Sedimentological and biostratigraphic reconstruction of the Early Pleistocene San Giuliano Lake section (Matera, Southern Italy)

In this paper, we present new sedimentological, biostratigraphic and paleoecological data from the area near San Giuliano Lake (Matera-Italy), located between the Apulia Foreland and the Bradanic Trough domains of the Southern Apennines. Combining the sedimentological and paleontological information coming from a borehole (Giuli 1) and from an outcropping section (Assiolo), we build the San Giuliano Lake composite section to reconstruct the evolution of the depositional system of the argille subappennine, an informal lithostratigraphic unit. The occurrence of the following calcareous nannoplankton bioevents: Top of Helicosphaera sellii, Base common of Reticulofenestra asanoi, Top of Reticulofenestra asanoi and the presence of regionally extinct tree taxa as Tsuga, Cedrus, Pterocarya, and Zelkova constrain the age of the composite section to the Early Pleistocene, spanning from 1.256 to 0.879 Ma and corresponding to the late Calabrian (MIS 38-MIS 23). The benthic foraminifera and ostracod assemblages documented a depositional environment characterised by repeated events of relatively high organic matter and low oxygen contents of the bottom water masses. The high percentages of small Gephyrocapsa, Globigerina bulloides, G. glutinata, and Turborotalita quinqueloba indicate an environment characterised by up-welling currents and strong river input. An increase in temperatures and salinity and a strong water column stratification occur from about 1090 ka upwards. The hypothesised stratigraphic architecture points towards a tectonic subsidence signature greater than the sea level change, at the base of the succession, with a subsiding basin formation. During the deposition of the Giuli 1 borehole sediments, the sea level change and tectonic activity acted together, giving rise to a progradation of the coastline. The sediments at the top of the borehole are interpreted as the Apennine peripheral bulge deposited during the Calabrian. At the Assiolo section, which represents the upper part of the San Giuliano Lake succession, the paleo depth through the parasequence increases progressively upwards, and this part of the San Giuliano Lake succession represents a slope and a ramp flexuring toward the chain with active subsidence phenomena. The coarsening upward trend, shown by the Assiolo parasequence set, indicates that the tectonic subsidence and the sea level change interacted to give the coarsening upward stratigraphic architecture.