2.11.3. Eigenbilzen Formation - Eg
Name
The sandy unit lying above the Boom Clay was already recognised in Limburg by Van Den Broeck (1884, 1893), and denominated by the symbol R2d. Gulinck (see for instance BGD-document MG/75/338) introduced the term Eigenbilzen Sands while describing wells. Eigenbilzen is a dependant municipality of Bilzen (Limburg province).
General characteristics
The Eigenbilzen Formation consists of dark green, glauconite rich, clayey, fine-grained to medium-grained sands, with bioturbations. As in the Boom Formation, a banded structure caused by grain size variations is observed in the outcrops along the Albert Canal. The thickness of the clayey sands can in the subsurface amounts up to more than 50 m.
Occurrence
The formation crops out along the Albert Canal east of Hasselt. Well log analysis in the Antwerp and Limburg provinces indicates the systematic presence of these sandy deposits east of the Mol-Rauw fault and its southern extensions. Furthermore the unit can be divided into informal subunits characterised by an upward increase in grain size (see fig. 1). Matthijs (1999) defined and subdivided in an analogue way the Ei-genbilzen Sands while drawing the geological map Hasselt (1/50.000, explanations, fig. 10).
Sandy and silty deposits are present above the Boom Clay west of the Mol-Rauw fault (Mol area and north more to the north). These deposits can also be divided in several subunits. The formal lithostratigraphic scheme distinguishes a lower Boeretang Mem-ber (belonging to the Boom Formation) and above even more siltier and sandier deposits, attributed to the Eigenbilzen Formation. More subunits can be recognised within the unit based on geophysical well logs (fig. 3). In the Antwerp Campine area, the uppermost clay layers disappear in the Eigenbilzen Formation (see fig. 3).
These silty to sandy layers west of the fault have most probably no direct genetical or sedimentological relation with the Eigenbilzen Formation east of the fault. However, for practical reasons, it is advisable to incorporate all silty and fine-grained layers, between the underlying Boom Caly and the superjacent Voort or Berchem formations, into the Eigenbilzen Formation. This is analogous and conform with the practice of including - more to the east - the sandy facies between the Boom Clay and the Voort Formation in the Eigenbilzen Formation (see Matthijs, 1999; see also well logs in Vandenberghe et al., 2001).
A detailed sedimentological analysis of the Eigenbilzen Formation is still lacking. It is however to be expected that the well log subdivisions from the east (see a.o. Vandenberghe et al., 2001, fig. 15), and the deposits west of the Mol-rauw fault, will be elevated to the status of member. This can be anticipated since the Eigenbilzen Forma-tion in the Mol area (above the Boertang Member) displays a noteable lower sand fraction than at the Albert canal sluices near Diepenbeek and Hasselt.
Stratotype
No permanent outcrops exist. The sands have been studied in the temporary outcrop when sluices were installed on the Albert Canal near Diepenbeek and Hasselt (Vandenberghe, 1974), and during the enlargement of the latter canal near Gellik (Steurbaut et al., 1999). The latter outcrop allowed a calibration of the boundary between the Boom Clay and the Eigenbilzen Sands near the place of the original definition, i.e. Eigenbilzen (see Halet, 1932; Vandenberghe et al., 2001). The lower part of the Eigenbilzen Formation appears to become more sandy towards the north (see also Mat-thijs, 1999, fig. 11).
Reference sections with geophysical well logs and analysed core samples are ap-praently non-existent.
Former designations
Geological map 1/40.000: R2d
Stratigraphical register (1929, 1932): no entry
Halet, 1932: R2d
New geological map: Eg.