LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Amino Acid Geochronology as an Independent Test of Numerical Dating Methods Applied to Eurasian Loess (Serbia, Romania, Tajikistan and Kazakhstan)
Machalett, B.1,2, Oches, E. A.2, Meng, S.3, Markovic, S. B.4, McCoy, W. D.5
1Humboldt-University of Berlin, Department of Geography, Unter den Linden 6, D-10099 Berlin, Germany;
2Natural and Applied Sciences Department, Bentley College, Jennison Hall 126, 175 Forest Street, Waltham, Massachusetts 02452-4705, USA
3University of Greifswald, Institute of Geography and Geology, Domstraße 11, D-17487 Greifswald, Germany
4Chair of Physical Geography, Faculty of Sciences, University of Novi Sad, Serbia
5Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA
Paleoclimatic investigations of loess-paleosol sequences depend on the application of numerical dating techniques, including radiocarbon, luminescence, and paleomagnetic methods, in order to develop reliable time series for the proxies being studied. Commonly, the utility of luminescence and radiocarbon dating is limited by their applicable dating range. In many European and Central Asian loess sites, luminescence results show a significant age underestimation for samples taken from loess of the last glacial cycle. Ages of lower to middle Pleistocene strata are limited to relatively coarse estimates using biostratigraphy and paleomagnetic reversal stratigraphy. Amino acid racemisation (AAR) geochronology, although primarily a relative dating method, offers an independent assessment of numerical age estimates when results are at or near their methodological limits and can assist in the chronostratigraphic evaluation of loess units beyond the applicable range of numerical dating methods.
In this study we present the first comprehensive aminostratigraphic results from a Central Asian loess site: the Remisowka loess sequence in southeastern Kazakhstan. We also present new results from the loess series at Stari Slankamen and Mosorin (Titel Plateau) in Vojvodina, Serbia, and offer initial results from the loess sequences Mircea Voda, Romania and Chonako, Tajikistan. We measured D/L ratios of glutamic acid, aspartic acid, phenylalanine, valine, and alloIsoleucine/ Isoleucine in fossil shells of the terrestrial gastropod genera Pupilla, Pseudonapaeus, Leucozonella, Helicopsis, Vallonia, Clausiliidae and Succinea, which were selected for their wide geographic occurrence and reliability and reproducibility in repeated D/L measurements.
The results of AAR analyses allow us to propose an independent age model for the studied loess series, and their combination with numerical dating techniques allows us to confidently determine a chronostratigraphic model for the last four interglacial-glacial cycles in Serbia, Romania and Central Asia loess sequences, casting new light on the Middle to Upper Pleistocene chronostratigraphy and paleoclimate record of Eurasian loess. At Stari Slankamen, AAR data identified a previously unrecognized unconformity, leading us to propose to a new chronostratigraphic interpretation for that long-studied loess profile.
In conjunction with other analytical and geochronological techniques, we aim to highlight the vast potential of highly resolved multi-proxy investigations of the terrestrial aeolian dust record. As loess sediments are widespread on the continents and offer semi-continuous palaeoclimatic reconstructions on regional and inter-hemispheric scales, we anticipate that the implementation of new and refined methods will lead to a renaissance in the study of these important terrestrial climate archives.