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5.30. Terwagne Formation – TER


Authors: Conil, 1967; Paproth et al., 1983; Hance, 1988.

Description: The formation rests abruptly on the pale, thick-bedded limestones (grainstones) of the Avins Mbr of the Longpré Fm. In the type section, the lower part of the formation comprises brecciated dolostones and thin-bedded limestones (lime mudstones and peloidal grainstones). The middle and upper parts are characterized by limestones of peritidal facies (oolitic and peloidal grainstones, fenestral lime mudstones to packstones). Thin beds of crinoidal limestone (packstones to grainstones) occur in the upper part. The formation is dolomitized and brecciated (Belle Roche Breccia) in places. Fossils are uncommon.

Stratotype: Discontinuous road section, 500 m ENE of Terwagne church (CSA).

Area: NSA, CSA, ASA. The formation is typical of the inner shelf areas. It is present in the Boulonnais (lower member of the Haut-Banc Limestone; Poty, 1994).

Thickness: The thickness is at its maximum of 100-110 m in the type section. It is only of 20 to 35 m in the NSA.

Age: Moliniacian (early Visean). The foraminiferal association is ecological but is probably younger than Cf4a. Rugose corals found in the upper part are indicative of the RC5 Zone (Dorlodotia briarti densa). The Terwagne Fm corresponds to the TST of the third-order sequence 6 of Hance et al. (2001), in the inner shelf.