НОВІ ДАНІ ПО МІКРОПАЛЕОНТОЛОГІЇ КОНКСЬКИХ ВІДКЛАДІВ ЗАХІДНОГО ПЕРЕДКАВКАЗЗЯ

Nannoplankton and benthic foraminifers from the Konkian sediments from the rivers Fars and Belaya have been studied. The obtained results allow us to characterize the cycles of the basin’s development, to determine interrelations of biotic assemblages of nannoplankton and benthic foraminifers in time.Проведено изучение наннопланктона и бентосных фораминифер из конкских отложений (реки Фаас и Белая). Полученные результаты позволяют охарактеризовать циклы развития бассейна, исследовать взаимоотношения биотических сообществ наннопланктона и фораминифер Проведено вивчення нанопланктону та бентосних форамініфер з конкських відкладів (річки Фарс та Бєлая). Отримані результати дозволяють охарактеризувати цикли розвитку басейну, дослідити взаємовідношення біотичних угруповань нанопланктону та фораминифер

ФОРАМІНІФЕРИ З МЕОТИЧНИХ ВІДКЛАДІВ РОЗРІЗІВ ПОПОВ КАМІНЬ – ХОЛОДНА ДОЛИНА, ТАМАНСЬКИЙ ПІВОСТРІВ. КОРЕЛЯЦІЯ З НАНОПЛАНКТОНОМ ТА ДІАТОМЕЯМИ

Fossil benthos and plankton studied from Maeotian deposits of the Taman Peninsula extend signifi cantly our knowledge about a cyclic change of marine and brackish environments of the Maeotian basin established earlier by diatoms. An alternation of poly- and euryhaline foraminiferal assemblages observed at the Early Maeotian-Late Maeotian boundary testifi es to its discontinuous pulsating connection with adjacent sea basins. The marine foraminiferal assemblage (D) characteristic of this interval is an indicator of marine ingression. Nannofossils present in some intervals of the Maeotian point to connection with open seas. Wide spread of marine environments at the end of the Late Maeotian is confi rmed by all three groups.Полученные данные об ископаемом бентосе и планктоне из меотических разрезов Таманского п-ова значительно дополняют знания о циклической смене морских и солоноватоводных обстановок мэотического бассейна, которая была раньше установлена по диатомеям. На границе раннего и позднего мэотиса фиксируется чередование поли- и эвригалинных комплексов фораминифер, что указывает на прерывистый характер связи с сопредельными морскими бассейнами. Появление морского фораминиферового комплекса (D) в этот период является индикатором морской ингрессии. Находки наннопланктона в отдельных интервалах мэотиса является показателем связи с открыто-морскими бассейнами. В конце позднего мэотиса по всем трем группам регистрируется мощный морской импульс.Отримані дані про викопний бентос та планктон з меотичних розрізів Таманського п-ова значно доповнюють знання про циклічну зміну морських та солонуватоводних обстановок меотичного басейну, що була встановлена раніше за діатомеями. На межі раннього та пізнього меотису фіксується чергування полі- та евригаліних комплексів форамініфер, що вказує на перервний пульсуючий характер зв’язку з суміжними морськими басейнами. Поява морського форамініферового комплексу (D) у цей період є індикатором морської інгресії. Знахідки нанопланктону в окремих інтервалах меотису є показником зв’язку з відкрито-морськими басейнами. В кінці пізнього меотису по всім трьом групам реєструється потужний морський імпульс.

The shutdown of an anoxic giant : Magnetostratigraphic dating of the end of the Maikop Sea

Paratethys, the lost sea of central Eurasia, was an anoxic giant during Oligocene – early Miocene (Maikop Series) times. With a size matching the modern-day Mediterranean Sea and a history of anoxic conditions that lasted for over 20 Myrs, the eastern part of this realm (Black Sea-Caspian Sea domain) holds key records for understanding the build-up, maintenance and collapse of anoxia in marginal seas. Here, we show that the collapse of anoxic Maikop conditions was caused by middle Miocene paleogeographic changes in the Paratethys gateway configuration, when a mid-Langhian (Badenian-Tarkhanian) transgression flooded and oxygenated the Eastern Paratethys. We present an integrated magneto-biostratigraphic framework for the early Middle Miocene (Tarkhanian-Chokrakian-Karaganian regional stages) of the Eastern Paratethys and date the lithological transition from anoxic black shales of the Maikop Series to fossiliferous marine marls and limestones of the regional Tarkhanian stage. For this purpose, we selected two long and time-equivalent sedimentary successions, exposed along the Belaya and the Pshekha rivers, in the Maikop type area in Ciscaucasia (southern Russia). We show that a significant but short marine incursion took place during the Tarkhanian, ending the long-lasting Maikop anoxia of the basin. Our magnetostratigraphic results reveal coherent polarity patterns, which allow a straightforward correlation with the time interval 15–12 Ma of the Geomagnetic Polarity Time Scale. The Tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with C5Bn, resulting in an age of 14.85 Ma. The regional Tarkhanian/Chokrakian stage boundary is located within C5ADn at an age of 14.75 Ma and the Chokrakian/Karaganian boundary is tentatively correlated with C5ACn and an age of 13.9–13.8 Ma. Our new Tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions. Instead of envisaging marine connections to the Indian Ocean, we show that major changes in connectivity between the Eastern and Central Paratethys seas have caused the influx of marine waters during the Tarkhanian. An increase in marine connectivity with the Mediterranean during a short episode of rapid sea-level rise triggered mixing and ended the widespread anoxia in the Eastern Paratethys. The mixing episode was short-lived (~100 kyr) as the sea-level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area

The shutdown of an anoxic giant : Magnetostratigraphic dating of the end of the Maikop Sea

Paratethys, the lost sea of central Eurasia, was an anoxic giant during Oligocene – early Miocene (Maikop Series) times. With a size matching the modern-day Mediterranean Sea and a history of anoxic conditions that lasted for over 20 Myrs, the eastern part of this realm (Black Sea-Caspian Sea domain) holds key records for understanding the build-up, maintenance and collapse of anoxia in marginal seas. Here, we show that the collapse of anoxic Maikop conditions was caused by middle Miocene paleogeographic changes in the Paratethys gateway configuration, when a mid-Langhian (Badenian-Tarkhanian) transgression flooded and oxygenated the Eastern Paratethys. We present an integrated magneto-biostratigraphic framework for the early Middle Miocene (Tarkhanian-Chokrakian-Karaganian regional stages) of the Eastern Paratethys and date the lithological transition from anoxic black shales of the Maikop Series to fossiliferous marine marls and limestones of the regional Tarkhanian stage. For this purpose, we selected two long and time-equivalent sedimentary successions, exposed along the Belaya and the Pshekha rivers, in the Maikop type area in Ciscaucasia (southern Russia). We show that a significant but short marine incursion took place during the Tarkhanian, ending the long-lasting Maikop anoxia of the basin. Our magnetostratigraphic results reveal coherent polarity patterns, which allow a straightforward correlation with the time interval 15–12 Ma of the Geomagnetic Polarity Time Scale. The Tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with C5Bn, resulting in an age of 14.85 Ma. The regional Tarkhanian/Chokrakian stage boundary is located within C5ADn at an age of 14.75 Ma and the Chokrakian/Karaganian boundary is tentatively correlated with C5ACn and an age of 13.9–13.8 Ma. Our new Tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions. Instead of envisaging marine connections to the Indian Ocean, we show that major changes in connectivity between the Eastern and Central Paratethys seas have caused the influx of marine waters during the Tarkhanian. An increase in marine connectivity with the Mediterranean during a short episode of rapid sea-level rise triggered mixing and ended the widespread anoxia in the Eastern Paratethys. The mixing episode was short-lived (~100 kyr) as the sea-level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area