2.1.20. Saint-Symphorien Calcarenite Formation- SSY

Authors: Rutot & Van den Broeck (1885a) and herein.

Description: Crumbly, porous, poorly cemented, grey when fresh, yellow to brownish at the altered surface, often bioturbated, calcarenites or calcirudites. Locally the calcarenites may contain grey, green or brown phosphatised granules and pebbles. Similarly, one or more flint bands may be intercalated within the Calcarenite (or "Tuffeau").

Numerous fossils are present, either complete, or in fragments or forming the bioclastic base of the rock: scaphopods, echinoid spines, oysters and other bivalves, belemnite guards, brachiopods.

The base of this formation is often clearly distinguished by the presence of an indurated and phosphatised chalk pebble conglomerate: the top is generally a hardground of 10 to 40 cm thickness, but known in places to reach a thickness of 140 cm, burrowed, with bivalve and gastropod internal moulds and small pyrite crystals.

Stratotype: No stratotype has been designated for the St.-Symphorien Fm.; it outcrops in abandoned quarries at St- Symphorien and in parts of the Vandamme (formerly André) quarry at Ciply.

Area: MonsBasin, in the disused quarries of St -Symphorien and Ciply and in boreholes. Towards the west it reaches Hornu.

Thickness: From one to a few metres, sometimes absent between the underlying Ciply Phosphatic Chalk Formation and the overlying Ciply Calcarenite (of Cainozoic age). Reaches about 10 m in boreholes near Ciply.

Age: Late Maastrichtian on the basis of belemnites (Jeletzky, 1951). The presence of numerous Thecidea papillata and Trigonosemus pectiniformis are good regional markers.

Remarks: References: Rutot & Van den Broeck (1885 a, b), Marlière (1957).