Plant and Insect Remains from the Wisconsinan Interstadial/Stadial Transition at Wedron, North-Central Illinois

Abstract

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ± 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated byPicea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, includingPicea, Larix laricina, and the mossCampylium stellatum; subarctic species includingBetula glandulosa, Empetrum nigrum, andSelaginella selaginoides; along with the predominantly arcticVaccinium uliginosumvar.alpinum, Dryas integrifolia, andRhododendron lapponicum. The insect fauna contains the western montane ground beetleOpisthius richardsoni; several arctic-subarctic ground beetles includingDiacheila polita, Helophorus sibiricus, andPterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation.

Landscape evolution, alluvial architecture, environmental history, and the archaeological record of the Upper Mississippi River Valley

“…; Fig. 2; Baker et al, 1986Baker et al, , 1989Garry et al, 1990;Woodman et al, 1996;Schwert et al, 1997;Baker and Mason, 1999;Curry and Yansa, 2006). The presence of ice-wedge casts (Péwé, 1983;Johnson, 1990;Walters, 1994) and extensive frost-shattered colluvial and solifluction deposits (Bettis and Kemmis, 1992;Bettis, 1994;Mason and Knox, 1997) suggest the significant impact of fullglacial climates on upland and valley-margin landscapes beyond the glacial margin.…”

Effects of late Pleistocene permafrost on the landscape of Wisconsin, USA

“…Other studies have documented plants and animals of the tundra or tundra-boreal transition zone before 11 450 yr BP in southeastern Minnesota, and as late as about 14 000 yr BP in northern and eastern Iowa, and northern Illinois (Amundson & Wright 1979;Baker et al 1997;Baker & Waln 1985;Birks 1976Birks , 1981Garry et al 1990;Holloway & Bryant 1985;Jelgersma 1962).…”

“…The beginning of the permafrost episode has been dated by Garry et al (1990), who studied a site at Wedron, in central Illinois, and found fossil plants and insects that indicate a transition from boreal forest to tundra about 21 460 § 470 BP. Baker et al (1989) gave a date of 22 000 yr BP for the beginning in Iowa and Illinois, and Curry & Follmer (1992) gave 23 000 yr BP for several sites in northern Illinois.…”

Mid‐Wisconsin seasonal temperatures reconstructed from fossil beetle assemblages in eastern North America: comparisons with other proxy records from the Northern Hemisphere

“…An organic deposit in a small swale fill was sampled from a sand pit at this site in north-central Illinois (Garry et al, 1990). Wood from this deposit has been dated at 21 460 ± 470 yr BP.…”