Orbital controls and high-resolution cyclostratigraphy of Late Jurassic Early-Cretaceous in the Neuquén Basin

Abstract

Detailed cyclostratigraphic analyses have been made from seven Tithonian–Hauterivian sections of the Vaca Muerta and Agrio Formations, exposed in southern Mendoza area of the Neuquén Basin. Both lithostratigraphic units are characterized by decimeter-scale rhythmic alternations of marlstones and limestones, showing a well-ordered hierarchy of cycles, including elementary cycles, bundles, and superbundles. According to biostratigraphic data, elementary cycles have a periodicity of ~18–21 ky, which correlates with the precessional cycle of the Earth’s axis. Spectral analysis based on time series of elementary cycle thicknesses allowed us to identify frequencies of ~400 ky, and ~90–120 ky, which we interpret as the modulation of the precessional cycle by the Earth’s orbital eccentricity. A third band frequency of ~40 ky was also identified that can be assigned to the obliquity cycle. Cyclostratigraphy enabled the construction of almost continuous floating astronomical time scale for the Tithonian–Hauterivian, for which a minimum duration of 5.67 myr for the Tithonian, 5.27 myr for the Berriasian, >3.45 myr for the Valanginian, and 5.96 myr for the Hauterivian have been assessed. Additionally, the likely transference mechanisms of the orbital signal to the sedimentary record are analyzed, proposing the coexistence of carbonate exportation and dilution as the dominant mechanisms.