Revising the tephrostratigraphy of Riparo l’Oscurusciuto, gravina di Ginosa, Apulia (Italy)

Riparo l’Oscurusciuto (Ginosa, Apulia, Italy) hosts a rich Middle Paleolithic stratigraphic record, consisting of structures, fireplaces, lithic and faunal assemblages, and was occupied by Neanderthals during Marine Isotope Stage (MIS) 3. The part of the stratigraphic record excavated so far encompassed a ~20-25 kyr time interval, spanning between ~42.7 BP and ~65 ka, based on i) ¹⁴C age determinations of bone collagen at the base of the uppermost stratigraphic unit (SU-1), ii) OSL dates, and iii) the correlation of SU-14 with the Mount Epomeo Green Tuff (MEGT)/Y-7 tephra layer derived from Ischia volcano in the Bay of Naples. Recent studies suggest that the MEGT and the Y-7 tephra potentially represent two, geochemically similar but temporally distinguished eruptive events on Ischia, dated between ~56 ka (MEGT) and ~60 ka (Y-7) respectively, with this having implications for the age model of Riparo l’Oscurusciuto sequence. Furthermore, ongoing excavations revealed the presence of further tephra layers underlying SU-14, with the excavated part of the Riparo l’Oscurusciuto sequence likely extending to the end of MIS 4. To better chronologically constrain the Riparo l’Oscurusciuto record further tephrochronological investigations are required.

A new sampling campaign for tephra and cryptotephra analysis, including both glass and minerals major, minor (EPMA), and trace element (LA-ICP-MS) composition determination, has been undertaken. Eight samples have been taken from SU-14 and the underlying macroscopic volcanic ash deposits in SU-19 and SU-24/26. Analyses performed on the macroscopic samples revealed the occurrence of Na-Fe pyroxene (aegirine) in SU-24/26, but not in SU-14. The aegirine phase is absent in the MEGT deposits and subsequent, younger eruptive units on the island, but is present in the distal Y-7 deposits and older eruption units, thus SU-14 is confirmed to belong to the MEGT, whilst SU-24/26 can be correlated to either the Y-7 or another pre-MEGT eruption on Ischia. This is supported also by trace element analysis of the glass, where SU-14 shows wider ranges of Th and Y concentrations (i.e., Th = 14-58 ppm; Y = 27-73 ppm) relative to SU-24/26 (Th = 30-50 ppm; Y = 45-69), and similar to other MEGT proximal and distal samples. Concerning SU-19, trace element analysis also reveal concentrations similar to SU-14, however without wide ranging Th content (i.e., Th = 30-72 ppm) making its attribution to a temporally separate Y-7 still unclear.