Potassium, Thorium and Uranium signatures of impact structures

by Cheikh Ahmadou Bamba NIANG

Cheikh Ahmadou Bamba NIANG is the first PhD student in Planetary Science in Senegal. With a first research experience (Master degree) on the remote sensing analysis of the potential impact structure of Velingara in Casamance, he decided to move forward and got enrolled in the PCSTUI (Physique,Chimie, Science de la Terre de l’Univers et de l’Ingénieur) Doctoral School of the University Cheikh Anta Diop in Dakar. His first scientific article, published as a peer-reviewed chapter of the Geological Society of America Special paper is now online:

Cheikh Ahmadou Bamba Niang, David Baratoux, Dina Pathé Diallo, Pierre Rochette, Mark W. Jessell, Wolf U. Reimold, Sylvain Bouley, Olivier Vanderhaeghe, Gayane Faye, Philippe Lambert, 2021. “Systematic survey of K, Th, and U signatures in airborne radiometric data from Australian meteorite impact structures: Possible causes of circular features and implications“, Large Meteorite Impacts and Planetary Evolution VI, Wolf Uwe Reimold, Christian Koeberl. https://doi.org/10.1130/2021.2550(15).

This research paper presents a systematic survey of the concentration of potassium (K), thorium (Th) and uranium (U) concentration at and around impact structures in Australia from radiometric maps and the implication of this research for impact science in general.

Fig. 1 – Radiometric map of Australia (color map of K, Th and U concentrations) with location of large impact structures.

Why this research is important ?


K, Th and U are heat-producing elements – the natural disintegration of 40K, 232Th and 238U is the source of energy of the Earth Interior, responsible for mantle convention or plate tectonics. This is eventually the source of energy captured and provided to users by geothermal power plants. 40K was also much more abundant in the early Earth than it is now, because of its faster decay rate, compared to 232Th, and 238U. It is therefore important to understand how impact cratering, which was more intense during early Earth, affected the redistribution of this heat-producing elements in the Earth’s crust.

Why Australia ?

Because Australia has old rocks and geological units and is host to many impact craters and impact structures. Therefore, It bas been considered as an ideal playground for this investigation. Australia has also been globally covered by airborne radiometric surveys (geophysical surveys which map the concentration of K, Th and U, based on the gamma rays emitted during the natural desintegration of 40K, 232Th and 238U, see Fig. 1)

What are the main results of this research ?

We have documented that impact craters are often associated with circular anomalies in either concentrations of K, Th or U. We have examined the potential origins of these signatures, and concluded that hydrothermal systems generated by the heat of meteoritic impact and post-impact erosion and alteration are the main causes of the observed geochemical patterns.

What could be the applications for impact science ?

There are may other parts of the globe where radiometric survey are available, at different scales. These surveys could could be used to search for potential impact structures, in particular in regions of the world with poor outcroping conditions (tropical regions), or where knowledge of recognition criteria for impact structures is limited, such as in West Africa. Radiometric data is proved to be a valuable data set that could be analyzed with other geophysical data set in case-studies of other impact structures.

What are your future projects ?

I am about to finish my Ph.D. thesis and have currently another manuscript in revision about the potassium signature of the Bosumtwi impact structure in Ghana. I am also working on potassium, uranium and thorium signatures of the Rochechouart impact structure in France, which is the last chapter of my PhD thesis. The next step is to defend the PhD thesis and find a post-doctoral fellowship to strengthen my skills in impact science.

My dream would be to lead future research about the potential impact structures of Velingara in Senegal, and find the ressources to achieve a drilling of this potential impact structure. The structure is covered by about 100 m of sediments, and drilling is the only way to find evidence for impact metamorphism.

What did you learn during your PhD ?

I learn impact science – which was the main topic of my PhD – but more importantly, I learn tools and develop skills that are used in many domains, in Earth, Space or Environmental science. I have been exposed to geophysical data interpretation, which is a common tool in exploration of mineral resources. I am now trained in using GIS (Geographic Information System). I learn programming in Python – a big challenge for students in Geology – I also made progress in the English language, as I had to present several times my research in International conferences, such as during the Large Meteoritic Impact and Planetary Evolution conference in Brazil in 2019. I has also the chance to participate to other projects, not directly related to the PhD – such as the astronomical observation of the stellar occultation by Polymele, in preparation of its flyby by the NASA mission Lucy (Fig. 2). I work on the consequences of the fall of asteroid on the Earth, and it’s also fascinating to be able to observe these asteroids with telescopes !

How your thesis was funded ?

My thesis was one of the first PhD launched within the framework of the Africa Initiative for Planetary and Space Science. I was encouraged by the professors of the geological department of the University Cheikh Anta Diop, and was welcome to work at the Institut Fondamental d’Afrique Noire Cheikh Anta Diop. My research received financial support from the Barringer Family Fund in 2016, the French embassy in Senegal, and from the Center for Research on Impact Structures and Rochechouart (CIRIR). I was also lucky to be trained by well-known impact scientists and geophysicists, including Prof. Wolf Uwe Berlin and Prof. Christian Koeberl, Dr. Philippe Lambert, and Prof. Pierre Rochette, in particular during the visits at the CEREGE.

Fig. 2 – Cheikh Ahmadou Bamba NIANG, during the observation campaign of the stellar occultation by Polymele in Senegal (Lucy MISSION/NASA) (c) Association Sénégalaise pour la Promotion de l’Astronomie.

Interview by David Baratoux

Contact for a pdf version of the article: cabniangeos@gmail.com

Follow and support Cheikh Ahmadou Bamba NIANG’s research on his blog

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