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The Sr chemostratigraphic characteristics of marine sediments of the Lower Permian in the Omolon massif of Northeast Asia have been obtained for the first time based on a study of well-preserved brachiopod shells. The 87Sr/86Sr ratio in brachiopods from the Lower Permian regional horizons (regional stages) is within the following ranges: 0.70786–0.70794, Orochian; 0.70744–0.70786, Ogonerian; 0.70745–0.70748, Koargychanian; and 0.70742–0.70735, Khalalian. The obtained Sr-isotope data demonstrate good agreement with the standard variation curve of the 87Sr/86Sr ratio in the Permian Ocean. New Sr-isotope data can be used to correlate the units of the Regional Stratigraphic Scale of Northeast Russia directly with the stages of the International Permian Stratigraphic Scale. Based on recent data, the Asselian age of the Orochian regional stage of the lower part of the Permian section in the Omolon massif has been proved, and the regional correlation of the Upper Sakmarian interval established previously from biostratigraphic data has been refined. [ABSTRACT FROM AUTHOR]

This article presents the results of major, trace, and rare-earth element study of the Permian terrigenous rocks of the southern part of the Omolon Massif. The lithochemical studies showed that sediments were accumulated in a warm climate with episodes of some cooling. The Omolon Basin had a normal salinity, with alternating oxic–anoxic environments. The interpretation of the obtained data indicates that the deposits accumulated in the basin are associated with the marginal continental island arc (Okhotsk–Taigonos volcanic arc). Probable sources were basic and intermediate arc volcanics, as well as acid igneous rocks (volcanics of the Kedon Group) and metamorphic complexes of the basement of the Omolon Massif. [ABSTRACT FROM AUTHOR]

The U–Pb dating of zircons from two samples taken in the stratotype sections of the Middle Permian Gizhiga Formation in the Omolon Massif has been carried out for the first time. Weighted average ages of 266 ± 2 and 265 ± 3 Ma taking the error into account are consistent with the Capitanian age calculated previously by paleontological determination. The observed detrital zircon population has made it possible to identify a few source areas in the Omolon Basin. Pre-Permian zircons are related to erosion of basement deposits of the Omolon Massif and the Middle Paleozoic volcanic rocks of the Kedon Group, while the Permian zircon population is due to the tuff supply from the Okhotsk-Taigonos volcanic arc. [ABSTRACT FROM AUTHOR]

For the first time very low values (up to 0.706707) of the ratio 87Sr/86Sr were recorded in the biogenic carbonates of the Omolon massif (Northeast Asia) of the Capitanian age. These results are in good agreement with previously obtained data on limestones in Japan (Kani et al., 2013; 2018). In general, the strontium ratio curve constructed by us repeats the well-known world trend, differing by its somewhat underestimated (by an average of 0.0005–0.0008) values. The Capitanian strontium minimum can be associated with the entry into the ocean of significant amounts of lightweight femic strontium due to a sharp increase in paleospreading. The maximum values of the strontium ratio, obtained from the middle part of the Intomodesma evenicum bivalve Subzone are 0.706986, which corresponds to the lower part of the Changhsingian stage. [ABSTRACT FROM AUTHOR]

A late Changhsingian bivalve complex including species from the genera Palaeonucula, Dacryomya, Malletia ?, Sarepta ?, Myalina, Pteria, Maitaia, and Unionites is discovered in northeastern Asia for the first time. The transition from the Permian to the Triassic in high-boreal basins has been shown to include two extinction episodes similar to those observed in the low-boreal basins and apparently evoked by trap volcanism activation in Siberia. Changes in benthic foraminifera diversity and vertical distribution of ammonoidea of the genus Otoceras in transitional Permian-Triassic deposits also are considered. Images of bivalves from the most typical taxa are presented. [ABSTRACT FROM AUTHOR]