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The de‑oxygenation of marine environments is thought to have played a significant role in many of Earth's major mass extinction events. This includes the end-Triassic mass extinction event (ETME), which witnessed the disappearance of conodonts, the near extinction of ammonoids and the most significant reef crisis across the entirety of the Phanerozoic. However, there are few high-resolution redox studies across the ETME, including across the main pulse of marine extinction, and few studies that directly correlate marine redox conditions with the biotic record in the same sedimentary succession. Here we present a high-resolution multi-proxy redox record from an expanded Triassic–Jurassic boundary section (Carnduff-2 borehole) from the Larne Basin, Northern Ireland. Redox conditions within the Larne Basin during the latest Triassic and earliest Jurassic were oxic to suboxic with suboxia being mainly restricted to sedimentary pore fluids. Such conditions differ from the photic zone euxinia reported from this time in other basins. Despite the Larne Basin being relatively oxygenated during the latest Triassic (Rhaetian) to earliest Jurassic (Hettangian), subtle pulsed marine redox changes within the Larne Basin had a profound effect on infaunal marine organisms. Suboxia within the Larne Basin coincided with the disappearance of 62.5% of bivalve species, of which 90% were infaunal, and the temporary absence of bioturbation. • A high-resolution palaeo-redox record from an expanded Triassic–Jurassic boundary location. • The Larne Basin remained relatively oxygenated during the Latest Triassic and Earliest Jurassic. • Infauna were significantly affected by subtle redox changes in the Larne Basin during the TJB. • A local redox shift is observed at the base of the initial CIE, coinciding with the ETME. [ABSTRACT FROM AUTHOR]