Carbon Isotope Stratigraphy of the Upper Kharaib and Shuaiba Formations: Implications for the Early Cretaceous Evolution of the Arabian Gulf Region

Abstract

The carbon isotope profiles of shallow-marine carbonates from the Barremian-Aptian Kharaib and Shuaiba formations of the Arabian Gulf region range between 0.5 and 7^pmil ^dgr13C PDB (Peedee belemnite). Systematic variations can be correlated with isotope profiles reported from Tethyan pelagic limestone sequences. The detailed correspondence between the isotopic signature of the relatively well-dated pelagic limestones and the poorly dated shallow-water limestones from the Arabian Gulf region suggests that global marine carbon isotope changes apparently affected deep-sea and shallow-water carbonate sediments similarly and at a similar time resolution. Although oxygen isotopes have been reset during diagenesis, carbon isotopes appear to have maintained their primary marine signature through time. No evidence has been found to connect carbon isotope trends to subaerial exposure or later meteoric diagenesis. In combination with other data, the investigated carbon isotope profiles can be used for basin-to-platform and regional correlations beyond the current resolution of biostratigraphy in shallow-water limestones. Carbon isotope stratigraphy confirms significant hiatuses in the investigated shallow-water carbonate sequences. Using carbon isotope trends as a proxy for sea level fluctuations, the carbon isotope cycles of the late Early Cretaceous of the Arabian Gulf region may represent four cycles of rising and falling sea level with a duration corresponding to that of third-order sea level fluctuations. Regional correlations derived from isotope trends provide a scenario for the larger scale stratigraphic evolution of the Arabian peninsula during the end of the Early Cretaceous. Differential rates of aggradation between realms influenced by siliciclastics and those characterized by siliciclastic-poor (clean) carbonate deposition apparently caused the development of a pronounced basin-platform topography during the early Aptian (Shuaiba intrashelf basin and platform).