Ichnology of eocene flysch deposits of the Istria peninsula, croatia and slovenia

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Abstract
The lower part of the Eocene deep‐sea deposits (450–500 m) in Istria is dominated by light‐grey marl‐stones; the middle and upper parts are dominated by thin‐and medium‐bedded siliciclastic flysch deposits. These accumulated in a narrow short‐lived basin. The marly strata are totally bioturbated and contain a low diversity trace‐fossil assemblage dominated by Planolites and Chondrites, in places also by Trichichnus Thalassinoides and Palaeophycus. It resembles the Zoophycos‐Cruziana transitional ichnofacies and indicates a welloxygenated environment. The low ichnotaxonomic diversity is partially a result of low preservation potential. Preserved trace fossils represent only the deeper tiers. Except for the totally bioturbated uppermost part of turbidite beds, the flysch deposits are only partially bioturbated. A very diverse trace‐fossil assemblage contains numerous K‐selected predepositional forms, including diverse graphoglyptids. It may be compared to the Nereites ichnofacies and indicates an‐ecologically stable, well‐oxygenated, slightly oligotrophic environment that existed between episodes of turbidite deposition. Its complex tiering pattern is related to sedimentation, mode of colonization, and taphonomic processes. Similar conditions characterize similar Eocene flysch deposits in the Alpine region. This may imply that similar oceanographic/climatic conditions and widespread oligotrophy existed over large areas during the Eocene.