Periodicities of CaCO3 cycles in the Pliocene of Sicily: discrepancies with the quasi-periods of the Earth's orbital cycles?

A high-resolution CaCO3 record in combination with a detailed magnetostratigraphy is presented for the rhythmically bedded marly sequence of the Pliocene Trubi Formation on Sicily ( Italy). Magnetostratigraphic age calibration and subsequent spectral analysis of the variatrions in CaCO3 content yield a remarkably consistent discrepancy between the resulting periodicities and the corresponding quasi-periods of the Earth's orbital cycles. This discrepancy can only be explained by assuming that ages assigned to polarity reversal boundaries in the geomagnetic polarity time-scale lack sufficient precision. A new polarity time-scale is presented for the major part of the Gilbert and Gauss Chron using the radiometrically dated Gilbert-Gauss Chron boundary at 3.40 Ma as an age reference point and extrapolating an average quasi-period of 21.7 kyr of the precession cycle as the periodicity of small-scale colour annex CaCO3 cycles.