EXPLORATION OF DEEP QUATERNARY VALLEY-FILL SEQUENCES IN CENTRAL INDIANA

Identification of deep valley fill in buried bedrock valleys of central Indiana is a wholly subsurface-based, sequence-stratigraphic approach. The Anderson-New Castle Valley (ANC), a tributary segment of the classic Teays Valley, extends north and northwestward from southeastern Indiana into central Indiana, opening into the Frankfort Lowland Section of the Layfayette Bedrock Valley System. The ANC is expected to provide the simplest record of valley-filling and landscape change related to first glaciation of the valley. Geophysical surveys were used to locate five testholes, ranging in depth from 250 feet to over 480 feet. These investigations began with Indiana Geological Survey (IGS) gravimetry transects, built upon previous refraction and water-well data, to locate the primary valley thalweg. In addition, a single reflection line (Illinois State Geological Survey Landstreamer methodology), a 5-mile transect perpendicular to the assumed course of the New Castle Valley, indicated sequence packages within a tributary-thalweg setting and a possible deepest valley testhole location. Several other deep testholes, including the deepest (504 feet) IGS glacial testhole, were located using data from the IGS iLITH and Gamma-log databases. Sample sets and downhole geophysical logs revealed a variety of vertical-sequence packages composed of: chert gravels, West Lebanon till lithologies, lake clays/silts, alluvial sediments, and glacial advance-sequence sediments. The character of these sediments gives indications of the nature of the earliest glacial influence on the valley.