Repeated Photic Zone Euxinia after the Triassic-Jurassic Mass-Extinction Event

The Triassic-Jurassic boundary (T-J; 201 Ma) marks one of the so-called Big Five mass-extinction events that may have led to the extinction of more than 80% of all marine invertebrates. The extinction of marine and terrestrial biota is increasingly linked to the outgassing of large volumes of CO₂ and SO₂ from the Central Atlantic Magmatic Province, however the exact kill mechanisms and the long-term effects of this large igneous province remain to be elucidated. Here, we present multi-disciplinary data, including organic geochemical, isotope (C, N) and microfossil data, from 3 cores in Luxemburg (Rosswinkel), and northern (Mariental) and southern Germany (Mingolsheim) that provide evidence for repeated and prolonged environmental instability during the earliest Jurassic. Organic geochemical analyses show elevated quantities of the biomarker isorenieratane in the lowermost Hettangian following a major overturn of terrestrial vegetation (fern spike) as documented by palynological analyses. Isorenieratane derives from the brown strains of photosynthetic green sulfur bacteria (Chlorobiaceae) that require both light and free hydrogen sulfide in the water column. The presence of abundant aryl isoprenoids (isorenieratane and its diagenetic products) in Luxemburg and N Germany suggests that marginal marine basins in NW Europe became salinity stratified and developed intense Photic Zone Euxinia (PZE). Development of shallow marine anoxia was accompanied on land by the establishment of an impoverished vegetation dominated by thermophilous cheirolepid conifers. Nitrogen and carbon isotope data from organic matter support a scenario of salinity stratification, anoxia and denitrification. Repeated and prolonged PZE in shallow basins bordering the Tethys Ocean may have contributed to the slow recovery of marine ecosystems, particularly reefs, after the Triassic-Jurassic boundary.