Heritage Cases

Geoarchaeological analysis of sediments from Blombos Cave and Klipdrift Shelter.BACKGROUND & RATIONALE Geoarchaeological and micromorphological investigations of many MSA cave contexts have demonstrated that these often mixed and reworked deposits often comprise of cm- to mm-thick micro-laminations and micro-stratigraphic relationships, many of which were formed through numerous interactions between humans, plants, animals and geological processes (Marean, et al., 2000, Goldberg, et al., 2009, Miller, et al., 2013, Karkanas, et al., 2015, Miller, et al., 2016). At these sites, the application of geoarchaeological methods to study the archaeo-stratigraphy in high resolution has been central in refining the nature, order and scale of prehistoric depositional events, as well as characterizing the environmental and occupational setting in which human behavioural and technological innovations took place. While the recovered archaeological record from BBC and KDS also derives from finely laminated deposits and has yielded a wealth of information on the development of MSA material culture and technology, subsistence strategies, few investigation of these cave and shelter deposits has so far been published (but see: Tærud, 2011, Haaland, et al., 2017, Haaland, 2018). A geoarchaeological and sediment-based investigation of the local micro-stratigraphy within this central cave site thus offers an excellent opportunity to advance our knowledge of MSA site formation, site structure and occupation patterns in the southern Cape. AIM By combining archaeological micromorphology and microspectroscopy with three-dimensional, high-resolution field documentation we aim in this project to investigate the MSA deposits at BBC and KDS through geoarchaeological and micro-analytical techniques, and to evaluate the archaeological sequences there in terms of: (I) prehistoric human and non-human depositional processes and activities; (II) the nature, order and scale of prehistoric sedimentation and depositional events; (III) the environmental and physical setting in which specific phases of MSA occupations took place. METHODS To evaluate the MSA archaeo-stratigraphy at BBC and KDS, and to identify the site formation processes responsible for its making and alteration, we apply archaeological soil micromorphology combined with strategic sampling of loose bulk samples. Soil Micromorphology is a method within the discipline of geoarchaeology that examines soil and sediments in their undisturbed state at the microscopic level (Courty, et al., 1989, Stoops, 2003). It involves the collection of structurally intact blocks of sediment in the field, and the subsequent preparation and study of these blocks through petrographic thin section analysis in a laboratory, thereby facilitating the identification of sedimentary constituents, post-depositional features and stratigraphic relationships on a microscopic level (Goldberg and Macphail, 2006). At KDS (2018, n=11) and BBC (2019, n=20) all block samples were cut directly from the exposed profile walls or surfaces during excavation. The blocks were stabilized by plaster bandages before transport due to the unconsolidated state of the sediments. The exact location of each block was documented by photographs, photogrammetry and by total station measurements. If the sampled blocks from BBC and KDS are granted permission for export, and they will be further processed at the Institute for Archaeological Sciences, University of Tübingen, Germany and at the physical geography laboratory at Royal Holloway, University of London, England. Here they will first be impregnated with polyester resin and styrene with an MEKP catalyst for 6-8 weeks, before being cut and made into thin sections. This process requires context-specific infrastructure and know-how that currently is not available in South Africa. Once the thin sections have been produced, they will be examined with petrographic microscopes under magnification ranging from 6.7 – 400x using different light settings – plane-polarized (PPL), cross-polarized (XPL), reflective (RL) and fluorescence (470nm). Some of the bulk sediment samples and thin sections from BBC and KDS will also be subjected to a range of microanalytical techniques, including: Micro x-ray fluorescence (µ-XRF), microscopic Fourier transform infrared spectrometry (micro-FTIR), Plant tissue reflectance (optical petrology), X-ray powder diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) and Micro Computed Tomography (micro-CT scanning). Combined with the micromorphological thin section observations, the microanalytical measurements would allow for the more accurate characterization of sediment composition, microstructure and post-depositional effects. The analytical methods above should be regarded as destructive, yet any unused portion of the sediment bulk samples may be returned if so required.