Effect of the Early Aptian Carbon Cycle Perturbations (OAE1a) on Carbonate Sedimentary Patterns of the Eastern Arabian Shelf (Oman and UAE)

Abstract

The injection of large volumes of CO2 linked to the emplacement of the Ontong–Java province triggered a sequence of global paleo-oceanographic and climatic events, which produced different responses of the carbonate platforms at high and low latitudes. The Arabian platform presents a continuous record during the early Aptian Oceanic Anoxic Event (OAE1a). Stable carbon and oxygen isotopes paired with petrographic and x-ray fluorescence analysis were used to conduct a high-resolution chemostratigraphic investigation on shallow water carbonates from Oman and the UAE. The identification of the characteristic OAE1a traits on the δ13C curves was complicated by the overprint of the original carbon–isotope signal. Wadi Rahabah and Sajja carbon–isotope curves emphasize the limited applicability of chemostratigraphy on shallow water sections and outside a multi-disciplinary approach. The depositional environments range from supratidal to the outer ramp, with fabrics typical of moderate to low energy environments. The elemental analysis highlights that the carbonate sediments were not affected by dilution with siliciclastics, which are below 2%wt even during the carbon-cycle perturbations. Mn and Fe produce limited evidence for anoxic/euxinic conditions. A regional correlation using δ13C records was established between Wadi Mu’aydin, Wadi Rahabah, Wadi Kebdah and well–known localities over the eastern Arabian shelf to reconstruct the evolution of the depositional environment during the OAE1a laterally and temporally. The result of the correlation opens the possibility that the release of CO2 was slow enough to prevent carbonate undersaturation. However, periods of subaerial exposure could have obliterated traces of the acidification event. Bioturbations and scarce pyrite indicate unfavourable conditions for developing a constant and widespread anoxia over the Arabian shelf. Sea level fluctuations influenced faunal changes and played an important role in regulating the accumulation rate of carbonate sediment over the platform.

Date of Award	26 Jun 2024
Original language	American English
Supervisor	THOMAS Steuber (Supervisor)