Repeated events of hardground formation and colonisation by endo-epilithozoans on the sediment-starved Pontine continental slope (Tyrrhenian Sea, Italy)

Rock samples dredged offshore the Pontine Archipelago (400-2000 m water depth) were studied by palaeontological analyses of planktic foraminifera and endo-epilithozoan faunas colonising Fe-Mn crusts and by petrographic analyses of volcanic samples. Palaeontological and petrographic analyses have revealed a complex Plio-Pleistocene depositional history controlled by hemipelagic sedimentation and volcanic activity with episodic non-depositional phases. The sedimentary deposits are associated with ferromanganese hardgrounds, more or less colonised by endo- lithic and epilithozoan organisms. The presence of foraminifera typical of tropical and subtropical waters (such as Globigerinoides ruber, Globigerinoides trilobus, Pulleniatina obliquiloculata and Sphaeroidinella dehiscens) indicates that the micritic deposition occurred during warm climatic periods, whilst micrite ce- mentation and hardground formation are here attributed to colder climates. The depositional processes recognised on the Pontine continental slope reveal a sediment-starved condition that locally resemble those of seamount environment. The slope sedimentation found in the Pontine Archipelago can be helpful in the interpretation of ancient de- posits from seamounts and continental slope depositional environments, characterised by hardground and hiatuses.