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1.2.13. Hampteau Formation - HAM

Authors: Gosselet, 1873; Asselberghs, 1946; Stainier, 1994c.
Description: The Hampteau Fm starts with the occurrence of gravelly or conglomeratic sandstones overlying the red, green and mottled detrital rocks of the Chooz Fm.  The rocks are characterized by thick masses of sandstones, coarse-grained to gravelly sandstones with disseminated quartz and sandstone pebbles and conglomerate banks alternating with shales and siltstones.  The top of the formation is placed at the last red and green bank underlying the grey shales and siltstones, quickly carbonate bearing, of the St-Joseph Fm.  The colour is very variable: red, green, often mottled or greyish green.  Some banks contain fossils.  The Hampteau Fm is divided into two members, respectively from bottom to top:
·       The Hamoûle Member (141 m thick at Hampteau), in which the sandstones contain crinoids and brachiopods.  A thin sandy layer is rich in ostracods;
·       The Chaieneu Member (432 m at Hampteau), in which pebbles are more abundant within the sandstone beds, conglomerates  more frequent and fossils represented by plant remains.  A thick level of red shale with burrows is situated close to the bottom.
The boundary between the two members is fixed at the last thick bank with macrofauna.
Stratotype: SE of Hampteau, along the road to La Roche-en-Ardenne.
Area: E side of the Dinant Synclinorium, from Hampteau up to the vicinity of the Xhoris fault.
Thickness: The thicknessdecreases to the N :573 m at Hampteau; 360 m in the Aisne valley; 250 m at La Roche à Frène; 45 m at Fagnoul, near the Xhoris fault.
Age: Upper Emsian (Arduspirifer arduennensis) for the Hamoûle Member.  Emsian/Eifelian boundary or Eifelian for the Chaieneu Member (Pro-Vel Subzones of the AP Oppel Spore biozonation).