2.1.8. Thivencelles Marls Formation - THV

Authors: Robaszynski (1975 a).

Description: Clayey, soft, "plastic" when wet, swelling when exposed, generally green when fresh, but yellow after alteration at outcrop: these are the "Dièves moyennes" of J. Cornet (1923). The lower part may becoloureddifferently: white, ochre, red ("Dièvesblanches, rouges" from northern France or "Dièves inférieures" of J. Cornet, 1923).

The base of the Formation consists of a pebble conglomerate and a black and shiny gravel: this is  more or less equivalent with the glauconitic Mons Conglomerate Bed " Lit du Conglomérat de Mons" (Robaszynski, 1975) or "Tourtia de Mons" auct. (cf. Marlière, 1957).

Stratotype: Saint-Aybert des Mines de Thivencelles Pit, between 266 and 218 m (see Robaszynski, 1975 b, p. 34).

Area:In the western part of the Mons Basin and in northern France.

Thickness:A few metres to 20 m.

Age:Latest Cenomanian for the Mons Conglomerate Bed in the western part and the white and red marls with Actinocamax plenus, Rotalipora cushmani, Whiteinella archaeocretacea; Early Turonian for the green marls containing Mytiloides labiatus, M. hercynicus, Mammites nodosoides, Helvetoglobotruncana helvetica, Dicarinella hagni.

Remarks:- The Mons Conglomerate Bed or "Tourtia" is diachronous: of Late Cenomanian age between Valenciennes and Mons, but of Early Turonian age east of Mons.

- References: J. Cornet (1923); Robaszynski (1971 a,b, 1975 a - c).

- The designation "Formation de Bruyelle" (Doremus, 1997) is a junior synonym of the  Thivencelles Marls Formation.