Curry et al. (2018) present a database of 785 reliable, finite radiocarbon ages > 10,000 C-14 yr BP of samples from locations primarily in Illinois. The list includes 507 ages determined by benzene scintillation methods, and 278 by accelerator mass spectrometry. In this paper, the data are used to revisit the evidence for the age of key diachronic units. A probability density function of all calibrated ages shows distinct periods of time when little organic matter was preserved in Illinois. These plots present interesting paradigms and questions regarding paleoclimate and environments of deposition. Below is an example of using a subset of these data for research extending beyond the glaciated Midwest. Lake Chicago. The geochronology of samples taken from high-level lacustrine deposits associated with Lake Chicago, the proglacial precursor of Lake Michigan, shows a pronounced near-absence of ages from about 15.0 to 14.2 cal ka, between high stands related to the Glenwood and Calumet phases. I presume that the lack of ages is due to a paucity of sediment to bury and preserve organic matter; indeed this is the case when examining the sediment accumulation rates for Riggle Pond, Indiana (Bruegger, 2016). What caused this low stand, and how significant is it? Regional correlations with Gulf of Mexico stable isotope records show strong evidence for enhanced meltwater discharge coming from Lake Chicago at 16.5, 16.0, 15.1, 14.1 and 13.4 cal ka, especially the 15.1 cal ka event, which is also observed in the dates associated with other sediment systems between the Chicago Outlet and Gulf of Mexico. I hypothesize that it relates to the catastrophic discharge of meltwater that caused major modification of the Grand River valley (Kehew, 1993).
|Original language||English (US)|
|State||Published - 2018|