A 20-million-year Early Jurassic cyclostratigraphic record and its implications for the chaotic inner Solar System and sea-level changes

摘要

We present high-resolution (every 2 cm) magnetic susceptibility (MS) data from the Sancerre-Couy drill core (Paris Basin), spanning the latest Sinemurian to the earliest Aalenian (Early Jurassic). This record allows to build a 20-million-year cyclostratigraphic interval using the stable 405 kyr (g2-g5) orbital eccentricity cycle and to focus on long-period cyclicities and their potential implications for the chaotic diffusion in the inner Solar System and sea-level changes. Time series analysis indicates evidence of two long-period cyclicities of 1.6 and 3.4 Myr. These Early Jurassic cyclicities likely correspond to the Cenozoic orbital cyclicities of 2.4 Myr (g4-g3) and 4.7 Myr eccentricity terms. Shortening of eccentricity terms during the Early Jurassic is potentially related to the chaotic orbital motion of the inner planets expressed in the resonant argument theta = 2(g4-g3) - (s4-s3). The 1.6 Myr (g4-g3) cycle matches the third-order eustatic sequences, whereas the 3.4 Myr cycle has no equivalent in the reference eustatic chart. These cycles of several million years are superimposed a cyclicity of ca. 7.5 Myr, which may correspond to the eccentricity term of 9.5 Myr, previously detected in the Cenozoic. Such cyclicity matches the global, 'shorter' second-order sea-level sequences and is strongly documented in the sedimentological and mineralogical proxy data, hence supporting the potential key role of orbitally paced climate and sea-level changes at this timescale.