Fossil site shows impact of early Jurassic’s low oxygen oceans

Scientists, using a combination of fossils and chemical markers, have found that a period of low ocean-oxygen globally caused the Early Jurassic marine ecosystem to collapse, shrinking diversity to just a few species.

The study, led by Rowan Martindale from the University of Texas at Austin in the US, zeroes in on a recently discovered fossil site in Canada located at Ya Ha Tinda Ranch near Banff National Park in southwest Alberta.

The site records fossils of organisms that lived about 183 million years ago during the Early Jurassic in a shallow sea that once covered the region.

The fossil site broadens the scientific record of the Toarcian Oceanic Anoxic Event, a period of low oxygen in shallow ocean waters which is hypothesised to be triggered by massive volcanic eruptions.

The Oceanic Anoxic Event was identified at this site by the geochemical record preserved in the rocks.

The oxygen level of the surrounding environment during the Early Jurassic influences the type and amount of carbon preserved in rocks, making the geochemical record an important method for tracking an anoxic event.

“We have this beautiful geochemical record that gives us a backbone for the timing of the Oceanic Anoxic Event,” said Martindale.

With that framework the researchers looked …read more