PALEONTOLOGICAL SUBSTANTIATION OF THE EARLY JURASSIC STRATIGRAPHY IN THE PIENINY ZONE OF THE UKRAINIAN CARPATHIANS BASED ON AMMONITES

Abstract

The most common Jurassic deposits in the Ukrainian segment of the Carpathians are concentrated in the Inner Carpathians, specifically within the Pieniny Zone. The complex geological structure of this structural-tectonic unit, which extends in a narrow belt for over 500 km (from the Vienna Basin in the west to the Romanian Carpathians in the southeast), remains a subject of scientific debate. Today, it is scientifically established that the Jurassic limestone outcrops in this area are represented by rootless tectonic klippen, displaced far to the northeast from their original in-situ positions. The best exposures of Lower Jurassic formations within this zone are recorded in the vicinity of the villages of Novoselytsia and Pryborzhavske, and the town of Perechyn in the Zakarpattia region. Although various authors, in their descriptions of the Pieniny Zone Liassic, mention the presence of deposits from all stages of the Lower Jurassic, conclusions regarding their correlation, section completeness, thickness, sedimentogenesis conditions, and the paleoecological features of the Early Jurassic basin require further refinement. Paleontological and stratigraphic studies of the Lower Jurassic deposits in the Pieniny Zone allow for the substantiation of the presence of the International Stratigraphic Scale stratons – stages and chronozones: Alsatites liasicus, Arietites bucklandi, Asteroceras obtusus, Echioceras raricostatum, Uptonia jamesoni, Dactylioceras tenuicostatum, Harpoceras falcifer, and Grammoceras thouarsense; the stratigraphic distribution of characteristic ammonite species is also provided. The results refine the subdivision of the lower (Liassic) part of the section and provide a basis for confident interregional correlation. The identified ammonites have a significant geographical distribution and are characteristic forms for many regions of the Mediterranean paleozoogeographic province. The research results will serve as a basis for reconstructing the geological history of the region, correlating the identified stratigraphic units with the stratons of the Western and South-Eastern Carpathians, and performing further paleobiogeographic reconstructions.