Oolites from the Arabian platform: Archives for the aftermath of the end-Triassic mass extinction

Abstract: The end-Triassic mass extinction (ETME) which occurred around 201 Ma is known as one of “the big five” mass extinction events of the Phanerozoic eon. Its effects were most severe on marine ecosystems, resulting in a global decline of invertebrate taxa and the complete extinction of the conodonts. The cause of the ETME can be attributed to the volcanic activity of the Central Atlantic magmatic province (CAMP), which resulted in drastic emissions of volcanogenic gasses such as CO2 and SO2. These eruptions caused severe environmental changes such as global warming and ocean acidification, which made the ETME particularly selective for acid sensitive taxa. These conditions also resulted in an almost global depositional hiati at the time of the Triassic – Jurassic boundary. In this study, marine strata from the Triassic – Jurassic boundary interval at Wadi Ghalilah in the United Arab Emirates have been petrographically and geochemically analysed. The examined strata are part of the Ghalilah Formation, namely the uppermost Sumra (Rhaetian) and the Sakhra (Hettangian) Members. The study had the goal to describe the geological, geochemical, and environmental conditions present after the ETME. Results were also compared with other Triassic—Jurassic boundary sections in order to understand the effects of the ETME on global and regional scales. Through the analyses conducted in this study, it seems evident that the ocean acidification caused by CAMP was indeed widespread enough to affect the southern latitudes of the UAE at the time. This can be seen in the form of a submarine dissolution surface and subsequent deposition of oolites and microbialites as anachronistic facies. The globally recognized Hettangian transgressions are also supported from Wadi Ghalilah, and was likely strongly influenced by the disappearance of carbonate producing organisms. Analyses of major, trace, and rare earth elements in ooids indicate a slight increase in anoxia after the onset of the Hettangian, as well as increased continental weathering which could be coupled with the start of increased biological productivity after the extinction.