The micromorphology of loess‐paleosol sequences in central Alaska: A new perspective on soil formation and landscape evolution since the Late Glacial period (c. 16,000 cal yr BP to present)

Abstract

The middle Tanana Valley of central Alaska contains a well‐preserved record of human occupation and paleoenvironmental change since the Late Glacial period (c. 16,000 cal yr BP) and is a critical region for understanding human dispersal into the Americas. Micromorphology analysis of soils and sediments from six archaeological sites yields valuable information about soil formation processes and landscape evolution during the Late Glacial and into the Holocene. At the macroscale, site stratigraphies are very similar, and thin organic‐rich layers (locally known as “stringers”) are commonly interpreted as buried soils. However, at the microscale, these layers exhibit significant differences in the degree of bioturbation, organic matter humification, and boundary abruptness, indicating that pedogenesis was not the sole process at every site. In this way, our microscale analysis addresses issues of equifinality related to site formation interpretations, a persistent problem with subarctic and high‐latitude stratigraphy. Additionally, this study reveals a certain level of landform and landscape instability within a broader trend of regional increases in pedogenesis and vegetation coverage, adding to the existing model of heterogeneity across this subarctic landscape. Here we demonstrate the utility of micromorphology to test field interpretations and improve models of Late Glacial landscape evolution in high‐latitude contexts.

The Swan Point Site, Alaska: The Chronology of a Multi-Component Archaeological Site in Eastern Beringia

“…Four buried soils are contained within Unit 4, along with the surface soil. Cultural material is associated with each of the buried soils and the surface soil (Dilley 1998;Holmes 2008Holmes , 2011Kielhofer et al 2020). The lowest buried soil within Unit 4 consists of a loamy sand that is a 1-2 cm thick, discontinuous, and very weakly expressed buried incipient soil (2Ab-2Ck horizons).…”

“…Excavations at Swan Point constitute an area of 85 m 2 to date (Holmes 2011; Potter et al 2014; Smith 2020). Four lithostratigraphic units (Units 1–4) and at least four buried soils have been described at the site (Figure 2; Holmes et al 1996; Dilley 1998; Kielhofer et al 2020). Unit 1 consists of the weathered gneiss bedrock.…”

“…The integrity of the stratigraphic record has been discussed in several publications including Dilley (1998), Holmes et al (1996), Kielhofer et al (2020), and Smith (2020). The cultural zones and subzones are generally vertically separated by culturally sterile loess.…”

“…Cultural Zone 3 is associated with at least two buried incipient soils (C3/Ab3 and C2/Ab2 horizons) separated by 10–15 cm of culturally sterile loess from CZ4 and the lowest 2Ab-2Ck paleosol (Holmes 2011; Kielhofer et al 2020). CZ3 features are hearths that were surficial fires leaving ovoid charcoal stains and oxidized sediments.…”

“…AD 1890–1910 (Holmes and Hemmeter 2017). This component is present in the sod and upper 10 cm of the mineral soil (O-A/E horizons; Kielhofer et al 2020; Smith 2020). Features from CZ0 include a storage or trash pit and a charcoal scatter, most likely a hearth, associated with artifacts.…”