The information on this page is a summary description.
The full formal description is available here: Merlin Member
| Abbreviation | MER |
| Parent unit | Vert Galand Formation |
| Child unit | |
| Lithological description | The Merlin Member corresponds to the traditional “Fortes Toises”. In the type area it could be observed in temporary and partial outcrops along the TGV line (Hennebert & Doremus, 1997a, b). It consists, from top to bottom of: – white chalky marl, with grey silicified concretions; – grey-white marl with greenish shine, with fine glauconite. In the area transitional to the Mons basin (Péruwelz, Hennebert, 1999a, b) the member is not subdivided in successive units but consists of grey marls to grey-white marly chalk with dull partly silicified concretions (“chailles”), better corresponding to the original definition as “Fortes Toises”. In the parastratotype area of the Flemish region observations are based on cores and geophysical well logs, allowing a less detailed but more consistent description. Cuttings (95W0153) consist of bright green silty marl in the upper part, mixed with fine glauconitic sand in the lower part. The core consists from top to bottom of light greenish chalk with oxidised specks of iron sulfide, turning into green silty chalk with clay laminations containing shell debris, with a basal layer of white very coarse-grained and porous chalk. The gamma-ray log allows to recognize two sequences in the Merlin Member, delineated by beds which show an increase of the gamma ray readings; these probably correspond to the more sandy glauconiferous base of a fining upwards sequence, grading into white chalks. Overall a steady increase in gamma ray level is observed from top to bottom of the Vert Galand Formation. Although the stratigraphic succession observed in boreholes in the Flemish region may be deposited in a more distal part of the sedimentary basin compared to the Tournaisis and does not show the silicifications (which are observed at a higher level and included in the overlying stratigraphic unit) it seems to confirm the subdivision in two units in the type area. |
| Age | Middle to Upper Turonian (from Hennebert & Doremus, 1997a, b); late Turonian (from Robaszynski et al., 2001). |
| Thickness | In the type area from 5 to 10 m. Parastratotype area of the Flemish region: 23 m in the parastratotype 1 095W0153, 10 m in parastratotype 2 110W0007. The thickness in parastratotype 1 appears slightly anomalous as the average regional thickness is in the order of 10-12 m. |
| Area of occurrence | As for the Vert Galand Formation. |
| Type locality | No formal stratotype defined. Nominal decimal geographical coordinates for Merlin 50,553 – 3,401; Lambert ’72 coordinates 81425 – 138500. Parastratotypes for the Flemish region: Parastratotype 1: Borehole GeoDoc 095W0153, Nieuwkerke Noordhoek, drilled 1985 by VMW (De Watergroep) as their cored borehole K11 (top of cored interval 190,78 m, continuing into underlying Paleozoic section). Lambert coordinates x = 40880, y = 162250, z (ground level) = 32 m; depth interval: 169 – 192 m. Stratotype selected because of presence of a core in the lower part of this member (no geophysical well logs over this interval). Parastratotype 2: Borehole GeoDoc 110W0007, Nieuwkerke-De Seule. Lambert coordinates x = 40290, y = 157985, z (ground level) 19,5 m; depth interval 136 – 146 m. Parastratotype selected because of presence of a geophysical well log over the corresponding depth interval. |
| Alternative names | |
| Authors | Dusar, M. |
| Date | 01/12/2017 |
| Cite as | Dusar, M., 2017. The Merlin Member, 01/12/2017. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Merlin-Member |
