The Cretaceous stratigraphy and geochemistry of the mixed siliciclastic-carbonate system of Saudi Arabia : implications for global correlation and paleoclimate




Fallatah, Mohammed Ibrahim

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The Cretaceous was a unique time period characterized by greenhouse conditions with multiple climatic perturbations. The interplay between the tumultuous Cretaceous climate and the depositional systems generated complex stratigraphic architectures. Such a complex stratigraphy is manifested in the interior of the Arabian Plate. Excellent outcrops of the Cretaceous succession in central Saudi Arabia offers an opportunity to document the response of the depositional system to the Cretaceous climatic changes. This study aims to investigate the evolution of the depositional system throughout the Cretaceous Period, including the interaction between siliciclastic and carbonate sedimentation in a greenhouse system, and the effect of any autogenic forces dominating over the Cretaceous extrinsic parameters on the resultant stratigraphy. These objectives will be achieved by adopting a multi-disciplinary integration of sedimentology, sequence stratigraphy, biostratigraphy, and high-resolution geochemistry (chemostratigraphy and trace elements). During the Late Jurassic–Early Cretaceous (late Tithonian–Valanginian), a shift from an arid to humid climate is recognized based on an influx of organic matter attributed to accelerated hydrological cycle, coinciding with the formation of a diachronous drowning unconformity in the early Valanginian. Following the shift to a humid climate, terrigenous sediment influx intensified and tidal siliciclastic sedimentation became prevalent during the Early to Late Cretaceous (Hauterivian–Turonian). The siliciclastic succession closely resembles modern tide-dominated depositional systems, which allowed to document the development of double clinoform deltas in an epeiric sea. It also allowed to conclude that lithological boundaries in greenhouse systems do not represent unconformities. From the Turonian to Maastrichtian, the climate shifted back to arid and evaporitic conditions marking the cessation of siliciclastic influx. Due to these conditions, seawater composition was altered such that it inhibited coccolith proliferation. This provides an explanation for the lack of chalk deposits over the Arabian Plate during the Campanian– Maastrichtian. The novelty of the study is also highlighted by recognizing a positive carbon isotope excursion at the J-K boundary. This signal is vastly identified in the Boreal Realm and is absent in the Tethys. Moreover, the study records the deposition of mud-mounds at K-Pg boundary, which could have an implication for the Cretaceous mass extinction


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