Geochemistry and mineralogy of sediments as tools for assessment of the cave biotic occupation: a case study of the Denisova Cave

The Denisova Cave, formed during the second half of the Middle Pleistocene in Altai is a key site representing some of the earliest and well-studied examples of hominid habitation and cultural traditions in the Northern and Central Asia. The Middle Pleistocene sedimentary sequence of the cave (the oldest layers 22C, 22B, and 22A of the Central chamber) was studied for the first time using the suite of chemical and mineralogical techniques, including profiling. The background values of major and trace elements were determined for modern soil, alluvium, and loess-soil profile sampled at the sites adjacent to the cave. Compositional difference of the oldest cave sediments as well as high degree of organic preservation allowed us to obtain a set of high-resolution profiles (mineralogical, major-, and trace-element ones). The study substantiates the utility of geochemical and mineralogical features of bulk sediments and their individual components for the purposes of reconstruction of both cave sedimentation regimes and sediment provenance. Combination of compositional characteristic and lack of biogenic component in sediments allowed to characterize the oldest layer 22C as sterile. This type of sediments is typical for caves with closed chambers, cracks, blind passages, and lacking a full through-flow of material. During the time of formation of the layer 22B the cave’s Central hall was poorly ventilated due to the lack of opening cracks. Rare findings of bones and geochemical indicators jointly suggest that from this temporal boundary, limited access to the cave appeared. The layer 22A marks the earliest boundary of active biotic adaptation and habitation of the Denisova Cave by different species. The results of geochemical and mineralogical profiling are strongly supported by paleontological and archaeological records, which allows one to use this approach as a reliable tool for analyzing the intensity of occupation of cave shelters by humans and animals.

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