Booischot Formation

Introduction of the Booischot Formation, a new formal lithostratigraphic unit for the Devonian in the Campine Basin (N. Belgium).

During systematic lithostratigraphic description of the deep subsurface of the Campine Basin (Northern Belgium) it was found that certain stratigraphic intervals in deep boreholes, already identified and described as separated units by different authors (Laenen, 2003; Lagrou, 2012), are not yet formally named. As one of the goals of the detailed stratigraphic study was to put all data in the Flemish web-based ‘Databank Ondergrond Vlaanderen’ (DOV), codes for the different lithostratigraphic units were needed. To have an accordance between DOV and the Belgium official stratigraphy, the newly proposed lithostratigraphic units are submitted to the Belgian National Commission on Stratigraphy.

For the Devonian lithostratigraphy the Booischot Formation is submitted.

The Booischot Formation is composed of red, green and mottled conglomerates interbedded with gray sandstones and shales. Locally paleosoils are present. In borehole Booischot (GeoDoc 59E146) the 400 m thick sequence can be subdivided in two units: an upper unit of mottled conglomerates, sandstones and quartzites and few thin shale beds in which several paleosoils are developed; and a lower unit dominated by red conglomerates with occassional paleosoils. In the Campine Basin the thickness and presence of the proposed formation are very variable as evidenced by its absence in borehole 007E178 (Heibaart 1/1bis). This is due to the deposition in a half-graben system along the northern boundary of the Brabant Massif (Muchez & Langenaeker, 1993).

The research is financed by the Flemish government (ALBON).

Booischot Formation

Description: Red, green and mottled conglomerates with intercalations of grey sandstones (sedimentary quartzites) and shales (Legrand, 1964). Locally paleosoils are present. In borehole Booischot the sequence can be subdivided in two units:

1. An upper unit (from 892 m to 1085 m) consisting of mottled conglomerates, sandstones and grey quartzites and few thin shale beds in which several paleosoils are developed;

2. A lower unit (from 1085 m to 1288 m) dominated by red conglomerates with occassional  paleosoils, mainly found at the base red sandstones and shales.

Area: In the Campine Basin thickness and presence are very variable as evidenced by its absence in borehole 007E178 (Heibaart 1/1bis). This is due to the deposition in a system of half-graben along the northern boundary of the Brabant Massif (Muchez & Langenaeker, 1993). Similar deposits are described in boreholes nearby the Krefeld High (Nordrhein-Westfalen) by Ribbert (1998).

Stratotype: borehole GeoDoc 059E146 (KB132, Booischot), X 177.651, Y 193.309, Z 12,6 m, 1963. Booischot Formation: depth range 892-1288 m (Legrand, 1964). Named after Booischot, village in the southwestern Campine (province of Antwerp).

Thickness: In the stratotype section the Booischot Formation is 396 m thick and rests unconformably on Silurian rocks of the Brabant Massif and is conformably covered by the Frasnian marine deposits of the Aisemont Formation (Coen-Aubert, 2014).

Age: Between 900,5 m and 1120m, Frasnian and Upper Givetian identified by plants and miospores (Streel & Loboziak, 1987). According to these data the top of the Booischot Formation is Upper Frasnian in age and the Frasnian transgression occurs very late in the Booischot borehole (Streel & Loboziak, 1987; Coen-Aubert, 2014). Below 1120 m, no precise determinations of fossils are available, so no hard evidence about the age of this unit.

References: Coen-Aubert, 2014; Laenen, 2003; Lagrou, 2012; Muchez & Langenaeker, 1993; Ribbert, 1998; Streel & Loboziak, 1987.

Figure 1: Litholog of the Devonian of borehole 059E146 (KB132, Booischot), stratotype for the Booischot Formation. Lithology based on detailed litholog from Legrand, 1963; GeoDoc 059E146 (unplublished).