Extinction by toxic waste pollution in the Tremadocian Baltoscandian Basin

The early Tremadocian marine transgression, associated with the transgressive phase of the Black Mountain Eustatic Event and concurrent with widespread deposition of kerogenous clay, coincided with the collapse of shallow-marine benthic communities in the Baltoscandian Basin. A possible major extinction driver, not previously considered, is toxicity resulting from the flooding of extensive Furongian shelly substrates of organophosphatic obolid brachiopods, which today form economically significant phosphorite ore deposits. Due to extremely low net sedimentation rates, broad accumulations of linguliformean shells and phosphatic hardground clasts remained exposed at the sediment-water interface, where redox processes continuously released phosphorous nutrients into the overlying water. This sustained nutrient influx likely caused widespread coastal eutrophication, culminating in biotic collapse. Moreover, the simple shallow-water ecosystems, dominated by obolids atop a very short trophic chain and virtually lacking predation, enabled uncontrolled proliferation of (nearly) monospecific obolid-rich nearshore communities, further contributing to extinction.