PREGLACJALNE OSADY RZECZNE ZE STANOWISKA BARUCHOWO (KOTLINA PŁOCKA)

Abstract

PREGLACIAL FLUVIAL DEPOSITS IN THE BARUCHOWO SITE (PŁOCK BASIN)

Abstract. The paper presents the results of geological investigations carried out at the Baruchowo exposure situated in the slope of the morainic plateau framing the P³ock Basin from the south. Non-calcite quartz-dominated sand and gravelly sand were examined in detail. The deposits are devoid of Scandinavian material. They fill a palaeovalley channelled in Neogene clays and are exposed in the lower part of the Baruchowo exposure. Mineral composition of the heavy fraction and petrography of the sands and gravels clearly distinguish the series from Pleistocene glacial deposits, and together with their position in the geological section they suggest that these are preglacial deposits sensu lato. Sedimentological, structural and textural investigations indicate that this is a bipartite series of channel deposits of a sand-bed braided river flowing to the NW. The uppermost part of the river series (B1b) represents fluvioperiglacial deposits dominated by round matt quartz grains, indicative of aeolian origin. Their accumulation proceeded under cold and dry climate conditions without a direct ice sheet effect and during a long-term aeolian process at the beginning of some cold period of early Pleistocene time. The braided river system and deposition of the alluvial series may have occurred from the end of the Preglacial Complex sedimentation (lower part of the alluvial sequence) up to the stage of periglacial conditions preceding the advance of the Narevian ice sheet (upper part of the sequence), or only during the Narevian Glaciation. We cannot exclude that the accumulation of the river series took place at the beginning of the Nidanian Glaciation, preceding the first invasion of the ice sheet onto the Płock Basin. Thermoluminescence (TL) dating of river sands suggests that the sediment is older than 1000 ka.