Search

The Arda and Stirone marine successions (Italy) represent key sections for the early Pleistocene; they were deposited continuously within a frame of climate change, recording the Calabrian cooling as testified by the occurrence of the “northern guests,” such as the bivalve Arctica islandica. In addition, although the first occurrence of A. islandica in the Mediterranean Sea was used as the main criterion to mark the former Pliocene-Pleistocene boundary, the age of this bioevent was never well constrained. Here, we describe the Stirone depositional environment and constrain for the first time the section age using calcareous nannofossil and foraminifera biostratigraphy. We also correlate the Arda and Stirone sections using complementary biostratigraphic and magnetostratigraphic data. Our results indicate that A. islandica first occurred in both the successions slightly below the top of the CNPL7 biozone (dated at 1.71 Ma). Comparisons with other lower Pleistocene Mediterranean marine successions indicate that the stratigraphically lowest level where A. islandica first occurred in the Mediterranean Sea is in the Arda and Stirone sections; these environments satisfied the ecological requirements for the establishment and the proliferation of the species, which only subsequently (late Calabrian) has been retrieved in southern Italy and other areas of the Mediterranean Sea.

The Arda River marine succession (Italy) is an excellent site to apply an integrated approach to paleoenvironmental reconstructions, combining the results of sedimentology, body fossil paleontology, and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early Pleistocene climate change and tectonic activity. The succession represents a subaqueous extension of a fluvial system, originated during phases of advance of fan deltas affected by high-density flows triggered by river floods, and overlain by continental conglomerates, indicating a relative sea level fall and the establishment of a continental environment. An overall regressive trend is observed through the section, from prodelta to delta front and intertidal settings. The hydrodynamic energy and the sedimentation rate are not constant through the section, but they are influenced by hyperpycnal flows, whose sediments were mainly supplied by an increase in Apennine uplift and erosion, especially after 1.80 Ma. The Arda section documents the same evolutionary history of coeval successions in the Paleo-Adriatic region, as well as the climatic changes of the early Pleistocene. The different approaches used complement quite well one another, giving strength and robustness to the obtained results.