High-resolution clay mineralogy as a proxy for orbital tuning: Example of the Hauterivian–Barremian transition in the Betic Cordillera (SE Spain)

Abstract

The response of clay mineral assemblages to potential orbital forcing is tested in Mesozoic hemipelagic marl–limestone rhythmites of the Río Argos section (Betic Cordillera, Southeastern Spain). Along the section, marls are pervasively enriched in kaolinite and illite, whereas limestones are enriched in smectite-rich illite/smectite mixed-layers, suggesting that marl–limestone alternations are produced by cyclic high-frequency fluctuations of continental runoff. Spectral analyses show that clay mineral assemblages evolve accordingly to precession, obliquity and eccentricity cycles. Durations of ammonite zones are assessed at 535kyr for the Late Hauterivian Pseudothurmannia ohmi Zone and at 645kyr and for the Early Barremian Taveraidiscus hugii Zone. These durations are in agreement with other cyclostratigraphic estimates but significantly differ from the Geologic Time Scale 2004 and 2008. Clay minerals display enhanced amplitude of the eccentricity cycles during the Faraoni Oceanic Anoxic Event due to enhanced continental weathering conditions prevailing at that time. Sedimentary expression of the 405-kyr eccentricity is disturbed by palaeoclimate changes during the Faraoni OAE, challenging the hypothesis of Cretaceous OAE triggered by eccentricity cycles. Although palaeoceanographic events (e.g. Faraoni OAE) may induce disturbances in the clay mineral record, this study demonstrates the potential of these minerals to be used as a proxy for orbital calibration in Mesozoic times.