Abstract

Geomorphologists seek to identify and isolate mechanisms dictating how climate changes impact erosion and sediment transport. South of the Last Glacial Maximum ice extent, central Appalachian headwater valleys contain extensive evidence of relict periglacial surface processes. Garner Run, a 1 km2 sandstone subcatchment of the Susquehanna Shale Hills Critical Zone Observatory, contains relict Pleistocene periglacial features such as solifluction lobes, block fields and thick colluvial valley fill. Such limited landscape modification since glaciation suggests periglacial processes are highly efficient compared to modern temperate processes, but the timing, magnitude, and spatial pattern of hillslope denudation processes in response to Quaternary climate change remain unclear. Here, we pair geomorphic mapping from lidar and field observations with in situ cosmogenic 10Be and 26Al measurements to estimate erosion rates and residence time of sandstone colluvium in Garner Run. Morphology of solifluction lobes and colluvium imply greater sediment discharge from south-facing slopes, suggesting an aspect dependence of periglacial processes consistent with regional morphologic observations. Catchment erosion rates in Garner Run, derived from detrital stream sediment, are slow (~8 m/My), similar to nearby sandstone catchments and summit erosion rates elsewhere in the Appalachian Mountains. Preliminary analyses of 10Be in boulders mantling north-facing slopes of Garner Run show effective ridgetop exposure ages of ~50 ky, and valley bottom ages of ~100 ky, suggesting cosmic-ray dosing during downslope transport. We estimate an average valley fill thickness of 10-15 m, representing 2-3 m of bedrock lowering equivalent to 105-106 yrs of sediment production based on erosion rate data. 10Be/26Al burial dating of a valley-bottom drill core recovering 9 m of colluvium will constrain fill age and potential temporal variation in erosion rate due to Pleistocene periglaciations. Our results suggest sedimentary records in slowly-eroding headwater valleys present opportunities to directly examine periglacial hillslope processes through colluvial fill sourced from adjacent hillslopes, potentially over many glacial/interglacial cycles, and may unlock new records of landscape response to climate change.

Citation

Del Vecchio, J., Denn, A., DiBiase, R., and Bierman, P. (2016): Colluvial signatures of Pleistocene sediment production in central Pennsylvania. 2016 Fall Meeting, American Geophysical Union, San Francisco, CA, 12-16 Dec..

This Paper/Book acknowledges NSF CZO grant support.