Enhanced global weathering in response to Central Atlantic Magmatic Province volcanism across the Triassic–Jurassic transition: an osmium isotope record from the Prees borehole (UK)

The Triassic–Jurassic transition (~201.5 Ma) is marked by abrupt positive and negative Carbon-isotope excursions in marine and terrestrial sedimentary records. These excursions reflect global carbon cycle perturbations occurring in response to the massive volume of carbon released from the Central Atlantic Magmatic Province (CAMP). The subsequent doubling to tripling in atmospheric pCO₂ led to ocean acidification and the development of marine anoxia, thought to have caused the end-Triassic mass extinction, one of the biggest mass extinctions of the Phanerozoic. Organic-rich sediments can record the evolution of the seawater osmium (Os) isotopic composition, which is controlled by the balance between weathering inputs from continental crustal rocks (¹⁸⁷Os/¹⁸⁸Os ~ 1.4) and from mafic and ultramafic basalts (¹⁸⁷Os/¹⁸⁸Os ~ 0.13). Here, we present the first ¹⁸⁷Os/¹⁸⁸Os isotope data across the Triassic–Jurassic transition from the Prees core (Cheshire Basin, UK), drilled for the International Continental Scientific Drilling Program (ICDP) Early Jurassic Earth System and Time-scale (JET) project. Our new Os-isotope data show two major excursions towards mantle ¹⁸⁷Os/¹⁸⁸Os signature across the Triassic–Jurassic transition which we interpret to be the result of the emplacement of CAMP and the fast weathering of juvenile basalts.