Aalbeke Member

The information on this page is a summary description.
The full formal description is available here: Aalbeke Member

Abbreviation KoAa
Parent unit Kortrijk Formation
Child units
Lithological description A very compact heavy clay without sand fraction of some 10 m thickness sharply contrasting with more silty to fine sandy overlying (Tielt or Hyon Formations) and underlying units (Roubaix Member or Mons‐en‐Pévèle Formation). The Aalbeke Member is mostly non calcareous. Small pale brown to yellow phosphate nodules are common in the Aalbeke Member. It can be pointed out that this pure clay unit is relatively thin and therefore can be mistaken for other even thinner clay units above, namely the Egemkapel and the Merelbeke units. To unequivocally identify these different clay‐rich layers, a complete vertical succession is often required or support by micropaleontological characterisation. In most geophysical log responses the lower boundary of the Aalbeke Member is sharply marked; at present there is no field outcrop of the contact between the Roubaix and Aalbeke Members. It is strongly suspected that the top of the Aalbeke Member is an erosive contactas it is overlain by different lithological units in different areas: in clay pits in Aalbeke, it is overlain by the Mont‐Panisel Member of the Hyon Formation, in central Flanders by the Kortemark Member, and in SE Flanders and Brabant by the Hyon Formation. Also, at the base of the overlying Kortemark Member in the De Simpel clay‐pit erosion can be observed (Steurbaut, 1998; Vandenbergh et al., 1998). The upper boundary can be sharp (e.g. Kerksen borehole 086E0340 in compendium, data Geological Service Company; Brugge ‐ 023W0454) or more generally the upper part of the clay unit shows a gradual coarsening upward. In the latter case, the upper boundary of the Aalbeke Member in contact with the Kortemark Member is put at the top of this coarsening upwards section.
Within the Aalbeke Member outcrops in the Kortrijk area a pronounced pinkish silty layer of some dm thickness occurs. It might serve as a stratigraphic marker bed. However the bed is not given an official bed status as it is not yet established that only one such layer occurs in a complete Aalbeke Member section.
Area of occurrence The Aalbeke Member is exposed in the hills around Kortrijk, where also the type locality Aalbeke is located, and in the adjacent border area of north France where it corresponds to the ‘argile de Roncq’ (see De Coninck, 1991 fig.9). It occurs in the subsurface of the whole Flanders and has an average thickness of about 10 m varying between 5 and 15 m. On the geological maps 1:40 000 the Aalbeke Member was part of the Yc unit and in the Stratigraphic Register of the Conseil Géologique (1929) and Aarkundige Raad (1932) it is part of Y1a. In the Kortrijk area, on the 1:40000 sheets it was mapped erroneously as the ‘P1m’ unit (Merelbeke Member of the Gentbrugge Formation).
Type locality Several clay pits exist in Aalbeke and the De Witte clay pit, the extension of the now filled‐up Kobbe clay pit – DOV kb29d97e‐B989 (X = 68.450, Y = 164.300, Z = + 49 m), designated as stratotype by Steurbaut (1998) (map sheet 29/5‐6 (Mouscron ‐ Zwevegem), is the logical new unit stratotype locality.
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 Aalbeke Member, 09/01/2017. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Aalbeke-Member


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