|Ostracods and lithofacies close to the Devonian-Carboniferous boundary in the Chanxhe and Rivage sections, northeastern part of the Dinant Basin, Belgium|
Casier, J.-G.; Lebon, A.; Mamet, B.; Préat, A. (2005). Ostracods and lithofacies close to the Devonian-Carboniferous boundary in the Chanxhe and Rivage sections, northeastern part of the Dinant Basin, Belgium. Bull. Kon. Belg. Inst. Natuurwet. Aardwet. = Bull. - Inst. r. sci. nat. Belg., Sci. Terre 75: 95-126
In: Bulletin van het Koninklijk Belgisch Instituut voor Natuurwetenschappen. Aardwetenschappen = Bulletin de l'Institut Royal des Sciences Naturelles de Belgique. Sciences de la Terre. KBIN: Brussel. ISSN 0374-6291, more
Carboniferous; Devonian, Upper; Lithofacies; Ostracoda [WoRMS]; Belgium, Sprimont [Marine Regions]; Marine
Ostracods, Sedimentology, Paleoecology, Devonian-Carboniferous boundary, Dinant Basin, Belgium
The Chanxhe and Rivage sections along the Ourthe River are two important reference sections for the Devonian/Carboniferous (D/C) boundary in the northeastern part of the Dinant Basin. Seven major microfacies types are defined in the D/C strata (50 m) of these two sections. They permit recognition of several levels encompassing the Comblain-au-Pont and Hastière formations. These levels record shallow open-marine sedimentation oscillating between the storm and the fair-weather wave bases in the euphotic zone. The microfacies in the upper part of the sections (Hastière Formation) indicates strong salinity variations with evaporitic reflux and lagoonal influences. The environment is again open-marine in the uppermost part of the Hastière Formation. The general environment consists of small shoals which have partly isolated an offshore domain (MF1-MF4) from a semirestricted area (MF6 and MF7) where salinity fluctuations were the predominant factor as indicated by monospecific fauna and flora (Earlandia, umbellinids, calcispheres, ...). Only ostracods and Earlandia minima (foraminifers) survived in these stressful environments. These organisms are related to cryptalgal bindstones or mats located at proximity and forming numerous "algal chips". The abundance of sulfate pseudomorphs in MF5, MF6 and MF7 indicate the importance of the diagenetic reflux of evaporitic brines in this general shallow marine environment. The main diagenetic overprint is the development of clear sparite cements replacing the original textures.The foraminiferal zonation indicates hiatuses throughout the series. Ostracods are moderately abundant in the Chanxhe and Rivage sections and sixty-two taxa, the majority of which are in open nomenclature, are recognized; nearly all are illustrated, and one new species (Cavellina chanxhensis nov. sp. ) is established. They belong to the Eifelian Mega-Assemblage and practically all samples containing identifiable ostracods contain podocopid ostracods indicative of well-oxygenated water conditions with salinity normal or very close to the normal. The abundance of Platycopina and Eridostraca (Cryptophyllus) in the Comblain-au-Pont Formation indicates a deposition in a very shallow slight restricted environment. Due probably to the strong salinity variations pointed out by the sedimentological analysis, ostracods are missing, rare or poorly preserved in the top of the Comblain-au-Pont Formation and in the base and middle part of the Hastière Formation. However, no assemblage indicative of really semi-restricted water conditions was recorded in these levels probably because these variations of salinity were too strong and (or) too rapid. In the upper part of the Hastière Formation, ostracods are very abundant and indicative of marine environments between fair-weather and storm wave bases. The distribution of ostracods in the Chanxhe and Rivage sections is slightly different compared to sections investigated in the southwestern border of the Dinant Basin and in the Avesnes Basin. The study of ostracods at Chanxhe and Rivage confirms also that the Hangenberg Event has probably no influence on their distribution in shallow settings.Our conclusion is that the Chanxhe and Rivage sections are not reliably continuous successions for the study of the D/C boundary.