SURFICIAL GEOLOGY OF THE DELTA, OH 7.5-MINUTE QUADRANGLE

A surficial geology map of the Delta, OH 7.5-Minute Quadrangle was constructed to elucidate the deglacial history of the Huron-Erie Lake Plain in northwest Ohio. Existing surficial, glacial or Quaternary geology maps in this region are at small scale and generalized. This map offers detailed mapping results using a sediment–landform approach to provide a framework for subsequent studies in the region. Methods included auger borings, drill borings, excavation of shallow pits, ground penetrating radar, and electrical resistivity surveys. Five terrains were mapped as depositional environments, and include: alluvial, eolian, glacial, glacial fluvial, and glacial lacustrine. Sediment types include littoral sand and gravel, glacial fluvial sand and gravel, eolian sand, and clay-rich diamicton interpreted as water modified till. Geologic features included strandlines, sand dunes, a possible delta, and abandoned channels. Electrical resistivity surveys across the till plain imaged two distinct, laterally-extensive units interpreted as early and late Woodfordian till and may provide a method of mapping these tills in the absence of natural exposures. The timing of deglacial events in this region is poorly understood and often based on relative dating techniques. Two optically stimulated luminescence (OSL) ages of 16.7 ± 0.8 ka and 16.8 ± 1.1 ka from shoreline sediment provide absolute ages for the formation of the Lake Maumee and Lake Whittlesey strandlines, respectively. Six OSL ages from eolian deposits overlying strandlines and from parabolic sand dunes between strandlines range in age from 11.8 ± 0.6 ka to 15.1 ± 0.8 ka, and record eolian activity for thousands of years after glacial lake drainage, consistent with results from a previous study. One additional OSL age from an apparent eolian deposit of 19.4 ± 1.1 ka is from the top of the Defiance Moraine, if accurate, it significantly minimizes the readvance distance during the Port Bruce Stadial. Many of the geological interpretations and maps for the region date to the early 20^th century and should be reevaluated using modern methodology.