INVESTIGATING A POSSIBLE NEW, LATE PLEISTOCENE PERIGLACIAL LANDFORM IN CENTRAL CONNECTICUT

Pingo scars – circular, rimmed depressions – are the remnants of ice-cored mounds that form as the result of expanding, near-surface permafrost. Previous research on pingo scars in Connecticut has argued that they are dominantly found within the exposed lake bottom sediments of glacial Lake Hitchcock, putting their age specifically in the 15.5-14.5 Ka range, with direct implications for the environmental conditions and average mean annual temperatures at that time. In this study, we focus on circular, rimmed depressions discovered at elevations in central Connecticut higher than glacial Lake Hitchcock sediments within glacial till deposits and typically on hillslopes (i.e., non-flat terrain) on the southeast side of hills and drumlins in the region. These landforms likely reflect a similar cold-climate, periglacial process as pingo formation and collapse, or they highlight another aspect of deglaciation and climatic transition in the region. We collected and analyzed a 288 cm vibracore from one of these circular depressions in Southwick, MA. Core subsamples were analyzed for organic content via loss on ignition, grain size, elemental composition via x-ray fluorescence, and 14-C dating. Stratigraphy is interpreted to record glacial till, sand and gravel layers in the lower 100 cm of the core, followed by persistent organic material associated with a wetland and present-day peat bog/vernal pool. Overall, a major sedimentological difference occurs at ~185 cm, above which organic content increases 10x, metals such as Cu and Zn exceed background levels (>1 PPM), and % fines (<63μ) increase from ~18% to 40%. Organic fibers from the sand layers below the wetland yielded an age of 14,534 ± 183 cal BP – which is a minimum age for when the depression began filling with sediment. This age is consistent with the site becoming a depression about the same time as the pingo scars in the Lake Hitchcock basin farther east, but because ice retreat here was at ~17.9 Ka, it suggests pingos could have been much longer lived. Further work will be done to map the distribution of these landforms, look for datable organic material deeper in the core, collect cores at similar sites, explore characteristics of open- vs closed-system pingos, and consider the implications of pingos forming at different gradients and in different lithology than expected.