Boeretang Member

The information on this page is a summary description.
The full formal description is available here: Boeretang Member

Abbreviation BmBt
Parent unit Boom Formation
Child units
Lithological description The Boeretang Member occurs in the top of the Boom Clay Formation and exclusively in the subsurface where it is well characterised by geophysical borehole logs. It differs from the underlying Putte Member by its steadily increasing resistivity values on the geophysical log and by the prominent high resistivity values of the silt-enriched layers leading to marked wiggles on the curve. However the grain size of the Boeretang Member, expressed on a silt-sand-clay triangular diagram, is similar to the grain size of the Putte and Terhagen Members (see Vandenberghe et al., 2014 fig. 27 and Frederickx, 2019 fig. 35). The Boeretang Member silt layers that alternate with the clay layers can be well identified in cores. The pronounced expression on the geophysical logs of the silt and clay layers makes it possible to apply a coherent numbering of the silt beds and to correlate boreholes (Figure 2 and 12). The full Boeretang Member detailed lithological layering, including septaria horizons S180, S185, S190 and S200, was established by Mertens and Wouters (2003) (Figure 12 with codes under heading I).
Age The lower part of the Boeretang Member, up to almost S190 level, has nannoplankton biozone NP23. Possibly also biozone NP24 occurs above (De Man et al., 2010). However the presence of the NP24 biozone as reported in literature (see Vandenberghe et al., 2014; Vandenberghe, 2017) is uncertain as the NP24 range figured in De Man et al. (2010), Vandenberghe et al. (2012) and Coccioni et al. (2018) is different from the range in the review in Speijer et al. (2020) and used in the biostratigraphy zonation in Figure 5. The discrepancy is probably linked to the absence in the North Sea Basin of the typical NP24 markers (see discussion in De Man et al. (2010).
Thickness When completely developed with the wiggles 0 to 9 present, the thickness of the Boeretang Member varies between 23 and 29 m.
Area of occurrence The Boeretang Member is typically present in the northern Antwerp Campine subsurface. It is absent in borehole ON-Doel-2b in the west, but eastwards part of the member is already identified in the boreholes Zoersel and Herentals (see Vandenberghe et al., 2001 figs. 5, 6). Further east of the Mol-Dessel area in Limburg, the Boeretang Member evolves into part C of the Eigenbilzen Formation (see 7. and Figure 4).
Type locality The reference boreholes are located in the Mol-Dessel area and in Weelde (SCK-NIRAS 98). The geophysical borehole measurements are presented in Vandenberghe et al. (2001 figs. 5 & 6; 2014 fig. 13) (Figure 2). Foraminifera and dinoflagellate cyst data in the Weelde SCK 98 borehole are described respectively in De Man (2006) and Van Simaeys (2004), and Sr-isotope dating is reported in De Man et al. (2010).
Alternative names Since the particular silty top of the Boom Clay Formation was recognised as an individual component in the wells at Mol, Dessel, Balen and Retie (018E0132), this silty top was designated as ‘transition layers’ (Neerdael et al.,1981). Because the layers within this silty top component can be well correlated on the basis of characteristic resistivity wiggles on logs, the interval has also been designated as ‘10-Wig package’. Based on further subdivisions of the geophysical well log signals in the top of this silty Boom Clay, an informal system W0, W1, W2, W3 was applied in Vandenberghe et al. (2001).
Authors Vandenberghe, N. & Wouters, L.
Date 05/04/2024
Cite as Vandenberghe, N. & Wouters, L., 2024. The Boeretang Member, 05/04/2024. National Commission for Stratigraphy Belgium.


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