Cardium edule Linne i C. glaucum Bruguiere w osadach eemskich i holoceńskich Mierzei Wiślanej

Abstract

W osadach Mierzei Wiślanej stwierdzono występowanie dwóch gatunków należących do rodziny Cardidae: Cardium edule Linné i C. glaucum Bruguiere. Pierwszy występuje w osadach morskich interglacjału eemskiego (kilkanaście metrów poniżej obecnego poziomu morza), drugi natomiast, pospolity współcześnie, pojawia się dopiero w osadach środkowoholoceńskich (6-7 lys. lat BP) morza lit orynowego.

CARDIUM EDULE LiNNÉ AND C. GLAUCUM BRUGUlERE IN THE EEMIAN AND HOLOCENE DEPOSITS OF THE VISTULA BAY BAR

In the palaeontological papers the unanimity due to the belonging of the family Cardiidae, existing in the deposits of Southern Baltic Sea, to the separate species is lacking.

Cardium edule Linné, the marine species of the atlantic-boreal origin, does not appear presenty in the Baltic Sea, but the brackish species Cardium glaucum (C. lamarcki) Bruguiere of the boreal-mediterranean origin, is common in the littoral area of the whole Baltic Sea. The aim of the present investigations was the definition of the specimens of Cardium found in the Vistula Bay Bar as belonging to the appropriate species and conformation, what species existed in the area of present-day Vistula Bay Bar in the geological past. Another aim consisted of finding the answer to the question, whether Cardium edule Linné or C. glaucum Bruguiere existed in the South Baltic Sea, and whether and in what period Cardium edule Linné existed and C. glaucum Bruguiere appeared there.

According to the actual knowledge of ecologic environment of these species, the authors tried to determine the contemporary climatic and ecologic conditions of this region. The ¹⁴C dating was very useful in establishing of the age of both species of Cardium.

In Sztutowo (L6, L11) Cardium edule Linné existed below the depth of 25.0 m, in Przebrno (ES) below 18.0 m, in Krynica Morska below 27.0 m and in Dziady (C1) below 16.5 m. The deposits in which it was found form the sands of the littoral zone, middle- to fine-grained with the presence of large amounts of muscovite, calcareous sands belonging to Eemian Interglacial deposits (A. Tomczak et al., 1989).

The coexistence of species was acknowledged at the depth 17.0-12.0 01. The occurrence of these two species, representing different ecologic environments, in connection with the age of deposits determined at 6-7 thousand years BP, can show that Cardium edule Linné was redeposited as a result of the abrasion of the Pleistocene deposits. The abrasion and redeposition is probable, because in this deposits the amount of Cordium glaucum Bruguiere increases, and that of Cardium edule Linné diminishes. The shells of the second species, which are small, and belong toyoung individuals, can be easier transported and redeposited.

The dating of the deposit allows to suppose, that just in this time the waters of the basin were populated by Cardium glaucum Bruguiere.

The exlusive occurrence of Cardium glaucum Bruguiere was noted in the borehole Sztutowo (L6) at the depth 18.0-16.0 m, in Dziady from 12.0 m to the surface, and in Krynica Morska from 15.0 m to the surface, that is in the deposits younger than 6-7 thousand years, formed in the littorine and post-littorine sea.