OSL and micromorphological samples from Rose Cottage Cave 2024

Previous efforts to build a site formation model with micromorphological analysis provided mixed results. Lyn Wadley (Evolutionary Studies Institute, University of the Witwatersrand) excavated the site from 1987 to 1998 and after finishing removed nine sediment peels from selected sections at Rose Cottage Cave, covering most of the sequence. Peter Kloos in his master thesis at the University of Tübingen then prepared fifteen thin sections from these peels. The impregnation of the peels, however, was uneven and did not penetrate the sediment deeply, restraining and controlling the selection of thin section samples as well as leading to uneven representation of the deposits in the thin sections. On average, the thin section coverage was only about 50% of what was hoped for, allowing only vague interpretations of the site formation.
The aims of the current micromorphological investigation of Rose Cottage Cave are to collect block samples directly from the exposed profiles to exam and improve on the impregnation process and to target all depositional contacts to build a site formation model of the site.
Micromorphological analysis in the Schmid/Archer excavation project at Rose Cottage Cave focus on examining the formation of the deposits associated with the MSA and LSA occupations above the MIS 5 MSA, providing contextual information for the OSL dating by Chantal Tribolo (CNRS, Archéosciences Bordeaux, University of Bordeaux) and building a comprehensive site formation model using archaeological soil micromorphology. In the first season in 2023, OSL and micromorphological sampling was undertaken in parallel to investigate the formation of strata associated with the MIS 5 MSA and the succeeding Howiesons Poort (HP) occupations. All four samples, RCC 23 1 to 4 were exclusively collected from the so-called Harper trench. RCC 23 1 to 3 cover the same layers as the OSL samples (Rose 1 to 3): LEN, KUA and KUB. Analysis of the blocks will center on the question of the depositional change by anthropogenic or environmental processes during the HP. This research is currently in progress.
In 2024, we collected 16 block samples for micromorphological analysis (see table 1 in appendix), and we now have the complete sedimentary sequence represented in the blocks, from the North and West section of the Harper Trench and the South Section in the Wadley excavation areas, allowing use to build a comprehensive site formation model. In parallel, we performed bulk sampling for ancient sediment DNA (sedaDNA) analysis. These samples were collected wearing protection against modern DNA contamination, masks and gloves, and with sterile tools. We collected sedaDNA samples from the back of the micromorphology blocks and in continuation of the layers represented in the blocks, this will enable us to provide microcontextual formation of the integrity of sedaDNA if preserved. In total, we collected 69 bulk samples for sedaDNA analysis. Ancient DNA extract and sequencing will be performed in the ancient DNA laboratory at the University of Vienna. OSL sampling was also performed in parallel with the micromorphological block sampling. In addition to the 3 samples from 2023, we collected further 6 OSL samples, each in parallel with a block sample that will allow us to analyse the formation history and its impact on dating of the sediment components.
The six OSL samples (Rose 4 to 9) are ~500g in weight, the sixteen micromorphological samples (RCC 24 1 to 16) are ~2-4kg per sample, and the sixty-nine bulk samples for sedaDNA analysis are ~20g per sample.
From the blocks, 1-2 thin sections will be produced by a designated thin section laboratory, Geopraep in Eggenburg, Austria or Mkfactory in Stahnsdorf, Germany. Thin section analysis will be conducted in the Microarchaeology Laboratory of the University of Vienna, using an Evident BX53 light microscope with oblique incident light (OIL), plane- (PPL) and cross-polarized light (XPL).