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During geological mapping of Istria (Croatia) numerous carbonate beds (megabeds) were recorded within the informal lithostratigraphic unit Istrian flysch. Istrian flysch deposits are mostly characterized by typical alternations of hemipelagical marl and gravity-flow deposits (BERGANT et al., 2003). The monotonous succession of marl and mixed carbonate-siliciclastic sandstone is intercalated with several relatively thick carbonate beds - megabeds, composed of breccia, conglomerate, bioclastic arenite/siltite and marl. The thickness of these megabeds varies between 0.5 – 5 m, rarely over 10 m. The megabeds are interpreted as complex sequences of rockfall, debrite and turbidite deposits, characteristic for the lower part of the basin fill (BERGANT et al., 2003). In eastern Istria, near the town of Pićan, an unusual carbonate layer is mapped, named “Pićan bed“, whose genesis cannot be explained by the depositional mechanisms of turbidite currents or debris flows, characteristic for the Istrian Flysch deposits. For this purpose, a more detailed field investigation was performed and a sedimentary log (Pić-I) was recorded within a tectonically undisturbed succession of Paleogene deposits. At the base of the succession an informal lithostratigraphic unit “Foraminiferal limestone” gradually transitions into “Marls with Crabs” and further into “Globigerina marls” informal lithostratigraphic units. The interval of massive “Globigerina marls” is approx. 100 m thick and transitions into the Istrian flysch lithostratigraphic unit, here represented with this unusual “Pićan bed”. Flysch deposits are composed of calcarenite beds, marl, sandstone, and, of course, megabeds are well documented in the surrounding area. The sedimentary log was used to complement the new lithostratigraphic map of the area (PETRINJAK et al., 2018). The geological model of the Pićan area was built based primarily on the lithostratigraphic map and geological cross-sections, and the Digital Surface Model (DSM) of the area. The data were modelled using Midland Valley Move geological modelling software. The new lithostratigraphic map together with other available data, such as Digital Orthophoto Images of the area were used to construct a series of geological cross-sections needed for the model, while an Unmanned Aerial Vehicle (UAV) was used to record the DSM of the area. Finally, the geological model of the Pićan area displays, faithfully as possible, the spatial distribution of the “Pićan bed“ and the interesting geological setting of the Pićan area, Istria. The research has been supported by the Croatian Science Foundation project IP-2016-06-1854, GEOSEKVA, as well as by Basic geological map of the Republic of Croatia 1:50, 000 project (HGI) and Horizon 2020 Twinning project GEOTWINN. |
