Sedimentology and facies distribution of the Lede Formation (Eocene) in Belgium and northern France

In outcrop and borehole sections of the Lede Formation (Eocene, Lutetian) in the Belgian Basin three facies have been recognised. Between Gent, Brussel and Ronse (the Meldert facies), the formation shows a general fining-upward trend in grain size distribution. This facies is characterised by the presence of various gravelly beds on top of erosion surfaces, marking the base of smaller-scale fining-upward sequences. Associated gravel and shell beds and sandy limestones display sedimentary structures typical of storm deposits. In a northerly and westerly direction, coarse-grained beds are missing since the sea here became deeper and the sea floor was no longer within reach of storm waves (the Mont des Récollets facies). Near Ronse, the Lede Formation partly consists of brown medium sand with silicifications (the Einsdale facies). It probably marks the northernmost extension of a very shallow marine deposit. The cyclic sedimentation seen in the Lede Formation has been brought about by tectonic movements of the southern border of the Brabant Massif. The facies distribution of the formation is largely similar to the thickness evolution of the underlying Cretaceous strata, which were also subject to movements of the Brabant Massif.