Astronomically tuned magnetocyclostratigraphy of late Burdigalian marine sediments at Monte Cardeto, Ancona, Italy

Abstract

The hemipelagic Monte Cardeto – Spiaggia della Scalaccia composite section is characterised by cyclic marl-limestone alternations, astronomically tuned between 17.08 and 16.18 Ma (late Burdigalian). The natural remanent magnetization is carried by greigite, based on IRM acquisition curves, thermomagnetic runs and thermal demagnetization. The resulting magnetostratigraphy reveals a straightforward correlation to subchrons C5Cr to C5Cn.1n of the Geological Time Scale 2012 (GTS2012). Spectral and wavelet analyses are performed to validate the cyclicity in the depth domain, which is transferred into the time domain using a first order age model with the ages of reversals from GTS2012. Wavelet and spectral analysis in the time domain confirm astronomically driven marl-limestone alternations. Based on CaCO3 content, Rb/Sr, Ba/Al, Ti/Al, Zr/Al, Mn/Al, V/Al, Si/Al and specific magnetic susceptibility, the limestones are correlated to insolation maxima (boreal precession minima). The reversal ages, originally used in the first order age model, are revised by tuning the Ca/Al and Rb/Sr records to the La2001(1,0.9) solution by first recognizing the eccentricity cycles, followed by the precession and obliquity cycles. This results in astronomically derived ages of the reversals between C5Cr and C5Cn.1n, which should replace the GTS2012 reversal ages. Furthermore, this high resolution age model enables the recognition of carbon isotope events CM1-CM3a and the oxygen isotope shift at the onset the Middle Miocene Climatic Optimum.