PL
Opisano faunę mięczaków morskich z margli eemskich z wiercenia w Brachlewie pod Kwidzyniem. Zawiera ona 30 gatunków ślimaków i małżów, w tym 15 gatunków nowych dla plejstocenu Polski. Uwzględniono zagadnienia ogólne, dotyczące warunków egzystencji badanych mięczaków, jak paleogeografię, stosunki biocenotyczne, zasolenie i warunki batymetryczne. Poza tym porównano faunę eemską z Brachlewa z fauną tegoż wieku Holandii. W części systematycznej podano opisy gatunków, uwzględniając w miarę możność i zmienność osobniczą.
EN
A description is given of Eemian molluscs from the bore-core in Brachlewo near Kwidzyń (fig. 1 on p. 238). Grey-greenish silty marls, 2. 3 m thick, occur at a depth of 50.4 m, together with other abundant macro- and microfossils. Among the microfossils, foraminifers are the most numerous, the genera Nonion and Elphidium being particularly abundant, with the predominance of " Rotalia" beccarii. The absence of arenaccous and planktonic forms is conspicuous. Ostracods are ratner numerous too. Other fossils here encountered are: skeletal plates, madreporous plates, spines and fragmentary skeletons of Asteroidea, also chelae of Crustacea Decapoda and fragmentary shells of Balanus sp. Molluscs are the most numerous fossils within the studied assemblage. A great number of shells have been recovered from the collected sample (ca. 0,7 cubic metre in volume) which have been referred to 30 species of marine bivalves and gastropods. Among these, 16 species have already been previously described from Eemian deposits of the lower Vistula region, while 14 species are for the first time being reported from Poland. Thus the number of Eemian mollusc species so far identified in Poland now comprises 36 species (see :table = tabela l on p. 237). This assemblage has been divided up into two groups according to their state of preservation and the numerical abundance of the various growth stages. One group comprises species represented by a great number of specimens of various age and, on the whole, satisfactorily preserved, the other group includes species sparcily represented by specimens that are either damaged or fragmentary. Table 4 (p. 244) has been drawn up on this taphonomic basis , with a view to determine the specific composition of the Eemian biocoenosis. The distribution of specimens is shown in this table according to the state of preservatlon. Those with valves well preserved or only slightly damaged are placed in columns 3 and 4; they had most likely lived in situ , all within the same biocoenosis. Species contained in columns 5 and 6 are with valves strongly damaged or only fragmentarily preserved and have most probably been transported from the adjacent biotopes. In order to obtain fuller details concerning the temperature, bathymetric and salinity conditions prevailing in the environment of the studied fauna, the writer started out from the standpoint that the life requiremenis of the Eemian species closely resembled those of the same today living species. The geographical zone in which an analogous mollusc assemblage may be now encountered is first discussed (table l ). The statistical method used by the writer is that of the American authors Schenk and Myra Keen (1940) applied during investigations of recent East Pacific molluscs and of those from the Pleistocene of California. The distribution range ot the here studied Eemian molluscs has been indicated with reference to parallels of latitude. Table 2 (p. 241) gives these latitudes with reference to the distribution range of living species, together with respective mean distribution range. Table 3 (p. 242) shows the occurrence frequency of particular species in corresponding mean latitudes. The mean latitude of the mean geographical range for the whole assemblage is 48°N. Hence the studied fauna corresponds to that now living off the south-western shore or the Bretonnian peninsula, I.e. the northern part of the Lusitanian province. Moreover, this is confirmed by the presence, within freshwater deposit s underlying marine marls, of the freshwater form Belgrandia marginata Mich. (pl, I, fi g. 10). The northern boundary of its distribution range is indicated by the July 18 isotherm, running approxirnatically south of 48°N. Conclusions regarding the salinity of sea water, in which the studied fauna had lived, are based on data given in table 5 (p. 245) , and thoso contained in a paper by Meyer and Mobius (1872) concerning the distribution of molluscs in the Kiel bay. The salinity there was reduced, being however not lower than 15-20%. This is likewise suggested by the reduced dimensions of the mollusc shells and their thinness. Table 6 (p. 246) deals with bathymetric conditions. It shows the bathymetric distribution of some of the species present in the fossil biocoenosis . Considerations leading to the determination of the vertical range for this biotope reasonably suggest that the studied assemblage had lived in a shallow sea, not below the lower limit of the sea meadows. The Lusitanian mollusc assemblage f rom the marine marls of Brachlewo is by the writer referred to the Eemian stage and correlated with the rich list of bivalves and gastropods reported by Spaink (1958) from the Eemian beds of Holland. The distinct specific impoverishment of the Brachlewo fauna is due to reduced salinity in the eastern gulf of the Eemian sea, and to the physieal character of the sea floor there. The part on systematics contains a dcscription of all the marine molluscs from Brachlewo. IndividuaI and ontogenetic variability has been considered in the case of species whose various development stages are sufficiently numerous and well preserved to enable biometric studies. A great number of specimens have been measured for maximum height and width of shells, and for maximum height and width of shell apertures, with a view to analyse their variability, in successive growth stages . On this ground the just mentioned characters have been correlated as follows: 1) correlation of the maximum height and width of shell, and 2) correlation of the maximum height and width of shell aperture.