The information on this page is a summary description.
The full formal description is available here: Brunssum Member
| Abbreviation | KzBr, KzB1, KzB2, and KzPe |
| Parent unit | Kieseloolite Formation |
| Child units | Pey Bed |
| Lithological description | The Brunssum Beds are layered dark lignitic clay and lignite horizons. Brunssum I can be more than 5 m in thickness and composed of several layers and contain larger wood fragments. Brunssum II is generally thinner and then consisting of a single clay layer. Root traces are visible in the clay. A few very thin sand layers can occur. The clayey intervals have marked gamma-ray signals. In between the 2 Brunssum Beds occurs a sand unit, the Pey Bed that can be a few meter to 30 m thick. |
| Age | In the Dutch part of the RVG, the Brunssum Member is considered Pliocene in age (Wong et al., 2007; TNO-GSN 2021). Palynological interpretations of Vanhoorne in Vandenberghe et al. (2005) seem to confirm a Pliocene age. However palynology reported from the Bocholt borehole by Van der Sluys (2000, 2.1.5) compares the pollen in the upper Brunssum I bed with the early Pleistocene clays of the Weelde Formation in Belgium and the Tegelen Member in the Netherlands. Donders et al. (2007) have demonstrated that stratigraphic correlations based on palynology need caution. |
| Thickness | In the reference borehole Bocholt the upper Brunssum I clay bed is almost 18 m and the lower Brunssum II clay bed 6 m. However thicknesses are variable as can be expected from the depositional conditions of the Brunssum clay in floodplain swamps and lakes and from its occurrence in an actively faulted block area in the west of the Roer Valley Graben (RVG). In the Maaseik borehole (049W0220) the upper Brunssum I bed is 12 m thick and the lower Brunssum II bed 5,6 m. Maximal thicknesses are observed in the Kinrooi (049W0230 /kb18d49w-B230) borehole: slightly more than 30 m for the lower clay unit and 20 m for the upper unit. The two Brunssum I and II clay beds can be separated 30 m apart by Pey Sand Bed (see Vandenberghe et al., 2005, fig. 10). |
| Area of occurrence | The Brunssum Member and the Brunssum Beds in Belgium are only recognised in the RVG area east of the Reppel-Heerlerheide faults. |
| Type locality | The Bocholt borehole (033W0153 / kb18d33w-B160) contains two intervals with Brunssum Member clay beds and lignite: 115,20 -133 m and 137,70-143,70 m. In between occurs the Pey Bed. The borehole is cored, sedimentological and mineralogical analyses are available as well as geophysical well logs and also palynological investigations are reported (Van der Sluys, 2000). The combination of marked high natural radioactivity and low resistivity signals allows a clear identification of the Brunssum Beds with respect to surrounding sand units. Regional profiles suggest the consistent existence in the area of at least two Brunssum Beds , labelled I and II (Vandenberghe et al., 2005; Vernes et al., 2018 , annex D fig. 7.5 in which the same beds are labelled B1 and B2), while the profile presented by Dusar et al. (2014) shows also continuity of an additional uppermost clay bed labelled as Ki-k-1 indicating the incorporation of this bed in the Kieseloolite Formation. |
| Alternative names | In the geological map sheet 18-10 Maaseik + Beverbeek (Sels et al., 2001) as in the Maaseik (049W0220) borehole interpretation (Vandenberghe et al., 2005), 2 levels with Brunssum Clay are identified and labelled I and II ; Van der Sluys (2001) labelled these two levels respectively upper and lower. The Brunssum Member defined as a formal unit in the present LIS is the interval between the base of the Brunssum II Bed and the top of the Brunssum I Bed. The Pey Sand Bed occurs in between both Brunssum Beds and is discussed in a separate LIS. In the hydrostratigraphy of the H30-project (Vernes et al., 2018 ; Dusar et al., 2014) the upper Brunssum I is labelled Ki-k-2 and the lower Brunssum II is labelled Ki-k-3. These authors have also introduced an additional uppermost clay level Ki-k-1 still included in the Kieseloolite Formation as defined by these authors ( see LIS Kieseloolite Formation). |
| Authors | Vandenberghe, N., & Dusar, M. |
| Date | 01/09/2023 |
| Cite as | Vandenberghe, N., & Dusar, M., 2023. The Brunssum Member, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Brunssum-Member |
