Syntectonic cements: complex records of the diagenesis induced by brittle deformations. Example of the cements of the hydrofractured chalks of the Omey area (Paris Basin, France)

The detailed study of the diagenetic signature (diagenetic time sequence an d geochemical composition) of syntectonic cements of the hydrofractured cha lks in the Omey area allowed to demonstrate that (1) hydrofracturing affect ed a water saturated aquifer where the temperature was below 50 degrees C, (2) the interstitial fluids of the diagenetic environment was meteoric, (3) the diagenetic system closed gradually with respect to the liquid phase, d ue to the diagenetic evolution of the chalk, (4) during hydrofracturing, th e temporal evolution of the oxidation-reduction potential of the diagenetic environment controlled the speciation of Mn and Ce, (5) the diagenetic tim e sequence of the cements represents a sensitive record of the tectonic con trol of the deformation of the aquifer.