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Download Original 4.86 MB Ruck 1 PROPERTIES AND MECHANISMS OF TRANSPORT OF COLLUVIAL SEDIMENT IN RELICT LOBATE LANDFORMS ON HILLSLOPES SOUTH OF THE LAST GLACIAL MAXIMUM ICE MARGIN, PENNSYLVANIA, AND POSSIBLE ASSOCIATIONS WITH LATE PLEISTOCENE PERMAFROST John Gregory Ruck, ‘20 Advisor: Dr. Dorothy J. Merritts Committee: Dr. Robert Walter, Dr. Timothy Bechtel, Dr. Zeshan Ismat ENE 490 May 2020 An honors thesis submitted to the Department of Earth and Environment at Franklin and Marshall College in conformity with necessary requirements Ruck 2 Table of Contents COVID-19 Impact …………………………………………………………….…...……………. 4 Abstract ………………………………………………………………………………………….. 5 Acknowledgements ……………………………………………………………………………… 6 Introduction …………………………………………………………………………………….... 7 Background ………………..………………..…………………………………………………… 9 Study Area ……………………………………………...……………………………………… 21 Methods ………………………………………………………………………………………… 26 Topographic Analysis and Field Area Surveying …………………………………….... 28 Sample Collection …..…………..……………………………………………………… 29 Grain Size and Angularity ……………...……………………………………………… 30 Drone Photogrammetry ………………………………………………………………… 31 Cosmogenic Laboratory Sample Preparation ………………………………………….. 32 Cosmogenic Nuclide Sample Analyses ………………………………………...……… 33 GIS Grain Size Distribution Analysis: Point Counts ……………………..……………. 33 GIS for Grain Size Distribution Analysis: Grain Covers ….....……………..………….. 34 Results ……………………………………………………………………….…………………. 35 Grain Size and Angularity Analysis for Samples from ATT Road: Site 1………..……. 35 Using GIS for Grain Size Distribution Analysis-Point Counts ………………..………. 38 ATT Road: Site 1 ………………………………………………………………. 38 ATT Road: Site 3 ………………………………………………………………. 41 Using GIS for Grain Cover Distributions ……………...……………………….....…… 43 Ruck 3 ATT Road: Site 1 ………………………………………………………….…… 43 ATT Road: Site 3 ………………………………………………………………. 45 Cosmogenic Isotope Analysis ………………………………………………………….. 49 Discussion ………………………………………………………………………………...……. 51 Conclusion …………………………………………………………………………...………… 62 References …………………………………………………………………………………….... 64 Ruck 4 COVID-19 Impact As described in this thesis, the majority of time for this one-year independent study was used to acquire data from controlled experimentation and modelling of gelifluction processes occurred in a laboratory on Franklin and Marshall College’s campus in 2019-2020. As COVID-19 spread globally in late 2019 to early 2020, especially throughout the United States, the administration of Franklin and Marshall College and the government of the State of Pennsylvania issued restrictions to student access of academic buildings and laboratories on campus. Due to these stringent limitations, the scope of my thesis, originally focused on modelling gelifluction through a series of freeze-thaw cycles in a freezer, was changed approximately two months before the end of the Spring semester. I adjusted the project goals to focus on mapping grain size distributions of outcrops of periglacial sediment at two field sites, and evaluating the sedimentary fabrics and spatial relationships of clasts in these outcrops in order to evaluate the processes that formed the deposits. Ruck 5 Abstract Relict lobate landforms and benches of poorly sorted colluvium are ubiquitous throughout unglaciated central and southern Pennsylvanian, yet the timing and processes associated with their formation are not entirely understood. Similar features known as gelifluction lobes are common in modern cold regions with permafrost, and form during permafrost thaw as a result of slow downslope movement of water-saturated soil or colluvium above a seasonally or perennially frozen substrate. Relict lobes preserved south of the Last Glacial Maximum (LGM) ice margin in Pennsylvania might be indicators of past permafrost conditions. This study characterizes colluvial sediment within relict periglacial lobes in Pennsylvania, using cosmogenic nuclides for age control and both sieving and Geographic Information Systems (ArcGIS) for grain size analysis. The primary objectives are to identify sediment transport mechanisms that were active on hillslopes during the LGM and Pleistocene-Holocene transition (PHT), and to determine if they might have been associated with permafrost conditions. The sedimentary fabrics of colluvium within relict periglacial lobes at a study site 16 km south of the LGM ice margin in eastern Pennsylvania change from clast-supported to matrix-supported in a downslope direction, with increasing distance from the probable bedrock source area of boulders within the sediment. Maps of grain (i.e., clast) cover from drone photogrammetry indicate that colluvium becomes finer-grained and more stratified 10 downslope. In situ cosmogenic Be​ concentration data for multiple samples from depths of ~1 ​ to 5.4 m near the terminus of one relict lobe are consistent with near-surface exposure during the last glacial cycle. They are also consistent with rapid erosion and deposition, and with minimal reworking of sediment since it was deposited. It is concluded that the relict, lobate features Ruck 6 studied here are likely gelifluction lobes that were active during the LGM and possibly the PHT, and were produced by freezing and thawing associated with regional permafrost. Acknowledgements This research was performed as part of a regional, multi-year effort by Dr. Dorothy Merritts, numerous Franklin and Marshall College students, and other collaborators, to evaluate the impact of cold-climate conditions, particularly those associated with permafrost, on landscapes in the mid-Atlantic US. This work is the first of that regional effort to apply cosmogenic nuclide analysis in evaluating the age of periglacial sediment. Cosmogenic nuclide analysis constrains the near surface exposure histories of rocks and sediments based on the accumulation of cosmogenic nuclides produced by cosmic ray bombardment in the uppermost few meters of Earth’s surface (Lal, 1991). The director of the NSF-funded University of Vermont (UVM) Community Cosmogenic Facility (CCF), Dr. Paul Bierman, and facility manager Dr. Lee Corbett, collaborated on this aspect of the work and assisted first in the sampling protocol, and then by guiding me and another student from Franklin and Marshall College, Nic Hertzler, to extract silica and cosmogenic nuclide aliquots at the NSF/UVM Facility. Dr. Merritts’ unparalleled guidance and support throughout the course of this study is greatly appreciated, and I am truly privileged to have experienced her novel and innovative perspectives. Dr. Robert Walter’s expertise in radionuclide geochemistry also was helpful for this part of the research. The guidance and input provided by Dr. Douglas Jerolmack (University of Pennsylvania), Dr. Frank Pazzaglia (Lehigh University), Dr. Jill Marshall (University of Arkansas), and Joanmarie Del Vecchio (graduate student, Pennsylvania State University) on Ruck 7 periglacial landforms, gelifluction mechanics, and mass movement on hillslopes was incredibly valued and appreciated. Julia Carr’s (Pennsylvania State University) methods of using ArcGIS for grain size data collection have been integral to the success of this study. The editing expertise and guidance of Jim Gerhart (USGS, retired) have been influential in writing and editing this thesis. I am grateful to Mr. Ron Gilbert for his permission to work on land that he owns along the newly excavated road built for an ATT cell tower on Chestnut Ridge; his kindness is greatly appreciated. Craig Robertson’s and Jane Woodward’s generosity and donation to the Moss Ritter fund to support field work and cosmogenic analysis was essential, and without it this research could not have happened. I would furthermore like to thank all of those who have donated and supported the Hackman Fund at Franklin and Marshall College, as well as Dr. Robert Walter, Dr. Timothy Bechtel, and Dr. Zeshan Ismat (all Franklin and Marshall College) for agreeing to be on my thesis committee. Without their benevolence and passion for the geosciences, I would have not been provided the opportunity to perform research as a student-scholar with leading researchers in periglacial processes, for which I am incredibly grateful. Introduction Periglacial processes and gelifluction, the slow downslope movement of water-saturated soil or colluvium above a seasonally or perennially frozen substrate, are of critical importance in understanding the response of landscapes in cold regions to modern global warming. Periglacial processes occur where the ground is frozen seasonally or year-round, but not covered by glacial ice. Distinctive lobate and terrace-like landforms produced on hillslopes by gelifluction, called Ruck 8 gelifluction lobes, are common in both formerly and modern periglacial landscapes (Fig. 1; Benedict, 1976; Johnsson et al, 2012). Average modern global temperatures are increasing at an unprecedented rate, with greatest rates of increase at higher altitudes and latitudes where glacial and periglacial processes and landscapes are predominant. As frozen ground thaws, saturated soil and boulders on hillslopes can become unstable, moving downslope via different types of mass movement processes and subsequently altering the morphology of landscapes (Gooseff et al, 2009). These areas can pose significant risks to inhabitants, as land sinks, cracks, and drains, becoming a weak, loosely consolidated mush. Thawing of frozen ground in Arctic coastal villages, for example, has eroded shorelines and streambanks, undermining schools, homes, and pipelines necessary for water and waste transport.
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