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Subfossil mollusc shells of the Baltic Sea and the possibilities of their usage in the stratigraphy and correlation of the Baltic Sea sediments

Tavast Elvi

Geologos

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2000

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Vol. 5

31--40

EN

Subfossil mollusc shells in Estonia are widely spread both in contemporary and ancient sediments and for a long time they have served successfully for stratigraphical, palaeogeographical and archaeological purposes. There are extremely good conditions for the investigation of the subfossil mollusc fauna in Estonia. The bedrock in coastal area consists here mainly of limestones and dolomites, which are covered with carbonaceous till and aqueoglacial deposits. In Estonian nearshore environs molluscs had suitable living conditions and enough material to build up the shells. They are better preserved than in neighbouring countries. The molluscs can give precise information about the conditions of palaeobasins. This is primarily due to their good preservation and a large number of species. Their history began in the Palaeozoic Era and they are spread nearly in all biotopes. The molluscs are rather susceptible to the environment they inhabit and can therefore give information about the water depth, salinity, temperature and isotopic composition of water. Malacological method will give a great help in the correlation of the on- and offshore deposits and landforms and this method is well developed in Estonia.

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Late Weichselian and Holocene development of the small valleys in the SE part of the Niemcza Hills, Sudetic Foreland, southwestern Poland

Alexandrowicz S. W., Ciszek D.

Geologia Sudetica

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1998

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Vol. 31, nr 2

213-220

EN

The deposits which fill the small valleys of the Niemcza Hills in the Sudetic Foreland were accumulated by meandering rivers. There are sequences that consist of both the channel and overbank facies, including lateral accretion deposits and soils. The overbank deposits are composed of redeposited loess, which forms the alluvial loam described in this paper as silty loam. Two main stages of accumulation occurred: Lateglacial/early to middle Holocene and late Holocene. During the first stage, accumulation rates were very low in spite of the drastic climatic change at the Weichselian/Holocene boundary. The second stage was characterised by very high accumulation rates and generally increased slope activity, which was probably a result of human impact and extensive agriculture, present in this area since ca 2300-2500 yrs BP. The mollusc fauna changes according to the valley evolution, at first (stage I) represented by poor, redeposited, mainly cold-tolerant loess fauna, and then (stage II) rich assemblages of snails living in shady and humid habitats.

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Late Quaternary mollusc-bearing deposits from Bechar (Algeria)

Alexandrowicz S. W.

Annales Societatis Geologorum Poloniae

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1998

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Vol. 68, No. 1

75-84

EN

Two subfossil assemblages of molluscs were found in terrigenous sediments forming two terraces of Wadi Bechar (Western Algeria). The older one, connected with the Late Pleistocene terrace of Saourien, is dated at 18500 years BP. It comprises 28 taxa of land and water snails including species, living recently in Africa and around the Mediterranean as well as Holarctic/Palearctic species. The younger fauna derives from the Holocene terrace of Guirien, dated at 5140 years BP, is poorer (11 snail species) and devoid of Holarctic/Palearctic taxa. Late Quaternary mollusc-bearing sediments from Bechar and from other localities known in Africa and Near East correspond with three phases of the humid climate (pluvials), correlated with the interpleniglacial and the ascending stage of pleniglacial of the Vistulian, with the Late Vistulian and with the climatic optimum of the Holocene.

PL

W terrygenicznych osadach tworzących terasy uedu Bechar (zachodnia Algeria) zostały znalezione dwa zespoły subfosylnej malakofauny. Starszy z nich, występujący w terasie młodoplejstoceńskiej, zaliczonej do Saourienu, jest datowany na 18500 lat BP. Obejmuje on 28 gatunków ślimaków lądowych i wodnych, żyjących współcześnie w Afryce i wokół Morza Śródziemnego, a także gatunki holarktyczne i palearktyczne. Młodsza fauna pochodzi z holoceńskiej terasy zaliczonej do Guirienu, datowanej na 5140 lat BP. Jest ona uboższa (11 gatunków ślimaków) i nie zawiera taksonów holarktycznych i palearktycznych. Osady późnoczwartorzędowe z malakofauną, znalezione w okolicy Bechar oraz cytowane z wielu stanowisk z obszaru Afryki i Bliskiego Wschodu, odpowiadają trzem kolejnym fazom wilgotnego klimatu, wyróżnianym jako pluwiały. Można je korelować odpowiednio z interpleniglacjałem i wstępującą fazą plenivistulianu, z późnym glacjałem oraz z klimatycznym optimum holocenu.