Benthic foraminiferal associations from Upper Quaternary deposits of southeastern Po Plain, Italy

Abstract

Quantitative analysis of benthic foraminifers from three continuously-cored boreholes (130m deep) at different distances from the Adriatic coast and focused within two marine intervals (0–30m and 100–120m depth) that on the basis of AMS 14C dating and pollen data are assigned to oxygen isotope Stage 1 and Substage 5e, respectively, has revealed seven foraminiferal associations. Associations Me (Textularia spp. and Miliolidae) and Md (Miliolidae, Elphidium spp. and Cribroelphidium spp.) are characteristic of infralittoral environments. Associations Mb (Ammonia tepida, A. parkinsoniana and Cribroelphidium spp.) and Ma (Ammonia tepida and A. parkinsoniana) are indicative of shallow-marine environments influenced by freshwater. Reworked and transported microfaunal association Rm corresponds to supralittoral environments (beach-ridge deposits). Associations Bd-b (Ammonia tepida, A. parkinsoniana and brackish ostracods) and Ba (Trochammina inflata) are characteristic of bay, lagoon and estuary environments.Comparison of benthic foraminiferal associations from coeval deposits provides information on the relative distance of cores from the Holocene and Tyrrhenian paleo-shorelines. Core 205-S10 is characterised by deeper marine associations than core 223-S12. Core 240-S13 contains exclusively associations characteristic of lagoonal and brackish marsh environments.Vertical variation in microfaunal associations within each marine deposit reveal in both intervals a transgressive trend, followed upwards by a regressive trend. Benthic foraminiferal associations from cores 205-S10 and 223-S12 show that the Tyrrhenian maximum flooding surface corresponds to a deeper marine environment than peak transgression in the Holocene. This is also shown by core 240-S13, where an open lagoonal microfauna characterizes Tyrrhenian deposits and a brackish marsh association marks the Holocene sediments.