Bacterial origin of the red pigmentation of Phanerozoic carbonate rocks: an integrated study of geology-biology-chemistry (Ernest Van den Broeck medallist lecture 2017)

1. Introduction The conference presented by one of us (A.P.) in September 2017 in honor of the Van den Broeck medal is the result of recurrent questions asked by many geologists, especially Belgians, about the origin of the red color of the Frasnian ‘marbles’ of our Ardennes. These marbles have been known throughout the world for several centuries both for their use as decorative material and also for the geological interpretation of their depositional setting and, naturally, of their red color. They are also known at a world scale by Dupont’s description (in 1881) who reported particular cavities, the ‘stromatactis’, later defined by Bathurst (1982). Since then an infinite literature has been devoted to them and the term ‘stromatactis’, originally described in the Belgian Frasnian, is commonly used in the Precambrian and global Phanerozoic carbonates. Finally, following numerous questions on the origin of these marbles, they were considered as ‘reefs’ as soon as they were discovered, Boulvain (1990) definitively established the depositional environment of these mud mounds showing how these ‘reefs’ were built in relation to relative sea level variations. The red color was also discussed in his work, and attributed to iron-bacterial activity in dysaerobic media. This study was initiated at the Universite Libre de Bruxelles, at the initiative of Professors A. Herbosch and B. Mamet. It is with the latter that one of us (A.P.) decided to extend this theme to other ‘marbles’ and