Le Gargasien de Gargas (Vaucluse, SE de la France) : synthèse des données de terrain et révision de la microfaune de foraminifères et d'ostracodes

Carnets de Geologie (Impact Factor: 0.41). 04/2010; DOI: 10.4267/2042/30051
Source: OAI


Because of urbanization the section at Gargas, historical stratotype of the Aptian stage and of the Gargasian substage, is no longer accessible. However, samples taken there in 1966 by one of us make feasible a reinterpretation of this series in the light of taxonomic and biostratigraphic data from a recent study of Aptian microfaunas from La Tuilière area, some 5 km away. This new micropaleontologic interpretation shows that the historical section is truncated at its base : the lower (not lowermost) Gargasian is in quasi-direct contact with Urgonian limestones ; the uppermost (marly) Bedoulian, known to be present westward towards Le Chêne as well as at La Tuilière, is absent in the stratotype outcrop. In the samples from the stratotypic succession we have identified (bottom upward): • the upper part of the Praehedbergella luterbacheri zone and the Globigerinelloides ferreolensis zone, • the G. barri zone, • the beginning of the G. algerianus zone, i.e. these zones comprise the major part of the lower Gargasian, the middle Gargasian and the transition to the upper Gargasian. The upper part of the G. barri zone and the passage to the G. algerianus zone are in sandy marls of which the upper terms were said to have yielded ammonites of the "Clansayes horizon" (sensu ante). The microfauna does not resolve this apparent discrepancy, for its state of preservation degrades rapidly in the detrital levels, to the point of quasi-disappearance in sands overlying the Clansayesian auct. A comparison with the sector of Banon, only some 10 km away, led us to suggest that these sands cropping out at top of the Gargas Hill might be of Late Albian-Vraconnian age. La coupe de Gargas, stratotype historique de l'étage aptien et du sous-étage gargasien, n'est désormais plus du tout accessible à l'observation par suite de l'urbanisation. À partir d'un ensemble d'échantillons prélevés en 1966 par l'un d'entre nous, nous avons pu cependant la ré-interpréter à la lumière des résultats d'ordre taxinomique et biostratigraphique acquis récemment sur la base de l'étude des microfaunes de l'Aptien du secteur de La Tuilière, distant d'environ 5 km. Cette nouvelle interprétation micropaléontologique montre que la coupe historique apparaît en fait tronquée à sa base, le Gargasien inférieur (non basal) s'y trouvant en contact quasi-direct avec l'Urgonien ; le Bédoulien terminal, marneux, connu plus à l'Ouest (vers le Chêne) ainsi qu'à La Tuilière, manque ici à l'affleurement. En effet, dans nos échantillons de la série stratotypique nous avons pu mettre successivement en évidence (de bas en haut) : • la partie supérieure de la zone à Praehedbergella luterbacheri et la zone à Globigerinelloides ferreolensis, • la zone à G. barri, • le tout début de la zone à G. algerianus, soit la majeure partie du Gargasien inférieur, le Gargasien moyen et le passage au Gargasien supérieur. La partie supérieure de la zone à G. barri et le passage à la zone à G. algerianus correspondent à une séquence marquée par l'instauration d'un faciès marno-sableux, dont les termes supérieurs ont historiquement fourni des ammonites de l' "horizon de Clansayes" (sensu ante). Cette donnée ne peut être confortée par les microfaunes, dont la conservation se dégrade rapidement dans les niveaux détritiques, au point même qu'elles vont quasiment jusqu'à disparaître dans les sables et grès sus-jacents au Clansayésien auct. Par analogie avec le secteur de Banon, distant d'une dizaine de kilomètres, ces termes détritiques du sommet de la Colline de Gargas pourraient appartenir à l'Albien supérieur-Vraconnien.

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    • "In the literature these beds have been generally assigned an uppermost Aptian (more particularly Clansayesian) and Albian age. On the basis of our work quoted above (Moullade et al., 2009) and a comparison with data from Friès (1987) in the neighbouring sector of Banon, it appears that these detrital levels which directly overly a Gargasian truncated at its top, would be ascribable to the upper Albian, with an important erosional gap between them. influenced by " Breistroffer's and Kilian's heritage " , is unsatisfactory for several reasons, among them the following: No respect for the initial concept of d'Orbigny, Stage and substage boundaries that have fluctuated without cease, Since 1947, use of an impractical ternary or, worse, a " hybrid binary " terminology for the subdivisions of the Aptian, rather than the simple binary mode employed for most of the other stages of the Lower Cretaceous. "
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    ABSTRACT: The original definitions of the Aptian, Albian and Urgonian stages by d'Orbigny (1840, 1842, 1847, respectively) on the basis of lithological and paleontological criteria were sufficiently clear and should not have generated the misinterpretations and confusion that began at the end of the 19th century and continue today. The purpose of this paper is thus to clarify the succession of stages within this period of the Cretaceous as well as their relationships, by a better respect for the thought of their creator and also in light of recent work on the historical stratotypes. This return to fundamentals leads us to propose the insertion of a Bedoulian stage between the Barremian (ex Urgonian) and the Aptian s.s. Our proposal includes also recommendations for the definition of the Barremian, Bedoulian (sensu novo), Aptian (s. s.) and Albian boundaries and the corresponding Global Boundary Stratotype Sections and Points (GSSP).
    Episodes 09/2011; 34(3). · 2.00 Impact Factor
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    Cretaceous Research 02/2013; 39:1–5. DOI:10.1016/j.cretres.2012.09.001 · 1.90 Impact Factor
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    ABSTRACT: Correlation of the main sedimentary, biological and geochemical signals observed within the historical lower Aptian stratotype in the Cassis-La Bédoule area leads to discern and to calibrate several significant breaks or discontinuities. The "Taxy", "Roch" (Barremian-Aptian boundary) and "Toucas" levels, the Δ2 major discontinuity (lower/upper Bedoulian boundary), and bench-mark beds 158 and 170, all stratigraphically well-defined in the stratotype, can be recognized at least regionally (SE France). Conversely, some worldwide events as the "Nannoconus crisis" or the OAE1a anoxic event, as well as the paleontological Bedoulian-Gargasian boundary, are either poorly expressed or even not recorded in the stratotype. Sequence stratigraphy surfaces and boundaries from the recently published global chart (HARDENBOL et al., 1998) are also difficult to correlate with the integrated stratigraphy established in the stratotype. From a biostratigraphic point of view, the Barremian-Aptian boundary is precisely marked by the first appearance of the ammonite genus Deshayesites, whose different species (D. tuarkyricus, D. weissi, D. deshayesi), with the addition of another deshayesitid (Dufrenova furcata) are used as index of a biozonation better conform to the Mediterranean standard. The upper Bedoulian only is clearly characterized by significant foraminiferal changes, with the successive appearance of several planktonic markers among which Blowiella blowi and Schackoina (Leupoldina) cabri, whereas any important foraminiferal change is observed at the Bedoulian-Gargasian boundary. By contrast the first occurrence of the calcareous nannofossil species Hayesites irregularis coincides with the Barremian-Aptian boundary, that of Rhagodiscus angustus with the lower/upper Bedoulian boundary and that of Eprolithus floralis with the basal part of the D. furcata zone. The dinoflagellate bio-events occur within the main ammonite biozones, with of particular interest the first occurrence of Tehamadinium tenuiceras, regarded as a significant datum at the European scale and here calibrated within the D. furcata zone.
    Geologie Mediterraneenne 01/1998; 25(3):289-298.
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