Eocene sediment supply in western Belgium as determined through heavy mineral distribution

The distribution of heavy minerals in Middle to Upper Eocene deposits of western Belgium is discussed with reference to ternary diagrams based on density (<3.4; 3.4-4.2; >4.2) and mineralogical composition (ubiquist, parametamorphic and garnet-epidoteamphibole-pyroxene groups). A corresponding diamond diagram is used to interpret the transport mode and the energy of the sedimentary environment. The Aalter Formation (middle Eocene), which was deposited in a quiet to turbulent coastal setting, contains high amounts of ubiquists, parametamorphic minerals and garnets, with a minor epidote and amphibole content. The Maldegem Formation (middle to late Eocene) of deltaic origin, is characterised by the dominance of ubiquists, particularly in the sands and silts. Garnets, parametamorphic minerals and small amounts of epidotes also occur. The heavy mineral distribution of the Zelzate Formation (late Eocene), an intertidal sand flat deposit, is similar to that of the Maldegem Formation, although it contains fewer parametamorphic minerals and more epidote and amphibole. Intrastratal dissolution of garnet due to subaerial weathering or continuous ground water flows occurred under shallow burial of the Maldegem and Zelzate formations in part of the study area. On the basis of palaeogeographical considerations, it is concluded that the Middle and Upper Eocene sediments were supplied by a precursor of the Rhine-Meuse-Scheldt delta sourced from western European massifs. This is opposed to earlier suggestions assuming a northerly origin from the British Isles or Fennoscandia.