THE MASS EXTINCTION IN ZUMAIA
A dark page in the history of the flysch
It is in the cove at Algorri, it is black in colour and only 2 mm thick, but it holds the clues to one of the largest extinctions in living history. This layer was central to the impact theory being proposed in 1980 and, since then, it has remained one of the most widely visited and studied K-Pg outcrops in the world.
Over 80% of all marine fossils disappeared in this black layer of clay, which also contains a very high concentration of iridium. That is the key. This element is very rare on Earth, but quite common in a particular type of meteorite.
Iridium anomaly
Concentration of iridium
The black layer:
The clues
- High concentration of iridium
- Nickel-rich spherical crystals
- Soot
- Disappearance of 70% of fossils
What happened?
- Meteorite impact in Yucatan
- Rain of molten particles
- Huge fires
- Mass extinction
Extinction under the microscope
If we look at Zumaia’s black layer of clay under the microscope, we can see small spheres barely 1 mm in diameter. These are called microspherules and they were generated by the cooling and condensation of the large cloud formed after the Chicxulub impact.
Microspherules
These spheres can be found thousands of kilometres away from the impact site. They have a glassy inner structure. They are formed by rapid cooling and sudden crystallisation.