Petrography and mineralogy of the Oligocene flysch in Ionian Zone, Albania: Implications for the evolution of sediment provenance and paleoenvironment

Abstract

Abstract In this study, the reconstruction of the formation condition in the Oligocene flysch (Berati and Zhitomi section), in the Berati anticline structure, north-eastern part of the Ionian tectonic zone (Albania), is elucidated using petrographic–mineralogical characteristics and grain size analysis. Outcrops from the Berati and Zhitomi and the drilled wells were selected for sampling based on previous stratigraphic and paleontological studies. The mineralogical study of the flysch deposits made it possible to evidence for the first time three mineralogical zones: (a) quartz–garnet (b) serpentine, epidote with mica, and (c) feldspar zone, and three these petrographic zones: (a) quartz, (b) quartz–serpentine, and (c) quartz with mica and feldspars. The reconstruction of the depositional environment is based on the petrographic study of rock types, their textural characteristics, and grain size statistics. The granulometry coefficients like mean, sorting, skewness, and kurtosis are calculated arithmetically and the C/M diagram as well. Referring to the mineralogical composition of the sandstones and siltstones, the obtained data were used for the correlation of the sections and the delineation of the leaching area and the direction of the sediment movement. The mineralogic and petrographic characteristics show that during the Oligocene, the region has been under continuous paleogeographic change and under intensive orogenic activity, which has influenced the character of the mineralogical–petrographic composition of these deposits. Based on the pebbles petrography present in the slump horizons and on heavy mineral assemblages, it was evidenced that the eastern tectonic zones of Kruja, Krasta, and Mirdita (Albania) were the main suppliers of sedimentary material. The Passega C/M diagram suggests suspension and saltation as the main mode of sediment transport prior to deposition.