Lithological expression of Milankovitch cyclicity in carbonate-dominated, pelagic, Barremian deposits in central Italy

Abstract

In continuous sedimentary sequences, cyclostratigraphy can provide good time control on the duration of stratigraphic stages and palaeomagnetic chrons. This approach has been applied to the Barremian pelagic marl-limestone alternations of the Umbria-Marche Basin. Two criteria have been used: variations in the thickness and carbonate content of limestones and the vertical distribution of intercalated black marls. Marl–limestone alternations are organized in bundles of generally four or five couplets. The cyclicity expressed by the vertical stacking of couplets and bundles has been interpreted as the sedimentary expression of the Earth's orbital parameters, specifically the precession of the equinoxes and the eccentricity.This breakdown of the Barremian Stage into astroclimatic cycles allows the calibration of the duration of the stage and of the magnetic chrons M-3 to M-0. The lower and upper stratigraphic boundaries of the Barremian Stage are picked at the base of the M-3 and M-0 chrons, respectively. The duration of the Barremian Stage is estimated at 5.13±0.34Myr by adding up contained cycles. The duration of related magnetic chrons varies considerably from 0.43 to 2.3Myr.