A record of global change: OAE 1a in Dariyan shallow-water platform carbonates, southern Tethys, Persian Gulf, Iran

Abstract

Early Aptian Lithocodium–Bacinella floatstone facies from the central Persian Gulf were a response of the Dariyan platform to a global disturbance. Carbon- and strontium-isotope data combined with facies analysis for the Late Barremian–Early Aptian Dariyan Formation record the timing of OAE1a and provide evidence for a causal relationship between OAE1a and Lithocodium–Bacinella occurrence. Carbon isotope stratigraphy allows the correlation of OAE1a-related segments in the Dariyan carbonates with other Tethyan shallow-water platform and pelagic reference sections. Strontium-isotope stratigraphy provides a numerical age of 124.3 ± 0.1 to 124.8 ± 0.1 Ma for OAE1a, indicating earliest Aptian, in the central Persian Gulf. Correlation of carbon isotope stratigraphy and Lithocodium–Bacinella-bearing facies shows that the Dariyan L–B occurrence post-dated OAE1a. The delay in the development of the Dariyan L–B facies is ascribed to the physiographic setting and a set of regional parameters including nutrient levels, alkalinity, and tolerance of dominant carbonate producers to OAE1a. Lithocodium–Bacinella floatstone facies of the Dariyan Formation is characterized by patchy-cloudy to columnar and oncoidal morphotypes. These growth patterns reflect the environmental conditions of probable high sedimentation rate, low alkalinity, low trophic level, and high oxygenation. Lithocodium–Bacinella facies and associated foraminifera and algae suggest peritidal to lagoonal (inner ramp) conditions for the upper Dariyan interval.