Heritage Cases

This application is to export geological samples from the archaeological site Boomplaas to Germany for the purpose of understanding the site’s formation and occupation history. The goal of the analysis is to provide the first microarchaeological understanding for Boomplaas Cave’s archaeological deposits. Micromorphology is the study of intact and oriented blocks of sediment that have been embedded in resin. The approach allows for the documentation of macro- and micro-stratigraphy, and aids in the identification of sediment sources as geogenic, biogenic, or anthropogenic. In addition, the presence of microscopic post-depositional features such as etched rock fragments and secondary mineral nodules can aid in the reconstruction of the chemistry of the burial environment. Microscopic materials such as phytoliths and diatoms may also be observed, which can lead to the initiation of further types of sediment analysis. For example, volcanic cryptotephra shards were first observed in micromorphological samples of sediment from Pinnacle Point, which led to the groundbreaking work of Smith et al. (2018). Micromorphology has been used at several other South African cave and rockshelter sites, where it has proven very useful for documenting anthropogenic features such as hearths and plant bedding (Goldberg et al. 2009, Wadley et al. 2011) as well as the post-depositional processes that impact their preservation (Miller et al. 2016). For this project, we propose to use micromorphology to better understand Boomplaas’ complex stratigraphic sequence more accurately and to better understand the site’s depositional history. Additionally, we will use these micromorphology samples to provide contextual data that will guide other aspects of the research at Boomplaas including the site’s excavation strategy, dating, and future sampling. Samples necessary for this project only consist of sediment of geological antiquity – NOT soils. No archaeological artifacts were included. All samples were piece-plotted and recorded. Samples will be analyzed by Dr. Susan Mentzer at the Institute for Archaeological Sciences at the University of Tübingen, Germany. Boomplaas Cave We are applying for an export permit to undertake the first micro-archaeological analyses of samples from Boomplaas (BPA) Cave. This project is taking place at ERF 30/33, Boomplaas, Cango Valley, Eden District, Western Cape (HWC permit case number 18021501AS0223E). BPA is an important site to study because it is located along the northern margin of the Little Karoo Basin within a year-round rainfall regime and can provide insight into how environmental change in this rainfall regime may have influenced past populations, specifically during the Middle Stone Age-Later Stone Age transition. The deposits date back to 80 ka; however, exact nature of the site’s occupation history and the site’s depositional history remain under-studied (Pargeter et al. 2018). Hilary Deacon’s excavations pioneered several field techniques at Boomplaas, however, that study did not employ micro-archaeological techniques, as they were not available at the time of the original excavations. Currently, the site’s stratigraphic record remains only coarsely defined and described leaving several questions about the human occupation record and taphonomic processes at the site unanswered. Micromorphological analyses have been recently conducted at Klasies River main site, another locality previously excavated by Hilary Deacon. The results have proven very informative about the nature of the microstratigraphy, human use of fire (Larbey et al. 2017) and taphonomy (Wurz et al. 2022). Field Methods In October 2022, we collected 28 micromorphology blocks from Boomplaas covering deposits dating to 80-19 ka. Before sampling, the exposed stratigraphic section is cleaned using a trowel and brush to limit potential contamination. High-resolution photography is taken before sampling so that sample locations can be directly placed on the stratigraphic profile in ArcGIS. For each micromorphology block, a block of sediment measuring on average 10x5x5 cm is cut from the section using a knife, trowel and mini-shovel and wrapped in gypsum plaster impregnated bandages. Every sample is piece potted with a total station so it can be placed on a 3D grid following analyses. All the samples are currently stored at the Palaeoecology Laboratory at Nelson Mandela University in Port Elizabeth. We propose to export for analysis 28 micromorphology samples of about 500 grams each. These micromorphology samples are essential for building a high-resolution geoarchaeological record at Boomplaas and building a contextual record that can be used to better understand and plan for other aspects of the site’s sampling record. Figure 1 shows an example of the samples on a rectified (=corrected to grid space) image. Laboratory Methods Samples will be analyzed in the Geoarchaeology Working Group labs (microscope lab and microanalysis lab) at the University of Tübingen by Susan Mentzer. Mentzer may also work in collaboration with PhD or MSc students, such as Thomas Beard, as well as laboratory technician Panos Kritikakis. The samples will be sliced or drilled open to allow air flow into and out of the blocks. The blocks will then be dried in an oven at around 40⁰C for up to one week. The samples are then slowly submerged in a mixture of polyester resin and styrene catalyzed with methyl ethyl ketone peroxide with additional resin mixture added over the course of one week until all void space within the samples is filled with resin. The blocks are then cured overnight in a ventilated oven, and further allowed to offgas for several weeks. The cured blocks are sliced open with a diamond blade rock saw, and areas of interest are photographed and documented. The slabs are then cut with a trim saw to approximately 5 x 7 cm “chips.” The chips are glued onto glass and ground down to 30 microns thickness using a grinding machine. The petrographic thin sections and remaining “chip” are then studied using light microscopes, as well as in situ molecular and elemental analytical techniques such as micro Fourier transform infrared spectroscopy and micro x-ray fluorescence. The leftover slabs are divided into archive pieces and remainders. When necessary, multiple thin sections are produced from the same sample – either to provide full coverage of the block, or to provide duplicate copies of the thin sections to share between multiple institutions. Both blocks and thin sections are digitized at high resolution with transmitted and reflected light, as well as elemental mapping.