Deep-water paleoenvironmental changes based on early-middle Miocene benthic foraminifera from Malta Island (Central Mediterranean)

A detailed quantitative, statistical and isotopic study on benthic foraminiferal assemblages from the upper Burdigalian -lower Langhian of Malta Island (St. Peter's Pool section) was carried out in order to gain more insights on paleoenvironmental changes that affected the central part of the Mediterranean Basin during the early-middle Miocene. The most abundant and/or palaecologically significant taxa were grouped into Group A (oxic/oligotrophic and oxic/oligo-mesotrophic opportunistic behaving) and Group B (hypoxic/eutrophic) and, on the base of their microhabitat in superficial microhabitat taxa (epifaunal + epifaunal to shallow infaunal taxa), intermediate microhabitat taxa (shallow infaunal + shallow to intermediate infaunal taxa) and deep microhabitat taxa (deep infaunal species). The changes in the structure of the benthic foraminiferal assemblages, together with isotopic data and statistical analysis results, identify five main intervals SPP1-SPP5, testifying the evolution of bottom water conditions between 16.12 and 15.36 Ma, corresponding to warm climate conditions due to the onset of the Miocene Climatic Optimum (MCO). The main benthic foraminiferal turnover occurred between 16.01 and 15.91 Ma. It has been recorded in both the palaecological and geochemical data and can be related to the Miller's Mi2 cooling event. This turnover correlates to a sea level falling that we believe caused an increase of the primary productivity due to runoff intensification. We suggest that the fluctuations of superficial microhabitat oxic/oligo/oligo-mesotrophic Group A, opposite to those of intermediate and deep microhabitat hypoxic/eutrophic Group B, and the occurrence of the superficial microhabitat, oxic/oligo-mesothrophic opportunistic behaving species are indicative of increased seasonality, which in turn affect food flux and oxygenation at the sea-floor. Moreover, the calculation of %P and the well-defined depth distribution range of some significant species allowed us to estimate a middle bathyal paleodepth, ranging from 600 m to 1000 m for the entire composite section.