Palaeogeographical significance of the Eemian biogenic sediments at the bór site (Warta river valley, central Poland)

Abstract

An investigated area is located in the middle reach of the Warta River valley. During drillings in the Bór site organic deposits such as detrital calcareous gyttja and calcareous detrital gyttja has been documented in a depth between 14.9 and 16.6 m. The organic deposits are covered by mineral, mostly sandy deposits. The accumulation took place in the small lake formed as an abandoned channel. Palynological anal y sis led to the conclusion that biogenic ac cumulation began at the end of Wartanian and took place at least to the Eemian Interglacial optimum. Results of palynological, Cladocera and geochemical analyses indicate water level changes and the increasing of the trophy status of the reservoir. Presence of Mesozoic substratum very close to the palaeolake bottom influenced significantly the chemical features of the organic deposits. As Eemian organic deposits are uncommon in the Warta River valley, the Bór site seems important for palaeogeographical reconstructions of the Warta River valley during Eemian Interglacial.