Строение осадочной толщи голоцена Северного Каспия как отражение изменений климата и уровня моря

Безродных, Ю.П.; Янина, Т.А.; Сорокин, В.М.; Романюк, Б.Ф.

Авторы: Безродных Ю.П., Янина Т.А., Сорокин В.М., Романюк Б.Ф.
Журнал: Вестник Московского университета. Серия 5: География
Номер: 5
Год издания: 2018
Издательство: Изд-во Моск. ун-та
Местоположение издательства: М.
Первая страница: 52
Последняя страница: 60
Аннотация: The analysis of the data on the Holocene sediments of the Northern Caspian Sea obtained by seismoacoustic profiling together with multidisciplinary studies of the bottom sediment cores using lithological, malacofaunistic, and geochronological (radiocarbon) methods revealed palaeogeographic events of different scale recorded in the sequence. The most significant of them are the Mangyshlak regression and the multiple-stage New Caspian transgression, both resulting from climatic changes varying in scale and direction. The large-scale Mangyshlak regression having left marks of the sea level at depths about -90 m occurred ~11 600–8000 yr BP, that is, in the Boreal period (according to the Blytt-Sernander scheme) of the early Holocene. That interval traceable all over the world was noted for a rather high level of heat supply and aridity. A short-term sharp cooling known as «8200 event» and a simultaneous increase in aridity resulted in a maximum drop of the Caspian Sea level at the final stage of the regression. The New Caspian transgression developed in several stages. There are three transgressive stages separated by short regressions. The first stage of transgression (8200-5600 yr BP) developed under conditions of a warm and wet climate of the Holocene optimum. The second stage (3600-3400 yr BP) could be a response to the Subboreal cooling and increase in moisture supply on the East European Plain. The third transgressive stage occurred after 2300 yr BP. There are two groups of dates obtained for the third stage: 1700-1100 and 700-360 yr BP. Neither of the two important climatic phases of the late Holocene – the Medieval Climatic Anomaly or the Little Ice Age – can be interpreted from the sedimentary sequence as belonging to that stage. However, there is a hiatus in the series of dates obtained for the transgressive sequence, which corresponds to the warm and dry medieval interval and suggests a lowered level of the Caspian Sea at that time. The second group of the dates fits the time interval of the Little Ice Age and gives grounds to assume that the Caspian Sea level rose during that episode of a cool and wet climate. The transgressive stages are characterized by different mollusk assemblages. Slight-ly brackish-water species of Monodacna, Adacna, and Hypanis genera were dominant in the early New Caspian basin, the presence of Didacna genus mollusks was insignificant. The marine Cerastoderma glaucum species was completely absent. The middle transgressive stage is noted for a more diversified malacofauna, with widely spread mol-lusks of Didacna genus and appearance of Cerastoderma glaucum. As to the late transgressive stage, its species composition is similar to the present-day one. At the latest stages of the sea basin evolution there appeared some of the Black Sea species – Mytilaster lineatus (brought in by chance with ships in the early 20th century) and Abra ovatа (acclimatized intentionally as a sturgeon feed in the mid-20th century). Two regressive phases occurred 5600-3700 and 3080-2300 yr BP, the sea level being lowered by 5–14 m. The first phase corresponded to the Subboreal thermal maximum of the Holocene marked by a low moisture supply over the European part of Russia. The second phase is considered to be the Caspian Sea response to the warming and rainfall decrease in the Volga drainage basin. In the Holocene sequence the regressive phases are manifested as erosional landforms and depressions filled with freshwater (occasionally slightly brackish-water) deposits. Supposedly those were secondary channels of the Volga or lakes similar to the present-day “ilmens” in the Volga delta.
Добавил в систему: Янина Тамара Алексеевна

	ИСТИНА	Войти в систему Регистрация
	ФНКЦ РР
	Главная Поиск Статистика О проекте Помощь

ИСТИНА

ФНКЦ РР

Строение осадочной толщи голоцена Северного Каспия как отражение изменений климата и уровня морястатья

Прикрепленные файлы