Phyllocarid crustaceans from the Devonian of Bolivia and a review of their occurrences in the South American Palaeozoic

International audienceThe Ordovician phyllocarids of South America, from the epoch preceding formation of the Malvinokaffric Realm, are pelagic caryocaridids of virtually pandemic distribution. Phyllocarids are unknown from the South American Silurian, presumably in result of environmental and taphonomic factors connected with glaciation of Gondwana, which prevented their life and/or fossilization. In the Devonian, the phyllocarid fossil record is restricted to Bolivia. The small-sized and having a thin exoskeleton Poupelicaris elegans n.g., n. sp. from the Lochkovian of Bolivia is the first 'Malvinokaffric' phyllocarid faunal element. The cool-water conditions that are considered to characterize the Malvinokaffric Realm ended in the Givetian with the incoming of the phyllocarid Dithyrocaris and, later, Paraechinocaris, probable immigrants from North America

Communautés benthiques à brachiopodes et variations eustatiques: exemple de la Formation du Faou (Dévonien, Massif armoricain, France)

A detailed study of the Seillou section (Le Faou Fm., Armorican Massif) on the ground of sequence stratigraphy and palaeontological content results in the definition of the relationships between the brachiopod benthic assemblages and the sea-level fluctuations. ((C) Academie des sciences / Elsevier, Paris.

Relations entre les variations des assemblages benthiques emsiens et l’eustatisme dans la coupe de Seillou (Massif armoricain, France)

Palaeoecological study and sequence stratigraphy of the Emsian part of the Seillou section (Le Faou formation, Armorican massif) allows the identification of benthic and pelagic associations, and shows the correlation between the distribution of associations and the sea level variations. A major change in sedimentation and faunas could represent the signature of the Basal Zlichov Event in the Armorican massif. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS

Crinoid columnal associations and sequence stratigraphy architecture: the Le Faou Formation, Lower Devonian of the Massif armoricain (France)

Crinoid columnals are major rnacrobenthic components of the Lower Devonian faunas of the Massif armoricain particularly in the Seillou section. Three crinoid columnal associations have been delineated based on R and Q-mode cluster analysis. Distribution of these associations is correlated to the sequence stratigraphic architecture, showing the close relationships between crinoid columnal association dynamics and relative sea-level variations. Comparing the distribution of benthic associations, we note a lesser diversity in crinoid columnal associations than in brachiopod ones. Crinoids (high-level Suspension feeders) seem to occupy broader specialised niches than brachiopods (reclining and low-level suspension feeders) and are characterised by a different ecological space utilisation

The Devonian of the Hodh area (Islamic Republic of Mauritania) : Paleontology and stratigraphy

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Replacements of benthic associations in a sequence stratigraphic framework, examples from Upper Ordovician of Sardinia and Lower Devonian of the Massif Armoricain

Sedimentological, palaeoecological and taphonomic analyses were carried out to establish the impact of relative sea-level variations on benthic faunas in a platform depositional context and to propose a reliable palaeoecological model for different palaeogeographic areas during different periods of the Palaeozoic. One Caradocian-Ashgillian section in Sardinia and one Lower Emsian section in the Massif Armoricain have been selected. The approach combines sequence stratigraphy, taphonomy and delineation of recurrent fossil associations. Several sedimentary facies have been recognized in relation to the distance from the shoreline. The succession consists of the stacking of genetic sequences related to sea-level changes linked to cyclic variations of orbital parameters. Several fossil associations, identified by means of multivariate analyses, are recurrent in similar facies. Eleven associations are recognized. These are the Longvillia, Nicolella, Paucicrura and Iberomena associations in the Upper Ordovician of Sardinia; the Adolfia, Stenorhynchia, Chonetid, Crinoid-Brachiopod, Ostracod-Tentaculitid, Bryozoan and Dacryoconarid associations in the Lower Devonian of the Massif Armoricain. The results of multivariate analyses based on the faunal contents are in good accordance with the clustering based on the sequence stratigraphic analysis. Benthic associations are closely related to relative sea-level variations. When the sea-level fluctuations were gradual and moderate, the association replacement is characterized by reorganization of the taxonomic composition, changes in diversity and trophic webs (association replacement by reorganization). When the sea-level changes rapidly, the association replacement is characterized by renewal of the ecological structure (association replacement by renewal). Palaeoecological changes are recognized to be strongly related to sea-level variations. (c) 2006 Elsevier B.V. All rights reserved