New concepts on the composition, structure, and age of the Lower Amur fragment of the Late Jurassic-Early Cretaceous accretionary prism, Russian Far East |
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| Authors: | V I Anoikin G L Kirillova L P Eichwald |
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| Institution: | (1) Federal State Unitary Enterprise Dalgeofizika, Khabarovsk, Russia;(2) Kosgygin Institute of Tectonics and Geophysics, Far East Division, Russian Academy of Sciences, Khabarovsk, Russia |
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| Abstract: | On the basis of geological observations and the study of conodont and radiolarian microfauna, a new stratigraphic scheme was proposed for the Mesozoic deposits of the Komsomolsk district of the Amur region. The lower Khorpy Group (T2-J3) consists of two units: the Boktor (T2-J2) and Kholvasi (J2–3). The Boktor Sequence (400 m thick) is represented by pelagic cherts with an admixture of cherty-clayey shales and volcanic rocks. The Kholvasi Sequence (500 m thick) is built up of the predominant siltstones and clayey shales with rare intercalations and lenses of clayey cherts and cherty-clayey shales. The upper Komsomolskaya Group (K1) has a terrigenous composition and includes the Gorin, Pionerskaya, and Pivan formations of 5 km total thickness. It is made up of intercalated sandstones, siltstones, mudstones, and often turbidites (proximal to distal). The rocks contain abundant buchia fauna of Volgian-Valanginian age, as well as carbonized plant detritus and flora of the Early Cretaceous habit. The described complex is characterized by a nappe-fold structure typical of the accretionary prisms in the ocean-continent convergence zones. The predominance of the coherent type of accretionary prisms reflects the simple morphology of the oceanic plate. |
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| Keywords: | litho and biostratigraphy Mesozoic accretionary prism Lower Amur region Far East |
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