A record of Eocene subaqueous large-scale mass movements in the external Tethys Ocean (Skyba Nappe, Outer Carpathians, Ukraine)

Abstract

Studies were carried out on the Popeli Beds, which were mainly deposited by mass movements along the northern slope of the Tethys Ocean and form an olistostrome sequence occurring within Paleogene deposits. The analysis focuses on the deposits exposed in the northern limb of the Pobuk Syncline – the structural element of the Oriv Skyba – in the external zones of the Skyba (Skole) Nappe. Structural, lithological, sedimentological and paleontological studies allowed for the identification and characterisation of the olistostrome sequence and revealed its structure. Six individual olistostrome complexes were distinguished and described in detail. Five of these are gravelly mudstoneswith oversized clasts, overlain by medium-bedded mudstones and sandstones, the last one consists of deformed packages of thin bedded mudstones and sandstones. The olistostrome sequence is composed of a wide range of lithological and stratigraphic components, including Tithonian – Berriasian shallow- water limestones (so-called Štramberk-type limestones), Upper Cretaceous limestones, sandstones, and siliceous rocks, as well as Paleogene mudstones, sandstones, limestones, and marls. Biostratigraphic analysis of foraminifera indicates the Bartonian as the time of displacement. The olistostrome niche migrated downslope from a lower shelf-upper slope position characterized by marl sedimentation, to slope areas dominated by turbidite sedimentation.