Organic matter in the lacustrine sediments of the Kama-Keltma lowland (Cis-Urals): assessment of distribution and dynamics in the Late Pleistocene and Holocene

Abstract

The short communication article presents the results of analyses of the lacustrine sediments of Novozhilovo and Chelvinskoe lakes, located at the Kama-Vychegda watershed. Big set (209) of sediments samples from three wells were analyzed by the loss on ignition (550 °C) method. Age of cores and the rate of sediment accumulation were based on the 14 radiocarbon dates. Six stages of deposits accumulation and nature dynamics during the Late Glacial and Holocene in the lakes catchment area are proposed. The first stage (14.15 – 13.5 cal. kyr BP) is characterized by high rates of deposits accumulation at low values of organic matter content, indicating alluvial sedimentogenesis. Peak of accumulation rates as well as a sharp rise in bioaccumulation were observed during the second stage (13.5 – 12.4 cal. kyr BP), which is interpreted as stabilization of the lake level and external environmental conditions. During the third stage (12.4 – 10.7 cal. kyr BP), the sediment accumulation rate decreases rapidly, reaching a minimum by the end of the period. The organic matter content also decreases significantly (to 30 %). The short-term fourth period (10.7 – 10.0 cal. kyr BP) records the transition from the Late Pleistocene (dominance of rarefied periglacial vegetation) to the Early Holocene (predominance of forest communities). This is marked by a drastic increase in the loss on ignition values (up to 92-95%). During the fifth stage (10.0 – 8.8 cal. kyr BP), the sediments accumulation rate increases and the organic matter content decreases to 77-82%. Synchronously with some increase in the concentration of mineral particles. Smoothing of the loss on ignition curve (average values - 92-96%), a marked increase in the sediment accumulation rate during the sixth stage (8.8 - 5.0 cal. kyr BP) probably indicates the stabilisation of external conditions in the lake catchment.