|Ostracods and sedimentology of the Devonian-Carboniferous stratotype section (La Serre, Montagne Noire, France)|
Casier, J.-G.; Lethiers, F.; Préat, A. (2002). Ostracods and sedimentology of the Devonian-Carboniferous stratotype section (La Serre, Montagne Noire, France). Bull. Kon. Belg. Inst. Natuurwet. Aardwet. = Bull. - Inst. r. sci. nat. Belg., Sci. Terre 72: 43-68
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; Ostracoda [WoRMS]; France, Languedoc-Roussillon [Marine Regions]; Marine
Ostracods, Sedimentology, Devonian-Carboniferous boundary, GSSP, Montagne Noire
|Authors|| || Top |
- Casier, J.-G., more
- Lethiers, F.
- Préat, A., more
Despite their low abundance, ostracods are very diversified in the La Serre Devonian-Carboniferous (= D-C) Global Stratotype Section and Point (= GSSP). Seventy-one species are identified, 58 in the Devonian and 29 in the Carboniferous. The ostracod fauna is composed of ostracods belonging to the Eifelian ecotype alone or to a mixed assemblage of the Eifelian and Thuringian ecotypes. The relative abundance of these two ecotypes, the abnormal number of instars in some beds, the presence of ostracods in oolites and the occurrence of reworked specimens in elements of microbreccia give evidence for important changes in the conditions of the environment close to the D-C boundary. In the Late Devonian, ostracods display a regressive trend from deep environments below storm wave base to highly agitated environments above fair-weather wave base. But the sea level curve is not completely recorded in the La Serre section since two tectonic disturbed beds are present in the upper part of the profile. The number of ostracod species disappearing during the Hangenberg Event at La Serre seems to be less important in comparison with other sections investigated in Germany and Poland.The sedimentological study displays a standard sequence composed of six carbonate microfacies (MFI to MF6) and shows a quite abrupt transition from shallow hemipelagic environments (MFI) to shoreface-foreshore microbioclastic and ooidal shoals (MF2-MF5) reaching the upper beach foreshore (MF6). No evidence of subaerial emergence is found, nor any sedimentary structures indicating intertidal restricted environments. Microbreccias are abundant in MF5 and MF6; they are moderately to poorly sorted, subangular to subrounded, and show mixing of different eroded microfacies. All this supports strong and brief erosional phases within the transitional zone around 10 m water depth.The sea level trend points to a general regression starting near the Hangenberg Horizon sensu FEIST et al. (2000), from our sample 37 (Fig. 2), to the top of the section (sample 64) as showed by the shift of microfacies 1 to microfacies 6 and the quite abrupt appearance of proximal coquina layers, interpreted tempestites, toward the upper part of the section. The energy level was very high as indicated by the broken oolites, the microbreccias and the lamination patterns. Finaly a sea level increase (transgression) seems to have occurred in the uppermpost pan of the profile. Sea-level fluctuations were probably about ten of meters or more, as indicated by the erosion of microfacies 1 whose fragments form part of the microbreccias of microfacies 6.The study of ostracods and the sedimentology confirm that the La Serre section is far from being an ideal GSSP.