Abstract
Benthic foraminiferal assemblages have been analyzed from the Holocene transgressive succession of core 187-S1, in the southern part of Po River delta. Above the wave ravinement surface, rare and poorly preserved microfossils, deposited at less than 11 m water depth in coastal zones, are replaced upwards by Miliolidae-rich assemblages (30% - 55%). These are interpreted as indicative of a highly vegetated gulf area with low organic carbon, low nitrogen and high CaCO3 at the sea bottom, and are consistent with a relative sea-level rise of up to 17-26 m water depth in coincidence with the maximum flooding surface. Above this surface, foraminiferal assemblages dominated by Ammonia tepida and Ammonia parkinsoniana reveal a relative sea-level fall (down to 10-15 m water depth) paralleled by an increase in runoff products of the Po delta system, which is consistent with a prodelta environment. High frequencies of specific Miliolidae, mainly Triloculina and Pseudotriloculina, which are recorded in the transgressive part of the succession, are not present in the Adriatic Sea. Although the observed species are consistent with a shallow-marine setting, the reason of this high amount remains unclear. The recognized rate of transgression, substantially higher than the one affecting historical times, may have produced peculiar environmental conditions different from today. However, a conclusive explanation, possibly regarding deposition in an inner or confined gulf, is not adequately supported by the available data.
Keywords: Foraminifera, Miliolidae, Palaeoenvironment, Holocene transgression, Po River delta