Visual cyclostratigraphy and tuning of the Monte San Nicola section: Quaternary GSSP and potential Gelasian Astro-Unit-Stratotype

Abstract

The Monte San Nicola (MSN) section on Sicily (Italy) hosts the Gelasian and Quaternary Global Stratotype Section and Points (GSSP). Despite its importance, the spatial and temporal continuity of the succession at MSN remains hotly debated and has not yet been convincingly proven, as tectonic deformation may disrupt and reduce continuity. Such deformation and lack of continuity would potentially make the section unsuitable for defining global chronostratigraphic boundaries and units. To solve the continuity problem, we conducted a visual inspection of the cycle pattern in the field. This method uses astronomical target curves and a simplified modelled log in the time domain that considers the anticipated expression of both glacial cycles and sapropels. Identification of the cycle pattern is specifically used 1) as an impartial check on the completeness and continuity of the succession, 2) to determine the optimal cyclic composite section and trajectory for logging and sampling, and 3) to establish a reliable astronomical tuning that is largely independent of previous attempts. Our field observations are in excellent agreement with the modelled ideal log, resulting in a robust tuning and age model. The tuning, which shows that a complete and continuous succession is preserved in the NW gully complex at MSN, is largely consistent with the tuning proposed by the SAGE team for the Mandorlo section located in the same complex. The SE complex, which currently hosts the GSSP, is more deformed, resulting in a tectonic reduction of the stratigraphy. Finally, we argue that the NW complex may serve as future Astro-Unit-Stratotype (AUS) for the Gelasian Stage with the astronomically controlled cycles being formally defined as Astrochronozones. Such a designation may provide an additional argument for relocating the GSSP at the same stratigraphic level from the more strongly deformed SE complex to the NW complex at Monte San Nicola.