Assessing Assumptions and Applying Cosmogenic Nuclide Methods to Earth Surface Processes

• Main Author: Halsted, Christopher T
• Format: Text
• Language: English
• Published: UVM ScholarWorks 2022
• Subjects: Cosmogenic Nuclides; Fluvial Erosion; Glacial Chronology; Methodological Assumptions; Geochemistry; Geomorphology; Ice Sheet
• Online Access: https://scholarworks.uvm.edu/graddis/1536; https://scholarworks.uvm.edu/context/graddis/article/2537/viewcontent/Halsted_uvm_0243D_11304.pdf

Terrestrial in situ cosmogenic radionuclides are powerful tools for quantifying rates and durations of Earth surface processes. Among the many applications of cosmogenic radionuclides are quantification of basin-scale erosion rates, burial durations of paleosols and terrace sediments, and unraveling of glacial chronologies. In this dissertation I use large data sets to investigate methodological assumptions critical for using cosmogenic radionuclides to interpret Earth surface processes, and I apply this isotope system to reconstruct the deglacial history of the Laurentide Ice Sheet in the northeastern United States. I use new and previously-published measurements of in situ 26Al and 10Be concentrations, over 300 from glacially-scoured rock surfaces and over 500 from fluvial sediments, to assess the veracity of cosmogenic radionuclide methodological assumptions. I use the glacial samples to investigate global variations in the 26Al/10Be production ratio, a critical value in dual-nuclide studies that has long been assigned a globally-constant value. I find robust evidence for a negative correlation between the 26Al/10Be production ratio and altitude, and a positive correlation between the production ratio and latitude, patterns that agree well with models of nuclide production. I use the fluvial sediment samples to investigate a key assumption in basin-wide erosion rate studies: that fluvial sediment samples experience, on average, a simple hillslope mobilization and fluvial transport history. My dual-nuclide analyses suggest that this assumption is violated in many samples from around the world, implying that erosion rates may be overestimated for these basins. I use regressions between the apparent complexity of sediment transport history and basin parameters to investigate if systematic patterns exist that explain the occurrence of non-simple sediment histories. I find that steep and/or small catchments are correlated with simple sediment transport histories, while low-slope and/or large catchments are ...