Astrochronology and radio-isotopic dating of the Alano di Piave section (NE Italy), candidate GSSP for the Priabonian Stage (late Eocene)

We have carried out an integrated chronostratigraphic analysis of the Alano di Piave section, proposed GSSP for the Bartonian/Priabonian boundary (late Eocene). Age constraints were derived independently from a floating cyclochronology based on carbon isotope and wt.% CaCO3 records, and (206)pb/(238)u dating of zircons from four volcanic tuffs. Orbital and radio-isotopic estimates of the duration of intervals bracketed by consecutive crystal-rich volcanic tuff layers are in good overall agreement, but discrepancies of 40-160 kyr are present between nominal volcanic tuff dates derived from astrochronology and (206)pb/U-238. The degree to which these discrepancies are statistically significant at the 2 sigma level depends on the interpretation of the U-Pb zircon data, and the uncertainties assigned to the astronomical age model. The possible source and significance of these discrepancies are explored in detail. The resulting age model, combined with published bio-, and magnetostratigraphic data, is used to establish the duration of individual magnetochrons in the interval spanning the Bartonian/Priabonian transition, and the timing of late Bartonian-early Priabonian biostratigraphic and magnetostratigraphic events relative to the proposed GSSP, the regionally traceable crystal-rich tuff layer "Tiziano Bed". The chronostratigraphic framework developed at Alano di Piave will facilitate the global correlation of the Priabonian GSSP based on both bio- and magnetostratigraphic criteria. The obtained astrochronology allows a precise correlation of the Alano di Piave delta C-13 record with oceanic successions confirming a strong dependency of the marine carbon cycle on astronomical forcing although with inter-site differences, which could be related to water mass organization