| Popis: |
Numerous localities in the Czech Republic, Slovakia, and Austria have been sampled for fossil gastropod shells for the purpose of an aminostratigraphic evaluation of loess sequences. In all three regions alloisoleucine/isoleucine (aIle/Ile) ratios are observed to be significantly higher in shells from loess deposited during the penultimate glacial period (cycle C) relative to samples from loess of the last glaciation (cycle B). The difference in aIle/Ile ratio reflects both difference in age of the samples plus the impact on the older samples of the relatively high effective temperature of the last interglacial period. Amino acid data support the previous correlation suggested between PK II+III in the Czech Republic and Slovakia and the ‘Stillfried A’ in Austria. Samples have also been recovered from older loess units, and previously published correlations within the Czech and Slovak Republics are tested. AIIe/Ile ratios appear to distinguish between samples from loess of the last four glacial cycles. Beyond cycle E (18O Stages 10 and 11), the increase in alle/Ile ratio is relatively small from cycle to cycle. In addition, shells tend to be poorly preserved and are absent at many localities. Nevertheless, amino acid geochronology offers a means of resolving ages of loess units in the critical time period that is beyond the range of radiocarbon and thermoluminescence methods but post-dates the Brunhes-Matuyama paleomagnetic reversal. |
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