The loess-soil sequence of the Central Ciscaucasia: chronostratigraphy, composition, and sedimentation conditions during the Late Neopleistocene

The study presents the results of sedimentological investigation of the core recovered from from the Pervomayskaya-1 (Pm-1) borehole, which revealed the most complete structure of the upland loess-soil series (LSS) in the central Pre-Caucasus. The borehole reached a depth of 13.8 m. Luminescence dating for two samples from the core yielded ages of 62±3 and 102±7 thousand years, attributing the entire studied sequence to the Upper Neopleistocene. Lithostratigraphic units were identified based on macroscopic core examination and geochemical analyses. The Mezin pedocomplex (13.8–9.1 m, MIS 5) consisting of three paleosols was identified at the base of the section. Above it lies a horizon of Valdai loess (9.1–1.2 m, MIS 4–2) of substantial thickness with weak signs of interstadial pedogenesis in its middle part. The section is capped by a Holocene chernozem (1.2–0.0 m, MIS 1) showing signs of anthropogenic transformation in its upper profile. The LSS structure revealed in the Pm-1 core shows stratigraphic unity with previously dated reference sections and boreholes of the Pre-Caucasus LSS: Beglitsa (Bg), Vorontsovka-4 (V-4), Sladkaya Balka-1 (Sb-1), and Otkaznoye-20 (Ot-20). Moreover, the Pm-1 column fits within the main trend of increasing loess thickness and grain size from west to east across the Pre-Caucasus. For the Pm-1 and Ot-20 columns, consistent variations in magnetic susceptibility and grain size were identified. Using these consistent variations as chronostratigraphic markers allowed for a more detailed depth-age model for Pm-1. Based on this model, estimates of loess accumulation rates for the Late Neopleistocene and Holocene were calculated: maximum rates (15.9–17.5 cm/thousand years) correspond to the interval of 36–16 thousand years ago; elevated rates (11.4–12.5 cm/thousand years) align with the interval of 80–40 thousand years ago; low rates (9.1–10.4 cm/thousand years) were recorded in the interval of 128–81 thousand years ago; minimal rates (6.0–6.6 cm/thousand years) correspond to the interval of 13–5 thousand years ago. The intensity of loess accumulation in Pm-1 shows consistency with the most complete LSSs of Eastern Europe, as well as with the mineral dust concentration in Greenland ice core NGRIP.

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