Mons-en-Pévèle Formation

The information on this page is a summary description.
The full formal description is available here: Mons-en-Pévèle Formation

Abbreviation Mp
Parent unit Ieper Group
Child units
Lithological description Succession of one or a few m thick laminated packages of pure very fine sand (60‐80μm), often cross stratified, and strongly bioturbated clayey sand; the latter are more important closer to the base. The sand is micaceous with commonly very fine glauconite. Several coarser beds are packed with Nummulites, appearing for the first time in the basin in the Mons‐en‐Pévèle Formation. Locally cemented layers occur, a.o. nummulitic limestone beds.
Area of occurrence The Mons‐en Pévèle Formation is occurring southeast of a line through Lille (North France) (see map in King, 1991), from Mons‐en‐ Pévèle (North France) to Tournai and Ronse and further eastwards. Mons‐en‐Pévèle is a locality south of Lille in North France and the name ‘Sables de Mons‐en‐Pévèle‘ was introduced by Ortlieb & Chellonneix (1870, p 27). Towards the east in Brabant, the Ieper Group thins and a typical clayey basal part is distinguished from an upper fine sandy unit. The basal clay corresponds to the Orchies Member of the Kortrijk Formation whilst the sand has been given a lithostratigraphic name, the Vorst/Forest sand. It was shown by King (1991) that these fine sands are equivalent to the Mons‐en‐Pévèle Member. Logically therefore the Bierbeek sand above the Orchies Member in the Leuven area (geological map 1:50 000 sheet 32 Leuven, Vandenberghe & Gullentops, 2001) can be considered as a decalcified sand of the Mons‐en‐ Pévèle Member, in a similar way as the sands above a thin clay unit in north Brabant (Rillaar) and Limburg (e.g. Veldhoven, Beringen) as figured by Gulinck (1967) and discussed by Fobe (1989a). From a nomenclature point of view, in the transition zone of laterally interfingering units such as the Roubaix and Mons‐en Pévèle units, the ICS Stratigraphic Guide recommends that a somewhat arbitrary boundary should be chosen in mapping and borehole description, obviously accompanied by an appropriate explanation in the legend or description. In the case of the Roubaix/Mons‐en‐Pévèle limit the present review suggest that if the unit consists of over 50 to 60% sand layers, the unit should be named Mons‐en‐ Pévèle Fm and otherwise the unit should be classified as Roubaix Member of the Kortrijk Formation. For example the 368‐407 m section in the Mol SCK borehole 031W0237 is mainly described as fine sand with minor clay layers (Gulinck & Laga, 1975) and is therefore to be named Mons‐en‐Pévèle Fm. Localities with Mons‐en‐Pévèle sand are listed in Steurbaut & Nolf (1991, Fig.3) and appear systematically between Ronse and Brussels. According to the lithological description (sand/clay proportion) the log signature in the borehole Merchtem 072E0229 should be classified as the Roubaix Mbr and in the Kester borehole 101W0079 as Mons‐en‐Pévèle Fm. However an inspection of shape of the RES and GR logs allows to consider the boreholes Merchtem (compendium), Meise (see profile Gent‐Zemst and Meise‐ Rotselaar), as transitional signatures between Roubaix and Mons‐en‐Pévèle. The criterion will need further refinement and the study of more wells. Also it has to be recognised that the descriptions of the boreholes, especially if destructive, are often not accurate enough to reliably decide on the number of sand layers. Also if grain‐size data are available, it will be needed to define how exactly to apply the criterion; e.g. at first glance the amount of >62μm fraction in the borehole Kattem (087W0479) south of Aalst (Geological Service Company, 2003) is high enough to describe the unit below the Aalbeke Member as the Mons‐en‐Pévèle Member. The same holds for the application of the GR/RES log values in determining how much sand layers occur in the interval. Maybe the 50‐60% sand layer boundary will need to be changed or maybe it will appear practical to introduce a new transitional lithological unit.
Type locality No formal stratotype has been designated. Logically the Mons‐en‐Pévèle hill south of Lille and north of Douai in North France is the preferred reference area (see Steurbaut, 1998 p 116); also the Waaienberge (Wayenberghe) railway section near Ronse (described in King 1988 (1990) p 359 and figured in Steurbaut & Nolf 1988 (1990) p 328) is a potential stratotype section.
Alternative names
Authors Steurbaut, E., De Ceukelaire, M., Lanckacker, T., Matthijs, J., Stassen, P., Van Baelen, H. & Vandenberghe, N.
Date 09/01/2017
Cite as Steurbaut, E., De Ceukelaire, M., Lanckacker, T., Matthijs, J., Stassen, P., Van Baelen, H. & Vandenberghe, N., 2017. The Mons-en-Pévèle Formation, 09/01/2017. National Commission for Stratigraphy Belgium.


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