Preliminary Analysis of Middle Holocene Lake-Level Change of Ancestral Lake Michigan, Wentworth Woods, Cook County, Illinois

Study of past lake-level change and isostasy in the upper Great Lakes has demonstrated the need to reconstruct relative lake-level history at each outlet during the Nipissing phase of ancestral Lakes Huron, Michigan, and Superior. Although elevation and age data exist for the Port Huron/Sarnia and Sault outlets of Lake Huron and Lake Superior, respectively, no paleohydrograph has been created for southern Lake Michigan near the Chicago outlet. The Wentworth Woods area of the Cook County Forest Preserve, Illinois, contains more than 30 beach ridges that formed during the rise and fall from the peak elevation of the Nipissing phase. These relict shorelines were vibracored to recover basal foreshore sediments that can be used as a proxy for lake-level elevation at the time of individual shoreline formation. In addition, sand samples from soil pits and vibracores were collected for optically stimulated luminescence age determinations. This report addresses the sedimentological data used to determine the elevation of the conjoined upper Great Lakes (Lake Nipissing) when each beach ridge formed. The age data will be presented in future reports.

Ancient Lake Maxima and Substrate-dependent Riverine Migration Have Defined the Range of the Mudpuppy (Necturus maculosus) in Southern Ontario Following the Wisconsinan Glaciation

The Mudpuppy (Necturus maculosus) is an entirely aquatic salamander whose geographic range is thus defined by immigration routes in watersheds that permit feasible travel. Significant barriers, such as large waterfalls, effectively bar this species from further colonization upstream. We compared the contemporary distribution of Mudpuppies in southern Ontario with varying post-glacial ancient lake maxima and riverine outlet-flow conditions. Topography does not appear to be a range-limiting factor, but the type of river grade (waterfalls versus riffles) does. The distribution of modern records of this species in Ontario aligns closely with maxima from the Nipissing phase occurring 4000–5000 years ago, leading us to suggest that this is when Mudpuppies invaded and proliferated in the Great Lakes Basin.

A paleoenvironmental study of the molluscs from the Don Formation (Sangamonian?) Don Valley Brickyard, Toronto, Ontario

The Don Formation comprises 8–9 m of fossiliferous stratified sand and clay, lying between glacial deposits of Wisconsinan and presumed Illinioan age. It has yielded a diverse fossil flora and fauna indicating a climate as warm as or warmer than present and is considered to be of last, or Sangamonian, interglacial age. About 2 t of sediment were processed from the type section of the Don Formation at Toronto, Ontario, and yielded approximately 18 000 identifiable mollusc shells, representing 45 taxa. Previously unpublished taxa include 11 freshwater gastropod species, 12 pelecypod species (Sphaeriidae), and 7 terrestrial gastropod species. The molluscs are mainly concentrated in the lower two-thirds of the formation and are dominated by Valvata perdepressa, with abundant Valvata sincera, Probythinella lacustris, Amnicola limosa, Amnicola walkeri, Pleurocera acuta, Elimia livescens, Pisidium casertanum, Pisidium compressum, Pisidium fallax, and Sphaerium striatinum. All the mollusc species are modern inhabitants of the Great Lakes region. Their known ecological tolerances suggest deposition in relatively shallow waters of a large temperate lake having substantial fluvial input nearby. Stratigraphic variations in the relative abundance of different aquatic taxa may reflect variations in water depth or fluvial activity. Stable isotope data from several mollusc species and a single wood specimen, together with taxonomic paleoenvironmental interpretation, are consistent with deposition during the climatic optimum of the Sangamonian interglaciation. Environmental conditions and faunas are similar to those of the Nipissing phase (Hypsithermal) of the eastern Great Lakes.

A Reevaluation of the Timing and Causes of High Lake Phases in the Lake Michigan Basin

Radiocarbon age control on the type Glenwood, Calumet, and Toleston shoreline features and on the abandoned Chicago outlet at the south end of the Lake Michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin. Radiocarbon dates suggest that Glenwood-level (195 m) shoreline features formed between 14,100 and 12,700 yr B.P. (Glenwood I and II phases), Calumet-level (189 m) between 12,700 and 11,000 yr B.P. (Calumet I and II phases), and Toleston-level (184.5 m) between 5000 and 4000 yr B.P. (Nipissing phase), and that the Chicago outlet was cut to its present level (180 m) on bedrock while the lake was at the Glenwood level. This new chronology is inconsistent with J H. Bretz' hypothesis ((1951) American Journal of Science 249 , 401–429) that the progressive lowering of lake level resulted from episodic down-cutting of the outlet. Instead, the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin. We hypothesize that the Glenwood phases correspond with times when discharge from the Huron and Erie basins also entered the Lake Michigan basin (Lake Border and early Port Huron glacial phases), the Calumet phases with times when drainage was from the Lake Michigan basin alone (late Port Huron and Two Rivers glacial phases), and the Nipissing phase with the postglacial middle Holocene transgression caused by differential uplift in the basin. Estimates of relative net inputs to the basin during the Glenwood, Calumet, and Nipissing lake phases are consistent with estimates of relative outputs (i.e., discharge through the Chicago outlet); the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake-level changes of 4.5 to 6 m.

The Lake Nipissing transgression in the Saginaw Bay region, Michigan

Lake Nipissing phase deposits occur between two cultural zones in exposures at the Weber I archeological site along the Cass River in Saginaw County, Michigan. Radiocarbon dates from the lower cultural zone suggest that the Lake Nipissing transgression did not reach an altitude of 180.7 m before about 4600–5000 BP, whereas dates from the upper cultural zone indicate that the lake level was lowered to the 181.3 m Lake Algoma level before about 3000 BP.