Formation of wedge structures in the permafrost deposits of the Batagay megaslump (Yana Highlands, northeast Siberia)

ABSTRACT In 2023, the Batagay megaslump exposure was studied and monoliths of composite and ice wedges were sampled from five cryostratigraphic units: the Lower Ice Complex of Marine Isotope Stage (MIS) 16 or older, the Lower Sand of MIS 6 or older, the Upper Ice Complex of MIS 4-3, the Upper Sand of MIS 3-2, and the uppermost permafrost layer of MIS 1. The main aim was to investigate the formation mechanism of wedge structures in connection with paleoenvironmental conditions. The study of composite wedges’ structure indicated crystals of segregated ice between and within sand veins. The segregated ice was formed in the thermal-contraction cracks infilled by unfrozen sediments from an active layer. Water separated and migrated to two cold walls providing ice lens formation. Stable O-H isotope values of most samples from the wedge structures are located between the global and local meteoric water lines and indicate extremely cold and dry conditions. Some of the samples, especially from composite wedges, have high dexc values that can be related to fractionation during evaporation in thin snow cover. Primary mineralization in ground ice can be related to extremely continental climatic conditions with associated evaporation, as well as secondary processes.