Calibration of bulk carbonate strontium isotopes to ammonite zones: Implication for global stratigraphic correlation of Callovian–Kimmeridgian strata in Central Saudi Arabia

Abstract

This study evaluates a strontium isotopic ratio (87Sr/86Sr) dataset from bulk rock carbonate samples of Middle–Upper Jurassic strata in central Saudi Arabia (upper part of the Tuwaiq Mountain Formation and entire Hanifa Formation). The objective is to use the 87Sr/86Sr dataset to determine ages to improve correlation to equivalent European ammonite zones to better link paleogeographic, paleoceanographic, and ecological events across the Tethys Ocean. The results show a scattered vertical pattern of 87Sr/86Sr, most likely caused by the introduction of radiogenic 87Sr during postdepositional (post-Jurassic) diagenetic modification. Data collected from mud-dominated facies not associated with subaerial exposure surfaces with pedogenesis or subaqeous marine firmground surfaces with Glossifungites Ichnofacies show a smoother sample-to-sample variation, is interpreted to be less altered by meteoric diagenesis. These data show distinct 87Sr/86Sr ranges that fall within the stratigraphic ranges and are in stratigraphic order. The absolute ages estimated from these data, however, show discrepancies with the ages previously interpreted by biostratigraphic data. The two age estimations (from 87Sr/86Sr and biostratigraphy) for the studied succession agree when the 87Sr/86Sr values are corrected for radiogenic (rubidium) contribution to mass 87. The corrected 87Sr/86Sr values are used to estimate the numerical ages and assign the ammonite zones of the studied succession. The proposed ammonite zones provide a temporal framework to link events that occurred in the Middle–Late Jurassic at different geographic locations in the Tethys Ocean.