Extreme volcanism did not cause the mass extinction of species at the end of the Cretaceous period

A study published in the journal Geology excludes that extreme volcanic episodes had any influence on the mass extinction of species at the end of the Cretaceous. The results support the hypothesis that it was a giant meteorite impact that caused the great biological crisis that ended with lineages of non-avian dinosaurs and other marine and terrestrial organisms 66 million ago. years.

The study was carried out by researcher Sietske Batenburg, from the Faculty of Earth Sciences at the University of Barcelona, ​​and experts Vicente Gilabert, Ignacio Arenillas and José Antonio Arz, from the University Institute for Research in Sciences of the environment of Aragon (IUCA-University of Zaragoza).

Limit K / Pg: The great extinction of the Cretaceous on the coasts of Zumaia

The scenario for this study was the cliffs of Zumaia (Basque Country), which have an exceptional section of strata that reveals the geological history of the Earth in the period 115-50 million years ago (Ma). In this environment, the team analyzed microfossil-rich sediments and rocks deposited between 66.4 and 65.4 Ma, a time interval that includes the known Cretaceous / Paleogene limit (K / Pg). Dated 66 Ma, the K / Pg limit divides the Mesozoic and Cenozoic eras and coincides with one of the five great extinctions of the planet.

This study analyzed the climate changes that occurred just before and after the mass extinction marked by the K / Pg limit, as well as its potential relationship with this great biological crisis. For the first time, researchers have examined whether this climate change coincides on the time scale with its potential causes: the massive Deccan volcanism (India) – one of the most violent volcanic episodes in the geological history of the planet – and the orbital variations of the Earth.

“The peculiarity of the outcrops of Zumaia lies in the fact that two types of sediments have accumulated there – some richer in clay and others richer in carbonate – which can now be identified as strata or marls and limestones. which alternate to form rhythms, ”notes researcher Sietske Batenburg, from the Department of Earth and Ocean Dynamics at UB. “This strong rhythmicity in the sedimentation is linked to the cyclical variations of the orientation and the inclination of the earth’s axis in the rotational movement, as well as in the translational movement around the Sun”.

These astronomical configurations – the known Milankovitch cycles, which repeat every 405,000, 100,000, 41,000 and 21,000 years – regulate the amount of solar radiation they receive, modulate the global temperature of our planet, and condition the type of sediment reaching the oceans. “Thanks to these periodicities identified in the sediments of Zumaia, we were able to determine the most precise dating of the climatic episodes which took place at the time when the last dinosaurs lived”, explains Ph.D. student Vicente Gilabert, from the Department of Earth Sciences at UZ, which will present its thesis defense by the end of this year.

Planktonic foraminifera: Revealing the climate of yesteryear

The isotopic analysis of carbon-13 on rocks combined with the study of planktonic foraminifers, microfossils used as high-precision biostratigraphic indicators, made it possible to reconstruct the paleoclimate and the chronology of this period in the sediments of Zumaia. Over 90% of Zumaia’s Cretaceous planktonic foraminiferous species became extinct 66 Ma ago, coinciding with a large disruption of the carbon cycle and an accumulation of impact glass spherules from the asteroid that struck Chicxulub, in the Yucatan Peninsula (Mexico).

Additionally, the study findings reveal the existence of three intense global warming events – called hyperthermic events – that are unrelated to the impact of Chicxulub. The first, known as LMWE and earlier than the K / Pg limit, was dated between 66.25 and 66.10 Ma. The other two events, after the mass extinction, are called Dan-C2 (between 65.8 and 65.7 Ma) and LC29n (between 65.48 and 65.41 Ma).

Over the past decade, there has been an intense debate over whether the hyperthermic events mentioned above were caused by increased volcanic activity from the Deccan, which emitted large amounts of gases into the atmosphere. “Our results indicate that all of these events are synchronized with Earth’s extreme orbital configurations known as eccentricity maxima. Only LMWE, which produced an estimated global warming of 2-5 ° C, appears to be temporally related to an eruptive episode of the Deccan., suggesting that it was caused by a combination of the effects of volcanism and the last maximum eccentricity of the Cretaceous “, add the experts.

Orbital variations of the Earth around the Sun

The global climate changes that occurred during the late Cretaceous and early Paleogene – between 250,000 years before and 200,000 years after the K / Pg limit – were due to the eccentricity maxima of the Earth’s orbit around of the Sun.

However, the orbital eccentricity that influenced climate change before and after the K / Pg limit is not related to the mass extinction of species in the Late Cretaceous. The climatic changes brought about by eccentricity maxima and increased by Deccan volcanism occurred gradually on a scale of hundreds of thousands of years.

“These data would confirm that the extinction was caused by something completely outside the Earth system: the impact of an asteroid that occurred 100,000 years after this late Cretaceous climate change (the LMWE),” explains the research team. “In addition, the last 100,000 years before the K / Pg limit are characterized by high environmental stability without obvious disturbances, and the great mass extinction of species has occurred instantaneously on the geological time scale,” conclude. they.