Wildfire-Induced Nutrient Flux and Marine Anoxia Across the Triassic-Jurassic Boundary: Biomarker Evidence from the Cleveland Basin, Uk

The end-Triassic mass extinction (ETME, ~201.6 Ma), one of the ‘Big Five’ Phanerozoic biotic crises, is temporally coincident with the emplacement of the Central Atlantic Magmatic Province (CAMP), which is widely inferred to have triggered climatic warming, ocean acidification, and widespread anoxia. Although multiple negative carbon isotope excursions (CIEs) have been documented across the Triassic–Jurassic transition, the mechanistic links between these isotopic shifts, specific environmental drivers, and the two distinct phases of the ETME remain poorly constrained. Here we present a new biomarker-based reconstruction from the well-exposed Triassic–Jurassic boundary succession of the Dove’s Nest borehole (Cleveland Basin). Soluble organic matter was extracted using accelerated solvent extraction (ASE) and characterised by gas chromatography-mass spectrometry (GC-MS). Our results show a sharp peak in wildfire-derived polycyclic aromatic hydrocarbons (e.g., coronene, benzofluoranthenes) within mudstones of the lower Cotham Member, immediately after the Precursor CIE. This wildfire maximum is stratigraphically followed by the onset of the Initial CIE. The second extinction phase coincides with the Main CIE, where lithofacies shift to laminated black shales that may record euxinic (sulphidic) conditions. Based on these stratigraphic constraints, one possible interpretation is that following the Precursor CIE (first extinction phase), intensified wildfire activity may have increased nutrient delivery to the marine realm, potentially promoting eutrophication, organic-matter accumulation, bottom-water oxygen depletion and sulphate reduction. These processes could have favoured the development of marine anoxia and euxinia, which might have contributed to the Main CIE and the second extinction pulse.