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The first geological record of a palaeotsunami on the southern coast of the Baltic Sea, Poland

Rotnicki K., Rotnicka J., Goslar T., Wawrzynniak-Wydrowska B.

Geological Quarterly

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2016

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Vol. 60, No. 2

417--440

EN

Tsunami deposits were unknown along the southern coast of the Baltic Sea for a long time. The results of present research provided evidence of high-energy event layers. They occur on the bottom of two hemispherical hollows that are cut into glaciolimnic silt and glaciofluvial sand and gravel from the Late Weichselian Age. The event deposits are represented by poorly sorted marine sand with admixtures of pebbles and allochthonous detritus of biogenic origin: marine, brackish and occasionally freshwater shells and shell debris of molluscs and snails, plant macrofossils from the marine nearshore zone, shreds and lumps of peaty material, gyttja and organogenic silt, lumps of charcoal, wood pieces and tree branches and trunks. All these features are commonly considered indicative of tsunamis. The age of the biogenic detritus found in the tsunami layer ranges from 10 390 to 6 630 cal. yr BP, whereas the oldest gyttja covering the event layers is 6 600 cal. yr BP old. This means that the tsunami occurred between 6 630 and 6 600 cal. yr BP. Various causes of tsunami event have been taken into consideration, including the impact of meteorites within the coastal plain and the littoral zone of the southern Baltic Sea.

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Stages of the formation of the Łeba Barrier-Lagoon system on the basis of the geological cross-section near Rąbka (southern Baltic coast, Poland)

Rotnicki K., Alexandrowicz S.W., Pazur A., Goslar T., Borówka R.K.

Studia Quaternaria

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2009

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Vol. 26

3-24

EN

The article presents the results of a detailed study of the geological structure of the Łeba Barrier in the Rąbka cross-section (Southern Baltic, Poland). The barrier separates Lake Łebsko from the Baltic. Five sedimentary complexes were distinguished there (M2-M6). The spatial variability of the grain-size distribution was examined and succession stages of the mollusc fauna occurring in the individual sedimentary complexes were distinguished. Radiocarbon dating was used to establish the age of the most important events during the process of formation of the barrier, which took place in the course of several relative sea-level changes. The first sedimentary complex (M2) at Rąbka is connected with the second ingression (i2) of the Baltic Sea (ca. 6,700-6,000 14C years BP), sea-level stabilization (6,000-5,500 14C years BP), and at last sea-level lowering (5,500-5,000 14C years BP) in the region of the Gardno-Łeba Coastal Plain. The sedimentary complex M3 developed in a lagoonal environment when the barrier was situated north of its present position (5,000-3,000 14C BP). The next lowering of the sea-level made the lagoon shallower and caused the emergence of small but already subaerial stretches of barrier land with a freshwater fauna in the north (4,880š40 14C BP). With the next ingression stage (i3), which took place between 4,500 and 3,000 BP, the barrier shifted to its present-day position and the lagoon changed into a freshwater lake. From 3,000 to 1,700 14C BP fossil soil and peats developed on the barrier surface as a result of another sea-level lowering. The last ingression stages (i4 and i5), younger than 1,700 BP, built up the barrier, practically in its today's location (sedimentary complexes M4 and M5). The youngest sedimentary complex (M-6) is represented by present-day beach sands.

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Statistical analysis of radiocarbon dates as a tool for reconstruction of the environmental changes

Michczyńska D. J., Michczyński A., Pazdur A., Rotnicki K.

Polish Geological Institute Special Papers

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2004

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Vol. 11

109-112

EN

Statistical analysis of large sets of 14C dates may be a source of information on global or regional environmental changes. Since the nineteen seventies, an analysis of the frequency distribution on a time scale of 14C-dated samples has been carried out for several selected geographic regions. This paper presents basics of the applied method and examples of cumulative probability density functions constructed for 14C dates of peat from territory of Poland. It is emphasised that preferential sampling plays an important role in such a type of analysis. The problem of absolute age determination has been discussed, too.