Holocene eolian sediment and organic matter from terraces and hillslopes around Healy, central Alaska

Walker, Caitlin Marie (2023) Holocene eolian sediment and organic matter from terraces and hillslopes around Healy, central Alaska. Masters thesis, Northern Arizona University.

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Abstract

As the most widespread surficial sediment in Alaska, eolian sediment plays an important role in burying organic matter, the aggradation of surficial sediment, and upward permafrost growth. Extensive archaeological excavations have taken place around Healy, central Alaska, where Pleistocene river terraces are capped by Holocene eolian sediment interstratified with organic-rich layers, sometimes called loess-paleosol sequences. In this study, I investigated Holocene eolian deposits in the Nenana Valley in two different depositional settings: exposures along river terrace cutbanks near the Nenana River and a suite of shallow hillslope cores from the nearby Eight Mile Lake watershed. The main goals were to investigate (1) if spatial trends in eolian sediment accumulation are coherent across the study area, and (2) if intervals of Holocene organic matter accumulation correlate across different depositional settings. Three exposures near Healy (Dry Creek, Panguingue Creek, and Healy Spur) and core transects from three hillslopes near Eight Mile Lake were investigated and compared to previously published studies from the area. Analyses include particle size distribution, loss-on-ignition for organic matter content, and radiocarbon dating. Across the valley, the surficial eolian cap was thickest in the southeast and thinned to the northwest, while particle size exhibited no spatial trends. On hillslopes, eolian accumulation depended on aspect relative to the prominent wind direction. Three particle size modes were identified through end member modeling used to interpret possible sediment sources: silt transported long distances by northerly winds, fine sand from the Nenana River carried on southeasterly winds, and coarser sand saltated from nearby tributary floodplains. Neither the stratigraphy nor the radiocarbon ages of interbedded loess-paleosol sequences overlying the river terraces are as consistent as expected. I tentatively suggest three periods during the middle and late Holocene when organic matter might have preferentially accumulated across the river terraces and hillslopes around Healy. A frequency distribution of radiocarbon ages in the area shows a downturn between 5.5 and 3.5 ka, which could reflect reduced productivity associated with Neoglacial cooling. It also highlights the different sampling strategies between archeological and paleoenvironmental studies. Heterogeneity in surficial sediment around Healy likely reflects local influence of topography and possibly vegetation on eolian sediment and organic matter, as well as variable inputs from multiple sediment sources. The complexity in correlating Holocene soil-forming periods is likely influenced by the multiple organic matter types. This study investigated Holocene eolian sediment across the landscape, highlighting the variability of the organic matter that it contains.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Central Alaska; Holocene eolian sediment; Loess; Organic Matter; Paleosol
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	29 Jul 2026 20:43
Last Modified:	29 Jul 2026 20:43
URI:	https://openknowledge.nau.edu/id/eprint/6332

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