SUBGLACIAL MELTWATER EROSION PRESAGES LANDSCAPE FOR RENEWED KARSTIFICATION

The Bellevue-Castalia Karst Plain (BCKP) landscape of north-central Ohio contains a variety of sinkhole types in comparison to more homogenous Midwest karst landscapes. Sediment 0–16 m thick overlies the Delaware and Columbus Limestones, that in turn overly mixed evaporites and carbonates of the Salina Group. Most of the ~1000 identified sinkholes are of a suffosion type 1.5–10’s m wide developed within sediment and usually without exposed bedrock. Active swallets may have exposed bedrock and range widely in size. Lastly, and of interest here, are the largest sinkholes commonly with irregular shapes, broad flat bottoms with bedrock sometimes exposed, and sizes of 0.5–1.3 x 10⁶ m². Our previous work classifying sinkholes relied on GIS routines to identify sinkholes, followed by verification visually on DEMs and by field work. Interestingly, renewed analysis reveals low-relief channels across the study area, in which many of the largest sinkholes are found. Topographically and geomorphologically the study area consists of: 1) an irregular till plain above the Maumee level of Ancestral Lake Erie (ALE); 2) a middle area hosting most of the ALE strandlines, thinner sediment, and bedrock at or near the surface; and, 3) the lowest elevation area with minor strandlines and glacio-lacustrine sediment thickening northwards. The low-relief channels are approximately 2–4 m deep, 7–11 km long, and 0.15–0.4 km wide. Some channels with widths of ~1 km have a scabland-like appearance. The channels are found across all three areas, are independent of most postglacial fluvial systems, host small eskers, and in places are cross-cut by littoral deposits of ALE. When the ice margin was further south, the channels formed from subglacial meltwater erosion into the underlying substrate. Some of the largest sinkholes may be channel segments. The spatial and formative relationship between channels and large sinkholes remains under investigation.