Cyclostratigraphy And Floating Astronomical Time Scale Of The Neoproterozoic Datangpo Formation In South China

The Cryogenian witnessed periods of extreme cold known as the Sturtian and Marinoan glaciations, during which ice sheets may have extended to equatorial continents and oceans, forming a “snowball” Earth. Determining the ages of Cryogenian glaciations is very important for the snowball Earth hypothesis. Existing age data provide faithful constraints on the initiation(ca. 717 Ma) and termination(ca. 660 Ma) of the Sturtian glaciation, and termination(ca. 635 Ma) of the Marinoan glaciation in multiple continents,but the onset of the Marinoan glaciation still unknown. To investigate the initiation time of the Marinoan glaciation, we have conducted a cyclostratigraphic study of the interglacial Dangtanpo Formation that conformably overlies and underlies Sturtian and Marinoan glacial diamictites, respectively, in a deep-water basin section in South China.28,888 magnetic susceptibility(MS) measurements from a drillcore(ZK1909) covering the 292-m-thick, siltstone/shale-dominated Datangpo Formation are used for cyclostratigraphic analyses. Power spectra and evolutionary fast Fourier transformation(FFT) analyses reveal significant decameter- to meter-scale sedimentary cycles of 14.1–10.5 m, 3.0–2.8 m, 1.0–0.8 m and 0.6–0.4 m. The ratio of these cycle wavelengths matches well with that of the Milankovitch cycles calibrated for the Neoproterozoic. Age tuning based on the eccentricity cycle indicates that the duration of the Datangpo Formation is 9.2 million years(myr). Coupled with the U-Pb age of ca. 660 Ma at the basal Datangpo Formation from an adjacent section, the astrochronological results confirm that the Nantuo glaciation in South China initiated at 650.8 Ma. Given that South China was located in middle latitudes of the Northern hemisphere during the Cryogenian,the onset of the Marinoan glaciation in middle latitudes is 650.8 Ma.