The ‘black marble’ of Denée, a fossil conservation deposit from the Lower Carboniferous (Viséan) of southern Belgium

The palaeoenvironment of the ‘black marble’ of Denée [Dinant sedimentation area (DSA), southern Belgium], included in the Molignée Formation of Lower Carboniferous (Viséan) age, is discussed. This fossil conservation deposit (‘fossil Lagerstätte’) yielded a rare but remarkably preserved macrofauna (including fishes, echinoderms and brachiopods). It developed in a confined intra-platform basin progressively filled by distal calcareous turbidites originating from the southward prograding shelf to the north. This basin was bordered to the south by a discontinuous barrier of Waulsortian mud mounds built against a major synsedimentary fault separating the DSA from the southern Avesnois sedimentation area (ASA). The alternations of laminated (‘black marble’ facies) and bioturbated (‘thick-bedded’ facies) lithofacies occurring within the Molignée Formation imply that the palaeoenvironment recorded several anoxic to dysoxic periods alternating with more oxygenated ones due to sea-level fluctuations of low magnitude and was strongly influenced by the basin architecture inherited from the late Tournaisian.