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2.1.15. Trivières Chalk Formation - TRI

Authors: Briart & F.L.Cornet (1880).

Description: A white to greyish marly chalk without flints. A conglomerate, from a few cm to one m thick, generally marks the base containing hardground fragments, phosphatised chalk nodules, phosphatised sponges and fossil fragments. The top is often a hardground (named  "durillon" by the quarry workers). To the east of the Mons Basin several hardgrounds corresponding to large channels are distributed within this formation.

Fossils are not abundant except in the basal conglomerate.

Stratotype:No stratotype has been designated for the Trivières Fm.  Depending on the activities at the cement quarries it is occasionally visible at Harmignies (C.C.C.) and Obourg (C.B.R.).

Area:  Mons Basin, in quarries and boreholes.

Thickness: More than 10 m in the southern part of the Basin to 120 m in the northern part.

Age: Early-Late Campanian - cephalopods: Gonioteuthis quadrata, Belemnitella gr.mucronata, Scaphites gibbus; bivalves: Oxytoma tenuicostata, Endocostea baltica; echinoids: Echinocorys gr.ovata, Micraster schroederi.

Remarks: References:  J. Cornet (1923), Leriche (1935), Marlière (1936a, b, 1957), Robaszynski & Christensen (1989), Robaszynski (1995), Christensen (1999).