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Did Neanderthals and Modern Humans meet? – Reexamining the chronology of sediments in Vindija Cave (Croatia) by using single-grain optically stimulated luminescence

Optically stimulated luminescence (OSL) dating is capable of constraining the sedimentary ages of a range of terrestrial and aquatic deposits and has thus become a widely used dating technique for the Quaternary over the past two decades (e.g. HUNTLEY et al., 1985 ; DULLER, 2004 ; LIAN & ROBERTS, 2006). Some key advantages of OSL dating are: (i) the dateable age range extends well into the Mid Pleistocene (whereas e.g. 14C dating has an upper age limit of ca. 40 – 50 ka), (ii) very young sediments can be dated with good precision (while radio carbon dating suffers from the effect of 14C plateaus over that time range) and (iii) – because OSL constrains the depositional age of sediments directly – reliable OSL chronologies can be obtained for sedimentary deposits which are organically sterile (i.e. contain no material suitable for radiocarbon dating) or where the organic material is much older (e.g. detrital charcoal) or much younger (e.g. modern tree roots) compared to the true sedimentary age of the deposit. The latest development in OSLdating is the single-grain approach. The move towards single-grain analysis parallels that in other modern geochronology methods, such as single- crystal dating in argon–argon (40Ar/39Ar) and fissiontrack, and microsample analysis in accelerator mass spectrometry radiocarbon (AMS 14C) and inductively coupled plasma mass spectrometry uraniumseries (ICP-MS 230Th/234U) dating. Single-grain OSL dating offers new opportunities to date deposits that were previously regarded as troublesome, including archaeological sediments deposited in cave mouths or rock shelters (e.g. ROBERTS et al., 1998 ; JACOBS & ROBERTS, 2007). OSL dating requires the complete resetting of the lightsensitive signal by exposing the sediments to sunlight (bleaching). Cave-mouth sediments may have formed from a mixture of unbleached authochthonous material (e.g. grains released via decomposition of roof spall material) and wellbleached allochthonous sediment, introduced into the cave via wind, slopewash or tidal processes. The main benefits of analysing individual grains include the identification of such contaminant grains in a sample and their exclusion before final age determination, as well as the ability to directly check the stratigraphic integrity of archaeological sites, where human activities and other sediment mixing processes (e.g. bioturbation) commonly result in ost-depositional disturbance. Furthermore, single-grain OSL dating allows the operator to reject unreliable data on a grain-by-grain basis – that is – to dismiss grains that fail well-defined acceptance criteria that are built in to the single aliquot regenerative (SAR) measurement. The same extent of data validation is not possible using aliquots composed of multiple grains because these give rise to a cumulative OSL signal from many tens, hundreds or thousands of grains, including some grains that might have been rejected if measured individually. Due to these inherent benefits, the single-grain approach (as opposed to multiple-grain OSL dating) is the tool of choice for complex archaeological sequences in order to improve the accuracy and precision of OSL-based chronologies. Here we describe our ongoing OSL dating campaign at Vindija Cave, a key archaeological site in central Europe that contains a 12 m-thick sequence of cave-mouth sediments spanning the Middle to Upper Palaeolithic. The cave is famous for its Neanderthal and modern human remains, and Neanderthal DNAhas been retrieved from several of the bones (GREEN et al., 2010), but the chronology and interpretation of these records remain a matter of lively discussion (KARAVANIĆ & SMITH, 1998 ; WILD et al., 2001 ; ZHILAO, 2009). We summarize the dosimetry of Vindija Cave, present the preliminary equivalent dose distributions measured via both, single-grain and ultiple-grain approaches and discusses our OSL data in the light of the cave sedimentology, as post-depositional disturbance of the cave- -mouth sediments has been recognised.

single-grain OSL dating; Archaeology; Palaeolithic; Late Pleistocene

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