Coco Emily, Schimdt Patrick, Hu Bin, Rodriguez Alice, Mamirov Talgat B, Bromage Timothy G, Iovita Radu
Center for the Study of Human Origins, Department of Anthropology, New York University, 25 Waverly Place, New York, NY 10009, USA.
Department of Anthropology, Yale University, 10 Sachem Street, New Haven, CT 06511, USA.
Archaeol Anthropol Sci. 2025 Mar;17(3). doi: 10.1007/s12520-025-02172-z. Epub 2025 Feb 5.
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 (Saryarqa, Kazakhstan), 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 differences in rock coating morphologies, elemental composition, and surface roughness between macroscopically identified weathering stages. Based on our analyses, we identify multiple processes involved in artifact weathering at Semizbugu. We suggest that artifacts at Semizbugu may be relatively 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 and dissolution of the artifact surface. 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."
考古学家常常利用因风化而产生的岩石表面变化来创建年代序列、研究气候条件以及鉴定文物。岩石表面变化对于通过“双重铜绿”的存在来识别回收文物也很重要。在塞米兹布古（哈萨克斯坦萨亚尔卡）的地表考古沉积物中，岩石表面风化阶段被用于根据风化特征与类型学之间的感知关联，对石器文物进行年代分类。尽管在地质科学领域对岩石表面风化的研究历史悠久，但由于其形成过程的复杂性和多因素性，石器文物上岩石涂层的形成在很大程度上仍是一个被误解的过程。鉴于塞米兹布古一直使用一种原材料，我们测试了宏观识别的风化阶段之间岩石涂层形态、元素组成和表面粗糙度的差异。基于我们的分析，我们确定了塞米兹布古文物风化过程中涉及的多个过程。我们认为，根据表面粗糙度降低和表面麻点增加的综合评估，塞米兹布古的文物可能在相对年代上是有序的，这两者都可能与文物表面的风蚀程度和溶解有关。考虑到磨损的破坏作用以及半干旱环境中清漆形成的不规则性，我们还建议不要使用岩石清漆颜色对塞米兹布古的文物进行年代评估。此外，我们建议通过光激发荧光（OSL - surf）对岩石表面暴露进行测年，以验证该模型。此外，与试图比较“双重铜绿”上不同文物表面风化情况相比，岩石表面暴露OSL测年可以以更有意义的方式让我们深入了解使用和回收事件之间的时间深度。
