Calcareous nannofossil assemblages from Paleocene sediments of the Ukrainian Carpathians

Abstract

Problem statement. Detail study of both vertical and spatial distribution of calcareous nannofossils from the Paleocene sediments of the Ukrainian Carpathians enabled to determine the evolutional development of Haptophyta algae during the Paleocene, and became the basis for correlation of boundary markers and correlative biohorizons. Here we summarize data obtained from previous research, and also our own, and propose an updad biozonation of Paleocene sediments of the Northern and Southern slopes of the Ukrainian Carpathians. Prerious work. Calcareous nannofossil research of the area goes back to the 1960’s. These studies had a fragmentary character with only few sections examined for their nannofossil content. Materials and research methods. The paper includes the results of nannofossil research from numerous sections of Paleocene Flysch developed in the Outer and Inner Carpathian nappes. Discussion of the research data. The paper discusses the biozonation and correlation of local lithostratigraphic units of the Ukrainian Carpathians based on the detail study of nannofossils. For the first time, the complete successions of nannozones of the latest Geological Time Scale have been identified in the Ukrainian Carpathians. In the Outer (Flysch) Carpathians several nannozones were determined within the Skyba and Boryslav-Pokuttya nappes. There include – Markalius inversus / Biantholithus sparsus (NP1), Cruciplacolithus tenuis (NP2), Chiasmolithus danicus (NP3) and Ellipsolithus macellus (lower NP4) in the Upper Striy subsuite; top Ellipsolithus macellus (NP4), Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6) in Yaremcha Formation, Discoaster mohleri (NP7) in Bytkiv layers, Heliolithus riedelii (NP8), Discoaster multiradiatus (bottom NP9) from the Yamna suite; Chiasmolithus danicus (NP3) from Upper Bereznyan subsuite of Dukla nappe; Fasciculithus tympaniformis (NP5) in Gnylets suite of Chornohora nappe and Markalius inversus (NP1) in Urdyn suite of Svydovets nappe. Within the Inner Carpathians nannozones were defined in the Lower Metova subsuite of the Vezhany nappe – Biantholithus sparsus (NP1), Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6), Heliolithus riedelii (NP8); Sushmanets suite of Monastyrets nappe contained Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6) and Tribrachiatus contortus (NP10) of the Early Ypresian. The stratigraphic positioning of nannofossil assemblages was rectified and their correlation with foraminifera and dinocyst zones was demonstrated. These nannozone assemblages from the Ukrainian Carpathians are correlated with the Danian, Selandian and Thanetian stages of the Geological Time Scale (GTS, 2012 and 2016). This integrated research enables to rectify and modify the stratigraphic scheme of the Paleogene from the Carpathian region. Conclusions. A modern calcareous nannofossil biozonation of the latest International schemes has been recognized from the studied Paleocene sections of the Ukrainian Carpathians. Nine (9) nannozones ranging from NP1 (Early Danian) to NP9 (Late Thanetian – Early Ypresian) and also the lowest NP10 nannozone of Early Ypresian have been identified in strata from different structural-tectonic units. The nannofossil biozonation is correlated with those foraminifera and dinocyst biochronology. The age and correlation for the Paleocene stratigraphic subdivisions has been justified based on the nannofossil biostratigraphy. This resulted in the upgrading of the existing stratigraphic scheme of the Paleogene of the Ukrainian Carpathians.