Kortemark Member

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

Abbreviation TtKo
Parent unit Tielt Formation
Child units
Lithological description A grey silty clay unit with sandy layers of several dm thickness have been observed near the base. The presence of silt and sand is distributed in layers of cm to dm. Several subunits can be distinguished as proposed by Jacobs et al. (1996a, b) and Steurbaut (1998). The Kortemark Member occurs between heavy clay units: the Aalbeke Member below and the Egemkapel Member above. The maximal thickness is about 25 m (Geets et al., 2000). In the top of the underlying Aalbeke Member a gradual coarsening upwards occurs, ended by a sharp coarsening that marks the start of coarser sediments in the Kortemark Member (see analyses from Geets (1991) and interpreted in Steurbaut (1998)). In geophysical log patterns the start of the coarsening upwards interval in the Aalbeke Mbr above its very clay‐rich main part, as well as the sharp coarse shift at the top of the coarsening upwards part of the Aalbeke Mbr which marks the position of a fine sand layer, can be observed fairly consistently (e.g. Torhout 052E0195, Tielt 053E0061, Gent 55W1020, On‐Kallo 1 014E0355). The formal boundary between the Aalbeke and Kortemark Members is drawn at the position of the major grain‐size shift and the income of the first fine‐sand layer (correlation profiles in Welkenhuysen and De Ceukelaire, 2009). This boundary definition at the base of the lowest fine‐sand layer has the advantage to correspond to an observable horizon with water outflow in the upper part of the Desimpel clay pit in Kortemark (Steurbaut, 1998, Fig.5). Detailed lithological analyses of the Kortemark Member sections in the Tielt borehole 068E0169 and the Kortemark and Egem extraction pits, are figured in Geets (1991) and Steurbaut (1998, p 117). Details in the geophysical well log signature in the Kortemark Member can be correlated between wells, especially the significant higher values of the resistivity, standing for more sandy layers, can be correlated between the different logs.
Area of occurrence The Kortemark Member occurs north of Kortrijk and in particular in the west of Flanders where it can reach 25 m thickness. It is also known towards the east and northeast of Flanders (Antwerp Province) where it becomes thinner. In the southeast of East Flanders and the neighbouring eastern Brabant provinces, the Mont‐Panisel Member overlies the Aalbeke clay Member in Kerksken (086E0340) and Kattem (087W0479) (Geological Service Company, 2003), implying the disappearance towards the east of the Kortemark Member and the Egemkapel Member (see also Mont‐Panisel Member). Also on the map sheet 23 Mechelen, Buffel et al. (2009) note that the Kortemark Member disappears to the east and is only present in the western part of the map. In the 1:40 000 geological map legend the Kortemark Member is included in the Yc unit and in the Stratigraphic Register of the Conseil Géologique(1929) and the Aardkundige Raad (1932) in the Y1a division. In the Bolle & Jacobs (1993) nomenclature the unit Yd1c unit is tentatively correlated to the Kortemark Member. In the present review the Yd2 unit of these authors, a 5 m densily packed fine glauconitic sand underlying the Egemkapel clay Member, is also included in the Kortemark Member, notwithstanding its resemblance to the Egem Sand above. (see also Egemkapel Member)
Type locality Steurbaut (1998) has proposed the level of about 71m below surface in the Tielt borehole (068E0169); map sheet 21/6 x=76.439; y=187.576; z=48) for the lower boundary with the underlying Aalbeke Member. However, in‐the-present‐text the base of Kortemark has been replaced at a level in the Kortemark Desimpel quarry corresponding to the level at 48 m depth in the Tielt borehole according to the log interpretation Tielt 053E0061 in the compendium. Indeed because the top of the Aalbeke Member gradually becomes siltier upwards (see analyses in Steurbaut, 1998 fig. 5) it has been argued in‐the‐present‐synthesis that the first marked sandy layer in the Desimpel clay pit in Kortemark (marked as ‘ sharp junction waterflow’ at the base of subunit C in Steurbaut 1998 p 117) (map sheet 20/3‐4 Kortemark‐Torhout, x= 57.050,y= 190.400, z= +16m) is a more easily recognisable lithostratigraphical horizon to mark the base of the Kortemark Member. In the present review this level is chosen as the formal boundary between the Aalbeke and Kortemark Members (see discussion in Description above). The top of the Kortemark Member has during many years (80’s and 90’s) been exposed in the classical Egem extraction pit – 053W0060 (map sheet 21/1, x= 70.150, y= 190.150) as an erosive contact with the overlying Egemkapel (see Steurbaut, 1998, p 117).
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 Kortemark Member, 09/01/2017. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Kortemark-Member


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