Astronomical calibration of the Tithonian-Berriasian in the Neuquén Basin, Argentina: a contribution from the Southern Hemisphere to the Geologic Time Scale

Abstract

Detailed cyclostratigraphical analyses have been made from five TithonianeBerriasian sections of the Vaca Muerta Formation, exposed in the Neuquén Basin, Argentina. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marlstones and limestones, showing a well-ordered hierarchy of cycles, where elementary cycles, bundles of cycles and superbundles have been recognized. According to biostratigraphic data, elementary cycles have a periodicity of w21 ky, which correlates with the precession cycle of Earth’s axis. Spectral analysis based on time series of elementary cycle thicknesses allows us to identify frequencies of w400 ky and w90e120 ky, which we interpret as the modulation of the precessional cycle by the Earth’s orbital eccentricity. Correlation between studied sections allowed us to estimate a minimum duration for each Andean ammonite zone. Moreover, cyclostratigraphic data allowed us to build the first continuous floating astronomical time scale for the Tithonian e Berriasian, which is anchored to the geological time scale through magnetostratigraphy. We estimated a minimum duration of 5.67 myr for the Tithonian and 5.27 myr for the Berriasian. The resulted durations of some polarity chrones are also different with respect to the GTS2016, however such differences could be due to condensation or discontinuities not detected in the studied sections.