2.11.2.4. Boeretang Member

Name

The introduction of the term Boeretang Member is the outcome of the extensive borehole investigations related to the subsurface nuclear waste disposal research project at Mol-Dessel and in the whole Campine area by NIRAS-ONDRAF. Boeretang is small locality and it has given its name to an upper interval in the Boom Clay with outspoken silt layering, particularly well expressed in geophysical resistivity logs (Mertens & Wouters, 2003).

General characteristics

The resistivity and also the gamma ray logs show a clear and gradual increase in silt content compared to the underlying Putte Clay Member.The outspoken very silty layers can be correlated layer by layer and numbered 0 to 9 (see a.o. Vandenberghe et al. 2001 and fig.1).In between the silty layers occur normal clay layers.

Conform the NIRAS-ONDRAF practice in the Mol-Dessel area,it is proposed to define the Boeretang Member between the lowest and the uppermost of these silt layers, respectively numbered 0 on the logs (layer 99 on fig.4) and 9 on the logs. The sedi-mentology and the physical properties of the Boeretang Member are closely related to the underlying Boom clay. Above the Boeretang Member, lithology and log signature change to a clear sandy facies that will be designated as the Eigenbilzen Formation.

Occurrence

The Boeretang Member is typically present in the subsurface of the northern Antwerp Campine area.The Member is already partly present in the boreholes of Zoersel and Herentals but it is just missing in borehole Doel 2b (see figures in Vandenberghe et al., 2001).

Stratotype

It is proposed to use the cores from the well Weelde (SCK-NIRAS) as reference. Borehole measurements and micropaleontological data of this well can be found in the studies by De Man (2006) and Van Simaeys (2004).

Other designations

Neerdael et al. (1981) have been the first to draw the attention to this particular silty sediment package in the wells at Mol, Balen and Retie and these authors have desig-nated this interval as the 'transition layers' Because of the correlatable resistivity wig-gles in that interval, the interval has also been designated as 10-Wig package. Based on the subdivisions that could be made on the geophysical well logs in all silty and sandy sediments in the top of the 'Boom clay' an informal system W0, W1, W2, W3 was applied in Vandenberghe et al., (2001) (see also figs. 1,3). The Boertang Member corresponds in this scheme to the top W0, W1 and the basis W2 (see fig.3).