The base of the Gelasian Stage is defined as the base of the marly layer overlying sapropel MPRS 250, located at 62m in Monte San Nicola section, Italy. The astronomical age of sapropel MPRS 250 (mid-point), corresponding to precessional cycle 250 from the present, is 2.588 Ma, which can be assumed as the age of the boundary.
The Monte San Nicola Section is located on the southern coast of Sicily (Italy). The section is represented on the Carta Topografica d'Italia in the 1:25,000 series, Foglio 272, Quadrante II, S.O (Ponte Olivio). The section outcrops in the badlands ("calanchi") on the southern slope of the Monte San Nicola, some 10km to the N-NW of the town of Gela (Caltanissetta province). The section can be reached by car, following a path that starts from the main road 191 between km 19 and km 20 and leads to an old farm from which, crossing a small field by foot, the top of the section is easily reached.
The lower 36m of the section are constituted by rhythmically bedded marls and limestones of the Trubi Formation, transitionally grading upward into marly-silty Monte Narbonne Formation. The Monte Narbonne Formation is characterized by brownish-red laminated intervals (sapropels) and by brownish non-laminated manganesiferous levels. Both are important for regional correlations; the sapropels are an important tool for astronomical calibrations.
The depositional environment for the boundary is inferred to be a slope-basin setting with water depth ranging from 500 to 1000m.
In the boundary interval a cluster of six sapropel or manganesiferous levels is recognized and correlated to coeval sections in Sicily, Calabria and Northern Italy. The single sapropels of this cluster have been coded as the Mediterranean Precession Related Sapropels (MPRS) and linked to the corresponding precessional cycle. The base of the Gelasian Stage is defined as the base of the marly layer overlying sapropel MPRS 250, According to Rio et al. (1998) the astronomical age of sapropel MPRS 250 (mid-point), is 2.588 Ma, which "can be assumed as the age of the boundary".
The section spans the interval from the upper part of the Gilbert Chron (C2Ar) to the Matuyama Chron above the Olduvai Subchron (C1r). The Gauss/Matuyama boundary is clearly detectable and located at 1m below the GSSP.
The last occurrence of Discoaster pentaradiatus occurs in most low and mid-latitude areas close to isotopic stage 99, some 80kyrs above the boundary.
Magnetic -- Matuyama/Gauss boundary (C2r/C2An) is 1m below GSSP. GSSP level is within Marine Isotope Stage 103.
The accepted age is 2.58 Ma as published in Gibbard & Head (2009, 2010) and Gibbard et al. (2010), and derives from the orbitally-tuned age of 2.588 Ma for the midpoint of the Nicola Bed, a sapropel assigned to precessional cycle 250 at the Monte San Nicola type section (Lourens et al., 1996, 2005). The GSSP is placed immediately above this sapropel and is therefore slightly younger than the sapropel's midpoint (Cita et al., 2012, p. 395). The age of the GSSP is rounded to 3 significant figures, reflecting uncertainties in tuning and sedimentation rates (Gibbard & Head, 2009, p. 412).
The base of the Quaternary System/Period, and thus the Neogene-Quaternary boundary, is formally defined by the Monte San Nicola GSSP and thus is coincident with the bases of the Pleistocene and Gelasian. The Gelasian Stage/Age was transferred from the Pliocene Series/Epoch to the Pleistocene. Ratified by IUGS on 29 June 2009
Cita, M.B., Gibbard, P.L., Head, M.J., and The Subcommission on Quaternary Stratigraphy, 2012. Formal ratification of the GSSP for the base of the Calabrian Stage (second stage of the Pleistocene Series, Quaternary System). Episodes 35(3): 388–397.
Gibbard, P.L., and Head, M.J., 2010. The newly-ratified definition of the Quaternary System/Period and redefinition of the Pleistocene Series/Epoch, and comparison of proposals advanced prior to formal ratification. Episodes, 33: 152–158.
Gibbard, P.L., Head, M.J., Walker, M.J.C. and The Subcommission on Quaternary Stratigraphy, 2010. Formal ratification of the Quaternary System/Period and the Pleistocene Series/Epoch with a base at 2.58 Ma. Journal of Quaternary Science, 25(2): 96–102.
Lourens, L.J., Hilgen, F.J., Shackleton, N.J., Laskar, J., and Wilson, D., 2005. Appendix 2. Orbital tuning calibrations and conversions for the Neogene Period. In: Gradstein, F., Ogg, J., and Smith, A. (eds.), A geologic time scale 2004: Cambridge University Press, Cambridge, U.K., pp. 469–484. [Imprinted 2004].