Quaternary Science Reviews 65 (2013) 39e52 Contents lists available at SciVerse ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Paleoanthropologically significant South African sea caves dated to 1.1e1.0 million years using a combination of UePb, TT-OSL and palaeomagnetism Robyn Pickering a,*, Zenobia Jacobs b, Andy I.R. Herries c, Panagiotis Karkanas d, Miryam Bar-Matthews e, Jon D. Woodhead a, Peter Kappen f, Erich Fisher g, Curtis W. Marean g a School of Earth Sciences, University of Melbourne, McCoy Building, Cnr Swanston and Elgin Streets, Parkville, Melbourne, Victoria 3010, Australia b Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, New South Wales 2522, Australia c Australian Archaeomagnetism Laboratory, Department of Archaeology, Environment and Community Planning, Faculty of Humanities and Social Sciences, La Trobe University, Victoria 3086, Australia d Ephoreia of PalaeoanthropologyeSpeleology of Southern Greece, Ministry of Culture, Greece e Geological Survey of Israel, 30 Malchei Israel St., Jerusalem 95501, Israel f Department of Physics, Faculty of Science, Technology and Engineering, La Trobe University, Victoria 3086, Australia g Institute of Human Origins, School of Human Evolution and Social Change, PO Box 872402, Arizona State University, Tempe, AZ 85287-2402, USA article info abstract Article history: Deposits in sea caves found along the southern coastline of South Africa have produced a rich and Received 27 September 2012 detailed archaeological record of early modern humans. There is, however, little evidence for coastal cave Received in revised form deposits and human occupation older than MIS5e (w120 ka). Based on the correlation of four different 20 December 2012 chronological methods we present evidence for remnant cave deposits of 1.1e1.0 Ma from the quartzite Accepted 22 December 2012 sea cliff of Pinnacle Point, near Mossel Bay. Initial uraniumethorium ages at isotopic equilibrium indi- Available online cated an age of >500 ka for two flowstone layers, confirmed by uraniumelead dating of these flowstones from 1.099 Æ 0.012 to 1.047 Æ 0.011 Ma. TT-OSL (thermally transferred optically stimulated lumines- Keywords: Æ Geochronology cence) provides an age of 1.02 0.088 Ma for the sand grains imbedded in the tufa underlying the fl Æ Æ UePb dating owstone and 0.720 0.066 to 0.665 0.056 for the overlying beach sediments, producing an internally TT-OSL dating consistent age sequence centring on 1.0e1.1 Ma. The normal palaeomagnetic signal of the younger Palaeomagnetism section of the flowstone is interpreted to represent the Jaramillo between 1.07 and 0.99 Ma. There is Pinnacle Point a clear hiatus in the middle of this flowstone, leading us to interpret the lower normal signal as the South African cave deposits Punaruu event at w1.115e1.1051 Ma. Together these four techniques point to an age of 1.1e1.0 Ma for these cave deposits at Pinnacle Point, far older than anticipated. The persistent presence of these 1.1 e1.0 Ma deposits means that the enigmatic lack of Earlier Stone Age (Acheulean) artefacts in the sea caves along this coastal region can no longer be explained entirely by the age of the caves or through removal of sediments by previous sea level highstands. We believe that these and other coastal caves from this region, if located high enough above sea level, may contain deposits of great antiquity, which could provide outstanding records of climate, environment, sea level change, and human occupation back into the early to middle Pleistocene. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction of South Africa (Fig. 1), contain a series of caves and rockshelters, formed as a result of previous high sea-levels stands (Marean et al., Sea caves and rockshelters along the west and south coasts of 2007). These caves and rockshelters contain rich anthropogenic South Africa provide some of the richest archaeological records of sediments, as well as ancient dune and beachrock deposits and cave early modern humans worldwide. The quartzitic coastal cliffs of carbonate layers, both pure speleothem and impure tufa deposits. Pinnacle Point (PP), near the town of Mossel Bay on the south coast The younger deposits at PP have been the subject of much recent investigation (Marean et al., 2007; Brown et al., 2009; Bar- Matthews et al., 2010; Matthews et al., 2011), during which * Corresponding author. Tel.: þ61 (0)3 8344 6531; fax: þ61 (0)3 8344 7761. E-mail addresses: [email protected], [email protected], a number of cave sites were shown to contain deposits older than [email protected] (R. Pickering). the 500 ka limit of UeTh dating. This was initially surprising as 0277-3791/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.quascirev.2012.12.016 40 R. Pickering et al. / Quaternary Science Reviews 65 (2013) 39e52 Fig. 1. A map of South Africa (A) showing the position of Mossel Bay and the cave sites of PP13G and PPOH at Pinnacle Point (B). The position of PP13G at between 16 and 22 masl is shown in (C) with the section dated here enlarged in (D) (scale bar is 10 cm). Pinnacle Points, along with the other archaeological sites along this age of the oldest deposits in these caves, and to determine when coast, usually only contain sediments younger than w120 ka. The the cave and rockshelter sites may have been available for human apparent lack of deposits, and indeed cave sites, older than 120 ka occupation in the past. A parallel aim was to test the concordance of has been the subject of much debate. One explanation could be that the UePb and TT-OSL age estimates, and their consistency with the the cave systems themselves are relatively young and postdate palaeomagnetic time scale. 120 ka, meaning that the preservation potential pre-120 was too low for a record to exist. Alternatively, Hendey and Volman (1986) 2. Pinnacle Points cave sites and their geology deposits argued that the pre-120 ka cave sediments from this coastal region were all removed by previous sea-level high stands. A third and The coastal cliffs at PP (Fig. 1) consist of heavily dissected different explanation is that this coastal region was not recognized exposures of the Skurweberg formation of the Palaeozoic as an attractive occupation site and the lack of pre-120 ka sedi- Table Mountain Sandstone Group (TMS) (Viljoen and Malan, 1993). ments is due to anthropogenic reasons. The most likely explanation Fault breccias formed by movement along shear zones within the is some combination of all three, in which there where few sites TMS are more susceptible to erosion by high sea levels, forming available, possibly un-used by early humans, all of which have been caves in the near vertical cliffs. There are numerous caves in varying subject to significant erosion from previous sea level high stands. In states of preservation along this coast, here we focus on two, small, any event, the prevailing understanding of these sites along the highly eroded cave remnants, sites PP13G and PPOH (Opera House). south and western coast of South Africa is that the probability of finding old occupation sites is unlikely. 2.1. PP13G Recent advances in uraniumelead (UePb) dating and palae- omagnetic analysis of speleothems (Woodhead et al., 2006; PP13G is a small cave that preserves an exposed sequence of Pickering et al., 2010; Herries and Shaw, 2011), and thermally- fossil beach sediments, a porous sand-rich tufa, a flowstone layer transferred optically stimulated luminescence (TT-OSL) dating of and an aeolianite deposit (Figs. 1 and 2). The cave is developed quartz grains (Wang et al., 2006b; Jacobs et al., 2011; Duller and between 22.16 and 16.37 m above present sea-level and in its Wintle, 2012) are opening up new opportunities to study these present configuration consists of two discrete small chambers earlier time periods by providing a precise and consistent chro- separated by a ledge of cemented sediments (Fig. 2C). The lower nological framework. Moreover, the ability of UePb to date spe- beach sediment is a bioclast-rich, moderate well sorted granule- leothems older than 500 ka and an increase in the sensitivity of sized deposit with up to boulder-sized quartzite blocks floating in magnetometers is allowing the ability to identify and directly date it. Microscopically the sediment consists of well rounded to sub- geomagnetic field events in speleothems throughout the Pliocene angular quartzite clasts and rounded bioclasts (30e40%). Bioclasts and Pleistocene (Dirks et al., 2010; Herries et al., 2010; Osete et al., tend to be elongated and there are thin long fragile fragments with 2012). To this end we employed a multiple chronometer study of only rounded edges (Fig. 2F). The sediment is very porous, only intercalated sandstone and speleothem deposits at Cave 13G slightly cemented by two phases of freshwater phreatic equant (PP13G) and Opera House Cave (PPOH). The goal was to resolve the calcite rims (Longman, 1980). R. Pickering et al. / Quaternary Science Reviews 65 (2013) 39e52 41 Fig. 2. Photograph of PP13G Cave showing the two chambers separating by a ledge of cemented sediments (C), including the location of the lower TT-OSL sample (X). The lower beach sediments (F) consists of elongated bioclasts (B) and rounded to subangular lithoclasts, quartzite (Qz) and calcitic cement (Cc). This grades into a tufa layer (E) showing a clastic-rich lower part overlain by alternating clastic-rich and calcite-rich layers, enlarged in (G) to show the different types of clasts and aggregates cemented with calcite (L ¼ beach lithoclast, Qz ¼ quartzite, B ¼ bioclast, V ¼ vug). The erosional contacts below and above the flowstone layer are shown in (D) and (A), where the flowstone layers of fibrous calcite (with arrows) are truncated by the upper beach sediments (sample 162570, XPL).