5.5 Engihoul Formation - ENG

Author: Poty, this paper.

Description: The formation includes a lower member of thick-bedded to massive, brown to dark, dolomite, with some calcite nodules, and an upper member of crinoidal dolomite with layers of dolo-mudstone and prismatic calcite, very rich in pluricentimetric to pluridecimetric nodules of coarse calcite, pluricentimetric prismatic calcite and sometimes quartz. The top of the formation is locally karstified and its upper member missing. It is overlain by the Flémalle Mbr (Longpré Fm).

Stratotype: Engihoul quarry, on the southern side of the Meuse valley (Conil et al., 1988), near the Engis bridge (NSA).

Area: The formation is known only in the eastern part of the NSA.

Thickness: About 75 m in the stratotype where the upper member is 15 m thick.

Age: Late Hastarian to early Moliniacian. The basal beds overlie the Pont d’Arcole Shales and yield rugose corals of the base of the RC2 Zone, suggesting that the lower member of the formation could correspond to a dolomitized equivalent of the Landelies Fm. The crinoidal layers of the upper member yield Sychnoelasma hawbankense, a guide of the RC4aCoral Subzone. There is probably a stratigraphic gap between the lower and upper members, corresponding to the Ivorian. The lower member probably corresponds to the HST of the third-order sequence 2 of Hance et al. (2001), and the upper member corresponds to the lower part of the HST of the third-order sequence 4.