The Kuznetsk Basin (Kuzbass) is one of the largest coal basins in Siberia and a reference area for the ancient Angaraland continent. The proximity of the Kuzbass and Siberian Platform caused their biotic similarities in the Late Palaeozoic. However, due to biota endemism, the Kuzbass Upper Palaeozoic does not correlate directly with the International Chronostratigraphic Chart (ICC). This paper discusses radioisotopic (CA-ID-TIMS) dating of zircons from a volcanic tuff located in the Starokuznetsk Formation (Fm). This level matches the interval of the Balakhonka/Kolchugino (B/K) floral change in Kuzbass, i.e., the gradual replacement of cordaitoid-dominated wet forests (Balakhonka flora) with more arid fern–pteridosperm–cordaitoid assemblages (Kolchugino flora). New age (276.9 ± 0.4 Ma) directly correlates the Starokuznetsk Fm with the Upper Kungurian of the ICC. We compared the Kuzbass data with data of the Western Verkhoyanie, where Middle Permian ammonoids (Sverdrupites assemblage) occur in strata recording the B/K floral change. The available (ICC) and new datings indicate the lag between the B/K floral change in low (Kuzbass) and high (Verkhoyanie) latitudes of Angaraland. The B/K floral change in the Kuzbass began in the early Late Kungurian and was completed by the end of this age. In contrast, the B/K floral change in Verkhoyanie began at the end of the Late Kungurian and was completed in the Late Wordian. The delay in the floral changes at different latitudes of Angaraland suggests that existing interregional correlations need further improvement.

This study presents the first U-Pb (CA-ID-TIMS) radioisotopic dating of zircon grains extracted from tonsteins within the uppermost Permian coal interval of the Minusinsk Coal Basin (Siberia, Russia). Petrographic, structural, and mineralogical analyses confirm the volcanic ash origin of the tonsteins. The parent pyroclastic materials are identified as rhyolite–pantellerite for tonstein I-22 and dacite–rhyodacite for tonstein I-12. Morphological analysis of zircon crystals, along with cathodoluminescence and melt inclusion studies, confirms their volcanic origin and crystallisation temperatures of 700–900 °C. New radioisotopic dates of 261.4 ± 0.7 Ma and 261.3 ± 0.4 Ma clarify the age of the Izykh Formation, enabling its direct correlation with the Capitanian Stage of the International Chronostratigraphic Chart. The results emphasise the possible discontinuity of the coal-bearing succession of Siberian palaeocontinent and highlight the potential for further stratigraphic refinement through continued radioisotopic dating of tonsteins.

The Kuznetsk Basin (Kuzbass) is one of the largest coal basins in Siberia and a reference area for the ancient Angaraland continent. The proximity of the Kuzbass and Siberian platform caused their biotic similarities in the Late Palaeozoic. However, due to biota endemism, the Kuzbass Upper Palaeozoic does not correlate directly with the International Chronostratigraphic Chart (ICC). This paper discusses radioisotopic (CA-ID-TIMS) dating of zircons from a volcanic tuff located in the Starokuznetsk Formation. This level matches the interval of the Balakhonka/Kolchugino (B/K) floral change in Kuzbass, i.e. the gradual replacement of cordaitoid-dominated wet forests (Balakhonka flora) by more arid fern-pteridosperm-cordaitoid assemblages (Kolchugino flora). New age (276.9 ± 0.4 Ma) directly correlates the Starokuznetsk Fm with the Upper Kungurian of the ICS. We compared the Kuzbass data with data of the Western Verkhoyanie, where Middle Permian ammonoids (Sverdrupites assemblage) occur in strata recording the B/K floral change. Available (ICC) and new datings indicate the lag between the B/K floral change in low (Kuzbass) and high (Verkhoyanie) latitudes of Angaraland. The B/K floral change in the Kuzbass began in the early Late Kungurian and was completed by the end of this age. In contrast, the B/K floral change in Verkhoyanie began at the end of the Late Kungurian and was completed in the Late Wordian. The delay in the floral changes at different latitudes of Angaraland suggests that existing interregional correlations need further improvement.

В статье обсуждается позднекунгурский радиоизотопный возраст (276.9 ± 0.4 млн лет) средней части старокузнецкой свиты (кузнецкая подсерия, кольчугинская серия) Кузнецкого бассейна, полученный высокоточным методом термической ионизационной масс-спектрометрии с разбавлением изотопов и химическим истиранием (Chemical-Abrasion Isotope-Dilution Thermal Ionisation Mass Spectrometry, CA-ID-TIMS). Анализ биостратиграфических данных подтвердил принадлежность датированного уровня интервалу, в котором балахонская (кордаитовая) флора сменяется кольчугинской (папоротниково-птеридоспермо-кордаитовой) флорой. Таким образом, сделан вывод о том, что смена балахонской флоры на кольчугинскую в низких широтах Ангариды произошла в позднем кунгуре. Полученные данные дают возможность напрямую сопоставить нижнюю часть кольчугинской серии с верхним кунгуром Международной хроностратиграфической шкалы. Сходные последовательности сообществ неморских двустворок в пермских разрезах Ангариды (гигантские Prokopievskia, Khosedaella–Redikorella– Palaeomutela, доминирующие Palaeomutela) и Восточной Европы (гигантские Sinomya, Palaeomutela–Khosedaella–Redikorella, доминирующие Palaeomutela) подтверждают обоснованность корреляции кузнецкой подсерии с уфимским ярусом. Положение нижней границы кольчугинской группы в верхней половине кунгурского яруса Международной хроностратиграфической шкалы ставит вопрос о сохранении уфимского яруса в качестве самостоятельного стратона в Общей стратиграфической шкале России. Нижняя его граница совпадает с началом смены балахонской и кольчугинской флор в низких широтах Ангариды, а также с фаунистическими обменами еврамерийских и ангарских сообществ неморских двустворок.

This study presents the first U-Pb (CA-ID-TIMS) radioisotopic dating of zircon grains extracted from tonsteins (altered volcanic ashfalls) within the uppermost Permian coal interval of the Minusinsk Coal Basin (Siberia, Russia). Petrographic, structural, and mineralogical analyses confirm the volcanic ash origin of the tonsteins. The parent pyroclastic material is identified as rhyolite-pantellerite for tonstein I-22 and dacite-rhyodacite for tonstein I-12. Morphological analysis of zircon crystals, along with cathodoluminescence and melt inclusion studies, confirms their volcanic origin and crystallisation temperatures of 700–900ºC. New radioisotopic dates of 261.4 ± 0.7 Ma and 261.3 ± 0.4 Ma clarify the age of the Izykh Formation, enabling its direct correlation with the Capitanian Stage of the International Chronostratigraphic Chart. The results emphasise the possible discontinuity of the coal-bearing succession of southern Angaraland and highlight the potential for further stratigraphic refinement through continued radioisotopic dating of tonsteins.