The information on this page is a summary description.
The full formal description is available here: Genk Member
| Abbreviation | BbGe |
| Parent unit | Bolderberg Formation |
| Child units | Opgrimbie Facies |
| Lithological description | Fine-grained to fairly coarse-grained sand with lignite and gravel layers (De Meuter & Laga, 1976; Louwye et al., 2020). Lignite is generally dispersed, but can locally form about 3 m thick complexes as observed in the Sibelco sand pit in Opgrimbie (Gullentops, 1963, 1972-1973). Molluscs are generally lacking, but become apparent in the northernmost parts of occurrences, such as the Wijshagen and Molenbeersel boreholes (Deckers & Louwye, 2017). The Genk Member has a modal grain size of 172 ± 12 μm, a clay content of 2.1 ± 0.7% and a D90 of 411 ± 274 μm, based on a small amount of samples (Verhaegen, 2020). One of those samples has a second coarse mode of 623 μm explaining also the large variation in D90. The colour of the sand is yellowish in the east Brabant area, brownish to yellowish in the subsurface in the Hasselt area and becomes white in the easternmost part of Limburg (Opgrimbie Facies). |
| Age | Palynological analysis with dinoflagellate cysts from the Wijshagen borehole indicate deposition during Langhian – earliest Serravallian interval (Deckers & Louwye, 2017; Louwye & Laga, 2008). |
| Thickness | The thickness of the Genk Member is 68 m in the Wijshagen borehole (DOV kb18d48w-B181; GSB 048W0180) and reaches a maximum of 128 m in the Molenbeersel boreholes (DOV kb18d49w-B225 and kb18d49w-B226; GSB 049W0225 and 049W0226) in the differentially subsiding Roer Valley Graben. |
| Area of occurrence | The Genk member is present in the central and eastern part of the Limburg province. |
| Type locality | The type locality is Genk. The first type section defined was in a now disappeared sand quarry near the railway station of Genk (De Meuter & Laga, 1976, after Mourlon, 1898). The Genk Member in the Wijshagen borehole (DOV kb18d48w-B181; GSB 048W0180; depth 94 m and 162 m) is an alternative type section. The Gruitrode borehole (DOV kb18d48w-B186; GSB 048W0185) is a type geophysical borehole (located near the Wijshagen borehole) with the Genk Member expressed by low gamma-ray and high resistivity values between 92 m and 159 m depth. |
| Alternative names | |
| Authors | Louwye, S., Adriaens, R., Deckers, J. Vandenberghe, N. & Verhaegen, J. |
| Date | 01/09/2023 |
| Cite as | Louwye, S., Adriaens, R., Deckers, J. Vandenberghe, N. & Verhaegen, J., 2023. The Genk Member, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Genk-Member |
