Milieu_formation

The environment of training of Norman chalks

Norman chalks settled at the bottom of the sea. In its origin the chalk was an established mud mainly established of skeletons of nannoplancton. The depth of deposit (space of accomodation) was more or less big. In certain sectors subsidents, as the graben of the North Sea, the depth was big and certain chalks have a turbiditic facies. At the end of the Cretaceous, because of a renewal of activity of the oceanic expansion, the average level of the oceans and the seas particularly increased. Continents were widely submerged. The sedimentary ponds so colonized are called of "seas épicontinentales" " because they rest on the continental crust. In the central parts of these seas reigned pelagic conditions of sedimentation, that is those were normally reserved for the open sea or for the ocean.

La mer de la craie européenne, extrait de Tallon (1976), d'après Aubouin (1968)

The model of sedimentary environment often adopted for the chalk is the one of the banister carbonated in domain intracratonique (Surlyk and al ., on 2001; Frykman and al ., on 2004)

facies

Paléo-position of chalks of Normandy with regard to chalks of the European NW, according to Frykman and al ., on 2004

We can identify (Lasseur, on 2007) various zones since the bank up to the open sea, every zone being characterized by a biological association:

Zonation facies, modified according to Lasseur (2007)