First Evidence of the Toarcian Oceanic Anoxic Event in the Northeastern Arabian Plate Margin (Iraqi Kurdistan Region): Insights From Stable Carbon Isotopes and Petrography

ABSTRACT One of the most significant Mesozoic disruptions of the global carbon cycle is the Early Toarcian Oceanic Anoxic Event (T‐OAE), which is associated with significant biotic turnover, rapid greenhouse gas release, and extensive marine anoxia. The T‐OAE's expression at the northeastern edge of the Arabian Plate is still poorly constrained, even though it has been well recorded from European and western Tethyan successions. Here, we present an integrated petrographic and stable carbon isotope (δ 13 C) study of the Early Jurassic Sehkaniyan Formation exposed in the Iraqi Kurdistan Region's Sirwan section, offering fresh perspectives on how global carbon‐cycle disruptions manifest in shallow‐marine carbonate platforms. The total thickness of the formation in the studied section is approximately 345 m and mainly consists of dolomitic limestone and dolomite. Petrographic investigations of 93 thin sections from the carbonate rocks of the Sehkaniyan Formation reveal that the majority of skeletal grains are shallow‐marine derivatives, whereas the non‐skeletal grains mainly consist of peloids and intraclasts. The age of the formation based on benthonic foraminifera and green algae suggests a Sinemurian–Toarcian interval. The identified microfacies types of the formation are grouped into two facies associations that were deposited in a shallow lagoonal environment with intertidal intervals. The stable carbon isotope profile of the Sehkaniyan Formation in the studied section, ranging from −4.25‰ to +0.52‰ VPDB, reflects the influence of both local depositional conditions and global carbon‐cycle changes. The considerable negative carbon isotope excursion recorded within the early Toarcian beds of the formation (−4.25‰) indicates a significant perturbation of the marine carbon cycle and corresponds to the globally recognised early Toarcian Carbon Isotope Excursion (T‐CIE), which has been documented in shallow‐marine carbonate successions. The magnitude of the negative δ 13 C shift matches that observed in other Tethyan areas and is associated with greenhouse gas emissions from the Karoo–Ferrar Large Igneous Province. Microfacies and petrographic analyses indicate that depositional and diagenetic factors influence the shape of the isotopic curve. Thus, the Sehkaniyan Formation offers compelling evidence that shallow‐marine carbonate platforms in the northeastern Arabian Plate were impacted by the T‐OAE. The observed shift in δ 13 C is consistent with the disturbance of the global carbon cycle caused by volcanic CO 2 and thermal methane release linked to the Karoo–Ferrar Large Igneous Province's emplacement. These findings show how sensitive tropical carbonate systems are to sudden climatic and biogeochemical forcing during greenhouse periods in Earth's history, and they also broaden the paleogeographic footprint of the T‐OAE.