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2.5.8 Petit Roeulx Formation - PER

Authors: Doremus & Hennebert, 1995.

Description: Cleaved mudstones and siltstone (called "phyllades" in older literature), with decimetric beds of obliquely stratified sandstone and other thin sandstone beds; variable colours from unweathered greenish grey, dark grey to black to weathered light yellow. Sedimentologically an alternation of distal turbidites and laminated hemipelagites. The variations in frequency and thickness of the sandstone beds allows to distinguish two recurrent types: (1) Brainette type: sandstone beds of a few mm to 2 cm separated by mudstone beds of 10 cm to >100 cm; (2) Senne type: thicker and more frequent sandstone beds, 2 to 10 cm thick, separated by mudstone beds of 2 to 20 cm. Pyrite cubes or their weathered rusty remnants are present in the upper third of the formation. Mica is rarely present.

Stratotype: Brainette type in the Brainette valley, between Petit-Roeulx-lez-Braine and Braine-le-Comte; in the abandoned quarry near the hamlet Pirou or behind a chapel near the confluence of the Brainette and the Ri Ceriseau; Senne type in the Senne valley south-west of the village Steenkerque in outcrops near the Ferme de l’Hotel or near the Ferme d’Horruette.

Area: Brabant Massif; outcrop area: Senne, Sennette and Thisnes valleys (Nivelles).

Thickness: Senne valley: about 430 m.

Age: Silurian, middle to upper Wenlock, based on chitinozoans, Cingulochitina cingulata global biozone (Verniers, pers. comm. 1995 in Doremus & Hennebert, 1995).