Stratigraphical and facial distribution of foraminifera in Miocene deposits of the western part of Ukrainian SSR

Abstract

In this paper, the author presents the detailed stratigraphy of the Fore-Carpathian Miocene deposits and compares them with analogous sediments of the Trans-Carpathians and the Volyno-Podolian margin of the Russian Platform. On the basis of micropalaeontological data several key zones are distinguished, among which planktonic Foraminifera zones are of particular importance. The following foraminiferal zones are distinguished: 1) Chattian-Aquitanian — the small Globigerina, Chilogumbelina and Bolivina zone and the siliceous microfauna zone; 2) Burdigalian — the Globoquadrina dehiscens zone and Porosononion insignis zone; 3) Helvetian — the Globigerina bollii zone and the Quinqueloculina distorta zone; 4) Lower Tortonian — the Candorbulina universa zone and the Uvigerina asperula zone; 5) Upper Tortonian — the Radiolaria zone, the Globigerina bulloides and Spirialis zone, the Bogdanowiczia pocutica zone, the Cassidulina crista zone and the Streblus galicianus zone; 6) Samiatian — the Cibicides badenensis zone and the Quinqueloculina reussi zone. Paleontological analysis has revealed some variations in the salinity of waters in the Miocene basin. Hypersaline conditions seem to have existed during the Chattian-Aquitanian and the Tortonian in facies of the Tyrassa and Tereblya suites. On the other hand, the Helvetian Berezhany Beds, Tortonian Ervilia Beds and Sarmatian Dashava suite were deposited in an environment of reduced salinity.