The formation of members or members formation (sic; abbreviation: Ld; called for members in East Flanders) is a geological formation in the background of Belgium. The formation consists of shallow lime and glauconite fine sand deposited in the sea covering the north and middle of Belgium during the Eocene (Lutetian).
The name "Sables de Lede" appears for the first time in a publication by M.F. Mourlon (1873). The name "Lédien" was later also introduced by Mourlon (1887). In Dutch, it got the (old) name: Lediaan, or "Zand van Lede" and as a symbol on old maps "Le".
Its typical shape is white, fine sand. The formation of daytime zooms in East Flanders, Flemish Brabant, Antwerp and in parts of Hainaut, Walloon Brabant and West Flanders. The formation consists of a laterally well-palpable layer of lime and glauconite-containing sand, sandy limestone and calcareous sandstone, with a thickness of 10 to 15 meters. The formation is characterized by the frequent occurrence of fossil nummulite Nummulites variolarius, Ditrupa and many nautiluses. It will not be subdivided into members. In Balegem there is a base grind layer rich in recycled fossil shark teeth.
The formation of members they have an age from Central Lutheran (about 44 million years old) and belongs to the Zenne Group. On top of the formation, younger deposits are usually found in the formation of Maldegem (marine sand and clay of Bartonian). Under the formation are mostly the formations of Brussels or Aalter, which also belong to the Zenne Group.
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