The dissertation is devoted to the lithologic-geochemical research was performed for the molasse strata of the Stebnyk suite of Lower Neogene of the Carpathian Foredeep, which is considered by author as deposits, which were formed in a contrast geochemical environment. Deposits of the Stebnyk suite are represented by two lithologic-facial complexes: the Vyrvynsky and Nadvirnyansky. The first one occurs in the northwest of the investigated area, lies on the eroded surface of the Vorotyshcha suite, and the second one – in the southeast and preserves the inherited nature of the sediment accumulation with the Dobrotiv suite.
Deposits of the Stebnyk suite are represented by the following rocks: conglomerates, gravelites, sandstones, siltstones, clays, marls, limestones, gypsum and salt breccia. The main role in the structure of the suite belongs to sandstones, siltstones and clays. Allothigenic and authigenic minerals of the Stebnyk suite have been investigated, new minerals have been found in the rocks of this succession and the change of the geochemical environment during the lithogenesis has been determined on the basis of post-sedimentary changes in the studied minerals.
The parameters of the geochemical environment, the lithologic-facial features of the deposits of the Stebnyk suite and the correlation sections made it possible to dissociate the sedimentary succession of the Stebnyk suite into three main sub-suites: Lower, Middle and Upper. Within the Upper sub-suite the continuous horizon of montmorillonite clay, covered with salt-bearing ones, has been established, an abrupt change of the geochemical environment and the formation of a geochemical barrier are observed.
The scientific novelty of the results obtained in this work is represented in the following key positions:
By the results of geochemical studies of minerals, for the first time, a change in the geochemical medium during the lithogenesis of the Lower Miocene deposits has been established and new minerals have been found in the rocks of this sequence.
Based on lithologic and geochemical studies of stratotypic sequences of the Nadvirnyansky lithologic-facial complex the geochemical barriers – the boundaries of the transition of variegated deposits into the salt-bearing ones, have been established.
By the geochemical and mineralogical-petrographic studies for the first time the continuous regional distribution of montmorillonite clay layer has been established, which is a marker stratigraphic horizon in the section of the Stebnyk suite of the Nadvirnyansky lithologic-facial complex.
For the first time the influence of structural and lithological factors and the geochemical environment on the metasomatosis of the Lower Miocene deposits caused by surface salt and hydrocarbon occurrences has been established.
The investigations covered the Lower Miocene deposits of the Carpathian Foredeep, which made it possible for this vast territory to obtain the results of practical significance. In particular, the geochemical barriers in the Lower Miocene sediments that could serve as local fluid seals and the marking horizons of montmorillonite clays were identified, which would allow a new estimate of the tectonic situation within the Carpathian Foredeep.
