Thermoluminescence Dating of Loess from Western Iowa

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Abstract
This study was conducted to evaluate thermoluminescence as an alternative to radiocarbon dating to determine age of soil materials low in organic carbon from major loess units from western Iowa. Thermoluminescence (TL) ages were determined for Upper Wisconsinan (Peoria), Basal Wisconsinan (“Farmdale”) and Loveland loesses using the fine‐grained technique on the 4 to 11 µm particle size fraction. Corrections were made for soil moisture and cosmic radiation influences. Thermoluminescence dating was effective in separating the three major loess units studied. The dates for Upper Wisconsinan (Peoria) loess were comparable to published radiocarbon dates, ranging between 13 150 to 24 130; however, there was considerable variability in the dates. The Basal Wisconsinan (“Farmdale”) loess gave considerably older ages (45 960–46 720) than reported with radiocarbon dating. Illinoian age Loveland loess yielded a date of 89 200 yr and was somewhat younger than presumed for the Illinoian advance. Thermoluminescence dating appears to be a viable alternative to radiocarbon dating of loess when organic material is not present, but more work is needed to rectify the age discrepancies. Although TL dating does not give dates in stratigraphic or chronological agreement with radiocarbon dating, it does differentiate the loesses studied.

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