Reconstruction of the Upper Cretaceous chalks removed by dissolution during the Cenozoic in the western Paris Basin

During the Cenozoic, in the western Paris Basin, atmospheric weathering of the chalks with flints of the Upper Cretaceous led to the creation of clay with flints. A reconstitution of the chalks lost to dissolution is proposed and is based on the determination of the age of the parent chalks of the c lay with flints and the quantification of the thickness of dissolved chalk. The chalks affected by weathering range in age from Turonian to Maastricht ian, thus confirming the deposition of calcareous sediments in the western Paris Basin up to the Maastrichtian. Chalk weathering took place in situ, a s indicated by the preservation of the stratigraphic succession of the chal k in the clay with flints profiles. Weathering led to the dissolution of 20 -200 m of chalk, with regional variations. The weathering rate varies betwe en 2.1 and 14.5 m/Ma.