Middle and Late Pleistocene loess of the Western Ciscaucasia: Stratigraphy, lithology and composition

Abstract

Due to the high preservation of the loess series and the availability of coastal outcrop sections loess cover of Western Ciscaucasia has ample opportunities for spatial paleogeographical reconstructions for the Middle and Late Pleistocene. Currently, the level of knowledge on the structure and composition of the loess-paleosol sequences of Western Ciscaucasia remains unequal. The Azov coast is studied in more detail in comparison with the inner part of the region. The structure and composition of the loess-paleosol sequences of different parts of Western Ciscaucasia (the Sea of Azov coast and western macroslope of the Stavropol Upland) for the Middle and Late Pleistocene are compared. Comparison of the key sections are based on litho- and pedostratigraphy, magnetic susceptibility, grain size, elemental and mineral composition, and luminescence dating. Recent results of luminescence dating allowed correcting the structure of the Mezin pedocomplex (S1). It was found out that this pedocomplex includes three phases of soil formation (S1SS1, S1SS2, S1SS3), which approximately correspond to the warm stages of marine isotope stage 5 (MIS 5) – 5a, 5c, 5e. In all sections, a clear trend towards an increase in the accumulation rates over the last three climatic macrocycles is observed. The last interglacial-glacial macrocycle (MISs 2–5) is characterized by the most significant increase in average accumulation rates, which were ∼1.8 times higher compared to MISs 6–7 and ∼2.3 times higher than during the MISs 8–9. A likely reason for the regional increase in the average dust accumulation rate was the directional increase in climate aridity. The patterns of the spatial distribution of the loess thickness and material composition indicate that the main source of aeolian dust is situated in the east. We suppose that the main sources of dust are sand masses of the alluvial plains of Lover Volga, Terek, Kuma and Kura rivers in the Caspian lowland. The Lower Don sandy province is reconstructed to be a secondary source. Dust is blown from the sandy terraces of the Don, and in the past - from the Don deltas, during the period when the Sea of Azov dried up.