The training of the dolomite
The chalk undergoes a phenomenon of dolomitisation, that is a partial substitution of the aragonite by the dolomite (CaMg (CO3) 2). Such a transformation is due to the percolation of brines enriched in Mg2 + through a still enough permeable sediment. The origin of the fluid remains still problematic. He could result from lagoons sursalées (sebkas) in littoral border where the haste of the calcite and the gypsum would have impoverished the liquid in ion Ca2 +. He would then have gained basins shallow by density and would have stagnated by soaking the mud there.
The main examples of dolomites are in the block of Callus (region of Etretat), as well as towards Saint-Pierre-en-Port.