Geochemistry of Lower Cretaceous terrigenous deposits of the Northern Sikhote-Alin and their paleogeodynamic nature

Abstract

Introduction: The study and interpretation of the geochemical features of terrigenous rocks provides objective information about the nature of the processes of weathering, transfer, and burial of the material, as well as about the provenance areas and the paleogeodynamic nature of sedimentation basins. The Early Cretaceous is the most important stage in the development of the geological structures of the eastern part of the Eurasian continent. Early Cretaceous deposits that make up these structures occupy more than a half of the area of the Sikhote-Alin range. Geochemically, the sedimentary rocks in the region have been poorly studied, therefore, it is difficult to make judgements about their geodynamic nature. The purpose of the study is to provide a detailed study and analysis of geochemical features of fragmented rocks in the Northern Sikhote-Alin with the focus on determining the composition of rocks in the provenance areas and restoring sedimentation environments. Methodology: Two sites were selected for research due to the availability of almost continuous sections of Lower Cretaceous deposits within their territory. The petrographic composition of the rocks was studied in thin rock sections using polarising microscopes. The content of petrogenic elements was determined by inductively coupled plasma atomic emission spectrometry on the iCAP 6500 Duo, CPM-25, and VRA-30 spectrometers. Concentrations of rare and rare-earth elements were studied by plasma spectrometry (ICP-MS) using the Agilent 7500c quadrupole mass spectrometer. Results and discussion: Data obtained as a result of geochemical studies indicate that the studied sandstones are greywackes and only some of them are lithic arenites. They were formed mainly due to the physical destruction of provenance area rocks, which explains a low level of their “maturity”, while chemical weathering played a secondary role. Their geochemical features indicate that the rocks belong to petrogenic variations that underwent one cycle of redeposition and were formed without any significant lithodynamic changes and sorting of fragmentary material. Conclusion: Interpretation of the results showed that sedimentation occurred in a basin which was spatially and genetically associated with a major transform fault that separated the Eurasian continent and the adjacent oceanic plate. The denudation area incorporated continental land composed of granitemetamorphic complexes and a mature, highly eroded marginal-continental arc, which supplied both acidic material for its foundation and the basic-intermediate volcanoclastics. The accretionary wedges of the Sikhote-Alin containing flint plates must have also been eroded. All this allows attributing the studied deposits to the Zhuravlevka terrain.