Shallow ocean oxygen decline during the end-Triassic mass extinction

The end-Triassic mass extinction (ETME) was associated with intensified deep-water anoxia in epicontinental seas and mid-depth waters, yet the absolute oxygenation state shallow ocean is uncharacterized. Here we report carbonate-associated iodine data from peritidal Mount Sparagio section (Southern Italy) that documents ETME (~ 200 Ma) western Tethys. We find a sharp drop carbonate I/(Ca + Mg) ratios across horizon persisting into Early Jurassic. This records local dissolved oxygen iodate decline near-surface of low-latitude Tethys due to development depleted concentrations. Consequently, during even shallow-water animals, such as megalodonts seen at Sparagio, were likely victims oxygen-poor conditions. deoxygenation coincides synchronous spread deeper anoxic waters widespread deposition on continental shelves slopes. An upwards expansion mid-water minimum zone latest Triassic shoaled oxycline triggered major marine crisis.