Sedimentology and carbon isotope stratigraphy from the Late Jurassic – Early Cretaceous of the Arabian plate: The Weissert event and the VOICE in the Tethys Realm?

Abstract

Unlike the Tethys Realm, the carbon isotope record from the Boreal Realm exhibits a prominent negative excursion before the Jurassic-Cretaceous boundary referred to as the Volgian Isotopic Carbon Excursion (VOICE). The VOICE has been ascribed to restricted-circulation conditions in northern high latitude basins, which decoupled these basins from the global carbon pool. Similar isotopic signal has been identified in the southern hemisphere where it has been attributed to humid conditions and influx of organic matter. The restricted-circulation hypothesis is tested here by examining the depositional record of the Tethyan Late Jurassic–Early Cretaceous succession from central Saudi Arabia. A multi-disciplinary approach, involving sedimentology, sequence stratigraphy, biostratigraphy, and geochemistry, was adopted for studying a composite section covering the Hith, Sulaiy, Yamama, and Buwaib formations. The succession is characterized by restricted salina and sabkha depositional settings at the base that transition upward into an open-marine depositional system. This trend records a long-term sea-level rise during the Early Cretaceous. The carbon isotope record for this succession illustrates two prominent positive excursions of 5.2‰ and 2.6‰ amplitudes at the base and top of the succession, respectively. The larger positive excursion coincides with the restricted-environment facies and shows similarities, in terms of magnitude and trend, to the recovery phase of the VOICE. The upper positive excursion is manifested after a steady drop in the carbon isotope values, and it corresponds to the globally-recognized Weissert event. The results indicate that restricted circulation in the Arabian shelf interior during the Late Jurassic duplicated the VOICE signal. The recognition of the Weissert event signal, on the contrary, denotes restored circulation of the shelf interior with the Tethys. The novelty of this study is demonstrated by the findings that the VOICE might indeed be a global signal and restricted circulation driven by eustacy is the main controlling factor for the VOICE signal.