A Grid-Based, Multi-Proxy Geoarchaeological Study of Umhlatuzana Rockshelter, South Africa
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ORIGINAL RESEARCH published: 05 July 2021 doi: 10.3389/feart.2021.664105 Making the Invisible Stratigraphy Visible: A Grid-Based, Multi-Proxy Geoarchaeological Study of Umhlatuzana Rockshelter, South Africa Femke H. Reidsma 1*†, Irini Sifogeorgaki 1†, Ada Dinckal 2, Hans Huisman 3,4, Mark J. Sier 5,6, Bertil van Os 3 and Gerrit L. Dusseldorp 1,7 1Human Origins, Faculty of Archaeology, Leiden University, Leiden, Netherlands, 2Institute for Archaeological Sciences, Senckenberg Centre for Human Evolution and Paleoenvironment, Eberhard Karls University Tübingen, Tübingen, Germany, Edited by: 3Section Archaeology, Cultural Heritage Agency of the Netherlands, Amersfoort, Netherlands, 4Groningen Institute for Christian Zeeden, Archaeology, University of Groningen, Groningen, Netherlands, 5CENIEH, Burgos, Spain, 6Department of Earth Sciences, Leibniz Institute for Applied University of Oxford, Oxford, United Kingdom, 7Palaeo-Research Institute, University of Johannesburg, Johannesburg, Geophysics (LIAG), Germany South Africa Reviewed by: Michael B. Toffolo, Université Bordeaux Montagne, Umhlatuzana rockshelter is an archaeological site with an occupational record covering the France Middle Stone Age, Later Stone Age, and Iron Age. The presence of both Middle and Later Mareike Stahlschmidt, Stone Age assemblages makes Umhlatuzana the ideal location for the study of the Max Planck Institute for Evolutionary Anthropology, Germany MSA–LSA transition (20–40 ka) in southern Africa. This transitional period is *Correspondence: characterized by important modifications in stone tool technology, from prepared core Femke H. Reidsma technology to a toolkit based on microlith production. These changes are argued to have [email protected] occurred in response to changes in climate and environment leading up to the Last Glacial †These authors have contributed equally to this work and share first Maximum. The deposits bearing the transitional assemblages at Umhlatuzana rockshelter authorship appear homogeneous with no visible stratigraphic boundaries. This study integrates geoarchaeological techniques in order to explore fine-resolution geochemical Specialty section: This article was submitted to differentiations of the sediments that are macroscopically invisible, and that will provide Sedimentology, Stratigraphy and insight into (post-)depositional processes over time. Samples were systematically retrieved Diagenesis, from the western profile of the site following a grid-based sampling strategy and analyzed a section of the journal Frontiers in Earth Science for pH, elemental composition (XRF), and Magnetic Susceptibility. Additionally, the results Received: 04 February 2021 were integrated with preliminary micromorphological observations. Our study reveals a Accepted: 15 June 2021 steady, gradual change in the geochemistry of the deposits throughout the Pleistocene, Published: 05 July 2021 related to a combination of environmental change and occupation intensity. We suggest Citation: Reidsma FH, Sifogeorgaki I, Dinckal A, that the part of the sequence reported to bear Middle to Later Stone Age transitional Huisman H, Sier MJ, van Os B and industries is characterized by wetter environmental conditions compared to the underlying Dusseldorp GL (2021) Making the deposits. Additionally, we support results from previous studies that excluded large scale Invisible Stratigraphy Visible: A Grid- Based, Multi-Proxy Geoarchaeological post-depositional movement of the sedimentary sequence. Our study offers a successful Study of Umhlatuzana Rockshelter, multi-proxy approach to systematically sample and study archaeological deposits at the South Africa. Front. Earth Sci. 9:664105. macro and micro scale, integrating a variety of geoarchaeological techniques. The doi: 10.3389/feart.2021.664105 approach provides insight into the depositional and post-depositional history of the Frontiers in Earth Science | www.frontiersin.org 1 July 2021 | Volume 9 | Article 664105 Reidsma et al. Making the Invisible Stratigraphy Visible site, and allows for questions of stratigraphic integrity, anthropogenic input, preservation, and environmental change to be addressed. Keywords: geochemistry, stratigraphy, Stone Age, pH, XRF, micromorphology, geoarchaeology, magnetic susceptibility INTRODUCTION MSA archaeology (Lombard et al., 2010). In 2018 a new field campaign was launched by a team from Leiden University (in The transition from the Middle Stone Age (MSA) to the Later collaboration with the KwaZulu-Natal Museum), aimed at using Stone Age (LSA) (∼40–20 ka) forms an important period within geoarchaeology to address questions about the site’s stratigraphic the behavioral evolution of early humans in South Africa (Villa integrity and degree of post-depositional disturbance. High- et al., 2012). While instances of sophisticated, modern behavior resolution geoarchaeological data proved to be of particular are already documented for the MSA (e.g., engravings and importance, since the Pleistocene deposits did not display jewelry) (see e.g., Henshilwood, 2012; Porraz et al., 2013), it is clearly visible stratigraphic boundaries in the field. Recent not until the LSA that modern human behavior is consistently work by the team has addressed this issue by using cluster- present within the archaeological record (Deacon, 1999; Villa analysis on the 3-dimentional distribution of the archaeological et al., 2012; Bader et al., 2020; Grove and Blinkhorn, 2020). materials (Sifogeorgaki et al., 2020), allowing the identification of During the transition from the MSA to the LSA the toolkit distinct horizontal artifact density zones and disproving the changes from one based on prepared core technology to one suggestion of large-scale sediment movement (contra Kaplan, characterized by microlith production, signaling a marked change 1990). in the way stone tools were produced and used (Lombard et al., The current study builds upon the study of Sifogeorgaki et al. 2012; Villa et al., 2012). These changes appear against a backdrop (2020) by taking a geochemical approach to better understand the of environmental change, during the time leading up to the Last visible and invisible variation within the sequence. It examines if Glacial Maximum (∼29.5–19 ka) (Clark et al., 2009; Yokoyama more subtle changes in depositional processes and post- et al., 2018). This period is characterized by a cold climate and depositional environment can be detected through the frequent severe changes in temperature and humidity, which combined application of several geoarchaeological analyses. would have had consequences for resource availability and Bulk sediment samples were systematically taken from the provided challenges for human groups to adapt to (Simon western profile using a grid-based sampling strategy. Each et al., 2015). It is often assumed that these drastic changes in sample was subsequently analyzed for pH, Magnetic climate were the driving force behind the MSA–LSA transition Susceptibility (MS), and elemental composition (XRF). In (Mitchell, 1988; McCall and Thomas, 2009). Unfortunately, only addition, some preliminary micromorphological and field very few sites with transitional deposits are available (e.g., Border observations are integrated, allowing a link between processes Cave, Rose Cottage Cave, Sehonghong). Moreover, age estimates occurring at the micro and macro scale. The pH can provide of these transitional assemblages differ widely between sites insight into the chemical balance of a depositional environment (d’Errico et al., 2012; Loftus et al., 2019; Pargeter et al., 2017). and give clues on which materials can be expected to preserve In order to resolve questions about the timing and nature of the (e.g., Weiner, 2010; Karkanas and Goldberg, 2018; Braadbaart MSA–LSA transition, more high-resolution data on its et al., 2020). The elemental composition of the deposits can archaeological, chronological, environmental, and stratigraphic provide information on the mineralogy and natural and context is needed. anthropogenic input (Holcomb and Karkanas, 2019). The Umhlatuzana rockshelter, located in KwaZulu-Natal, South presence of reactive (mineral) phases such as carbonates or Africa (Figure 1), is a good case-study site to address questions organic matter determine the long-term preservation of related to the MSA–LSA transition. The site preserves an vulnerable archaeological material like bone or organic matter archaeological archive spanning the last 70,000 years (Kaplan, (van Os et al., 2012). MS is used to characterize the magnetic 1990; Lombard et al., 2010; Sifogeorgaki et al., 2020), covering the mineral (iron) content within geological deposits. Mapping of MS later part of the MSA as well as the LSA (and some more recent, can provide insight into lateral and vertical changes in this Iron Age deposits deposits). This makes Umhlatuzana one of the magnetic mineral content, and provide further insight into rare sites that has a continuous occupation sequence covering the underlying processes (Dearing, 1999; Herries and Fisher, 2010; MSA–LSA transition, making it paramount to understanding the Dinckal et al., submitted). Micromorphology is the study of nature of the transition in the region (see overviews in Lombard undisturbed sediment samples under the microscope (Courty et al., 2012; Mackay et al., 2014). The site was originally the et al., 1989; Macphail and Goldberg, 2017), which provides subject of a rescue excavation in the 1980s (Kaplan, 1990). valuable insights into the micro