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The objective of this study was to determine if visible reflectance spectroscopy and quantitative colorimetry represent viable approaches to classifying the heat treatment state of silcrete. Silcrete is a soil duricrust that has been used as toolstone since at least the Middle Stone Age. The ancient practice of heat treating silcrete prior to knapping is of considerable interest to paleolithic archaeologists because of its implications for early modern human complex cognition generally and the ability to manipulate the material properties of stone specifically. Here, we demonstrate that our quantitative, non-invasive, and portable approach to measuring color, used in conjunction with k-Nearest Neighbors "lazy" machine learning, is a highly promising method for heat treatment detection. Traditional, expert human analyst approaches typically rely upon subjective assessments of color and luster and comparison to experimental reference collections. This strongly visual method can prove quite accurate, but difficult to reproduce between different analysts. In this work, we measured percent reflectance for the visible spectrum (1018 variables) and standardized color values (CIEL*a*b*) in unheated and experimentally heat-treated silcrete specimens from three sources in South Africa. k-NN classification proved highly effective with both the spectroscopy and colorimetry data sets. An important innovation was using the heat treatment state predicted by the k-NN model for the majority of replicate observations of a single specimen to predict the heat treatment state for the specimen overall. When this majority voting approach was applied to the 746 individual observations in this study, associated with 94 discrete silcrete flakes, both spectroscopy and colorimetry k-NN models yielded 0% test set misclassification rates at the specimen level. [ABSTRACT FROM AUTHOR]

Open-air Middle Stone Age (MSA) contexts in southern Africa have received relatively little research attention compared to caves/rock-shelters. MSA caves/rock shelters can provide long sequences of MSA behaviors dominated by residential activities in circumscribed contexts but most procurement activities occurred on the landscape in uncircumscribed space. We have a limited understanding of these activities at present, making studies of open-air sites crucial. To alleviate this bias, the South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology (SACP4) project expanded its research scope to include MSA archaeology from open-air contexts. We report on a series of MSA open-air assemblages that are exposed on ancient land surfaces suggestive of intact paleosols at Vleesbaai and Visbaai, South Africa. Importantly, these sites occur in close proximity to the long cave/rock shelter sequences at Pinnacle Point. This presents the novel potential to study evidence of MSA behavior in closed and open settings where their proximity to each other approximates the typical hunter–gatherer daily foraging radius documented in ethnography. We present a fabric and technological analysis of MSA stone tool assemblages from three “Areas”. Analysis of total-station piece plotting of artifact bearing/plunge suggests that the lithic assemblages have undergone limited post-depositional disturbance. The technological analysis and exploratory comparisons between these open-air assemblages and MSA cave and rock shelter contexts at Pinnacle Point Cave 13B and 9, and Cape St. Blaize Cave suggest that the quartzite artifacts from Vleesbaai were procured from locally available sources and may have been field processed there before being transported elsewhere, perhaps to the caves/rock shelters. Further, the analysis suggests a dichotomous pattern of retouched tool discard, where quartzite tools are discarded similarly across the landscape. In contrast, non-quartzite tools may have been made primarily at the cave sites, and discarded or lost more frequently on the landscape. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of a series of experiments for the identification and analysis of fire modified rock (FMR). FMR is a common but frequently overlooked artifact type. Experiments were conducted simulating the effects of different hypothetical burning scenarios on rocks similar to those found in a South African Middle Stone Age site. A digital imaging method was then used to quantify FMR color values, designed to limit intra-analyst bias. Statistical tests and a blind test suggest that unburned rocks and experimental FMR can be separated statistically based on physical appearance. Two burning scenario models, based on measured experimental data were applied to archaeological FMR from a South African Middle Stone Age site named Pinnacle Point 5-6 (PP5-6) and show that the archaeological samples are not statistically different from a simulated campfire and possibly a lithic raw material heat-treatment fire. [Copyright &y& Elsevier]

The Palaeo-Agulhas Plain (PAP), when exposed, presented Middle Stone Age (MSA) foragers at Pinnacle Point (PP) on the South Coast of South Africa with new sources of raw materials to make stone tools. Sea-level fluctuations and the changing size of the Paleo-Agulhas Plain throughout the Pleistocene PP record ∼165 ka to 50 ka would have altered the availability of different resources, thus potentially forcing new raw material procurement strategies. The relative frequencies of raw material throughout the PP sequence shows that frequencies of raw material types did change, especially after 90 ka. What caused these changing frequencies is debated and centers on whether targeted procurement of specific raw materials was the cause, or if simple raw material availability and abundance due to the changing environmental context in conjunction with opportunistic procurement drove such shifts. The application of a neutral model of stone raw material procurement presented here evaluates whether random walk in the region surrounding the PP site during different coastline configurations (Marine Isotope Stage 6, 5, and 4) explains the observed shifts in raw material usage. Put differently, did opportunistic acquisition of raw materials during random walk in these different environments cause the observed raw material pattern? Model simulations and a sensitivity analysis provide no convincing evidence that observed raw material frequencies at PP resulted from opportunistic acquisition during random walk. • Incorporates marine geophysics survey data with agent-based modeling simulations of foraging behavior. • Applies a neutral model of stone tool raw material procurement to a landscape with three different modeling states. • Study focuses on the stone tool raw material record of the Late Pleistocene locality of Pinnacle Point, South Africa. • Finds little support for random walk explaining the raw material pattern during three different Marine Isotope Stages. [ABSTRACT FROM AUTHOR]