Long- and short-term hydroclimatic variabilities in the Aptian Tethys: Clues from the orbital chronostratigraphy of evaporite-rich beds in the Apennine carbonate platform (Mt. Faito, southern Italy)

Abstract

The stratigraphic signature of the global Late Aptian cooling episode and sea level lowstand has been investigated in the Mt. Faito section of the Apennine Carbonate Platform (ApCP) of southern Italy. Several, meter scale fine-grained limestone intervals with abundant quartz pseudomorphs after anhydrite and minor calcite pseudomorphs after gypsum are present in the middle-upper Gargasian straddling the marly Orbitolina Level, a regional key-marker correlative with part of the Fallot Oceanic Anoxic Event. The evaporite-rich intervals were deposited in a mudflat-saltern setting and together with frequent transgressive shallow-marine interlayers alternate quite regularly with lacustrine, paralic or very shallow-marine deposits suggestive of overall wetter conditions. Three-to-five couplets of cyclic arid–wet phases are thus identified. Their timing and duration, determined by an original cyclostratigraphically constrained age model tuned with the astrochronology from deep-water Tethyan reference sections, suggest fluctuating hydroclimatic conditions (arid/semiarid vs. wet phases) over time scales as brief as 100 and 400ky. They are considered to reflect astronomically-induced latitudinal migrations of intertropical climate belts. A secular climate shift from arid to humid conditions, supra-regionally correlatable across the Upper Gargasian of the Tethyan realm, is dated at ~118.1My. It corresponds to the onset of persistent lacustrine deposits on the partially emerged ApCP and of abundant river-borne supply of siliciclastics along the opposing Tethyan margin. The observed climate fluctuations occurred during a major ApCP subaerial exposure which lasted for ~4.4My. Precise supra-regional correlations suggest that the platform exposure was glacioeustatic in origin and coeval with a long-lived Late Aptian cooling episode which interrupted the mid-Cretaceous greenhouse. Biostratigraphic and astrochronological tuning from the ApCP indicates that the glacioeustatic lowstand terminated in the earliest Albian, just above the O. reicheli key-marker.