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2.1.13. Maisières Chalk Formation- MAI

Authors:F.L. Cornet & Briart (1874).

Description: Glauconitic, granular, calcarenitic green "chalk", with erosion surfaces and/or perforated hardgrounds at the base. Becomes more chalky towards the west and is the equivalent of lithological units known in France as "Verts", "Gris des mineurs" and "Bonne Pierre de Valenciennes" (where this chalk was worked in underground quarries as a building stone). Basal beds yield phosphate grains or pebbles. Fossil content: many bivalves.

Stratotype: Disused quarry "du Cimetière" at Maisières.

Area: Mons Basin, in France corresponding to the "Pierre the Lézennes" near Lille, "Craie grise du Cambrésis", and " Bonne Pierre de Valenciennes".

Thickness: 2 to 7 m, a very good marker level in boreholes.

Age: Coniacian on the basis of theplanktonicforaminifers Dicarinella gr. concavata and Globotruncana linneiana (Moorkens, 1969; Godfriaux & Sigal, 1969); numerous oysters Hyotissa semiplana and Gryphaeostrea canaliculata, and the brachiopod “Cretirhynchia” plicatilis. The Late Turonian age given by J. Cornet (1923) was based on the presence of " Neoptychites peramplus", but the specimen in the collections of the Faculté Polytechnique de Mons, is indeterminate according to F. Amédro.