Early Evidence for the Extensive Heat Treatment of Silcrete in the Howiesons Poort at Klipdrift Shelter (Layer PBD, 65 ka), South Africa

Abstract

Heating stone to enhance its flaking qualities is among the multiple innovative adaptations introduced by early modern human groups in southern Africa, in particular during the Middle Stone Age Still Bay and Howiesons Poort traditions. Comparatively little is known about the role and impact of this technology on early modern human behaviors and cultural expressions, due, in part, to the lack of comprehensive studies of archaeological assemblages documenting the heat treatment of stone. We address this issue through an analysis of the procedure used for heating and a technological analysis of a lithic assemblage recovered from one Howiesons Poort assemblage at Klipdrift Shelter (southern Cape, South Africa). The resulting data show extensive silcrete heat treatment, which adds a new dimension to our understanding of fire-related behaviors during the Howiesons Poort, highlighting the important role played by a heat treatment stage in the production of silcrete blades. These results are made possible by our new analytical procedure that relies on the analysis of all silcrete artifacts. It provides direct evidence of a controlled use of fire which took place during an early stage of core exploitation, thereby impacting on all subsequent stages of the lithic chaîne opératoire, which, to date, has no known equivalent in the Middle Stone Age or Middle Paleolithic record outside of southern Africa.

Climatic controls on Later Stone Age human adaptation in Africa's southern Cape

“…South Africa's southern coastal margin is a key region for the evolution and development of our species (Ambrose, 2002;Ambrose and Lorenz, 1990;Brown et al, 2012;Henshilwood et al, 2004a;Henshilwood et al, 2002;Marean, 2010;Powell et al, 2009). The southern Cape archaeological record has reframed the debate about the evolution of human behavior, providing early examples of engravings, ornaments, heat treatment of tool-stone and the focussed consumption of marine resources (Delagnes et al, 2016;Henshilwood et al, 2004b;Henshilwood et al, 2002;Henshilwood et al, 2014;Marean, 2014). The region also exhibits regular technological turnover through the last 100,000 years, with the intermittent production of bladelets, bifacial points and backed artefacts and the use of fine-grained rock, interspersed with periods lacking regular retouched flake forms and dominated by locally available rocks such as quartzite and quartz (Deacon, 1984;Wilkins et al, 2017).…”

Variance in the response of silcrete to rapid heating complicates assumptions about past heat treatment methods

“…Experimental and ethnographic observations on the heating of other rock types may thus not be relevant to the process as it applies to silcrete. In support of this proposition is evidence for carbonised green wood exudates (residues) on heated silcretes from archaeological sites in southern Africa, along with frequent evidence for heat fracture prior to flaking that, as noted above, is difficult to reconcile with an insulated or 'sand-bath' heating technique (Delagnes et al 2016;Schmidt et al 2015aSchmidt et al , 2017a. It has also been noted that there is no ethnographic evidence that the sandbath approach was ever used during heating of silcrete (Schmidt 2016).…”

“…Current debate on heat treatment research and its implications for human behavioural evolution is guided by two different concepts of how the process was enacted. The earliest known use of heat treatment involved thermal alteration of the sedimentary rock silcrete and occurs in the southern African Middle Stone Age (Brown et al 2009;Delagnes et al 2016;Schmidt and Mackay 2016;Schmidt et al 2013). Building on prior research, initial experiments to recreate that process worked on the assumption that successful heat treatment that is, having the stone remain relatively intact after heatingrequired slow heating and cooling rates, and control over maximum temperatures (Brown et al 2009).…”

Differential etching after lithic heat treatment: First results of an experimental study

“…Slight heating enhances structure and as a result flaking properties are enhanced (see Luedtke 1992: 103-104). Prehistoric examples have been found in various parts of Africa (Brown et al 2009, Domański & Webb 2007Delagnes et al 2016), Asia (Domański & Webb 2007;Inizan et al 1977;Nadel 1989;Zhou et al 2013), Australia (Domański & Webb 2007;Flenniken & White 1983), North-America (Luedtke 1992), South America (Domański & Webb 2007;Frank 2004), and Europe. Within Europe, heat treatment has been applied in France (Aubry et al 2003;Collins 1973 (Eriksen 1997;Heinen 2005), Italy (Santaniello et al 2016), Portugal (Aubry et al 2003), Poland (Domański et al 2009), and Spain (Tiffagom 1998).…”