High-resolution chronostratigraphy of palaeoecologic and isotopic changes in shallow-marine carbonates: Deciphering the completeness of the Aptian record in the Apennine carbonate platform (southern Italy)

Abstract

We present here a companions study dealing with the chemostratigraphy, palaeocology, chronostratigraphy and palaeoclimate of the upper Barremian-lower Aptian in the Mt. Faito section that build on our earlier work on the Apennine Carbonate Platform (ApCP, southern Italy). The high-resolution correlation of the Mt. Faito record with the cyclostratigraphically and chemostratigraphically tuned Mt. Raggeto reference section of the APCP has provided crucial evidence to reappraise previous views of a substantial stratigraphic continuity in the lower Aptian of the region. Combining δ13C, δ18O, palaeoecologic and petrographic data herein with available sedimentologic and biostratigraphic information together with reappraised cyclostratigraphic and astrochronologic analyses for the Mt. Faito section, we document substantial gaps throughout the lower Aptian. The timing of two major unconformities, with duration of 1.43 and 4.94 ± 0.10 Ma, as well as the fidelity and completeness of the stratigraphic record have been established using precession (20 ka), short- (100 ka) and long- (400 ka) eccentricity geochronometers. The adopted high-resolution event stratigraphy (HIRES) anchored to the 2012 Geological Time Scale, has provided further valuable insights for assessing the timing and pace of the observed biofacies and chemostratigraphic changes as well as achieving a highly resolved chronostratigraphic framework of the ApCP record for very detailed regional to supra-regional early Aptian correlations.Our analysis at Mt. Faito encompasses 7.5 ± 0.1 Ma ranging from the latest Barremian to the early late Aptian (Unit A to basal Unit D) and demonstrates that only 15% of the investigated time yields rock record. Two missing intervals, including most of the Selli Level Equivalent (SLE), span the late C2-early C5, and the late C5–C8 p.p. isotope segments. These gaps are interpreted as the erosive and/or non-depositional effects of glacioeustatic sea level falls linked to main global scale cooling episodes prior to (125.6 Ma), during (∼124.6 Ma) and after (123.0 Ma) OAE1a, which appear to be linked with the onset of overall humid climate conditions.The transition from a chlorozoan, “Urgonian”-like carbonate factory (C1–C2 p.p. isotopic segments) to the “warm-water” foramol of the greenhouse Crisis Interval (CI) (middle C2 isotopic segment) and, finally, to the waxing and waning of “temperate-water” foramol and microbial productivity mode interludes (middle C5 isotopic segment) are interpreted as the response of the early Aptian neritic ecosystem of the ApCP to the global-scale palaeoceanographic and palaeoclimatic changes driving the OAE1a.The stratigraphic implications of the icehouse interludes in the greenhouse early Aptian are discussed.