BIOSTRATIGRAPHY AND SEDIMENTARY ENVIRONMENTS OF THE LOWER/UPPER CRETACEOUS BOUNDARY DEPOSITS BY SMALL FORAMINIFERA (PIENINY KLIPPEN BELT, UKRAINIAN CARPATHIANS)

Abstract

The Pieniny Klippen Belt extends 600 km from the Slovakian Carpathians to the Romanian Carpathians. The Pieniny KIippen Belt narrows in the Ukrainian Carpathians. It is called the Pieniny Zone here. The Cretaceous succession of the Pieniny KIippen Belt in the Ukrainian Carpathians consists of the upper part of the Svalyava Formation (Titonian- Neocomian), Tyssalo Formation (Aptian-Senomanian), Puchov Formation (Turonian-Maastrichtian) and Yarmuta Formation (Maastrichtian). This succession is overlapped by the Eocene Vylhivchyk Formation with angular uncomformity. The Lower/Upper Cretaceuous boundary sediments of the Pieniny KIippen Belt in the Ukrainian Carpathians is located in the Tyssalo Formation. The paper presents the results of the analysis of foraminifera from the marls of the Tysalo Formation developed in the Tysalo tract, in the sections of the Tereblya and Luzhanka rivers, in the quarries of Perechyn and Pryborzhavske villages (Transcarpathians region). 27 species of foraminifera were identified in this study in the age range of Late Albian — earliest Turonian including 15 planktonic species and 4 benthic species. The biostratigraphic succession of foraminiferal subdivisions ranging from late Albian to Senomanian is identified. Upper Albian-Senomanian sediments of the Tyssalo Formation are divided into three lithological members. The lower member consists of black limestones and marls with dark grey limestones which correspond to early Late Albian. The middle member is represented by gray and gray-green marls with gray siltstones and sandstones which correspond to middle Late Albian. The upper member consists of light green-gray marls with pink marls which correspond to late Late Albian-Senomanian. The Hedbergella gaultina Zone (late Late Albian), Pseudothalmanninella ticinensis Zone (middle Late Albian) and Parathalmanninella appeninica Zone (late Late Albian) were identified in the Tyssalo Formation both by previous researchers and in the material presented. The layers with Thalmanninella globotruncanoides (early Senomanian), Thalmanninella reicheli Zone (middle Senomanian) and Rotalipora cushmani Zone (later Senomanian) are established in the Tyssalo Formation for the first time. The Lower/Upper Cretaceous boundary corresponds to the boundary between the Parathalmanninella appeninica Zone and the layers with Thalmanninella globotruncanoides, which are not found in the same section due to the intense deformation of the deposits in the Pieniny KIippen Belt. Changes in the generic composition of planktonic foraminifera in the boundary deposits of the Lower and Upper Cretaceous of the Tysalo Formation are gradual, from the dominance of small Biglobigerinella, Globigerinelloides, Hedbergella, Ticinella in the Upper Albian to the bloom of large complex-built Pseudothalmanninella, Rotalipora, Thalmanninella, Parathalmanninella, Praeglobotruncana Pseudothalmanninella, Rotalipora, Thalmanninella, Parathalmanninella, Praeglobotruncana in the Senomanian. The black marls of the lower member contain pyritized foraminifers, so it can be assumed that they were formed in oxygen-deficient botton-water conditions (early Late Albian). In the middle member change in the color of sediments from black to gray and green and the presence of calcareous benthic foraminifera belonging to genera Parella, Anomalina, Pleurostomella, Gavelinella indicate an improvement in oxygen conditions in bottom waters (middle Late Albian). The marl of the upper member is dominated by (70-100% of associations) planktonic foraminifera mainly from the genera Parathalmanninella, Rotalipora, Thalmanninella, Praeglobotruncana, which indicates the depth of the middle batial (late Late Albian-Senomanian).