A record of coupled hlllslope and channel response to Pleistocene periglacial erosion in a sandstone headwater valley, central Pennsylvania

Open Access
Author:
Delvecchio, Joanmarie
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 25, 2017
Committee Members:
  • Roman A. DiBiase, Thesis Advisor
  • Susan L. Brantley , Committee Member
  • Li Li , Committee Member
Keywords:
  • geomorphology
  • periglacial
  • cosmogenic nuclides
  • paleoclimate
  • critical zone
Abstract:
Outside of the Last Glacial Maximum ice extent, landscapes in the central Valley and Ridge physiographic province of Appalachia preserve soils and thick colluvial deposits indicating extensive periglacial landscape modification. The preservation of periglacial landforms in the present interglacial suggests active hillslope sediment transport in cold climates followed by limited modification in the Holocene. However, the timing and extent of these processes are poorly constrained, and it is unclear whether, and how much, this signature is due to LGM or older periglaciations. Here, we pair geomorphic mapping with in situ cosmogenic 10Be and 26Al measurements of surface material and buried clasts to estimate the residence time and depositional history of colluvium within Garner Run, a 1 km2 sandstone headwater valley in central Appalachia containing relict Pleistocene periglacial features including solifluction lobes, boulder fields, and thick colluvial footslope deposits. 10Be concentrations of stream sediment and hillslope regolith indicate slow erosion rates (6.3 m ± 0.5 m m.y.-1) over the past 38-140 kyr. From dating of buried valley-bottom deposits recovered from a 9 m drill core, we interpret two depositional pulses since ~290 ka, a record which spans at least three glacial terminations and implies limited removal of valley bottom deposits during interglacials. This age is consistent with independent calculations determined from debris volume estimates, total hillslope contributing area, and catchment erosion rate integrated over multiple climate cycles. Thus, we infer that erosion rates measured in upland basins in Central Appalachia reflect the integration both temperate and periglacial processes, and that in cold-warm transitions, erosion rates reflect only moderate departures from otherwise slow background rates. Furthermore, due to slow erosion rates, we show that sedimentary records in sandstone headwater valleys present opportunities for direct examination of climate-modulated hillslope processes.