TECTONIC NATURE AND PALEOGEOGRAPHIC ASPECTS OF CRETACEOUS SEDIMENTATION IN WESTERN SIKHOTE-ALIN AND LOWER AMUR REGION
Authors:   Kosygin Institute of Tectonics and Geophysics, Far East Branch, Russian Academy of Sciences, Kudymov A.V. , Peskov A.Yu. ,   Kosygin Institute of Tectonics and Geophysics, Far East Branch, Russian Academy of Sciences, Didenko A.N. ,   Kosygin Institute of Tectonics and Geophysics, Far East Branch, Russian Academy of Sciences
Published: November 2024

Analysis of the sections of Cretaceous deposits in the Western Sikhote-Alin and the Lower Amur region suggests two stages in Cretaceous sedimentation: 1) Berriasian-Valanginian for the Gorinskaya, Priamurskaya and Priussuriyskaya structural-formational subzones (SFS) of the Western Sikhote-Alin structural-formational zones (SFZ); and 2) Aptian-Albian for the Priamurskaya SFS and Albian-Cenomanian for the Chayatynskaya SFS of the Western Sikhote-Alin SFZ. Berriasian-Valanginian deposits of the Western Sikhote-Alin and the Lower Amur region are predominantly sandy sediments, in contrast to similar deposits of the Luzhkinskaya SFS of the East Sikhote-Alin SFZ, where they are mainly silty-argillaceous in composition and contain basalt flows at the base of the section. Geochronological studies showed that Berriasian-Valanginian deposits of the Komsomolskaya Group of the Gorinskaya and Priamurskaya SFS are widespread only within the western zone adjacent to the Badzhal-Gorinskaya SFZ of the Sikhote-Alin orogenic belt and to the Ulbanskaya SFZ of the Mongol-Okhotsk orogenic belt that extends from the Ussuri lower reaches in the south to the Sakhalin Gulf coast in the north. Studies of source types indicate formation of Berriasian-Valanginian deposits in a subcontinental setting. We believe that since the deposits contain outliers of Jurassic siliceous rocks, they are mainly of accretionary nature. As for their tectonic nature, we consider these deposits to be a terrane, as they formed in subequatorial latitudes (10–18°N) and then drifted in a northerly direction for more than 4000 km into their current position. We propose to call this complex the Gorinsky terrane of the Berriasian-Valanginian accretionary prism. The Berriasian-Valanginian deposits of the Priussuriyskaya SFS also display an accretionary nature. We assign them to the Gorinsky terrane. Since Berriasian-Valanginian deposits of the Priussuriyskaya SFS correlate well with deposits of the Khor-Dalnenskaya SFS of the Central Sikhote-Alin SFZ, we believe that the latter were in close proximity to the Gorinsky terrane at that time.	Berriasian-Valanginian rocks of the Komsomolskaya Group that formed in subequatorial latitudes are separated by a break from the overlying Aptian-Albian deposits of the Priamurskaya SFS and Albian-Cenomanian deposits of the Chayatynskaya SFS. In addition, paleomagnetic studies of volcanogenic rocks of the Cenomanian-Turonian Utitsa Formation, which complete the section of Albian-Cenomanian sediments, showed its autochthonous position. This suggests that Aptian-Albian and Albian-Cenomanian deposits emplaced between the latitudes at which Berriasian-Valanginian deposits of the Komsomolskaya Group accumulated and the latitude of development of the Cenomanian-Turonian Utitsa Formation. Thus, both Aptian-Albian and Albian-Cenomanian deposits, as well as Berriasian-Valanginian ones, should be considered as a terrane, with Aptian-Cenomanian sediments sourced mainly from a volcanic arc. The structure of these deposits clearly suggests the structure of an accretionary prism. Moreover, biostratigraphic studies demonstrated a close spatiotemporal link between the Albian-Cenomanian sedimentary complex and the accretionary complex of the Kiselevka-Manoma terrane. Based on this, we propose to identify the Aptian-Cenomanian sedimentary complex as a separate Chayatyn terrane of the Aptian-Cenomanian accretionary prism.