Age of the Fontainebleau sandstones: a tectonic point of view

The age of the cementation of the Fontainebleau sandstones, located in the upper part of the Rupelian Fontainebleau Sand Formation and largely outcropping in the south of the center of the Paris Basin, remains a matter of debate: did the silicification occurred at early times during Miocene, following sedimentation, or did it occurred during Quaternary cold climate episodes? In this work, we determined an orthogonal fracture network (main directions N115 degrees +/- 5 degrees and N025 degrees +/- 5 degrees) over an area of similar to 6000 km(2). The fractures are oblique to the adjacent valley orientation and to the quarry working face orientation, discarding a gravitational origin. This tectonic fracturing is superimposed on regional scale antiforms and synforms that may be at least partly controlled by inherited basement faults reactivation during Alpine episodes. The whole Fontainebleau Sand Formation seems to be folded, including the Fontainebleau sandstones. We establish a relative chronology of the various phenomena and propose that silicification at the origin of the Fontainebleau quartzite occurred during early or middle Miocene. Alpine stresses then induced Fontainebleau sand and quartzite folding and fracturing during late Miocene and Pliocene. Finally, the fracture network facilitated fluid circulations and secondary carbonate sandstones or quartzite precipitation probably during Quaternary cold climate episodes.