Early Holocene soil cryoturbation in northeastern USA: Implications for archaeological site formation

The study of buried soil archives in alluvial settings can be used to characterize floodplain and terrace habitats and complement other paleoenvironmental and archaeological archives. This study examines the early Holocene alluvial paleopedology along the Delaware River Valley in the northeastern USA. Chronological and alluvial stratigraphic data show that a widespread loam alluvial paleosol formed from 10.7 to 9.3 ka, herein referred to as the Jennings Lane Pedocomplex (JLP). The JLP at the Jennings Lane locality along the Delaware River, NJ, is a loam to silt loam soil that formed on mixed alluvium and windblown and/or reworked dust, likely sourced from nearby periglacial fines. This finding supports previous interpretations of late Quaternary dust deposition and reworking in the region. Fragic properties (e.g., firm peds with brittle manner of failure and rapid slaking in water) and cryogenic micromorphological features (lenticular pores, stone jacking and shattered grains) present within the JLP suggest cryoturbation. Soil mass-balance modeling suggests that the strain (ɛ) in immobile elements Ti and Zr show a dilation–collapse profile. These data indicate that organic matter and/or dust addition, and freeze-thaw created soil dilation at the JLP paleosurface. Mass-balance additions in Fe, K, and Mg are consistent with illuviated Fe-rich clay coatings present in thin section. The X-ray diffraction results show that these clays are illite, vermiculite, and kaolinite. Paleosol data presented here suggest that the JLP was overprinted by later pedogenic processes during the middle Holocene. τTi,Na shows minimal loss throughout much of the profile. Although rapid thaws may have promoted downward translocation of fines, the cold environment impeded base loss through either minimal release of cations from primary minerals or negligible water flux, as suggested by τTi,Na profiles and gains in τTi,K and τTi,Mg. This silt-rich JLP pedofacies experienced minimal chemical depletion over the course of ∼1200–3500 years. This cold-climate weathering coincides with rapid temperature fluctuations (10.5, 9.3, 8.2 ka) during the early Holocene in northeastern USA. This soil cryoturbation evidence has archaeological implications as well. The cryoturbation in this early Holocene pedocomplex suggests that vertical and lateral artifact redistribution is possible. Archaeologists should use caution when interpreting archaeological stratigraphy and intrasite artifact patterns at mid- to high-latitude archaeological sites.