oa Carbonate Factory Evolution and Carbon Isotope Stratigraphy Across the T-J Boundary from the Musandam Peninsula (UAE)

Triassic and Jurassic carbonates across the Middle East host large amounts of hydrocarbons and might serve as reservoirs for CO2 storage in the future. The Triassic-Jurassic transition was marked by global changes, including carbon-cycle perturbations and the opening of the Atlantic Ocean. These changes were accompanied by one of the major extinction events of the Phanerozoic. In this study we investigate the evolution of a carbonate ramp across the Triassic-Jurassic boundary on the Musandam Peninsula in a series of wadis approximately 35 km apart (Wadis Naqab, Ghalilah and Al-Ghabbah) in the United Arab Emirates. In the proximal part of the ramp the Triassic benthic carbonate factory dominated by automicrite and microbialites was replaced by an ooidal-bioclastic ramp during the Jurassic. In the more distal part of the ramp, microbialites with abundant siliciclastic detritus are overlain by muddy carbonates with few oolites. The very abundant clastic components are being sourced most likely from the Arabian Craton. The change in the carbonate factory across the Triassic Jurassic transition, especially evident in the proximal part of the studied carbonate ramp is the result of an important change in palaeoenvironmental conditions. The carbon-cycle perturbations across the Triassic-Jurassic boundary have been recorded in carbon isotope curves from bulk carbonates, organic carbon and fossil wood in several Tethyan locations and have been used for chemostratigraphic purposes. Our site was located at the equator and on the southeastern margin of the Tethys throughout the Late Triassic and the Early Jurassic, and this study provides the first constraints of environmental changes at the low-latitudes for the Triassic-Jurassic boundary. Our stable isotope results on micrite show a prominent negative shift in carbon isotope values of approximately 2 ‰ just below the inferred position of the Triassic-Jurassic boundary. A similar isotopic trend is also observed across the Tethys with amplitudes ranging from ~2 ‰ to ~4 ‰. These results seem to indicate that the neritic carbonates from our studied section can be used for chemostratigraphic purposes. We gratefully acknowledge funding from Qatar Petroleum, Shell and Qatar Science & Technology Park.