Sonnisheide Member

(approved 02/2011)

Authors: Dusar, M. & Lagrou, D.

Name: Derived from Sonnisheide in Houthalen-Helchteren, location of borehole KS29.

Stratotype: Borehole KS29, GeoDoc 062E0280; DOV kb25d62e-B284, Lambert coordinates x = 224190, y = 194595, z (ground level) = 80 m; depth interval: 568 - 633 m. Stratotype selected because of representative geophysical well logs and good quality cuttings which were used for ecozonation (Figure 1).

Description: Greenish grey lightly silty marl (cuttings).

In the many (partially) cored sections from coal exploration boreholes, this member is clearly distinguished and described as glauconite-bearing grey marl, often bioturbated with Gyrolithes (typical for Herve Smectite) and other ichnofossils, transported molluscs, occasional indurated limestone beds; richer in glauconite and more coarse-grained towards the base, seldomwith basal gravel bed.

The Sonnisheide member is rather homogeneous, with average carbonate content of 50%, remaining more sandy in the east and more silty-marly in the west. It consists of glauconitic marls with fine sands or silts. This sequence displays a slight upward increase in clay and carbonate content (Laenen, 2002).

Underlying strata: Asdonk Member, lower part of the Vaals Formation

Overlying strata: white chalk ('Schreibkreide') of the Zeven Wegen Member, lowest member of the Gulpen Formation. Contact by hardground.

Area: Campine basin, with exception of its western margin, corresponding to the subcrop area of Vaals Formation

Thickness: From 568 m to 633 m (65 m) in the stratotype KS29, delineated by geophysical well logs. Generally somewhat thinner, around 30 m in thickness. Thickness variation is in line with general up and down trends for the entire Cretaceous section, indicative for the influence of the Rur valley Graben inversion.

Age: early to late Campanian.

Dinoflagellate Xenascus wetzelii Zone, Exochosphaeridium? Masurii Subzone, Zonule a (Slimani, 2000) present in borehole Turnhout but not in Hallembaye quarry.

Ecozonation Felder 2001: IIa, Id & Ic.