Ostracodes et lithologie du stratotype de la formation du mont d'haurs (Givétien, Synclinorium de Dinant)

The stratotype of the Mont d'Haurs Formation (Early Givetian, Polygnathus timorensis conodont Zone) is composed of a thick alternation (>130 m) of massive limestones rich in stromatoporoids and corals, and of thin beds of finely granulated limestones. The environment is open marine, shallow (in the photic zone) and is characterized by strong energy fluctuations along a proximal-distal gradient from an inner shelf where numerous bioconstructions with stromatoporoids and corals (tabulata and rugosa) developed. The constructors display numerous mutual encrustment relations and are frequently fragmented. The reworking is mainly due to storms activities, sometimes to the swell. Crinoidal meadows and Girvanella mats are destroyed, and their products were mixed with other benthic bioclasts (brachiopods, ostracods, mollusks, bryozoa and algae). More than 5,000 ostracods have been extracted from 95 samples in the top of the Terres d'Haurs Formation and in the Mont d'Haurs Formation. Sixty-six ostracod species are recognized and they belong exclusively to the Eifelian Mega-Assemblage. In the Mont d'Haurs Formation, the associations of ostracods are indicative of shallow well oxygenated marine environments. Sometimes ostracods indicate the proximity of agitated environments. This study of ostracods of the Mont d'Haurs Formation is the last of a series on the Mont d'Haurs geological structure. One hundred and sixteen ostracod species have been recognized from the upper part of the Hanonet Formation to the upper part of the Mont d'Haurs Formation. They give evidence for the frequent changes of the sedimentation conditions during the Early Givetian in the locality-type region for the Givetian since lagoonal, semi-restricted, agitated shallow to deep calm marine environments are recognized.SCOPUS: ar.j