The dinosaur killer asteroid would have amplified Deccan eruptions

The scenario of the disappearance of the dinosaurs is complicated with new dates of the Deccan eruptions. Global warming would have occurred well before the maximum lava emissions, which would have occurred just after the impact of Chicxulub. The new data, however, confirm the thesis of a causal link between the two events.

One could believe that the theory proposed in the early 1980s by Helen Michel, Frank Asaro, Walter, and Luis Alvarez, and who argued that the massive extinction of the late Cretaceous, spectacularly manifested by the disappearance of the dinosaurs, came from the fall of an asteroid, is now well demonstrated and without surprises. Nature is however malicious. More than once, it has foiled the intellectual constructions that concern it and that we believe to be definitive, as appears from an article published in the journal Science exposing the work of an international team of researchers in geoscience.

To understand what is going on, let us recall that, according to the theory of the impact of a small celestial body about 10 km in diameter, the resulting shock would have generated a giant tsunami; but it would mostly disrupt the biosphere in many ways, for example by ejecting so much material into the atmosphere that the sun would have dropped considerably. It would have caused the death of plants and many animal species, in fine. This cooling would have been followed then by a runaway temperature by the greenhouse effect.

This theory was confirmed in the early 1990s when an impact crater was finally identified in Chicxulub, Yucatan Peninsula, Mexico, whose age and size was perfectly compatible with this hypothesis. But some researchers have not been convinced, preferring the theory put forward by Vincent Courtillot and his colleagues, which involves the colossal eruptions that occurred in India about 65 million years ago.

A greenhouse effect and ocean acidification

The work of this French geophysicist, conducted with his collaborators in the field of paleomagnetism, allowed him to estimate the age and the time put by these eruptions to form the basaltic trays (the traps ) of the Deccan, west of India. It followed that in a period of less than a few million years at the most, these flows had piled up over a thickness of more than 400 meters, and sometimes a few kilometers, occupying a vast territory. It was natural to assume that the large amounts of gaseous carbon dioxide and other volcanic products released on this occasion had engendered a climate change greenhouse. Generating, in addition, acidification of the ocean, the CO 2 could also have killed much of the plankton, causing a collapse of the food chain.

In fact, in both cases, difficulties arise as to why some species survived and not others. Uncertainties about the ages and durations associated with the Cretaceous-Tertiary (KT) Crisis, Deccan eruptions, and the fall of the Asteroid at the origin of the Astroblem Yucatan, are added to this observation. The debate is still going on about the respective share of these catastrophic events in one of the largest mass extinctions that the biosphere has experienced.

One of the means implemented to try to close it is to increase the temporal resolution to date these events. This is precisely what the researchers have just done, leading them to a surprising conclusion about Deccan volcanism and its role in the great Cretaceous late biological crisis.
Again, members of the University of Berkeley (like Michel, Asaro, and the Alvarez), looked at the KT crisis and still with the methods of dating the isotope geochemistry, in this case with isotopes of the argon in the couple  39 Ar 40 Ar. in fact, the refinement of dating work by these researchers already back in 2013 and 2018, when they determined from samples of rocks found in Montana (United States), that the problem of Chicxulub was formed 66,052 million years ago with an uncertainty of only 8,000 years. Meanwhile, in 2015, samples from a single region of the Deccan traps have delivered a more precise dating and today, two essential information appears to understand the change of perspective to which we are probably led.

First of all, the onset of eruptions in India is now in a time interval at, at most, 50,000 years from the impact of Yucatan, which confirms that both events are almost simultaneous at the geological scale whose unit of time is the million of year.

The majority of eruptions of the Deccan are posterior to Chicxulub

But above all, because the dating argon-argon now come from many parts of the Deccan, we realize that there has been a spike in emissions of basalt on almost all traps. But that's where it gets interesting, this peak emissions occurred after the asteroid fell and, contrary to what we thought before, is at least 75% of the volume of lava that after the fall, volcanism continued for a million years.

At first glance, this poses a problem because, during the last 400,000 years of the Cretaceous period, there was global warming leading to an increase in temperatures of about 8 ° C on average. This warming was interpreted as the effect of massive CO 2 degassing due to the Deccan eruptions that spewed 80% of the basalt volume before the impact of Chicxulub.

There is a contradiction, unless we admit, in agreement with what the study of volcanoes like Etna or Popocatépetl has taught us, that important degassing can occur in the absence of massive eruptions and that they did indeed occur while the activity at Deccan was not maximum, far from it.

Last probable implication, this new result comforts a little more the theory which wants that the plumes of hot matter , under the Indian continent which, in the Cretaceous, occupied then the place of the island of Reunion with its hot spot which one can think that it is the remnant of the one that caused the eruptions of the Deccan, were destabilized by the seismic waves produced by the impact of the Yucatan. Indeed, because of the drift of the continents, India was almost the antipodes of Yucatan 66 million years ago. The rotundity of the Earth would have led the seismic waves of an event as violent as that at the origin of the crater of Chicxulubto refocus. The rise of the plume would then have been accelerated, which would have amplified the volcanism on the surface.

This theory (see our Futura article below) is still debated, but perhaps we will come to the conclusion that all major basaltic flows, such as the Siberian traps, seem to coincide with major biological crises, have been amplified by falling asteroids or decay kilometric comets.

WHAT YOU MUST REMEMBER

• 65 million years ago, due to the drift of the continents, India was at the place of the present hotspot of the island of Reunion.
• About a million years later, an impact occurred on the other side of the world, giving rise to the famous Chicxulub crater in Yucatan, as the dinosaurs disappeared.
• New dates suggest that global warming had begun 400,000 years ago, in relation with basalt flood emissions in India and the origin of the Deccan traps, but the majority of the volume of lava was 'is set up after the impact of Yucatan.
• The hot spot would have started to digest massively with lower volcanic activity than we thought. The concentrated effect of seismic waves at the antipodes of Yucatan may well have amplified volcanism by destabilizing and accelerating the rise of hot material at the hot spot.

Dinosaur killer asteroid could trigger Deccan Traps

Article by Xavier Demeersman published on 13/05/2015

Is it the impact of an asteroid that decimated the dinosaurs about 65 million years ago or is it the massive lava flows called Deccan traps? Which of these two events is responsible for the mass extinction of the Cretaceous-Tertiary? Scientists are still debating it. According to a team of geophysicists led by Mark Richards, volcanic eruptions may have grown after the fall of the asteroid.

To explain the massive extinction of the late Cretaceous, marked by the famous disappearance of dinosaurs, which took place between 65 and 66 million years, scientists invoke both the impact of an asteroid and a sequence intense volcanic eruptions occurred in the same period in western India, known as the Deccan traps.

According to the researchers, the two events have considerably weakened our biosphere but one of them would not be the main responsible? There is no doubt that the asteroid impact was very violent and caused the brutal deaths of millions of living beings, but more importantly, the eruptions probably initiated a brutal climate change, which deeply affected the biodiversity of our planet, on Earth and in the oceans.

Curiously, these disasters, which had global repercussions, occurred almost at the same time. For Professor Mark Richards and his team at UC Berkeley, California, the collision of the asteroid "made the Earth ring like a bell" and caused the Deccan's large lava flows. "If you're trying to explain why the greatest impact the Earth has had in the past billion years has occurred over the 100,000 years of massive lava flows at the Deccan ... the chances of it being a coincidence are tiny: it's not a credible coincidence, " says the geophysicist.

This theory is reinforced by the results of the survey developed in the April 30 edition of  The Geological Society of America Bulletin. The researcher points out that it differs from an earlier hypothesis that also suggested that the Deccan traps were awakened by the impact of the asteroid but that the latter had occurred at their antipodes. However, the discovery, in 1990, of the crater of Chicxulub, in the Yucatan peninsula, places the Deccan at 5,000 km from the antipode of the astroblème (the traces left by the impact). The proposal was therefore abandoned.

At least four massive extinctions associated with huge volcanic eruptions

The lava flows date from the same period as the impact and was also contemporaneous with the most recent mass extinction in the history of the Earth. For the team, it's more than a coincidence. In 1989, Mark Richards proposed the hypothesis that "plumes" grow in the Earth's mantle every 20 to 30 million years and cause gigantic lava flows.

He recalled that the group of his colleague, Paul Renne, had shown a few years ago  "that the magmatic province of the Atlantic Center is associated with the extinction of the Triassic-Jurassic, which occurred 200 million years ago, that traps Siberia is associated with that of the late Permian, there are 250 million years  ago. Then you have the Deccan eruptions - which include the largest lava flows mapped on Earth - that occurred 66 million years ago and coincide with the massive extinction of the KT [Cretaceous-Tertiary, NDLR ]. "

Co-author of the present study and director of the  Berkeley Geochronology Center, Professor Paul Renne determined two years ago that the impact and mass extinction were almost simultaneous and had occurred over the last 100,000 years or so. large lava flows from the Deccan traps. The latter experienced three phases. One of them, designated as the Wai sub-group, is responsible for about 70% of the covered area between Mumbai and Calcutta.

Also within the framework of Richards' theory, the researchers also referred to the study of their colleague Michael Manga, also a co-author, who shows that major earthquakes of magnitude 9 or higher - like the so-called Tohoku, Japan in 2011 - can revive volcanoes in the same region. Assuming that the fall of the asteroid in the Yucatan caused the whole Earth to tremble with an equivalent magnitude, or even higher, the geophysicist had shown that the energy was then sufficient to warm the Deccan basalts, adding that it could also trigger eruptions in multiple places of the Globe ... "It's inconceivable that the impact could have melted rocks far away from the astrobleme," says Professor Manga. But if you have a system that already has magma and you give it a little extra kick, it could produce a big eruption. "

A whiplash at the Deccan eruptions?

The chemical composition of the lavas, different before and after the Chicxulub event, reinforces this theory defended by their authors. "There is a profound break in the style of eruptions, volumes, and their compositions," says Paul Renne who asks:  "Is this discontinuity synchronous with the impact? "

When they traveled to India a year ago to collect lava samples from this period, the team spotted damaged " terraces " in the western part of the Ghats mountain range, which marks the beginning of an important outpouring of the Wai subgroup. For the researchers, they testify to a "rest period" of Deccan volcanism, prior to the impact of the asteroid.

A few weeks ago, after the article was accepted, a team from Princeton University published a new radioisotopic dating of Deccan basalts that is consistent with the predictions of Mark Richards' theory. According to the author himself, the interest of this hypothesis is that it is verifiable. It predicts that it must have been about 100,000 years between the impact and the peak of eruptions at the Deccan and therefore the beginning of massive eruptions. It is this delay that must be found.