Critical Evalution of Fossil Reports and Biostratigraphical Synthesis of the Ordovician of Belgium

In Belgium, lower Palaeozoic deposits, mostly siliciclastics, are known from six Caledonian massifs (or inliers), namely (roughly from north to south) the Brabant Massif, the Condroz, Stavelot–Venn, Rocroi, Serpont and Givonne inliers, the last four being collectively referred to as the Ardenne inliers. Fossil occurrences have been reported in these rocks on several occasions, since the pioneering discoveries in the early 19th century, but most of these records lack illustrations. Unfortunately, recent re-examinations of historical collections have not confirmed the authenticity of several reports of Ordovician fossils mentioned in the literature. In the Ardenne inliers, only graptolite and brachiopod macrofossil records can be accepted. All other records (trilobite, phyllocarid, sponge and bivalve) appear to be non-biological artefacts. The Brabant Massif and the Condroz Inlier provide some macrofossil groups, usually with very low numbers of specimens, and sometimes tectonically distorted. Many of the historical collections need re-examination, but a few identifications can be confirmed. Fortunately, research on organic-walled microfossils, primarily acritarchs and chitinozoans, is providing significant biostratigraphic insights for the Cambrian–Ordovician siliciclastic successions. This paper reviews a selection of fossil and ichnofossil reports in the literature devoted to the Ordovician of Belgium, from pioneering times to the present day. It presents a synthesis of the Ordovician of Belgium, that is clearly associated with the easternmost part of the microcontinent Avalonia.