2.5.1 Deerlijk Formation - DEE

Authors: Legrand, 1966; Martin, 1969a.

Description: Mostly grey shale unit, with centimetric to sometimes decimetric alternation of thin fining upward cycles from light grey fine sandstone to medium grey shale, and dark to black graptolitic shale.

Stratotype: Deerlijk, NW of Kortrijk; Van Neste-Verwee borehole (BGS N° 83E404) between depths of -150 to -188,25 m.

Area: Area in the subsurface of the SW of the Brabant Massif.

Thickness: >83 m.

Age: Graptolites described by Legrand (1966, 1968) indicated the acuminatus, vesiculosus and cyphus biozones (Rhuddanian) and the gregarius, convolutus and sedgwicki biozones (Aeronian). A restudy by Maletz (1999) of the lower Rhuddanian Deerlijk 404 borehole confirmed the presence of the acuminatus (from the middle part upward) and the vesiculosus biozones; however the base of the Silurian is not reached in this borehole. A restudy of the graptolites in the Aeronian in boreholes by Zalasiewicz (in Van Grootel et al., 1998), recognised the triangulatus, magnus and ?leptotheca biozones (previously parts of the gregarius biozone), also the convolutus and sedgwicki biozones. The chitinozoans belong to the maennili and alargada global biozones (Van Grootel, 1990 ms; Van Grootel et al., 1998). Both groups prove the presence of Rhuddanian and Aeronian (lower and middle Llandovery).

(J. VERNIERS)