Microfossils and depositional environment of late Dinantian carbonates at Heibaart (Northern Belgium)

The core intervals of five boreholes in the Dinantian carbonates of the Heibaart area in northern Belgium have been investigated on their microfossil contents and lithofacies. The foraminifers suggest an early Warnantian age. No conodonts have been recovered. Twenty-eight species of ostracodes are described, two of them being new : Bairdia robinsoni nov. sp. and Rectobairdia conili nov. sp. The carbonates consist of bioclastic wackestones, bioclastic-peloid grainstones and algal bindstones. The depositional environment varied from an open marine shelf lagoon in the earliest Warnantian (Cf 6a zone) to very shallow lagoons with a restricted water circulation in the Cf 6a - ß zone. The extreme large size of the ostracode species recovered from the Cf 6a - ß zone is not characteristic of the very shallow lagoon environment. Extremely large ostracodes have also been recognized in other carbonate facies of Dinantian age