STRATIGRAPHY, LITHOLOGY, AND GEOCHEMISTRY OF COASTAL AND SHALLOW-SEA SECTIONS OF THE UPPERMOST MIDDLE JURASSIC-LOWERMOST CRETACEOUS IN THE ANABAR RIVER REGION (Arctic Siberia)
B.L. Nikitenko1,2, V.P. Devyatov3, E.B. Pestchevitskaya1, A.Yu. Popov1,2, E.A. Fursenko1,2, S.N. Khafaeva1
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
3Siberian Research Institute of Geology, Geophysics and Mineral Resources, Krasny pr. 67, Novosibirsk, 630091, Russia
Keywords: Upper Jurassic and Lower Cretaceous, stratigraphy, foraminifers, dinoflagellate cysts, spores and pollen, lithogeochemistry, organic geochemistry, Arctic Siberia, Anabar River
Abstract
Concepts of the stratigraphy of the coastal and shallow-sea sections of the uppermost Middle Jurassic and Lower Cretaceous, exposed on the right bank of the Anabar River, have radically changed many times. The performed study and analysis of the published data are aimed at refining the bio- and lithostratigraphic subdivision of the section, substantiating its stratigraphic completeness, and describing the identified stratigraphic units in detail. Comprehensive biostratigraphic studies of the uppermost Bathonian-lowermost Boreal Berriasian reveal a sequence of nine biostratigraphic units with dinocysts and palynoflora in the ranks of zones and local zones. Some of the palynological biostratigraphic units have been identified for the first time. Foraminifer assemblages of the boreal standard zones are recorded in the sections under study. The obtained biostratigraphic data and analysis of all known ammonite occurrences make it possible to demonstrate the stratigraphic continuity of the section in the Anabar River region, despite the reduced thickness of the stratigraphic units. The stratigraphic position of the boundary between the Sodiemykha and Buolkalakh formations is accurately defined. According to the interpretation proposed, the basal horizon of the Buolkalakh Formation is associated with a beginning of a new major sedimentation stage in the late Oxfordian-early Kimmeridgian, identified as the lower boundary of lithostratigraphic units of different ranks throughout the entire Arctic Region and partially in the Boreal Region. The lithogeochemical parameters of the studied formations are obtained for the first time. The content of Corg in the studied samples does not exceed its Clarke values, and the pyrolytic parameter T max indicates that the organic matter is immature and the petroleum potential is low. The considered organic matter of the rocks is characterized by a heavy isotope composition of carbon, suggesting its mostly terrigenous genesis.
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