The Hickory Run Boulder Field, Carbon County, Pennsylvania, USA: Morphology, sedimentology and development

Abstract Boulder fields are low‐angle, open‐work clast accumulations and are among the most distinctive geomorphic expressions of long‐term periglacial processes. Although boulder fields are widely used as indicators of past periglacial environments, uncertainty remains regarding the specific climatic conditions and processes responsible for their formation. The Hickory Run Boulder Field (HRBF) in Carbon County, Pennsylvania (41°03′02” N, 75°38′44” W), located ~2 km south of the Last Glacial Maximum margin, is the largest and most striking feature of its kind in the eastern USA, covering approximately 6.5 ha. The dominant hypothesis suggests allochthonous formation, whereby frost wedging of scarp‐like bedrock source outcrops and slow downslope movement of weathered material over impermeable permafrost resulted in HRBF's development. However, direct quantitative analyses of this hypothesis remain sparse, and the geological history of HRBF is incompletely resolved. This study presents a sedimentological investigation evaluating the allochthonous hypothesis through a combination of relative weathering indices (clast volume, sphericity, flatness and rebound hardness) and clast macrofabric analysis. Field data were collected from 22 sites along two subparallel transects, including locations in both the major and minor boulder fields. Statistical analyses, including polynomial regression of relative weathering indices and eigenvalue‐based macrofabric assessments, reveal dynamic spatial trends in clast weathering and orientation. Results indicate systematic increases in clast weathering with distance from a local bedrock outcrop and non‐random macrofabric orientations consistent with mass movement. These findings confirm that HRBF represents a time‐transgressive surface formed under periglacial conditions, with flow‐like integration of clasts from bordering upslope areas. The study provides quantitative evidence supporting emplacement by periglacial mass movement, reinforcing the utility of HRBF in paleoclimatic reconstructions of the Appalachian Highlands.