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Distribution bathymétrique des Pentacrines du Pacifique occidental : essai de modélisation et d'application aux faunes du Lias (problèmes de tectono-eustatisme au cours du rifting téthysien)

Abstract : Morphological analysis of south-western Pacific stalked crinoids points up that the majority of external features of skeleton are related to bathymetry (biotope depth). Thus we observe ecophenotypic convergences but no on taxonomic affinity. Among Pentacrinids, these ecophenotypic convergences-type wich are independent of taxonomic affinities and can be used as zoobathymetric markers. This fact is particularly illustrated by Pentacrinids in which species, recognized in the last century, are collected within morphological continuum. Adaptative strategy and heterochrony of development are involved to interpret the different constituents of these continuum. They depend on ecological setting, especially on environmental stability (hydrodynamism, sedimentation). Because the New Caledonia fauna includes opportunistic species and a majority of "living fossils" descended from mesozoic Mesogean fauna, the recent model has been put forward for Liassic Pentacrinids. Then, the zoobathymetry of recent fauna suggests a dynamic model according to geological events such as eustatic fluctuations and main tectonic phases. On the tethyan margin, about level with French western Alps, bathymetrical variations are well illustrated by stalked crinoid fauna from Lias of Digne nappe. So, at Lias beginning (from Hettangian to Middle Domerian), the first rifting phase coincide with an increase of the water column. This deepening comes before a main phase of distensive tectonic dated from Upper Domerian and Lower Toarcian. Following this phase, the water column stayed Lower than Lower and Middle Domerian one. The stalked crinoid fauna from other part of western Europe, emphasize the general nature of these tendencies. The relationships between overall tectonics, eustatism and the evolution of stalked crinoid fauna is discussed.
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Nadia Ameziane-Cominardi. Distribution bathymétrique des Pentacrines du Pacifique occidental : essai de modélisation et d'application aux faunes du Lias (problèmes de tectono-eustatisme au cours du rifting téthysien). Sciences de la Terre. Université Claude Bernard - Lyon 1, 1989. Français. ⟨tel-02314185⟩

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