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Интеллектуальная Система Тематического Исследования НАукометрических данных |
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DEVELOPMENT OF HOLOCENE TRANSGRESSION IN THE NORTH OF THE BLACK SEAтезисы доклада
- Авторы: Myslivets V.I., Porotov A.V.
- Сборник: «Where East meets West: Pontocaspia, the historical dimension of the evolution of a unique biodiversity». Abstracts of the International youth school-conference
- Тезисы
- Год издания: 2017
- Место издания: SSC RAS Publishers Rostov-on-Don
- Первая страница: 53
- Последняя страница: 55
- Аннотация: Three problems are expected to be considered in this communication. The first is the basin level in the time of the last glacial maximum. The second is the age of the modern coastal zone. The third is the problem of Fanagorian regression.The level of the Black Sea in the time of the last glacial maximum. Evidence on the position of the level, based on the structure of the deeper valleys of the Caucasian coast, is given in the paper (Ostrovsky, 1967). The deepest after-karangatian regression is estimated at 112 - 122 m. In 1975, data were published on the pebble belt on the shelf of the Southern coast of the Crimea at depths of 80 to 90 m (Kuprin et al., 1975). Conducted by us echolocation in the same area showed the presence of a terrace at depths of 90 to 105 m separated from the overlying shelf by a ledge several meters high (up to 10 m). Seismoacoustic studies revealed its nature: the ledge is the outer edge of the clinoform and its foot does not indicate the sea level (Lokhin, Maev, 1989). The depth of the ancient shore is 80 - 90 m. On the outer edge of the northwestern shelf, data have been obtained not only about a drop in the level to 80-100 m, but also about the morphological features (terraces) of the sea regression to minus 130-140 m (Evsyukov, Rudnev , 2013). Later, reports of regression signs appeared up to - 150 m and even up to - 180 m. The time of regression by the researchers is estimated at 19-20 thousand years ago. On the edge of the shelf, cut by the canyon of the Danube, an abrasion terrace (Popescu et al., 2004) is traced at depths of 90 to 98 m at a distance of about 100 km.On the Romanian shelf at depths of 95 to 100 m, as the researchers believe, were found abrasion terraces overlapped with dunes. The age of the lake sediments at depths of 70 to 90 m is from 11 to 8.5 thousand years. The region was dominated by the arid climate at that time, and the decrease in the flow of river water caused a drop in the level to such significant levels (Lericolais et al., 2009). The dunes on the shelf are divided into two categories: large, up to 10 m high, desert eolian forms with deflation troughs between them at depths of 55 to 80 m, and smaller coastal dunes located at depths of 80 to 90 m (Yanchilina et al., 2017).In the development of the relief of the Black Sea depression, regression was an important stage. During the regression, the river valleys developed on the north-western shelf and in other regions, and the alluvium carried by the rivers to the continental slope fed turbid streams that descended along numerous canyons. As a result, an extremely dense network of erosion forms formed on the shelf, continental slope and bottom of the depression: their total length exceeds 50 thousand km, and the length of the most developed - the Supsinsko - Chorokhsko - Harshit system reaches 398 km (Melnik, 1996).Age of the modern coastal zone. There are two points of view on the nature of changes in the level of the Black Sea in the second half of the Holocene. According to one, the sea approached the modern level relatively recently, about 1 thousand years ago. Depending on local tectonic conditions (for example, the Anapskaya spit), traces of his stay near the modern shore of about 3 thousand years can be fixed. On the whole, the course of the transgression was of a stepped nature: the phases of directed ascent were replaced by delay phases, during which time the sea managed to create underwater accumulative forms (Neveskii, 1967). In the ancient era, the level was lower than today's, and then rose, and this explains why the lower parts of many ancient cities of the Northern Black Sea Coast are flooded.According to another point of view, the level approached the modern depths - 3, - 4 m about 6 thousand years ago and about 5.8 - 5.5 thousand years B.P. has reached a modern position. Since then, the level has been near modern zero, sometimes dropping and then returning back (Balabanov, Izmailov, 1988; Izmailov, 2005; Balabanov, 2009, etc.). The datings of the spits of the estuaries of the North-Western Black Sea region indicate 5 thousand years (Konikov et al., 2007; Konikov et al., 2010). In the western Crimea, the formation of barrier spit separating the future lakes Sakskoye and Dzharylgach from the sea and leading to the change in sedimentation in open bays by the formation of sediments of estuaries is estimated at 5340-5610 cal. years ago (lake Sakskoye) and 5590 - 5350 cal. years ago (Dzharylgach; Subetto and others, 2007). The shell sediments of the Arabatskaya spit, lying on Novoevksinsky and Bugaz sediments, date from 6.5 to 5 thousands years ago (Balandin, Trashchuk, 1982). However, the section is located within the Azov tectonic high and the Holocene deposits here are raised by 10-15 m, being above sea level. The depth of accumulation of dated sediments is estimated at 5 m. U. V. Artyukhin gives the earliest dating of sediments accumulative forms of the Azov Sea: 4600 B.P. for a spit Biryuchy Island and 5890 B.P. for the Arabat spit (Artyukhin, 2010). In the delta of the Kuban river, the age of the most ancient, early-Dzhemete, generation of coastal levees is determined in 5.8 - 4.5 thousand years ago (Izmailov, 2010). The earliest datings of the coastal sediments of the Anapa spit from a depth of 0.15 to 1.15 m below the current level lie in the range 5.2 to 5.3 thousand years ago (Izmailov, 2005).Thus, the age of the modern coastal zone is 5 - 5,800 years.The problem of Phanagorian regression. There are representations according to which in the late Holocene the level experienced small oscillations, dropping by 2 - 3 m relative to the current situation (Shuisky, 2011). Studies on the shores of the Taman Peninsula led a number of researchers to the conclusion that the Phanagorian regression, postulated in 1963 by P.V. Fedorov, was not or its amplitude was negligible (Porotov et al., 2004; Fouache et al., 2011). The study of traces of level changes in the Azov delta of the Kuban gave grounds for making a different conclusion. Here the coastal levees of the Dzhemete generation (absolute age 5.8 - 2.9 thousand years) are separated by regressive deposits from the levees of the Nymphaean stage (2330-510 B.P., Izmailov, 2010). Regression is dated from buried peat sediments; its age lies in the range of 2500 - 2300 B.P., and the depth is 10 - 15 m (Izmailov et al, 2001). Phanagorian regression includes the buried river channel in the Don delta (Zaitsev, Zelenshchikov, 2009), the late Holocene erosion channel of the pra-Don in the Taganrog Bay (Sheikov, 2012). The seismic profiling carried out by us in the Taganrog Bay revealed the erosional surface at a depth of 1 m under modern sediments, up to water depth about 8 m, and traces of wave activity at depths of more than 5 m (Maev et al., 2006).Drilling in the Saki lake in the Crimea found a lens of rock salt with a thickness of 3.5 - 4 m, accumulated over 150 - 175 years (Dzens-Litovsky, 1936). Modern accumulation of table salt in the lake does not occur. According to the calculations of annual (?) layers, the overlapping lens sediments has accumulated over the last 2 thousand years. This indicates the arid conditions and can explain the nature of the Phanagorian regression.The works were carried out on the theme of the state assignment AAAA-A16-11632810089-5 "Evolution of the natural environment, the dynamics of the relief and geomorphological safety of nature management" and supported by the RGO-RFBR, project No. 17-05-41041 "Shelf of the Crimean Peninsula: Geomorphology and Recent Development History".
- Добавил в систему: Мысливец Владимир Иванович