The information on this page is a summary description.
The full formal description is available here: Retie Member
| Abbreviation | MlRt |
| Parent unit | Mol Formation |
| Child units | |
| Lithological description | The Retie Member is a fine-grained pale grey sand unit, with a median grain size around 180 µm and only trace amounts of dispersed glauconite pellets, that occurs underneath the Donk Sand Member of the Mol Formation. At the top of the Retie Member drilling mud is reported to start colouring slightly green, obviously on the condition that at the start clear water is used to make up the drilling fluid. By colour, the Retie Member can hardly be distinguished in boreholes from the overlying Donk Member. In the Retie-Geel-Kasterlee area only a notable size fraction >250 µm in the Donk Formation allows to detect the boundary between both members. Eastwards, in the Mol-Dessel area the grain size of the the Donk Member becomes coarser and the boundary with the underlying Retie Member is clear (Vandenberghe et al., 2020, fig.2). In the Poppel-Rauw Fault area and eastwards of it, a relatively thin but marked high gamma-ray clayey bed occurs on top of the Retie Member sand that is named informally the ‘level 3 clay’ bed and on top of which the drilling mud starts to become green. Below the Retie Member occurs the much more clayey Heist-op-den-Berg Member of the Kasterlee Formation in the Retie-Geel-Kasterlee-Dessel area and the boundary is marked by a clear gamma-ray signal increase in the top of the Heist-op-den-Berg Member. In the Poppel-Rauw Fault area and eastwards of it, occurs a slightly coarser unit, the informal ‘level 1-2 sand’ of the Mol Formation. The top of the latter is indicated by the start of a trend in gamma-ray and resistivity signals whereas in the Retie Member these signals are stable. Although the few grain-size data available in the top of the ‘level 1-2 sand’ suggest a coarser grain size compared to the Retie Member, the gamma ray signal of the ‘level 1-2 sand’ unit is higher (Vandenberghe et al., 2020) requiring further data. |
| Age | It is suggested that chronostratigraphically the Retie Member occurs in the same time interval as the Lichtaart Member of the Kasterlee Formation but that lithostratigraphically it fits in the younger Mol Formation due to the westward migration of the continental over the marine facies during the Neogene (Louwye et al., 2020). See also LIS file Mol Formation for information on the age of this member. |
| Thickness | Between Kasterlee and Mol-Dessel the thickness varies between 7 and 22 m and from the Poppel-Rauw Fault zone and eastwards of it, the thickness is about 25 m. |
| Area of occurrence | The Retie Member occurs from the east of Kasterlee until the Reppel Fault in the east, across which the Kieseloolite Formation occurs (Buffel et al., 2001). It is assumed that the ‘Kasterliaan’ as described in the Hechtel (kb17d47e-B186; 047E0192), Wijshagen (kb18d48w-B181; 48W 180), Helchteren (kb25d62e-B265; 62E 261) boreholes in the Archives of the Belgian Geological survey, as well as the so called Dorperberg sand in the Opitter Molen (GSB048e0151C) outcrop (geological map 26 Rekem) also belong to the Retie Member as discussed in Vandenberghe et al. (2020). |
| Type locality | The reference for the Retie Member is the section between 8 and 19,5 m in the ONDRAF-NIRAS ON-Retie-2 (031W0375) borehole, of which also geophysical data , sediment analyses and a CPT log are available ( Vandenberghe et al., 2020). For the Retie Member occurring east of Kasterlee, gamma-ray logs are interpreted (ON-Retie-1; ON-Dessel-3; ON-Dessel-4; ON-Mol-2B). An additional reference geophysical expression on the gamma-ray log of the Retie Member together with the informal ‘level 3 clay bed’ above it and the informal ‘level 1-2 sand ‘ unit below it is the Postel SCK 13 borehole (032W0415 / kb17d32w-B385) between 69 and 92 m depth. |
| Alternative names | ‘Lower Mol’ or ‘Kasterlee-sensu-Gulinck’ unit / including Dorperberg sand as discussed in Vandenberghe et al. (2020) |
| Authors | Vandenberghe, N., Berwouts, I. & Vos, K. |
| Date | 01/09/2023 |
| Cite as | Vandenberghe, N., Berwouts, I. & Vos, K., 2023. The Retie Member, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Retie-Member |
