A middle Eocene shallow-water drowning ramp in NW Italy: from shoreface conglomerates to distal marls

In this study we examine a sedimentary succession deposited within a foreland basin during the early stages of a transgressive succession recorded in NW Italy. The succession unconformably overlies Upper Cretaceous deep-water calcareous marls that act as substrate for the incipient nearshore to shallow-water sedimentation. The early stage of the transgressive succession is registered by beach deposits consisting of pebbly conglomerates that gradually pass to very well-sorted quartz arenites. The succession continues with an increase in carbonate content, and the sudden appearance of fossils, almost exclusively nummulitids; only farther up-section a more diverse benthic fauna is visible. Marls and marly limestones appear toward the top of the section. The succession was studied in terms of lithological and microfacies variations, fossil content diversity and variations including invertebrates, microfossils and ichnofossils with their taphonomic footprint and lastly gamma ray emission in Potassium (K), Uranium (U) and Thorium (Th) elements. The data permitted a comprehensive interpretation of the succession which is explained as the result of a drowning ramp that was affected by a combination of both continuous tectonic activity and climatic variations that led to very unstable ecological conditions, reducing the efficiency of the carbonate production typical of larger foraminifera. The study reveals a very slowly deepening succession, only partially compensated by the intense biogenic activity of rock building foraminifera, characterized by enhanced sedimentary rates triggered by both active tectonics and unstable climates that led to stressed ecological conditions at the sea floor.