Zmiany zespołów otwornicowych w kredzie piszącej (kampan/mastrycht) Mielniką nad Bugiem jako przejaw wahań głębokości zbiornika

Abstract

THE CHANGES OF FORAMINIFERAL ASSEMLAGES FROM CHALK DEPOSIT (CAMPANIAN/MAASTRICHTIAN) AT MIELNIK ON BUG AS EVIDENCES OF BASIN DEPTH FLUCTUATIONS Summary At Mielnik-on-Bug (eastern Poland) a 20-meters thick section of the Campanian and Maastrichtian chalk is exposed (fig. 1). The relative bathymetrical trends in this section are shown basing on the palaeoecological studies of the foraminiferal assemblages, including plankton/benthos (P/B) ratio analysis (fig. 2B, fig. 3) and the changes in the foraminiferal spectra (fig. 2C, D). The analysis indicates the two shallowing episodes in the Campanian Sea (fig. 4). The first episode is recorded by the omission surface with which the epidiagenetic flints are associated, the secend one by the hard ground at the Campanian/Maastrichtian boundary. A brief sea-level lowering at Campanian/Maastrichtian boundary is a common phenomena in the epeiric basin of northern Europe (8, 25). The chalk overlying the hard ground (the lower Lower Maastrichtian) was deposited during the successive weak transgressive episode.