SEDIMENTATION PROCESSES OF LOWER EOCENE FORMATIONS OF THE SKIBOVY NAPPE AND BORYSLAV-POKUTS NAPPE (UKRAINIAN CARPATHIANS)

Abstract

The aim of the research is to study the main features of sedimentary processes in the Lower Eocene deposits of the Skybа nappe and Boryslav-Pokut nappe of the Outer Carpathians.Lithostratigraphic, sedimentological, geomapping, material methods of study and the results of paleontological and geodynamic studies by modern authors were used. Sedimentological analysis of the formations of the Lower Eocene Manyavska suite (Upper Thanetian-Lower Ypresian) of the Skybа and Boryslav-Pokut nappes, according to the data of previous researchers and the author, contributed to the identification of lithodynamic (sedimentological) types in the structure of its sections and the clarification of paleogeomorphological and paleogeodynamic conditions of sedimentation. The straton flysch is mainly represented by lithodynamic types of event-related fine- and medium-grained turbidites and background (hemi)pelagites, which are rhythmically and cyclically interbedded. Event deposits of contourites occur episodically.Based on the nature of the lithodynamic types of sections, we parallel them with the lower fans of submarine transport cones, which periodically captured the adjacent abyssal plain.Mineralogical and petrographic characteristics of sandstones from turbidites and contourites of the Manyava suite made it possible to distinguish several petrotypes. Sandstones with ordered structures belong to turbidites with elements of the Bouma cyclite Tbcd and obliquely layered contourites. Sandstones with disordered structures have elements of the Bouma cyclite Tа. All turbidites belong to graywackes. The identified petrotypes indicate different hydrodynamic features of event-induced flow sedimentation.The mineral composition of the background mudstones on the classification diagram for the systematization of clay rocks of the Manyava suite demonstrates a stable association, which indicates essentially montmorillonite (smectite) mudstones and rocks, from a three-component mixture of chlorite + montmorillonite + hydromica. The results obtained are well paralleled with modern materials on the study of mineral associations of pelagic facies and emphasize the presence of a magmatogenic component. The influence of the endogenous component in straton formations is indicated by other signs. Discriminant paleogeodynamic diagrams CaO-Na2O–K2O and SiO2–K2O/Na2O based on the results of petrochemical analyses of mudstones of the Manyava swathe distinguish two groups of figurative points of rock composition. They belong to sources of rock-forming minerals of mudstones (hemi) pelagites that are different in genesis: endogenous (in particular, hydrothermal) and exogenous. The lithodynamic type of contourites is localized at the foot of the continental slope, serves as an indicator of the tectonic separation of the lithosphere of the Outer Carpathian Basin into (sub)continental and oceanic crusts and is marked by deep-seated fault zones, which are transporters of endogenous matter. The above features allow us to emphasize the hybrid volcanogenic-sedimentary nature of background sedimentation in the Early Eocene period of the Outer Carpathian Basin. The paleoceanographic processes of sedimentation of the Manyava suite sediments have been reconstructed by modern researchers based on foraminiferal associations and environmental factors, and the data we obtained indicate the conditions for the formation of sediments in a marine basin of normal salinity at the depths of the lower bathyal–abyssal near or below the carbonate compensation level. Deep-sea turbidite currents in the form of drift cones (fens) transported terrigenous material here. Episodic actions of turbidite flows partially eroded (hemi) pelagites and contourites. The identified features of the rock sections of the Manyava suite were formed on the northeastern edge of the Outer Carpathian residual water area of the Tethys Ocean under conditions of Early Eocene tectonic calm during the subduction of the base of the Carpathian flysch basin under Tisius-Dacia.