Mięczaki z interglacjału eemskiego w Żmigrodzie nad Baryczą

Abstract

Na podstawie próbek. uzyskanych z trzech otworów wiertniczych ze Żmigrodu opracowano mięczaki (33 gatunki) z osadów rzecznyo-jeziornych interglacjału eemskiego. W próbkach stwierdzono również pancerzyki małżoraczków (Ostracoda) i szczątki ryb (Pisces). Analiza warunków ekologicznych wskazuje, że opisany zespół rozwijał się w płytkim zarośniętym zbiorniku wody stojącej ze stałym lub okresowym przepływem.

EEMIAN INTERGLACIAL MOLLUSCANS FROM ŻMIGRÓD UPON THE BARYCZ RIVER

Molluscans from Żmigród were studied on the basis of core material from three drillings made in the Żmigród Basin, north of Wrocław (SW Poland - Fig. 1).

Geological structure of the Żmigród Basin was recently discussed by S. Dyjor and T. Kuszell (1975). These authors showed that this basin originated before the South-Polish Glaciation and acted as lacustrine reservoir during successive interglacials including the Eemian. The Eemian age of the studied fauna is shown by correlation with the neighboring Raki locality (SW of Żmigród), where the share of hazel (Corylus) pollen was found to be very high (64.3%). Such interpretation of age of the Żmigród locality differs from that of M. Schwarzbach (1942), according to whom it belongs to an interstadial located between the maximum and Masovian-Podlasie ones of the Mid-Polish Glaciation.

The fauna) assemblage from Żmigród comprises 33 molluscan species (21 gastropod and 12 bivalve species - Table 1). Besides molluscans, the studied samples were found to yield ostracods: Candona neglecta Sars, C. sp., Herpetocypris reptans (Baird), llyocypris sp., Limnocythere inopinata? (Baird), fish remains: vertebrae, fish bones, throat teeth of roach - Rutilus rutilus (L.), and scales of some species including perch - Perca fluviatilis L., and one otolith, as well as teeth of rodents (Rodentia) and remains of wing case of beetle (Coleoptera).

The analysis of ecological requirements of individual molluscan species made it possible to interpret life environment of the assemblage as shallow, overgrowth stagnant-water reservoir with constant or seasonal flow.

The presence of warm-water molluscans·in this assemblage: Belgrandia marginata (Michaud), Lithoglyphus sp., Valvata naticina Menke, Viviparus sp., Sphaerium rivicola (Lamarck), makes possible treatment of molluscan-bearing sediments as interglacial ones. The most warm-water element recorded here is B. marginata, with the northernmost range not overpassing 18^oC isotherm of July. This species marks the position of climatic optimum in this geological column. The optimum is confirmed by the record of fruit of maple (Acer) at the depth of 22.1 m in the borehole 4b.

The Żmigród locality is one of the richest in molluscans in the case of the Eemian Interglacial in SW Poland. Some of the recorded species are fairly rare in the Quaternary in Poland: Belgrandia mar-ginota (Michaud), Lilhoglyphus sp., Pisidium moitessierianum Paladilhe, P. supinum Schmidt, Sphaerium rivicola (Lamarck), Valvala naticina Menke and Viviparus sp., whereas Pisidium stewarti Preston was here found for the first time.