Insights from Quartz Single and Multiple Grain Luminescence Dating
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Quaternary International 501 (2019) 289e302 Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint Chronology of the Late Pleistocene archaeological sequence at Vanguard Cave, Gibraltar: Insights from quartz single and multiple grain luminescence dating * Nina Doerschner a, , Kathryn E. Fitzsimmons a, b, Ruth Blasco c, Geraldine Finlayson d, e, Joaquín Rodríguez-Vidal f, Jordi Rosell g, h, Jean-Jacques Hublin a, Clive Finlayson d, e, i a Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, DeutscherPlatz 6, 04103, Leipzig, Germany b Research Group for Terrestrial Palaeoclimates, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128, Mainz, Germany c Centro Nacional de Investigacion sobre la Evolucion Humana (CENIEH), Paseo Sierra de Atapuerca 3, 09002, Burgos, Spain d The Gibraltar Museum, 18-20 Bomb House Lane, Gibraltar e Institute of Life and Earth Sciences, The University of Gibraltar, Gibraltar Museum Associate Campus, 18-20 Bomb House Lane, Gibraltar f Departamento de Ciencias de la Tierra / Earth Sciences, Facultad de Ciencias Experimentales, Universidad de Huelva, Campus del Carmen, Av. Tres de Marzo s/n, 21071, Huelva, Spain g Area de Prehistoria, Universitat Rovira i Vigili (URV), Avenida de Catalunya 35, 43002 Tarragona, Spain h IPHES, Institut Catala de Paleoecologia Humana I Evolucio Social, Zona Educacional 4, Campus Sescelades URV (Edifici W3), 43007 Tarragona, Spain i Department of Anthropology, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada article info abstract Article history: Vanguard Cave is an archaeological site located on the shoreline of the Rock of Gibraltar at the south- Received 31 October 2016 western extreme of the Iberian Peninsula. It is part of a limestone cave system facing the adjacent Received in revised form Governor's Beach on the south-eastern coast of Gibraltar and has been filled to the roof with more than 12 October 2017 17 m of sedimentary deposits. Due to its long stratified sequence, comprising rich palaeoenvironmental Accepted 16 February 2018 and faunal records as well as multiple Palaeolithic occupation layers, Vanguard Cave provides valuable Available online 7 March 2018 information for our understanding of human behaviour and dispersal across south-eastern Iberia in general and particularly about the strategic role of the promontory of Gibraltar for past human pop- Keywords: Optically stimulated luminescence ulations. The development of a reliable absolute chronology for the sedimentary sequence at Vanguard Quartz single grains Cave is therefore of great importance in this context. Multi-grain aliquots In this study, we applied optically-stimulated luminescence dating to sand-sized quartz grains from Vanguard Cave the uppermost ~4 m of the Vanguard Cave deposits, as well as from the Hyaena Cave sediments e a small Gibraltar niche adjacent to the main cave chamber. We use single-grain and multiple-grain dating to clarify the Middle Palaeolithic depositional history of the sedimentary sequence, as well as to assess the reliability of the two dating approaches and their potential for future chronological studies at the site. The single-grain and multi- grain ages are consistent with one another and indicate no partial bleaching or post-depositional mix- ing of the sediments. Our results suggest that Vanguard Cave experienced continuous sediment accu- mulation probably since the last sea-level highstand in MIS 5, and was completely filled by ~43 ka (MIS 3). The eastern side of the Rock of Gibraltar faced an exposed coastal shelf covered with savannah and an active coastal dune system during MIS 3. Our results indicate that similar environmental conditions are likely to have persisted also during MIS 4 and large parts of MIS 5. © 2018 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction the Iberian Peninsula was more complex than previously thought (Finlayson et al., 2006; Higham et al., 2014). While the timing of Current data suggest that the disappearance of Neanderthals in Neanderthal persistence in southern Iberia is still a matter of ongoing scientific debate, general consensus exists that there was a temporal overlap between anatomically modern human (AMH) and * Corresponding author. Neanderthal populations on the European continent (e.g. Finlayson E-mail address: [email protected] (N. Doerschner). https://doi.org/10.1016/j.quaint.2018.02.020 1040-6182/© 2018 Elsevier Ltd and INQUA. All rights reserved. 290 N. Doerschner et al. / Quaternary International 501 (2019) 289e302 et al., 2006; Higham et al., 2014; Mellars, 2006; Wood et al., 2013). ubiquitous within the sediments; unlike heated lithics required for Recent genetic studies have showed that these two human groups thermoluminescence dating, and the fact that the organic matter even interbred outside Africa (Green et al., 2010), which contradicts preserved at the site is likely to be older than the upper limits of the a rapid replacement of Neanderthals by AMHs and supports the radiocarbon technique. OSL dating measures the time elapsed since more complex model of a population mosaic during the Middle to mineral grains were last exposed to sunlight, with quartz and Upper Palaeolithic transition in Europe (Finlayson et al., 2006; feldspar grains acting as natural dosimeters for the surrounding Higham et al., 2014). environmental radiation (Aitken, 1998). Technical improvements in Central to understanding the process of Neanderthal replace- recent years have enabled the refinement of measurement pro- ment by, and their interaction with, AMHs in Europe are robust tocols (Murray and Wintle, 2000) as well as the measurement of chronological frameworks, coupled with palaeoenvironmental luminescence arising from individual grains (Bøtter-Jensen et al., contexts for the conditions under which the contact between the 2000; Duller et al., 1999; Jacobs and Roberts, 2007). Single-grain two human groups took place. High resolution archives can be OSL dating of quartz enables e unlike dating of multi-grain ali- obtained from sites with long stratigraphic sequences yielding in- quots - the identification of potential problems such as incomplete dications of long-term occupation by humans in the territory. The signal resetting, post-depositional mixing or beta dose rate het- archaeological sites of Gibraltar present a unique opportunity to erogeneity in sediment samples (Jacobs and Roberts, 2007). Quartz assess the persistence of the last Neanderthals in the same single-grain dating is increasingly adopted for archaeological sites geographical setting as the first AMHs. in particular, where these sorts of issues are relatively common and The Vanguard Cave (VC) site of Gibraltar contains evidence of need to be identified (e.g. Doerschner et al., 2016; Fitzsimmons Middle Palaeolithic human occupation within a >17 m thick sedi- et al., 2014; Jacobs et al., 2012; Tribolo et al., 2010). The measure- mentary sequence. The site is located on the south-eastern coast of ment of multi-grain aliquots remains advantageous over single- the peninsula in close vicinity to the better known Gorham's Cave. grains when i) each of the aforementioned factors that may bias Unlike Gorham's e which was discovered in 1907 by A. Gorham and the real depositional age of a sediment layer can be excluded, since has experienced a long history of academic research since then e measurement and analyses time is reduced; and ii) luminescence the first series of excavations at VC was conducted much more signal intensities of individual grains are comparatively low and recently (1995e1998) as part of the Gibraltar Caves Project (Barton difficult to measure, so an aggregate signal can be measured. Ac- et al., 2013; Stringer et al., 2000). Despite its later discovery, cording to what we know from previous studies, the sediments at investigation at VC has had the benefit of more sophisticated VC should have been completely bleached and not subject to post- analytical methods and the systematic integration of modern depositional mixing; nevertheless this is important to test. Conse- sedimentological, archaeological and geochronological data quently, VC provides an excellent context for comparing single- (Table S1). grain with multi-grain dating results, and so we undertake both Up until now, 16 ages provide a chronological overview of VC, sets of measurements in this study. Our new, high resolution dual but their usefulness and reliability is limited. Seven radiocarbon chronology for the uppermost part of the VC sequence and HC aims dates published by Pettitt and Bailey (2000) showed that the cave not only to clarify the timing of sediment deposition and human deposits accumulated close to or beyond the limit of that dating occupation in the cave, but also to assess the reliability of single- method, and therefore that VC had probably filled to its present grain vs. multi-grain ages and their suitability for future dating of level by ~45 thousand years ago (ka). These results were confirmed the lower stratigraphic units at VC. Finally, we place our chrono- by the results of multiple (multi-)-grain optically stimulated logical results in the context of existing Late Pleistocene archaeo- luminescence (OSL) dating e also often referred to as single aliquot logical and palaeoenvironmental data for the region. dating - on three sediment samples ranging in age from 46 ± 3kato 112 ± 10 ka (Pettitt and Bailey, 2000). Later work,