New data on the composition, structure and conditions of formation of the boundary Jurassic-Cretaceous section of the southeastern part of the Anabar-Lena sedimentary basin (north of Eastern Siberia)

Research subject. The Upper Jurassic and Lower Cretaceous sections of the left bank of the lower Lena River, opened by a new well (93-80). Aim of the research is to identify the features of the composition, structure and characterize the conditions of sediment formation. Methods include the dismemberment and stratification of strata by litho- and biostratigraphic methods, petrographic study of rocks in sections, analysis of data on the mineralogical and chemical composition of rocks obtained by physical–chemical methods. When reconstructing the sediment formation conditions, complex methodological techniques used in the IPGG SB RAS in genetic interpretations for terrigenous Mesozoic strata of Siberia were used. Results. It was found that the clay-siltstone part of the section with a basal conglomerate layer (31.8–43.5 м) corresponds to the Buolkalakh Formation (Volgian–Boreal Berriasian). The overlying sandy part (4.0–31.8 м) corresponds to the Kigilakh Formation (Boreal Berriasian(?)–Valanginian). The mineralogical-petrographic and lithochemical characteristics of individual beds and members of the studied section have been revealed. It is reconstructed the directed regressive trend of the formation of the Volgian–Valanginian section, expressed in the change of shallow-marin, coastal-marine and delta environments. At the boundary of the Buolkalakh and Kigilakh Formations a sedimentation regime change was fixed. It is characterized by a significant increase in the rate of terrigenous material entering the basin. It was found that the main sources of demolition were closely located older sedimentary formations rich in quartz, as well as felsic igneous rocks. The parent strata were subject to low and moderate chemical weathering.