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4.2.9. Ciney Formation - CIN

Authors: Thorez et al., 1977; Dreesen & Thorez, 1980.
Description: The Souverain-Pré Fm passes laterally to the north-northeast, i.e. in a more inshore direction, to a more sandy facies defined as the Ciney Fm.  Indeed, the Ciney Fm is essentially made up of fine-grained micaceous sandstones and siltstones with nodular limestone intercalations occurring both to the top and the bottom, and with stratified limestones to the top only.  The series starts with metric to plurimetric-thick bars of fine-grained laminated massif carbonate sandstones containing long flattened dolomitic nodules.  Sandstones surmount them, with carbonate nodules alternating with metric-thick beds of grey siltstones and sandstones taking a yellow ocher or orange brown weathering patina (due to iron dolomitic cement).  The main sedimentary structures are planar parallel laminations, cross-beddings, hummocky cross-beddings and load casts.  Its depositional environment has been defined as distal subtidal.  A Dorinne Mbr is distinguished at the lower part of the formation.
The Ciney Fm wedges out northwards where it disappears between the Esneux and Comblain-la-Tour Fms.
In the geological maps Hastière-Dinant (Delcambre & Pingot, 1993) and Achêne-Leignon (Boulvain et al., 1995), the Ciney Fm comprises all the Famennian rocks overlying the Souverain-Pré Fm.  In the Silenrieux-Walcourt geological map (Dumoulin & Marion, 1997), the Etroeungt Fm was distinguished from the Ciney Fm, although both were represented by the same color, as the poor outcrops of the Etroeungt Fm did not permitted an accurate mapping.
Stratotype: Quarries around Ciney, in the Bocq valley.
Area: Dinant Synclinorium.  The Ciney Fm is well developed in the Dinant area, but is lacking in the Ourthe valley, south of Liège.
Thickness: 200 to 300 m for the Ciney and Etroeungt Fms in the Silenrieux-Walcour area; 250 to 300 m in the Dinant area (including 120 m for the Etroeungt Fm at Hastière); > 300 m in the Rosée borehole.
Age: Upper part of the Middle Famennian (Fa2b).  Sc. veliferand P. trachytera conodont zones.