Thread by @EileanClach

NEW PAPER in #ScienceAdvances. The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impact structure science.org/doi/10.1126/sc… 1/14

The paper describes a remarkable, symmetrical crater imaged using seismic reflection data, and buried below >300 m of sediment and 900 m of water in the outer Guinea Plateau 2/14

It shows characteristics consistent with an impact origin, including geometric relationships between crater depth and width, rim elevation, as well as a pronounced central uplift and intense deformation in the ‘brim’ outside of the central crater 3/14
Data courtesy of TGS

Our numerical models @SpaceNerdAtWork show that a complex (technical definition) crater of this scale could have been formed by a 400 m asteroid at water depths of around 500-800 m. If confirmed, this would make this one of only ~20 marine impact craters discovered on Earth 4/14

This is approximately the same size as the Bennu asteroid in near-Earth orbit – considered to be one of the two most hazardous objects in near space. It has a 1-in-1750 chance of colliding with Earth in the middle of next century. Image courtesy of NASA 5/14

Our numerical models also show the consequences of such an event, generating a magnitude 6.5 earthquake, likely triggering landslides on the continental slope, and certainly generating a large (km-scale) tsunami in the near field 6/14

Note that such an impact would release nearly 1000 times as much energy as the recent Tonga eruption (image below from NOAA) so the atmospheric shock wave could also have major consequences, possibly including amplification of any tsunami in the far field 7/14

Based on the conjugate margin in South America, there is a thick sequence of black shales beneath the crater - we see similar facies below the crater. This could have resulted in significant methane emissions as well... 8/14

Intriguingly, this crater formed at or very near the K-Pg boundary at 66 million years ago . Could this have been genetically related to the Chicxulub event which led to the extinction of the dinosaurs? 9/14

Image from New Scientist:

We have several hypotheses regarding this. One is that the asteroid may have been part of a long-lived (~1-2 million year) cluster. We see a similar situation back in the Ordovician following the breakup of an L-chondrite parent asteroid at 466 million years ago - 10/14

Another is that the parent asteroid broke apart closer to home, during a close encounter with the Earth itself and that the fragments subsequently collided with Earth. A similar situation occurred when the Shoekmaker-Levy comet fragments bit Jupiter in 1994 11/14

Or, alternatively, it may have been entirely coincidental! The chart below from Bland and Artimieva (2006) shows that the impact frequency of a 400 m asteroid is around once per 700 ky. 12/14

But all this – the impact crater hypothesis, consequences and age/relationship to Chicxulub – cannot be tested without physical recovery of shocked minerals from the crater. We’ve submitted an IODP proposal to do just that! This is currently well down the review process... 13/14

Finally, our thanks to TGS, Schlumberger and the government of Guinea for data and #NERC for recent funding. This discovery, and the science around it, would not have been possible without the generous provision of data, and funding. 14/14

And thanks to co-authors, @SpaceNerdAtWork @SeanGulick and Ben Aduomahor from the @DeepWaterHWU group!

And FINALLY thanks also to @McDaidPR for promoting the story - I've lost track of coverage now!

Oh, I just realised that the acceptance date was June 30th - National @AsteroidDay! How fortuitous. It was also the day that the sister drilling proposal was being reviewed in the IODP Science Evaluation Panel @anzic_iodp @ECORD_IODP @uk_iodp