New data on the structure and age of the terminal Permian strata in the South Verkhoyansk region (northeastern Asia)

Abstract

We present new data on the structure and age of the upper Permian strata in the basin of the Setorym River (tributary of the Vostochnaya Khandyga River) in the South Verkhoyansk region, represented by the Imtachan Formation and the lower part of the Nekuchan Formation. Based on the new findings of bivalve fossils from the Intomodesma costatum Zone, as well as on the study of carbon isotopes in the shells and carbon isotopes of the organic matter of the host mudstones, we have for the first time proved the completeness of the Permian section. The detailed description of the contact between the Imtachan and Nekuchan Formations bears evidence for a certain continuity of the lithologic characteristics of the sandstones. The sharp lithologic contact between the formations reflects not a regional sedimentation hiatus but a shift of depositional settings from the upper parts of a delta to the deep shelf, caused by forced marine transgression. It is concluded that there was no long-term hiatus between the accumulation of the Imtachan and Nekuchan Formations. Images of the most characteristic species of bivalves and crinoids from the Imtachan Formation are presented.

U-Pb Dating of the Kolchugino Group Basement (Kuznetsk Coal Basin, Siberia): Was the Change in Early–Middle Permian Floras Simultaneous at Different Latitudes in Angaraland?

“…Previously, we noted a possible diachronism in the disappearance of the genus Rufloria in the Kuzbass and Verkhoyanie [88]. This event in the Kuzbass occurred approximately at the beginning of the Wordian and was related to the elimination of large freshwater basins during the sedimentation of the Leninsk Fm.…”

Radioisotopic U-pb Dating of the Kolchugino Group Basement (Kuznetsk Coal Basin, Siberia): Was the Change of Early-Middle Permian Floras Simultaneous at Different Latitudes in Angaraland?

“…Previously, we noted a possible diachronism in the disappearance of the genus Rufloria in the Kuzbass and Verkhoyanie [104,105]. This event in the Kuzbass occurred approximately at the beginning of the Wordian and was related to the elimination of large freshwater basins during the sedimentation of the Leninsk Fm.…”

Stratigraphic position of the ammonoid Paramexicoceras Popow in the PermianTriassic deposits of the Southern Verkhoyanie, Northeast Russia

“…Соглашаясь с мнением А.С. Бякова [26], что маломощная пачка 2, отражающая начало некучанской трансгрессии, седиментологически ближе к пачке 3 некучанской свиты, чем к пачке 1 имтачанской свиты, мы условно к слоям с Paramexicoceras aldanense относим и пачку 2. Касательно биогеографического и седиментологического аспектов, инвазия парамексикоцерасов, несмотря на то что она происходила в чансинском веке поздней перми, исторически связана не с пермским седиментогенезом, а с началом триасового, когда началось формирование осадков некучанского гори-зонта [27].…”