The Pennsylvania State University The Graduate School College of Earth and Mineral Sciences A RECORD OF COUPLED HILLSLOPE AND CHANNEL RESPONSE TO PLEISTOCENE PERIGLACIAL EROSION IN A SANDSTONE HEADWATER VALLEY, CENTRAL PENNSYLVANIA A Thesis in Geosciences by Joanmarie Del Vecchio © 2017 Joanmarie Del Vecchio Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science December 2017 The thesis of Joanmarie Del Vecchio was reviewed and approved* by the following: Roman A. DiBiase Assistant Professor of Geosciences Thesis Advisor Li Li Associate Professor of Civil and Environmental Engineering Susan L. Brantley Professor of Geosciences Tim Bralower Professor of Geosciences Interim Head, Department of Geosciences *Signatures are on file in the Graduate School. ii 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. iii TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................ v LIST OF TABLES ............................................................................................................. vi ACKNOWLEDGEMENTS .............................................................................................. vii INTRODUCTION .............................................................................................................. 1 STUDY AREA ................................................................................................................... 2 METHODS ......................................................................................................................... 7 Topographic Analysis ..................................................................................................... 7 Field Mapping of Regolith Texture ................................................................................ 7 Grain Size Analysis of Surface Clasts on Hillslope and in Channels ............................. 8 Cosmogenic Nuclide Analysis ...................................................................................... 11 Determining Colluvial Fill History ............................................................................... 13 RESULTS ......................................................................................................................... 14 Topographic Analysis ................................................................................................... 14 Field Mapping of Regolith Texture .............................................................................. 15 Grain Size Analysis of Surface Clasts and Hillslopes and in Channels ....................... 16 Cosmogenic Nuclide Analysis ...................................................................................... 21 Constraining Colluvial Fill History .............................................................................. 21 DISCUSSION ................................................................................................................... 26 Controls on Spatial Variability in Regolith Texture and Morphology ......................... 26 Colluvial Fill History and Implications for Hillslope-Channel Coupling .................... 30 Implications for the Evolution of the Critical Zone ...................................................... 33 CONCLUSIONS............................................................................................................... 34 References ......................................................................................................................... 36 Appendix A: Workflow of GPS-assisted soil mapping at Garner Run ............................ 41 Appendix B. Soil pit descriptions ..................................................................................... 45 Appendix C. Modeling Scenarios and Constants ............................................................. 52 Appendix Tables ............................................................................................................... 55 Appendix Figures .............................................................................................................. 58 iv LIST OF FIGURES Figure 1. Study site in central Pennsylvania (p. 10) Figure 2. Field photos showing heterogeneity in surface cover (p. 16) Figure 3. Clast measurements from point counts conducted on hillslopes and in the channel (p. 24) Figure 4. Shaded-relief models of colluvium (p. 25) Figure 5. Summary of 10Be concentrations in samples (p. 26) Figure 6. Core samples taken from within the HV1 core (p. 29) Figure 7. Forward-model outputs simulating deposition of debris recovered from valley core (p. 32) Figure 8. Schematic diagram of geomorphology at the surface and subsurface at Garner Run (p. 34) v LIST OF TABLES Table 1. Table 1: 10Be and 26Al data for all samples (p. 30) vi ACKNOWLEDGEMENTS This document is modified from a manuscript in preparation as of May 31, 2017 written with input from Paul Bierman and Alison Denn, including surface cosmogenic samples from Al. Field data collected and compiled with assistance of S. Granke, C. Martin and P. Silverhart. Funds for cosmogenic work provided by the Marie Morisawa Research Award through GSA’s Quaternary Geology and Geomorphology Division. LiDAR data collection was funded by the National Science Foundation (NSF) and performed by the National Center for Airborne Laser Mapping (NCALM). Financial and logistical support were provided by the NSF-supported Susquehanna Shale Hills Critical Zone Observatory EAR – 1331726. This research was conducted in Rothrock State Forest which is funded and managed by the Pennsylvania Department of Conservation and Natural Resources, Bureau of Forestry. G. Mount, J. Hayes, X. Comas, F. Zarif, L. Guo, D. J. Merritts, F. J. Pazzaglia, B. Hoagland, V. Marcon and others provided thoughtful discussion. I would like to thank my geoscience classmates and intramural sports teammates for being a source of inspiration, enthusiasm and friendship. I thank my committee members, Susan L. Brantley and Li Li, for thought-provoking questions over the last two years, and I thank my advisor, Roman A. DiBiase, for his wonderful mentorship and encouragement as I began my journey in graduate school. vii INTRODUCTION Quaternary climate fluctuations profoundly influenced the style and pace of erosion in glaciated landscapes (Hallet et al., 1996; Koppes and Montgomery, 2009), but the extent to which erosion rates in nearby periglacial landscapes were affected by concurrent changes in temperature and hydrology remains unclear. While a switch to colder temperatures is thought to stimulate bedrock lowering through increased frost cracking (Hales and Roering, 2007; Anderson et al., 2013; Rempel et al., 2017), downslope transport of regolith by ice-driven creep, solifluction, and permafrost-thaw mass wasting is more efficient during transitional warming periods (Taber, 1929; Matsuoka, 2001; Lewkowicz and Harris, 2005). Additionally, headwater channel networks may be periodically overwhelmed by periglacial hillslope sediment flux (Pizzuto, 1995; Simpson and Schlunegger, 2003), insulating hillslopes from regional base level change and thus complicating the overall landscape response to changing climate. In landscapes where erosion rates are slow compared to the frequency of climate shifts, weathering profiles within regolith integrate the effects of multiple glacial-interglacial cycles (Yoo et al., 2011; Anderson et al., 2013). In central Appalachia, the periglacial debris mantling hillslopes