MICROMORPHOLOGY OF BURIED SOILS IN CENTRAL ALASKA: A PETROGRAPHIC APPROACH TO UNDERSTANDING SOIL FORMATION DURING THE LATE PLEISTOCENE AND HOLOCENE IN INTERIOR SUBARCTIC LOWLANDS

Micromorphology is a valuable tool for identifying soil characteristics that are difficult or impossible to observe in the field. This technique has great potential to elucidate soil formation in high-latitude settings, where buried soils are often thin, discontinuous, and weakly developed. The Shaw Creek Flats (SCF) catchment and Delta River Valley (DRV) of interior Alaska are ideal regions for micromorphology, as they contain numerous buried soils in Late Pleistocene and Holocene aeolian deposits. However, little micromorphological research has been conducted in these regions, with most samples collected directly from archaeological excavations. In these cases, past human activity and cultural features could obscure the true soil-stratigraphic record. Therefore, previous samples may not accurately reflect the role of paleoenvironmental conditions on soil formation.

To address such concerns, this micromorphology study examines soils from non-archaeological localities. Samples were collected from a deeply buried, stratified loess deposit near the Mead archaeological site in SCF and at the Hurricane Bluff loess exposure in the DRV. At Mead, buried soils dated to the Younger Dryas (12,120-11,850 cal BP) exhibit abundant and well-preserved organic matter, dusty clay coatings, and clay infillings, suggesting a moderate degree of pedogenesis. Abundant iron (Fe) oxide nodules and mottling indicate a fluctuating water table. In contrast to prior studies, frost action features are not observed, indicating that these soils were not strongly impacted by freeze/thaw processes. It is also possible that later soil formation under warmer Holocene climatic regimes obliterated such features. Hurricane Bluff samples show evidence of clay translocation, Fe oxide accumulation and moderate soil development throughout the Holocene, confirming field interpretations. Ultimately, soil micromorphology at these sites indicates moderate pedogenesis and weathering under relatively wet conditions or alternating wetting and drying cycles in the Late Pleistocene. Micromorphology also reveals the importance of vegetation growth in forming Late Pleistocene soils. Despite the modern prevalence of permafrost in this area, Late Pleistocene and most Holocene soils do not appear altered by frost action.