Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : We present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the Famennian (Late Devonian) at Col des Tribes (Montagne Noire, France). The succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp. Facies contain poor fauna, widely dominated by nektonic organisms. This section is complete and one of the most conodont-rich for the Famennian of the north Gondwana-related area. The Upper Kellwasser event (Frasnian–Famennian boundary) and the Hangenberg (Devonian–Carboniferous boundary) have been lithologically identified. They are characterized by decimetre-thick black dysoxic to anoxic argillaceous sediments. The Condroz and annulata events, although not materialized by lithological changes, have been positioned due to the precise stratigraphy. The first event occurred during the deposition of condensed ferruginous facies (griotte limestones) and the second event during the deposition of micrites barren of benthic fauna. The combination of information from both facies and conodont biofacies changes allows a general sea-level curve through the entire Famennian for north Gondwana to be proposed for the first time. At Col des Tribes, the general trend is a slight deepening upwards from triangularis to trachytera zones, then a pronounced shallowing-upwards trend from upper trachytera to praesulcata zones. This curve correlates with the well-known reference curve from Euramerica concerning the late Famennian (trachytera to praesulcata Zones). There are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the Variscan belt in Europe.
ISSN: 0016-7568

hal-01115222
https://hal.archives-ouvertes.fr/hal-01115222
DOI : 10.1017/S0016756813000927

Éditeur(s) : HAL CCSD Borntraeger Science Publishers
Résumé : This study characterizes the stratigraphical context as well as the palaeoenvironmental and sealevel trends during the Late Frasnian and Famennian in the Buschteich section (Thuringia, Germany). An integrated approach combines conodont biostratigraphy, chemostratigraphy based on carbon and oxygen isotopes, conodont biofacies analyses and investigations of the morphotypes of foraminifera that occur in the section was applied. Conodonts provided a fine-scale biostratigraphical framework. All the Famennian conodont biozones were identified, with the exception of the three lowest. The Frasnian – Famennian transition was further identified by a positive carbon isotope excursion. This continuous Famennian record is developed in a condensed limestone succession. The reddish Griotte facies, typical of strata of this period, were not documented. Black shales were not developed except for an interval of dark colored mud rocks corresponding to the Hangenberg event at the top of the section. The carbonate succession of Buschteich was deposited in an outer ramp environment, pelagic organisms are the dominant fauna. This is corroborated by the overall dominance of the deep-water conodont genus Palmatolepis. Microfacies, conodont biofacies and foramini fera indicated a deepening trend from the Lower crepida to the Lower rhomboidea Zone, followed by a shallowing trend from the Upper rhomboidea to the praesulcata Zone. This sequence overall matches the sea level reference curve for Euramerica. The timing of maximum water depth at Buschteich, as well as the general sea-level reference record, differs from the Col des Tribes (Montagne Noire, France). Differential uplift or overprinting of the long-term eustatic changes may be the cause of the discrepancy in the local sea-level records.
ISSN: 0078-0421

hal-01623111
https://hal.archives-ouvertes.fr/hal-01623111
DOI : 10.1127/nos/2016/0318

Éditeur(s) : Gauthier-Villars
Résumé : The paper summarizes the biostratigraphic results of eighteen dives of the French submersible Cyana at the Mazagan Escarpment (CYAMAZ cruise), based on calcareous nannoplankton and foraminifera. This paper is restricted to the study of the Early Cretaceous to Quaternary post-platform series. Most of the stratigraphical data are based on the determination of calcareous nannofossils (P. Cepek) which, however, are mostly poorly preserved and of rare occurrence. From the 170 studied subsamples 49 are barren of calcareous samples are listed according to the species epithets, separated for the Cretaceous and Tertiary. The biostratigraphy based on foraminifera and the microfacies was studied in thin-section (H. hagn). Foraminiferal microfaunas of Late Cretaceous, Paleocene, Eocene-Oligocene and Quaternary age are described and shown in Plates.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1985

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00247/35827/34337.pdf
http://archimer.ifremer.fr/doc/00247/35827/

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
The Ben Zireg anticline NW of Bechar yields the currently most-important Frasnian succession on the northern margin of the Algerian Sahara. It represents 26.5 m of calcilutites which are attributed to the middle–late Frasnian. As the early Frasnian is not represented, the succession rests conformably on undifferentiated, probably late Givetian, substrate. Fine-scaled conodont biostratigraphy reveals a continuous sequence of Montagne Noire Zones 5–13, superseded by the earliest Famennian Lower triangularis Zone. The deposits are organized into 15 sedimentary cycles that are initially condensed and become dilated upwards. Conodont biofacies indicate an overall deepening towards the top of the section with an episode of slight shallowing at the MN11/12 transition marked by an increase of ancyrodellids, which is also seen in the Marhouma section of the Ougarta region (SW Algeria). Homogeneous calcareous microfacies with only a few shaly intercalations determine a predominantly oxygenated depositional environment on an outer platform, submarine rise or ramp setting. This is also indicated by relatively low sedimentation rates which are similar in selected sections from the Tafilalt platform, and contrast with those from the Marhouma trough and the Maider basin. Unlike other Frasnian successions south of the Atlas Fault, but similar to the Moroccan Meseta, the Upper Kellwasser horizon is clearly discriminated at Ben Zireg by an outstanding occurrence of black shales on top of the oxygenated latest Frasnian deposits.
ISSN: 0016-7568

hal-01217151
https://hal.archives-ouvertes.fr/hal-01217151
DOI : 10.1017/S0016756814000715

Éditeur(s) : Institut Francais du Pétrole
Résumé : The study of the rock and sediment dredgings carried out on the Armorican margin between 47 and 48° latitude North enables us to precise this latter's paleogeographical and tectonic evolution and to integrate it to the Bay of Biscay's. The microfacies analysis of the rock samples dating back from the Upper Jurassic to the Neogene era demonstrates: - on the one hand, the belonging of the northern edge of the Armorican margin to the Mesogean domain, at least up to the Mid-Cretaceous period; - on the other hand, the persistence of a carbonated platform regime which seems to operate from the Tithonian to the lower Tertiary phase, and on which reef could grow, especially in the Mid-Cretaceous period. Over the whole period, sedimentation compensated for subsidence; - lastly, the increase of subsidence from the Eocene period (accompanied with a decrease in the calcium production?) which is most probably related to the major tectonic phenomena that affected the southern edge of the European plate at that time.
L'étude des dragages de roches et de sédiments effectués sur la marge armoricaine entre 47 et 48° de latitude Nord permet d'en préciser l'évolution paléogéographique et tectonique et de l'intégrer à celle du golfe de Gascogne. L'andyse de microfaciès des échantillons rocheux dont l'âge varie du Jurassique supérieur au Néogène met en évidence : - d'une part, l'appartenance de la bordure nord de la marge armoricaine au domaine mésogéen au moins jusqu'au Crétacé moyen ; - d'autre part, la permanence d'un régime de plate-forme carbonatée qui paraît fonctionner du Tithonique au Tertiaire inférieur, sur laquelle ont pu s'installer des édifices récifaux notamment au Crétacé moyen. Pendant toute cette période la sédimentation a compensé la subsidence ; - enfin, l'accentuation de la subsidence à partir de l'Éocène (accompagnée d'une diminution de la production de calcium ?) qui est vraisemblablement en relation avec les phénomènes tectoniques majeurs qui ont affecté à ce moment la bordure sud de la plaque européenne. [OCR NON CONTRÔLE]
Revue de l'Institut Francais du Pétrole (Institut Francais du Pétrole), 1976-06 , Vol. 31 , N. 3 , P. 401-425

Droits : Institut Francais du Pétrole
http://archimer.ifremer.fr/doc/1976/publication-5100.pdf
http://archimer.ifremer.fr/doc/00000/5100/