Severe environmental crises led to a series of large-scale extinction events during the Jurassic Period 178–186 million years (myr) ago. The unrest has been attributed to the abundant release of volcanic gases, but the temporal link between volcanism and the extinctions has remained controversial.
“Our results strongly support the idea that episodic magmatism in the Karoo province may have been the culprit for the repeated Jurassic environmental and biological crises,” says Arto Luttinen of the Finnish Museum of Natural History, lead author of the article published in Gondwana. Research.
“Previous dating of volcanism in the Karoo Province indicated a short duration of activity 182-183 myr ago. Although this age coincides with the largest Jurassic extinction, it cannot explain the recurring environmental crises that began millions of years earlier and continued long after,” says Luttinen, and explains that indications of longer duration and periodicity of volcanism have generally been considered unreliable. due to possible methodological problems.
The uranium-lead method needed to unveil historical events
The new ages were measured at the Nordsim laboratory in Stockholm using the so-called uranium-lead method on submillimetre-sized zircon crystals in volcanic rocks. The production of lead from the radioactive decay of uranium provides the most reliable chronometer for dating ancient geological processes.
At the Nordsim laboratory, the crystals studied are drilled with a narrow beam of ionized particles and the ages of the tiny zircons are defined by mass spectroscopic measurements of the abundances of uranium and lead.
“This approach allowed us to date individual crystals formed at various evolutionary stages of long-lived magmatic systems,” explain co-authors Matti Kurhila, Geological Survey of Finland, and Martin Whitehouse, Swedish Museum of Natural History.
Examination of samples taken from a magmatic zone more than 1000 kilometers long in Mozambique shows that the peak of activity previously established 182-183 myr ago was preceded by volcanism 185-190 myr ago, and was followed by another major magmatic stage 178-181 myr ago. , and decreasing activity over the following millions of years.
“These results pave the way for further research on dating and magmatic outgassing to better understand the coincidence between Karoo volcanism and global biosphere crises,” concludes Luttinen.