2.2.2 Andenne Formation
Authors: Dumont, 1832; Purves, 1881; Stainier 1901; Van Leckwijck, 1957, 1964; Paproth et al., 1983.
Description: The Andenne Formation consists of non-marine mostly silty shales, sandstones, thin coal seams (30 to 75 cm) or rootlet beds, with some intercalations of thin marine, goniatite-bearing shales and limestone beds (paralic facies). The cyclic nature is the most characteristic feature of the paralic sediments (Fiege & Van Leckwijck, 1964). Many grits (up to 30 m thickness) and ganisters (bleached quartzitic rootlet beds) have been distinguished at different stratigraphic levels within this formation. Local unit names such as Poudingue houiller, Grès d’Andenne, Gives, Java, Villerot, Salzinnes have been in use (Renier, 1912, 1928).
The Andenne Formation is conformably overlying the much thinner Chokier Formation, but may exceptionally rest directly on older Dinantian strata, as is the case on the Heibaart dome (Campine basin)(Bouckaert, 1967). The Andenne Formation is always overlain by the Châtelet Formation whenever the stratigraphic record is complete.
Stratotype: Java gallery, former Andenne coalfield (cf Paproth et al., 1983).
Area: As for the Belgian Coal Measures Group. Thin coal seams (30 to 75 cm) have been exploited in the Namur and Verviers (Herve) synclinoria.
Thickness: 300 to 800 m, with thinnest sediments in the Namur synclinorium (Andenne transversal ridge) or Dinant synclinorium and increased thicknesses in the Campine basin. Thickness attaining 1800 m is postulated in the northern Campine basin, north of the Hoogstraten listric fault, according to Vandenberghe (1984).
Age: Latest Serpukhovian to early Bashkirian (Chokierian or Alportian to Yeadonian, based on goniatite zonation) or Namurian B-C according to traditional subdivision.
Remark: Originally defined by Dumont (1832) as ‘Houiller avec houille’, including all overlying coal-bearing formations of Westphalian age. More restrictively used by Purves (1881) as ‘Schistes et psammites avec houille maigre’. Used in the actual sense by Stainier (1901) as ‘Assise d’Andenne’.