The Montalbano Jonico Section (Southern Italy): A Candidate for the GSSP of the Ionian Stage (Lower–Middle Pleistocene Boundary)

Abstract

The Lower–Middle Pleistocene Subseries boundary and the Ionian Stage still lack formal ratification. The use of the name “Ionian” as a stage of the Middle Pleistocene follows Cita et al. (2006, 2008) and Gibbard et al. (2009). The GSSP of the Ionian Stage should be defined at a point close to the Matuyama–Brunhes (M–B) reversal, in a marine section exposed on land. However, magnetic reversal is considered as only one of multiple criteria that may be used for the definition of a GSSP (Head et al. 2008). The Montalbano Jonico section (Southern Italy) is a continuous marly–clayey marine succession, well exposed and astronomically calibrated, which extends from 1.24 to 0.645 Ma (Ciaranfi et al. 2009). It spans the interval from Marine Isotope Stage (MIS) 37 to 17/16 and covers, together with the Vrica section, the sedimentary record of the entire Calabrian Stage. The section encompasses MIS 19, whose base corresponds closely to the M–B boundary (Lisiecki and Raymo 2005); unfortunately, the M–B palaeomagnetic reversal was not identified in the Montalbano sediments (Sagnotti et al. 2010). The isotopic signals are considered acceptable for the definition of a boundary stratotype (Remane et al. 1996) and the practice has been recently adopted for the definition of the GSSP of the Serravallian Stage (Hilgen et al. 2010). The interval including MIS 19 is chronologically well constrained and is a maximum flooding surface, as shown by the occurrence of the Neopycnodonte palaeocommunity, and the mesopelagic tropical–subtropical Atlantic teleostean Bonapartiapedaliota marks the base of the interglacial. Evidence of glacio-eustatic sea level rise, correlated with MIS 19 and the M–B boundary, are well known in several geographical areas, supporting the wide traceability of this oxygen isotope shift. The onset of MIS 19 in the Montalbano Jonico section may represent an appropriate stratigraphic horizon for the definition of the GSSP of the Ionian Stage, also fulfilling the additional criteria of Remane et al. (1996) for boundary stratotype definition, such as continuous sedimentation, a high sedimentation rate, an absence of synsedimentary disturbance, and good preservation and protection of the section.