Lower-Middle Pleistocene ostracod assemblages from the Montalbano Jonico section (Basilicata, Southern Italy)

The Montalbano Jonico section is a Pleistocene sequence, about 450 m thick, comprising silty clays and silty sands deposited during the upper part of the Calabrian Stage and lower part of the “Ionian” Stage. It is a candidate global boundary stratotype section and point for the Middle Pleistocene Subseries. Ostracod assemblage analyses were carried out on 40 samples from the uppermost levels of the Lower Pleistocene and the lowermost part of the Middle Pleistocene, with the aim of reconstructing the paleoenvironmental evolution around the Matuyama–Brunhes boundary. Taxonomic investigations, quantitative distribution data and statistical analysis (Q-mode cluster analysis) define four intervals, correlated with sea-level changes linked to Marine Isotope Stages (MIS) 21–18. The lower part of the section, ranging from 864.00 to 820.00 ka, was deposited in an outer shelf paleoenvironment during a period of high sea level associated with MIS 21. The transition to the second interval (815.42–785.62 ka) is marked by a shallowing trend, reflecting the MIS 20 decrease in sea level. The overlying part of the section (783.54–749.91 ka) yielded assemblages indicating a return to deeper-water conditions corresponding to the warm phase MIS 19. The uppermost interval was deposited during 746.60–740.54 ka, when cooling in MIS 18 produced a sea level drop. Here, some levels (164.20 m, 745.51 ka; 170.10 m, 743.05 ka; 176.10 m, 740.54 ka) show the presence of both “deep” and “shallow” autochthonous taxa, suggesting the occurrence of upwelling episodes during this cold phase. In some layers, deposited during warm stages, the ostracod assemblages indicate the presence of kenoxic bottom waters. The lowest paleo-oxygen levels are correlated with Marine Isotope Substages 21.3 and 19.1.