Appel à manifestation d’intérêt – Expédition « Into the Nadir »

Pour mieux comprendre la nature et l’origine des hétérogénéités lithologiques et géochimiques au niveaux de dorsales à expansion lente, l’expédition se propose de caractériser les processus de rétroactions complexes entre des processus magmatiques, des phénomènes de déformation et des interactions fluides-roches en réanalysant d’anciens échantillons issus de forages océaniques

Motivation scientifique (en anglais)

Impacts of asteroids or comets are a very important Earth hazard over geological time scales. A recent IODP drilling expedition showed that collision of a 12 km wide asteroid offshore Mexico (Chicxulub) unequivocally caused the major end Cretaceous extinction event, 65 million years ago, when the dinosaurs and 80 per cent of all other species became extinct. Smaller events are also likely to be a significant local hazard, as shown by the destruction caused by the airblast from the 50 m wide Tunguska asteroid in Russia in the early 20th Century.

However, the geological record of these events is scarce, with only 200 confirmed impact craters anywhere on Earth. Very few of these are under water, which should be the most common type of impact, and not many are well preserved or imaged by geophysical techniques.

A new candidate impact crater has recently been discovered offshore West Africa and this expedition, planned to take place in early 2028, plans to drill this to test whether it was caused by a marine impact. Computer models suggest this impact could have been caused by a 400 m wide asteroid, a similar size to the Bennu asteroid in near Earth orbit, considered to be the most hazardous object for an Earth impact in the coming centuries (1 in 1,750 chance of collision). The potential crater is exceptionally well imaged with seismic reflection data, but we require hard data to test our models of crater formation. We propose to drill a single well through this crater, and into the sedimentary rocks beneath it, to understand how it formed and what its consequences were. This will be used to constrain computer models of the impact itself and associated earthquakes, tsunami, ejecta and gas emissions.

One intriguing aspect of this crater is that it appears to be the same age, or close in age, to the Chicxulub event at the Cretaceous-Paleogene (K-Pg) boundary. This suggests that it might have been part of the same impact event, perhaps caused by breakup of a parent asteroid, or a binary asteroid. Alternatively, it may have been part of a cluster of impacts that occurred in close succession (several million years), perhaps as a result of an earlier collision in the asteroid belt. Or it may be a completely independent impact from Chicxulub. Dating impact melts in the crater will help us to test these alternative hypotheses.

Even if the crater turns out not to have been formed by an asteroid impact, this drilling expedition will help us to understand what other process could have formed such a feature (perhaps an underwater volcanic eruption), as well as providing important new records of the Earth’s climate and ocean conditions during a ‘hothouse’ world, when temperatures were significantly higher than at present. This will include new equatorial records of Ocean Anoxic Event 2, which occurred when the Earth’s oceans were starved of oxygen around 90 million years ago. It will also include the Paleocene-Eocene Thermal Maximum (PETM), when global temperatures rose rapidly around by 5-6°C, 55 million years ago, often considered to be one of the closest analogues to present day global heating.

Logistique

Les candidatures pour participer à cette expédition seront ouvertes en 2027. Toutefois, si vous souhaitez être parmi les premiers à recevoir des informations sur cette expédition passionnante, nous invitons les candidats potentiels à remplir le formulaire de manifestation d’intérêt ci-dessous.

Cette démarche n’est pas obligatoire, ne vous engage pas à postuler lors de l’appel principal, et le fait de ne pas remplir ce formulaire n’aura aucune incidence sur l’évaluation de votre candidature ultérieure. Nous vous encourageons toutefois vivement à remplir ce formulaire afin que nous puissions vous accompagner au mieux. Remplir le formulaire prend 2 minutes!