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The lower reaches of the Nemunas River at the end of the Last (Weichselian) Glacial and beginning of the Holocene

Bitinas A., Druzhinina O., Damušytė A., Napreenko-Dorokhova T., Guobytė R., Mažeika J.

Geological Quarterly

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2017

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Vol. 61, No. 1

156--165

EN

The Russian–Lithuanian cross-border area around the Nemunas and Šešupė rivers confluence is a key area for solving palaeogeographic issues important for this region: when the Nemunas Delta started to form, why the essential changes of hydrographic network occurred, and so on. The results of conventional radiocarbon (14C) dating and pollen analysis in the present dry valley between the Šešupė River and the Įrutis River as well as the results of former studies at the Riadino-5 archaeological site suggest that the essential changes in the Nemunas River hydrographic system occurred before 9.5 ka, most likely in Preboreal time, when the Nemunas River cut through the Vilkiškė Marginal Ridge and started to flow directly to the west from this ridge into one of the former basins of the Baltic Sea – to the Yoldia Sea, or to the Ancylus Lake. A new divide was formed between the Šešupė and Įsrutis rivers, and the basins of the Nemunas and Prieglius rivers (formerly a single hydrographic system) became two independent drainage basins of the Baltic Sea. The present Nemunas Delta formation started after the Litorina Sea transgression when the Nemunas River mouth moved from a Baltic Sea nearshore position to close to the western margin of the Vilkiškės Marginal Ridge. A set of palaeogeographic reconstructions of the Nemunas and Šešupė rivers confluence area for different periods of the very end of the Last (Weichselian) Glacial and the beginning of the Holocene have been constructed.

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Evolution of Arkona Basin environment in the Holocene in the light of diatom research

Janczak-Kostecka B.

Landform Analysis

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2015

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Vol. 29

19--25

EN

This article presents the results of diatom studies from three cores taken from the Arkona Basin. The main stages of the Baltic Sea evolution in the Holocene – Ancylus Lake, Mastogloia Sea, Littorina Sea, and Post-Littorina Sea – were identified in diatom assemblages. The transition stage between Ancylus Lake and Littorina Sea, called Mastogloia Sea, was not such a long period as in the Mecklenburg Bay but was essential in the evolution of the Baltic Sea. The most pronounced feature of this period was an increase in the number of halophilous species, which reflected the existence of the littoral environment at the onset of this stage. The appearance and development of halophilous species was stimulated by stepwise inflows of saline waters. The composition of diatom assemblages reflected natural eutrophication of the Baltic Sea during the Littorina Sea stage.

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Age and evolution of the Littorina Sea in the light of geochemical analysis and radiocarbon dating sediment of cores from the Arkona Basin and Mecklenburg Bay (SW Baltic Sea)

Kostecki R.

Landform Analysis

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2015

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Vol. 29

27--33

EN

Two sediment cores from the Mecklenburg Bay and Arkona Basin were analysed in terms of their geochemical composition and stratigraphy. The main stages of the Baltic Sea evolution – Baltic Ice Lake, Ancylus Lake, and Littorina Sea – were identified in both analysed cores. The most pronounced period was the transition between the Ancylus Lake and the Littorina Sea. The character of the initial stage of the Littorina Sea was clearly defined in the Mecklenburg Bay sediments and is marked by a stepwise increase in loss on ignition and contents of biogenic silica, calcium, magnesium, iron, and strontium. The record of the onset of the Littorina Sea in the Arkona Basin sediments is marked by an abrupt change of the geochemical parameters. The age of the initial Littorina Sea in the Mecklenburg Bay was estimated at about 8200 cal years BP and was probably older than the transgression within the Arkona Basin.

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Stages of the Baltic Sea evolution in the geochemical record and radiocarbon dating of sediment cores from the Arkona Basin

Kostecki R.

Oceanological and Hydrobiological Studies

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2014

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Vol. 43, No. 3

237--246

EN

Four sediment cores from the southern part of the Arkona Basin were analyzed in terms of their geochemical composition, age and stratigraphy. The main stages of the Baltic Sea: the Baltic Ice Lake, the Ancylus Lake and the Littorina Sea were identified in all the analyzed cores. The data confirmed the high water fluctuation and significant environmental changes during the Baltic Sea evolution in the Late - Glacial and the Holocene. The signs of the second regression of the Baltic Ice L ake, dated at around 11 000 cal BP, were identified at a depth of 24 m b.s.l. Regression of the Ancylus Lake, dated at 9300 cal BP, was identified at a depth of 23 m b.s.l. The most pronounced period was the transition stage between the Ancylus Lake and th e Littorina Sea. The record of the Littorina Sea onset in the sediments of the Arkona Basin is marked as a sudden increase in loss on ignition, biogenic silica, magnesium, calcium, iron and strontium. The age of the Littorina Sea in the Arkona Basin was es timated as younger than 8200 cal BP.

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An attempt to resolve the partly conflicting data and ideas on the ancylus-littorina transition

Björck S., Andrén T., Bo Jensen J.

Polish Geological Institute Special Papers

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2008

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Vol. 23

21-26

EN

Lagoon gyttja layers occurring in anomalously high position (up to 2.5 m above the present-day sea level) The transition phase between the Ancylus and Littorina stages of the Baltic Sea is an old controversial topic. With the newest data available we try to reach a compromise between the "dramatic" model, including a sudden and large drainage of the Ancylus Lake, and the idea of a non-existing Ancylus drainage through Denmark. This new model includes a minor, perhaps 5 m, sudden erosion and forced regression slightly before 10,000 cal. yrs BP. This was followed by a 200–300 yr long period when the outlet through Denmark and Great Belt (Dana River) was characterized by a variable fluvial environment creating fluvial, levée and lacustrine deposits. During this period of rapidly rising sea level, we postulate that the gradient between the Ancylus Lake and sea level gradually decreased from some 5 m until sea level had reached the Ancylus and Darss Sill level. After this point in time occasional pulses of marine water could easier enter into the Baltic basin, which is seen as brackish pulses as early as 9800 cal. yrs BP in records from the Bornholm and Gotland basins, but also from Blekinge. It would, however, take another c. 1500 years before the Öresund threshold was flooded by the rising sea level, causing a significant rise in salinity sometime between 8500–8000 cal. yrs BP, and marking the true onset of the Littorina Sea.