Revisiting K-Pg boundary with lithium isotopes: divergent marine and continental responses

Résumé fourni par la source

Seawater lithium isotope records (δ7Li) are powerful tools for investigating long term climate change and its relationship with continental silicate weathering. While most past ocean δ7Li reconstructions rely on foraminifera-rich carbonates, we introduce a novel approach using marine authigenic clays. Our findings demonstrate that clay authigenesis is an abiotic process that fractionates Li isotopes consistently in laboratory settings and across marine sediments. We apply this method to the Cretaceous-Paleogene (K-Pg) boundary, a critical interval marked by one of Earth’s five largest mass extinctions, and present a new clay derived seawater δ7Li record (64–69 Ma). Our results, compared with those of the carbonate record, uncover a dual environmental disturbance. The clay record indicates a protracted perturbation initiated at 69 Ma, driven by gradual shifts in soils, fluvial systems, and continental weathering, which remained largely unaffected by Deccan volcanism or the meteorite impact. In contrast, abrupt fluctuations are recorded in marine carbonates at 66 ± 0.3 Ma, signaling short lived yet significant changes of oceanic carbon chemistry. These findings highlight the asynchronous behaviour of terrestrial and marine systems during this major ecological transition.

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