Date of Award
Master of Science (MS)
Two highly organic sediment sequences from central and western Illinois (the Athens North Quarry and Biggsville sites, respectively) of Middle and Late Wisconsinan age were studied to gain knowledge about the environment and climate of this area during the time immediately prior to the maximum extent of the last glaciation. Paleoenvironmental and paleoclimatic inferences are based principally upon knowledge of the habitat preferences and geographic distributions of extant species of beetles that are represented as fossils. These data are supplemented by information from sedimentological and taphonomic studies and from previously published palynological and plant-macrofossil studies.
The Athens North Quarry site is a 2.8 m-thick sequence of organic silt, ranging in age from about 25,000 to 22,000 11 c yr B.P. Two faunal zones based upon beetle fossils were recognized; a third was defined using gastropods. The environment, inferred from the fauna, was the margin of a eutrophic lake surrounded by a moist coniferous forest. The sequence of events at the Athens North Quarry site began with the expansion of a nearby lake or pond over the forest floor, and ended with the infilling of the water body by Woodfordian loess and organic material. The Biggsville site is a channel-fill deposit consisting of fluvial deposits, organic sediments, peat, and loess. Samples for beetle analysis were collected from a 2.2 m-thick section of organic loams and peat ranging in age from 27,870 ~ 290 to 21,410 ~ 290 ~Cyr B.P. Two coleopteran faunal zones were recognized. Habitats inferred from the beetle species present in these zones are interpreted as representing the development and demise of a bog in an abandoned stream channel, surrounded by a thin, spruce-dominated coniferous forest. The bog and forest were eventually choked by peat and loess deposits. This was followed by a period of pedogenesis.
An interpretation of the climate of central and western Illinois between about 28,000 and 21,000 14c yr B.P. is based upon the present ranges of the species represented by fossils in the Athens North Quarry and Biggsville sites. The majority of these species now occur in the southern boreal forest region of southern Canada and northern United States. The climate during this period apparently was relatively stable, in contrast to the interpretation of previous workers in this area; compositional changes in the coleopteran assemblages are interpreted as reflections of local changes in the environment rather than as indications of the shift from interstadial to full glacial conditions.
Carter, Kristine D., "Middle and Late Wisconsinan (Pleistocene) insect assemblages from Illinois" (1985). Theses and Dissertations. 52.