| mhorn | Дата: Wednesday, 31.08.2011, 13:09 | Сообщение # 1 |
Admin
Group: Администраторы
Posts: 1060
Reputation: 0
Status: Offline
| Dommergues J.-L., Guiffray A., Dumont T., Chevalier F. (2011) La lumachelle à Cardinia (Bivalves) et Alsatites (Ammonites) du «Revers de Côte Dure» dans l’Hettangien de la couverture sédimentaire du Massif du Rochail (Oisans, Isère, France) // Revue de Paléobiologie, Genève. Vol.30. no.1. P.193-221.
Pdf: http://www.ville-ge.ch/mhng/paleo/paleo-pdf/30-1/pal_30_1_10.pdf
This work is dedicated to a poorly diversified but abundant and finely preserved middle Hettangian (Liassicus Chronozone, Laqueus Subchronozone) fauna which characterises a remarkable very fossiliferous bed within the usually hardly fossiliferous Triassic and Early Jurassic sedimentary cover of the Rochail massif (Subalpine basin, Dauphinois zone). This fauna, collected in the “Revers de Côte Dure” section (Villard-NotreDame, Isère, France), is chiefly constituted by bivalves (e.g., Cardinia, “Astarte”) and ammonites (e.g., Alsatites, Saxoceras) but some rhynchonellids and gastropods are also present. Bivalves (4 species) and ammonites (2 species) are considered according to taxonomical, stratigraphical, palaeoecological and palaeobiogeographical viewpoints. Two successive biohorizons can be identified within the fosiliferous episod. At base, the Alsatites laqueus biohorizon is characterized by many Alsatites laqueus (QuensteDt, 1856) associated with plentiful bivalves (= shelly limestone with Cardinia). This first biostratigraphical units is followed by the Saxocerassp. indet. biohorizon which yields some peculiar Saxoceras – perhaps a new species – associated with few late Alsatites laqueus. The Saxoceras sp. indet. biohorizon is a new unit for the NW European biostratigraphical scale and it is probably intercalated between the A. laqueus and the A. laqueolus biohorizons within the Laqueus subchronozone. In Palaeoecological terms, the most significant bivalves and ammonites species are perhaps opportunist taxa (r-strategy) able to colonise a temporarily propitious biotope. In Palaeobiogeographical terms, faunas clearly indicate NW European affinities. The “shelly limestone with Cardinia” faunal assemblage is especially plentiful and diversified in the “Revers de Côte Dure” main section but the bed can be identified and followed up to about one kilometre eastward. Moreover, the fossiliferous bed can be clearly understood as an unusual deposit associated with a transgressive surface in an active synsedimentary extensional tectonic setting, which marks the onset of the Tethyan rifting in the Dauphiné area
Middle Jurassic - Lower Cretaceous ammonites & aptychi
|
| |
| |
