New data on the mayflies (Ephemeroptera) of North-Western Yakutia

New data on the fauna of mayflies in the Anabar River basin are given. A total of eight species of Ephemeroptera have been identified in the fauna of North-Western Yakutia for the first time. Though the mayfly fauna in this region consists mainly of East Palaearctic species, the only seven of them are characterized by arctic-alpine distribution. In general, mayfly species richness of the studied subarctic and southern rivers of Yakutia is similar.

Comparative characteristics of lithogeochemical features of the upper jurassic deposits of the paksa and lower lena facies regions (north of Сentral Siberia)

A comparative analysis of lithogeochemical features of Upper Jurassic rock composition of the lower reaches of the Anabar river and the Urdyukh-Haya cape (Nordvik peninsula) was performed. Several common features, differences and regularities of changes in the section of lithogeochemical characteristics of the studied strata were revealed. The rocks of the Kimmeridgian and upper-middle Volgian have the greatest differences from the higher and lower layers. They are characterized by an increase in the content some of impurity elements (Co, Ni, Zn, U, and some TR). The identified features can be used for correlation when comparing faunal mute strata in the considered part of the sedimentary basin.

Mineralogical-geochemical types and 190Pt-4He age of ferroan platinum of placers of the Anabar River basin, northeastern part of the Siberian Platform

Typical features of platinum group minerals (PGMs) and the results of 190Pt–4He dating of the Fe–Pt solid solutions are presented for complex gold–platinum–diamond placers with unidentified sources of the Anabar River basin. For the first time, the 190Pt–4He isotopic system is used for determination of the possible age of the primary source of a PGM placer from the example of ferroan platinum with a disordered structure along with isoferro- platinum. The PGMs of these placers mostly include ferroan platinum and isoferroplatinum and rare Ru–Ir–Os alloys. The calculated bulk composition of the silicate inclusion of Ir platinum corresponds to the rocks of the ijolite–melteigite series. The 190Pt–4He age of the Fe–Pt solid solution grains is 261 ± 13 Ma. Thus, our data indicate the relation between placer PGMs of the Anabar River basin and Permian-Triassic complexes of alkaline-ultramafic rocks.

PETROGRAPHIC AND LITHOCHEMICAL FEATURES OF THE UPPER MIDDLE – UPPER JURASSIC OF THE LOWER REACHES OF THE ANABAR RIVER

Petrographic and lithochemical characteristics of the upper middle – upper Jurassic of the lower reaches of the Anabar river are presented. Patterns of change in rock-forming oxides contents in silty-sandy rocks of the upper part Yuryungtumusskaya Fr., Sodyemikhainskaya Fr. and silty-clay rocks Buolkalahskaya Fr. are revealed. Petrographic and lithochemical features of specific "junk" and phosphorite layers are noted.