Stratigraphy, age, and flora of the Southport forest bed, Southeastern Wisconsin

A mid-Holocene buried organic layer 10 to 60 cm thick is present along the Lake Michigan shoreline in southeastern Wisconsin. Named the Southport forest bed for its location in Kenosha County, the unit has yielded abundant wood specimens, including large logs, branches, twigs, stumps, and root material. Roots of truncated in situ oak (Quercus) and elm (Ulmus) trees extend into the underlying till of the late Wisconsin Oak Creek Formation. Nearshore lacustrine sand above the organic layer contains abundant driftwood, overlain by 2 to 3 m of cross-bedded dune sand. More than 50 wood samples have been identified; the assemblage is that of a mixed hardwood forest dominated by oak (Quercus) and hickory (Carya), which account for about 60% of the assemblage. Although the site has been mostly concealed for many years, it was beautifully exposed in the 1960s and early 1970s, when it was initially studied by Phil Sander, who discovered the site and documented it with field notes and numerous photographs. Here we report several new (unpublished) radiocarbon dates and details of the stratigraphy and arboreal flora. Radiocarbon dates suggest that the Southport forest probably lived for 900-1000 ¹⁴C years, possibly longer, reaching its climax at about 5300 B.P. The site is of particular importance because of its proximity to the Nipissing shoreline and provides a significant point on the Nipissing transgression time curve. The unusually large number of identified specimens affords an accurate evaluation of the warm and relatively dry climate that characterized the southern Great Lakes region during the mid-Holocene.