Quantitative characteristics of artifact rock coatings at the Semizbugu surface site complex in semi-arid Central Kazakhstan

Rock surface alterations due to weathering have often been used by archaeologists for creating chronologies, studying climatic conditions, and authenticating artifacts. Rock surface alterations are also important for identifying recycled artifacts through the presence of “double patina.” In the surface archaeological deposits at Semizbugu, rock surface weathering stages are used to chronologically categorize stone tool artifacts based on perceived associations between weathering characteristics and typology. Despite a long history of studying rock surface weathering in geological sciences, the formation of rock coatings on stone tool artifacts is a largely misunderstood process due to its complexity and multi-factored formation process. Given the consistent use of one raw material at Semizbugu, we test for quantitative differences in rock coating morphologies, elemental composition, and surface roughness between weathering stages. Based on our analyses, we propose that artifacts at Semizbugu should be chronologically ordered based on a combined assessment of decreased surface roughness and increased surface pitting, both of which are likely related to degree of wind abrasion. We also recommend against using rock varnish color for chronological assessment of artifacts at Semizbugu given the destructive effects of abrasion and the irregularities of varnish formation in semi-arid contexts. Additionally, we suggest this model be validated with rock surface exposure dating via optically stimulated luminescence (OSL-surf). Furthermore, rock surface exposure OSL dating could give us insight into the time-depth between use and recycling events in a more meaningful way than trying to compare differential artifact surface weathering across “double patina.”