| Lithostratigraphic, magnetostratigraphic, and rock magnetic cyclostratigraphic data were combined to create a high-resolution chronology of 636 m of Messinian-middle Pleistocene siliciclastic marine deposits exposed in the Stirone River, northern Italy. These deposits are part of a growth section on the forelimb of the Salsomaggiore anticline. Magnetostratigraphic analysis of 146 oriented samples at 41 stratigraphic horizons supplements published studies to create a composite magnetostratigraphy correlated to the geomagnetic polarity timescale. Magnetic susceptibility (chi) was measured for unoriented samples, collected every meter, and subjected to Multi-Taper Method (MTM) spectral analysis. The resultant power spectra revealed significant peaks associated with 405 kyr eccentricity, 41 kyr obliquity, and 23 kyr precession Milankovitch cycles. Magnetic susceptibility (chi) data tuned to the 41 kyr obliquity cycle, and anchored at a well-known biostratigraphic horizon assigns cyclostratigraphic absolute time in the Stirone section between 3.00-1.78 Ma, where stratigraphic positions of the magnetic chron boundaries are poorly defined. This cyclostratigraphy reveals two important features of the Stirone section. First, the age of an important biostratigraphically-determined unconformity at the base of the C2An.1n chron is 200 kyr older than previously determined. Second, forelimb rotation rates for the Salsomaggiore anticline are shown to be unsteady at 41 kyr time scales and not correlated to deposition. The chronostratigraphic time resolution in the Stirone growth strata are new paleogeodetic data that help bridge short-term geodetic and long-term geologic rates of crustal deformation. |
