Proposal for Pliocene and Pleistocene land–sea correlation in the Italian area

Abstract

The present study attempts a correlation between calcareous plankton (foraminifera and nannofossils) and terrestrial (pollen and mammal fauna) bioevents in Italy and Mediterranean Sea, through the last 3.3 million years, within a standard chronostratigraphical time scale. The approach was basically interdisciplinary and considered biochronological, biostratigraphical, chronostratigraphical, climatostratigraphical, and tephrochronological data. Despite different timing and mode characterised evolution of marine and continental organisms in relation to their ecology and relationships with environment, the main biota changes seem related with severe climate changes. The short interval of the known global scale Pliocene warmth (∼3.0 Ma) has been documented by the last significant expansion of the warm subtropical forest before the progressive disappearance of its main components and possibly by the paracme of some nannofossil species. The first evidence of cooler conditions near 2.8 Ma has been mainly indicated by both the progressive decrease of subtropical to warm temperate pollen taxa and by the notable change in the ecological structure of mammalian faunal complexes as well as by the first incursion of left-coiled cold N. pachyderma into the Mediterranean. The first glacial phases related to Northern Hemisphere ice-sheet growth (∼2.5 Ma) are indicated by the drastic drop of Discoaster spp. and by the first (cyclical) expansion of steppe or cooler coniferous forests, as well as by the progressive dispersal of mammalian taxa dwelling in open landscapes. The most significant biotical changes have been observed during the Calabrian–Ionian transition; several calcareous plankton appearances and extinctions occurred across marine isotope stages 25–20, together with the expansion of cold steppes (glacials) and the progressive disappearance of the most thermophilous arboreal and non-arboreal taxa. The late Early to Middle Pleistocene terrestrial faunal “revolution” actually was not an “abrupt” phenomenon, which started from about 1.3 Ma giving rise to a progressive reconstruction of mammalian faunal complexes, which ended during the early Ionian. The last node of 1.2 Ma obliquity cycles, centred at about 0.9 Ma, significantly influenced changes in the structure and composition of palaeocommunities. After the Ionian, fluctuations in biota assemblages, without any significant appearance–extinction events, testify that the new oceanographical and climate system is related to dominant periodicity of 100 ky in glacial–interglacial cycles. Although the changes observed in fossil assemblages do not always correspond to the standard chronostratigraphical boundaries, the data suggest that the Piacenzian–Gelasian and Calabrian–Ionian transitions are also noticeable by large, even if gradual, biota modifications.