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old Kortrijk Formation - Ko replaced 01/2017

Authors: Geets (1988a), Steurbaut (1998).

Description: the formation is an essentially marine deposit, consisting mainly of clayey sediments.

A standard sequence contains from bottom to top:

- an alternation of horizontally laminated, glauconiferous clayey sands or sandy clay, and compact, silty clay or clayey silt, locally bioturbated. The base consists of oxidized and indurated clayey sand, with lenses of pure sand;

- a homogeneous deposit of very fine silty clay, with some thin intercalations of coarse silty clay or clayey, very fine silt;

- a less homogeneous deposit of clayey, coarse or medium silt, with some sand containing layers; fossil rich layers occur; the whole deposit becomes more sandy to the east and the south;

- a very fine silty clay.

To the east, in the Brabant and the Campine, and towards the Mons basin, the deposits become more sandy.

Stratotype: the formation is defined by boundary stratotypes (Steurbaut, 1998). The lower boundary stratotype is placed at 288 m depth in the Knokke borehole at the base of the Het Zoute Mbr. Sheet 5/6 (Westkapelle). Co-ordinates: x = 78.776, y = 226.37, z = +4.91 m. The upper boundary is placed at 71 m depth in the Tielt bore-holes at the top of the Aalbeke Mbr. Sheet 21/6 (Wakken). Co-ordinates: x = 76.425, y = 187.55, z = +48 m.

Area: the formation is found in the western and central part of Belgium. It outcrops in the north of Hainaut, the southern and central part of West-Flanders, the south of East-Flanders Flanders and the southwest of Brabant. Outliers occur in the Mons Basin and south of the river Sambre.

Thickness: 125 m in the northern part of West-Flanders, but the thickness decreases in eastern and southern direction.

Members: the formation is subdivided into the Het Zoute Mbr, Mont Héribu Mbr, Orchies Mbr, Roubaix Mbr and the Aalbeke Mbr.

Age: Early and Middle Ypresian.

Remarks: the formation is also discussed by Cornet (1874), De Ceukelaire & Jacobs (1998), De Coninck (1973), De Coninck et al. (1983), De Heinzelin & Glibert (1964), De Moor & Geets (1975), Geets (1990), Gosselet (1874), Gulinck (1965a, 1967), Gu-linck & Hacquaert (1954), King (1990), Laga et al. (1980), Lyell (1852b), Maréchal (1993), Ortlieb & Chelloneix (1870), Steurbaut (1988), Steurbaut & Nolf (1986), Vandenberghe et al. (1990) and Wouters & Vandenberghe (1994).