Orbital forcing of calcilutite-marl cycles in southeast Spain and an estimate for the duration of the Berriasian stage

Cyclicities observed in a (hemi-)pelagic rhythmic calcilutite-marl succession of late Berriasian age near Caravaca, southeast Spain, match well with the quasi-periodicities of the Milankovitch model. The shortening of the precession and obliquity in pre-Quaternary times is taken into account. The interval of the Miravetes formation studied has a thickness of 77.5 m, extends from the base of the Calpionellopsis simplex subzone (D1) to the top of the Calpionellopsis oblonga subzone (D2), and has an estimated duration between 1.1 and 2.9 Ma. The evolution of the cyclicities in this succession was analyzed by comparing the spectra of ten successive overlapping segments. From this comparison we conclude that ∼11 m at the top and base of the succession show variations in accumulation rate. Disregarding these parts, the spectrum of the remaining interval (56 m) reveals well-defined spectral peaks. The cyclicity is ascribed to orbital forcing, because all cycles longer than the bedding cyclicity can be matched with the known orbital quasi-periodicities reported in Berger and others (1989a, 1989b). This match with Milankovitch cyclicities produces a considerably more precise estimate for Berriasian zone durations. The range of the duration of the combined calpionellid subzones D1 and D2 reduces to an interval between 1.1 and 1.2 Ma, and the length of the entire Berriasian stage is estimated to fall between 2.9 and 3.1 Ma.