ZMIANY ŚRODOWISKOWE POPRZEDZAJĄCE SEDYMENTACJĘ GIPSÓW BADEŃSKICH I NA POCZĄTKU ICH DEPOZYCJI W REJONIE RZEKI WSCHODNIEJ (PÓŁNOCNA CZĘŚĆ ZBIORNIKA PRZEDKARPACKIEGO)

Abstract

ENVIRONMENTAL CHANGES PRIOR TO AND AT THE BEGINNING OF DEPOSITION OF THE BADENIAN GYPSUM (WSCHODNIA RIVER REGION, NORTHERN PART OF THE FORE-CARPATHIAN BASIN)Abstract. Composition and changes in foraminiferal assemblages recorded in the uppermost part of the sub-evaporite deposits of the Busko (Młyny) PIG-1 borehole (depth 188–192 m) in the northernmost part of the Fore-Carpathian Basin (Central Paratethys) indicate that the basin, in which marly deposits have originated, was poorly ventilated with a great oxygen deficit in the bottom waters, and was characterised by mainly eutrophic conditions in surface waters. The basin was 50–70mdeep. The waters were cool and of normal seawater salinity, although the recorded (in the uppermost part of the section) almost complete disappearance of Uvigerina foraminifers, occupation (for a short time) of the vacant niche by Fursenkoina acuta (assemblage D4c), and the dominance of Bulimina elongata (tolerant to increased salinity) in theyoungest assemblage (D4d) may indicate a considerable increase of seawater salinity during the deposition of the uppermost part of the subevaporite strata. The gypsum section is characterised, when compared to the more marginal gypsum sections of the Nida Trough, by a reduction of the lower, autochthonous part of the gypsum section and a specific development of the lowermost gypsum unit. It contains gypsum nodulesresembling small, chaotically arranged gypsum intergrowths in the clayey matrix. Such facies is regarded as the skeletal facies of the giant gypsum intergrowth facies of the Nida Trough and Moravia, and is related to depositional lows at the beginning of the gypsum deposition. The gypsum sequence in this borehole indicates a deeper sedimentary environment than inferred for the Nida Trough.