The secret of sedimentary rocks
10/26/10

Historically much more embedded in Anglo-Saxon countries, the study of sedimentary rocks and the processes which create them were only rarely the subject of publications in French. Frédéric Boulvain, a professor at the University of Liège, has just filled this gap by publishing, through Ellipses, a complete updating of his course on ‘Sedimentary Petrology’ (1). Primarily addressed, obviously, to students who are tackling Earth Sciences in their curricula, but also, he writes, ‘to the curious with some general scientific baggage and who wish to understand what sedimentary rocks tell us about the past and the present of our planet.’

COVER Prétrologie sédimentaireAs, let us remind ourselves, sedimentary rocks cover…90% of the planet’s surface. And it is they which enclose the majority of the raw materials used by humankind. Beginning with coal, petrol or…water. Moreover, sedimentary rocks teach us enormously about the history of the planet. Petrology is the study of rocks,’ explains Frédéric Boulvain. ‘What is important is their genesis: we wonder how they have been formed, and in asking ourselves this question, we open onto something essential: the evolution of the Earth. As rocks are the witnesses to the environment in which it was formed. And that is a piece of the jigsaw puzzle of understanding the planet. Thanks to rocks we can reconstruct the landscapes of the past, as well as climate conditions and their evolutions.’

In sedimentary petrology that can go very far indeed: the rocks retain visible traces of waves, currents or living organisms of course. ‘I do a lot of actualism with my students. In other words we go to see the ripples of waves on the beaches and then show equivalents which have been in the rocks for 325 millions of years! Actualism is the basis of sedimentology. But it doesn’t always work! The physical processes at work on the planet change little over the course of time, but when life intervenes, it becomes a lot more complicated. Analogies are more difficult as the ancient organisms are no longer there.’

 

(1) Pétrologie sédimentaire, Des roches aux processus, Ellipses éditeur. Collection « Technosup », Paris, 2010. 259 p. 

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