Expanding our understanding of the Toarcian Oceanic Anoxic Event in the Tethys Ocean: New insights from the Arabian Plate

Abstract

The Toarcian Oceanic Anoxic Event (T-OAE) has been reported widely across the Tethyan region and globally. In Arabia, and based on ammonite dating, the T-OAE coincided with the deposition of the reddish siliciclastic unit of the Marrat Formation. However, no evidence of the T-OAE was ever reported from Arabia because these red beds were previously interpreted as continental deposits. Recently, these red beds have been recognized as shallow marine deposits which open an opportunity to assess the occurrence of T-OAE in Arabia. In this study, a multiproxy geochemical characterization was performed on the Toarcian Marrat Formation to infer the chemistry of the paleowater column and identify intervals of possible T-OAE in Arabia. The coupled negative excursion of δ13Corg and enrichment of redox-sensitive elements (Mo, U, V, Cr) indicate a period of marine anoxia during the deposition of Marrat red beds, suggesting that they were deposited in shallow marine settings and under anoxic, potentially ferruginous ocean conditions. The reddening is interpreted to have occurred later due to the stabilization of unstable hydrous iron oxides to hematite under oxic marine conditions. This study records the first documentation of the T-OAE in the Arabian Plate. This will have significant implications for the overall understanding of the T-OAE globally and for exploration of hydrocarbon through realizations of potential new source rocks associated with the OAEs in the Toarcian and other time intervals.