QUATERNARY GEOLOGY OF PICKAWAY COUNTY, OHIO: THE GEOMORPHOLOGY, STRATIGRAPHY, AND CHRONOLOGY OF TWO LATE WISCONSIN GLACIAL ADVANCES IN CENTRAL OHIO

Pickaway County contains two distinct physiographic regions—glaciated plateau in the west and till plains in the east—bisected by the Scioto River which runs nearly north to south through the county. New data collected from newly described till outcrops, Light Detection and Ranging (LiDAR) derived digital elevation models, and radiocarbon ages from six sites provides evidence for two glacial advances of the Scioto Sublobe into central Ohio during MIS 2. The first advance of the sublobe is associated with the Caesar Till, characterized by its loamy matrix texture, blue-gray tint (10 YR 4/1) and loess cap. Wood found entrained within Caesar Till at the Parsons site (22,700 ± 300 ¹⁴C yr BP), Great Southern Metro Park (22,500 ± 270 ¹⁴C yr BP), and the Deer Creek Dam (23,000 ± 250 ¹⁴C yr BP) provide an age for advancement of the Scioto Sublobe into Pickaway County. The sublobe reached its terminal position at the Lattaville Moraine in southeastern Pickaway County approximately 1,500 years later as indicated by wood found within the Caesar Till near Moccasin Creek (21,000 ± 210 ¹⁴C yr BP). After construction of the Lattaville Moraine, the glacial ice began to retreat northward, depositing the Circleville Outwash Fan. A second advance of the sublobe, correlated with the Darby Till, occurred ~3,000 years later. Found atop the Caesar Till in outcrops, the Darby Till is often less than six meters thick except where the ice front paused long enough to construct a moraine. The relative thinness of the Darby Till allows preservation of palimpsest features such as the New Holland Moraine. The Darby Till is browner (10YR 4/4) and siltier than the Caesar Till, perhaps due to incorporation of the latter’s loess cap. Where overrun, the Caesar Till is missing its distinctive loess cap making differentiating the two tills difficult due to their similar physical characteristics and provenances. Some exposures, such as one along Little Walnut Creek, exhibit a shear zone between the two tills, providing some distinction between the two glacial advances. Caesar Till is exposed at the surface in southeastern Pickaway County. However, wood in outcrops near Biers Run (18,600 ± 150 ¹⁴C yr BP) and Anderson Run (18,150 ± 150 ¹⁴C yr BP) in Ross County indicate ice reached the Lattaville Moraine and the Last Glacial Maximum west of the Scioto River during this later advance.