Abstract
<jats:p>The Dynow Marls (siliceous marls) represent a sedimentary record of a salinity-decreasing event, anoxic bottom sediment conditions, and strong endemism that occurred throughout the Central Paratethys during the Lower Oligocene (NP 23), and is referred to the Solenovian Event (loss of connection of the Paratethys with the World Ocean). A comprehensive study of the Dynów Marls on a regional scale, in the context of their sedimentatary environment, source rock potential and importance for the petroleum system, were conducted in the Western Carpathians, mainly in the Czech Republic and Austria. The obtained results indicate shallow-water conditions of their deposition, which is consistent with paleogeographic and paleoclimatic reconstructions. The occurrence of these deposits has been identified in the lower part of the Menilite Beds throughout the Carpathian arc. The succession of Menilite Beds in the Polish Outer Carpathians was considered until recently to be a product of deep-water sedimentation. As a result of research work in the southern part of the Silesian Unit (Gorlice fold), this interpretation has been verified. In this area, it was shown that sedimentation took place on a shallow, periodically existing shelf. This interpretation only partially took into account the occurrence of Dynów Marls in the Menilite Beds profile (distinguished at the rank of a member), which are of key importance for confirming the previous interpretation and determining their origin in a broader regional context. Therefore, for a complementary interpretation of the entire succession of Menilite Beds within the Silesian Unit, detailed sedimentological studies of Dynów marls were conducted, which was supported by geochemical studies in three selected sections in Gorlice (section A), Zborowice (section B) and Jabłonica Polska (section C). providing support. Within these studies, six sedimentary facies F.1 (menilite shales), F.2 (cherts); F.3 (stratified marlstone); F.4 (massive and sandy-pebbles marlstone), F.5 (marly-mudstones heterolithes)’ F.6 (Stratified and laminated sandstone) were distinguished, with a consistent interpretation of their depositional environment being provided for all. The origin of facies, which in different sections occur in different relationships, gives a logical scheme of the changes that occurred during the deposition of the Dynów Marls, which is also reflected by three facies associations ZF.I, ZF.II and ZF.III. Both the facies and the associations (mainly in profiles B and C) indicate deposition in a shallow sedimentary basin, (in a periodically isolated and periodically flooded) basin, to which, in addition the carbonate deposit, siliceous material was supplied (or was produced in situ), where also tsunamites-like sedimentation occurred periodically, tracked over a large distance. The record in the Dynów Marls section in Gorlice (section A) has a clear succession of facies from the upper to the intertidal zone, additionally indicating cyclic changes in the depth of the sedimentary basin. This is also confirmed by present in the Dynów Marls deposits interpreted as tidal rhythmites, with a record of spring and neap tides. The facies succession, in addition to the fluctuations in the depth of the basin, indicates the deepening of the shallow shelf. In this area above the Dynów marls the development of a shallow deltaic system is documented consisting of series parasequences formed under forced regression condition (Magdalena Sandstones). Additionally, the results of geochemical studies from the F.1 facies from the area of the Silesian unit were compared with the results of geochemical studies obtained from this facies from the Skole unit, from the Dynów region (Futoma and Straszydle exposures), show differences in the composition of biomarkers, which may be caused by different conditions of their deposition than in the Silesian unit. The proposed shallow-water interpretation of the study area does not preclude the existence of deep-water regions elsewhere in the Paratethys sedimentary basin during Lower Oligocene time. The inferred evidence for tides in the studied sections, despite an interpreted lacustrine setting there, possibly reflects the basin’s connection to the open ocean in this area. This described and documented discovery of the occurrence of tidalites and tsunamites within the Dynów Marls is an important step in understanding the paleoevolution of the Carpathians, but is also important from the point of view of understanding the conditions of deposition of the Menilite Beds - the main source rock for hydrocarbons. The obtained results confirm and specify the previous research results and previously reconstructed paleogeographic conditions. Keywords: The Carpathians, Menilite Beds, Dynów Marls, depositional environments, biomarkers, tidal deposits, tsunamites.</jats:p>