south. At the peak of glaciation, a fine-grained sequence thickening toward the southeast developed, interbedded with deltaic sands. This sequence is equivalent in time with the deposition of diamicton-cored moraines at the maximum MIS 6 glacial ice extent to the northwest. After GLP drainage, the EFWR was redirected north of its pre-MIS 6 position. This drainage reorganization must have been in place before MIS 2 deposition of slackwater lakes whose termini lie along the modern river valley. The Sangamon Geosol developed during interglacial MIS 5, and accreted continuously during MIS 3 and 2, until it was buried by loess deposition in the relatively flat landscape of the filled basin.