TECTONIC ZONING OF THE SEDIMENTARY COVER OF THE SEA OF OKHOTSK BASED ON LITHOPHYSICAL, STRUCTURAL AND STRUCTURAL-LITHOPHYSICAL INDICATORS

In terms of tectonics, the Sea of Okhotsk (Fig.1) is the epi-Mesozoic Okhotsk plate comprising the heterogeneous basement that is mainly pre-Cenozoic (the lower structural stage) and the sedimentary cover that is mainly represented by the Paleogenic-Neogenic-Quaternary deposits with the Upper Cretaceous sedimentary rocks observed locally without a visible hiatus (the upper structural stage).

Results of tectonic zoning of the sedimentary cover based on  lithophysical indicators (Fig. 2) are represented in the format of maps showing lithophysical complexes (LC) within the limits of four regional seismo-stratigraphic complexes/structural layers (RSSC I-IV) corresponding to the following time intervals: the pre-Oligocene К₂-P_1-2 (RSSC I), the Oligocene – Lower Miocene P₃-N₁¹ (RSSC II), the Lower-Mid Miocene N₁^1-2 (RSSC III), and the Upper Miocene – Pliocene N₁³-N₂ (RSSC IV). Diverse lithological-facies associations composing the RSSCs are grouped into the following lithophysical complexes (LC): 1 - coal-bearing silty-clayey-sandy terrigenous, 2 - sandy-silty-clayey terrigenous, 3 - silty-clayey-siliceous, and 4 - sandy-silty-clayey volcanic [Sergeyev, 2006].

Tectonic zoning of the sedimentary cover based on structural indicators is carried out with reference to the sediment-thickness map [Sergeyev, 2006], including a significantly revised segment showing the area of the Deryugin basin [Semakin, Kochergin, 2013]. Results of such zoning are represented in the format of a structural-tectonic map (Fig. 3) showing orientations and morphology of the structural elements of the sedimentary cover, the thickness of the sedimentary cover, and amplitudes of relative uplifts and troughs.

With reference to the structural-tectonic map (see Fig 3), the structural elements of different orders are grouped by their sizes, spatial positions and orientations and thus comprise tectonic sistems (Fig. 4), structural zones (Fig. 5) that unclude relative uplifts and troughs that are considered as structural elements of smaller sizes (Fig. 6)

Tectonic zoning of the sedimentary cover based on the structural-lithophysical indicators (Fig. 7-10) is carried out with reference to the maps of the lithophysical complexes of the four regional seismo-stratigraphic complexes/structural layers (see Fig. 2) and the map of high-order structural elements in the sedimentary cover (see Fig. 6).

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