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1.2.19. Acoz Formation - ACO

Authors: Legend of the geological map of Belgium at the scale 1/40,000, 1892; Asselberghs, 1946; Dejonghe, Hance & Steemans, 1994d.
Description: Detrital rocks mainly of maroon (red) colours characterize the Acoz Fm.  The lower boundary is fixed at the first maroon (red) siltstone and argillaceous sandstone layer overlying the quartzites of the Bois d'Ausse Fm.  The upper boundary is situated below the sandstones and quartzites of the Wépion Fm.  Two members are distinguished at the stratotype, respectively from bottom to top:
·       The Bième Member (140 m) : essentially made up of maroon (red) siltstones and shales;
·       The Ruisseau d'Hanzinne Member (160 m): containing progressively more maroon (red) sandstones and m to several m-thick layers of quartzites, generally light-coloured in the maroon (red), pinkish, greenish or yellowish shades.  Quartzites often contain pebbles of maroon (red) shales.
This division in two members is questionable at other places and is certainly not valid in the Vesdre Nappe (there, light-coloured quartzites are concentrated at the bottom and not at the top of the formation).
Stratotype: Acoz, Bième and Hanzinne valleys, between the old quarries of the Bois de Châtelet and the Bois d'Acoz.
Area: N and E flanks of the Dinant Synclinorium and in the Vesdre Nappe.
Thickness: 300 m to the W of the Meuse and 400 m to the E.  The thickness varies much in the Vesdre Nappe, depending on the erosion level of the Vicht Conglomerate (thickness = 250 m at Eupen, < 50 m at Pépinster, 0 m at Heusy).
Age: Pragian (Su Subzone of the PoW Oppel Miospore Biozonation N and E of the Dinant Synclinorium; Po-W to Su Subzones of the PoW Oppel Miospore Biozonation in the Vesdre Nappe).