Houthem Formation - Ho
Authors: Romein (1962), Felder (1975), De Geyter & Laga (1988a).
Description: this marine entity consists of soft, pale grey to pale yellow, mostly coarse and porous limestone with firm shell layers and limestone knolls. The basal part looks more greenish and contains glauconite grains. At the contact with the underlying Maastricht Fm, a hard layer with bioturbations ("hardground") is found.
Stratotype: The section between -240 m and -274 m in the borehole Opoeteren (KS 22 or 63E222) can be considered as a hypostratotype. Sheet 26/2 (Opoeteren). Co-ordinates: x = 238.831, y = 191.238, z = +88 m.
Area: the formation is found in the subsoil of Central and North Limburg and in the northern part of the province of Antwerp. It is locally found in outcrops southwest of Maastricht (Vroenhoven).
Members: the formation is subdivided into following members in The Netherlands (Felder, 1975): Geleen Chalk, Bunde Chalk and Geulhem Chalk.
Thickness: probably maximum 63 m (Turnhout).
Age: Early and Middle Danian.
Remarks: the formation is also discussed by Cogels & Van Ertborn (1886), Felder et al. (1985), Gulinck (1961), Hofker (1957), Legrand R. (1968), Marlière (1968), Mei-jer (1965), Moorkens (1972a, 1982), Slimani (1994), Streel et al. (1977) and Vincent (1928).
Complementary data (M. Dusar, 2011): In the Geologica Belgica volume with the lithostratigraphic scale of Belgium, the Houthem Formation is described as part of the Paleogene Haspengouw Group (Laga, Louwye & Geets, 2001, p. 138). This assignment does not take into account that in boreholes it is very difficult to distinguish the Houthem calcarenites from the underlying Maastricht calcarenites. Lithological arguments should prevail on paleontological arguments and therefore the Houthem Formation should be included in the Chalk Group, as has been done in the Netherlands and the North Sea Basin.
Acknowledgements (DL): The subsurface mapping of the Cretaceous in Flanders is financed by ALBON the Natural Resouces Service of the Land and Soil protection, Subsoil, Natural Resources Division of the Flemish Community.