UPPER CRETACEOUS–LOWER EOCENE MUDSTONES OF THE OUTER CARPATHIANS (PETROCHEMICAL AND PALEOGEODYNAMIC ASPECTS)

Abstract

The mineral types of the Upper Cretaceous–Lower Eocene greenish-gray mudstones of the Skyba and Boryslav-Pokuttya nappes of the Outer Carpathians were studied. According to sedimentological features, these mudstones belong to hemipelagites and contain information about the background sedimentation conditions of the deep-sea oceanic basin. The purpose of the work is to clarify the paleogeodynamic features of the basin based on the results of studying the material composition of the Upper Cretaceous–Lower Eocene background mudstones, which in particular are part of the variegated-colored horizons. Research methods were geological mapping, X-ray structural, sedimentological, lithostratigraphic, petrogeochemical, geodynamic analysis. On the classification module diagram (Na2O+K2O)/Al2O3–(FeO*+MnO+MgO)/SiO2, the figurative points of the contents of the Upper Cretaceous–Lower Eocene mudstones of the Stryi, Yamna, and Manyava suites fall into the fields corresponding to two mineral types: a mixture with a predominance of montmorillonite and three-component mixture of chlorite+montmorillonite+hydromica composition. According to the obtained data, a gradual change in the conditions of the sedimentary environment from the Late Cretaceous to the Eocene can be traced, with a successive increase in the normalized alkalinity modulus and a decrease in the phemic modulus. On the paleogeodynamic discriminant diagrams (FeO*+MgO)–TiO2 and F1–F2, figurative points of Upper Cretaceous–Lower Eocene mudstones form petrochemical distribution trends that cover the fields of geodynamic conditions from passive to active margins of the sedimentation basin. The Cretaceous–Paleogene pelagic mudstones of the Sicilian domain of the Alpine Belt have a similar distribution of petrochemical components. The mineral assemblages found in the mudstones of the Skyba and Boryslav-Pokuttya nappes are typical for deep-sea clay sediments of modern oceans. The presence of montmorillonite and chlorite in the background argillites indicates a high probability of a contribution to the background petrofund of the sedimentatary basin by a femic magmatic component of endogenous origin, realized as a manifestation of volcanic and hydrothermal activity, synchronous to sedimentogenesis. An exogenous source could be the magmatic material transferred or changed by the processes of halmyrolysis, which is not synchronous with sedimentation. The Late Cretaceous–Early Eocene geodynamic events of the Outer Carpathian sedimentary basin developed in front of the ALCAPA and Tisza-Dacia terranes of the Alpine Tethys. Convergence, which caused the formation of the accretionary prism in front of the terranes, could contribute to the riftogenic (?) opening, deepening of the Outer Carpathian Basin, where the penetration of synsedimentary endogenous material, mainly of the basic composition, took place. This material could be the rock-forming source of the basin substrate, on which the mineral assemblages of the background hemipelagic mudstones were formed.