Sedimentological Evidence Supports a Periglacial Origin of the Hickory Run Boulder Field, Northeast Pennsylvania

Keywords: Periglacial, Boulder Fields, Cryoplanation Terraces
Session Type: Virtual Poster Abstract
Day: Saturday
Session Start / End Time: 2/26/2022 09:40 AM (Eastern Time (US & Canada)) - 2/26/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 37

Abstract

Boulder (block) fields are open-work clast accumulations, often occupying low-angle topographic positions. Two primary hypotheses apply to the formation of ancient boulder fields in the eastern USA. One centers on periglacial (cold, nonglacial) weathering and mass-movement processes active during cold intervals of the Quaternary. This periglacial interpretation emphasizes repeated cycles of mechanical weathering (e.g., freeze-thaw cycling and frost shattering) and periglacial mass movements (e.g., frost creep and gelifluction). The competing hypothesis emphasizes weathering during the warmer and wetter conditions of the Neogene. The Hickory Run Boulder Field (HRBF), in northeastern Pennsylvania is the largest boulder field in the eastern USA, with dimensions of 120 x 550 m. HRBF lies in close proximity (~1.5 km) to the terminus of the Laurentide Ice Sheet during the Last Glacial Maximum. The research reported here used relative weathering indices (clast dimensions, fabric, and hardness) collected at the HRBF to investigate its geomorphic origin. Bedrock outcrops upslope provided a source of clastic material for the field. Relative weathering indices reveal trends along HRBF’s long axis, parallel to its local slope. Sedimentological evidence supports our hypothesis that HRBF was formed through the coalescence of two once-separate boulder fields, a clear demonstration of its allochthonous nature. Convergence of these lines of evidence supports the periglacial interpretation of HRBF’s formation.