Rémy Gourvennec

Biogeography of Late Silurian and Devonian acritarchs and prasinophytes

Abstract The palaeobiogeography of Late Silurian-Devonian acritarch and prasinophyte microfloras is assessed using qualitative data, similarity indexes and cluster analysis. Based on the recent palaeogeographic reconstructions, the northwards movement of Gondwana initiated during the Ludlovian with the progressive narrowing of the Rheic ocean, resulted in North Africa and south European regions being closer to the equatorial zone and hence in a warmer climate. An apparent homogeneity of Late Silurian assemblages from regions of southern Baltica and the North Gondwanan margin could be explained by such a configuration. The phytoplanktonic associations could also have benefited from the equatorial currents system for trans-Rheic connections. In addition, the qualitative study and the cluster analysis allow for delineation of a biogeographic unit, including part of South America, North Gondwanan and perigondwanan regions, which is comparable to the cold Malvinokaffric realm of the southern hemisphere, based on invertebrates. During the same time, major differences recognized in the distribution of acritarchs from near shorelines to deep oceans, emphasize the potential of mazuelloids (previously referred to as acritarchs) as indicators of deep-water facies and outer margin sites. The Early Devonian shows a geographic restriction of several acritarch genera and species, with a pronounced lateral differentiation between North Gondwanan and eastern North American microfloras, that seems to have been controlled by physical barriers rather than climatic differences. The similarities in acritarch assemblages between northern Europe and the North Gondwanan margin argue for a decrease in acritarch provinciality on both sides of the Rheic ocean, and precludes the presence of a wide Devonian ocean north of western Gondwana.

Biogeography of upper Llandovery and Wenlock acritarchs

Abstract The world-wide spatial distribution of upper Llandovery and Wenlock acritarch microfloras is assessed using qualitative data, similarity indexes and cluster analysis. The database consists of comprehensive lists of taxa available essentially from eastern North America, South America, western Europe, Baltoscandia, Siberia, North Africa and adjacent regions, and a few additional data from China. The data are plotted on the most recent palaeogeographic map. The results of qualitative and quantitative analysis clearly show that patterns of distribution of the acritarchs are under the interdependence of continental arrangement, latitudinal position, environmental conditions and oceanic currents. While climate was undoubtedly a significant factor governing the distribution of microfloras, the associations do not necessarily coincide with palaeolatitudes as predicted in Cramers provincialism model proposed for Silurian acritarchs. Thus the suggestion of a low latitude Deunffia-Domasia realm near the Llandovery-Wenlock boundary has to be modified; several new data from the North Gondwana margin indicate a relation of the D-D association with outer-shelf environments independent of latitudinal control; in the same way, Neoveryhachium carminae appears to be facies-controlled in relation to clastic facies and turbid environments; the supposed benthic cysts belonging to the Pulvinosphaeridium-Estiastra group coincide with the distribution of climatically sensitive carbonate lithofacies in the equatorial zone. These conclusions are supported by the results of quantitative analysis. In addition, the spatial distribution of other taxa is discussed, in order to provide new tools for paleogeographical reconstructions.

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

Crinoid columnals are major macrobenthic 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.

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

Abstract A detailed study of the Seilou 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.

THE DEVONIAN OF THE HODH AREA (ISLAMIC REPUBLIC OF MAURITANIA): PALEONTOLOGY AND STRATIGRAPHY

Abstract Paleontological study of 16 samples from four sections through the Silurian-Devonian marine deposits of the Hodh region establishes the development of the Middle Devonian and adds to our knowledge of the Paleozoic sequence in the West African platform. Above Silurian deposits locally dated by graptolites from the Llandovery, Devonian shales yield an abundant although low diversity benthic fauna, which is assigned to a Givetian age. The brachiopod fauna shows strong affinity with the NE Americas Realm. Two new species are described, Arcuaminetes deynouxi and Eleutherokomma monodi. The revision of the Devonian fauna of the Hodh area supports: 1) the apparent lack of Lower Devonian deposits; 2) the Givetian age of the Devonian succession; and 3) the strong eastern Americas Realm affinity of the fauna, as previously established for the Mauritanian Adrar area.

La conquête des mers siluriennes par les Spiriferida (Brachiopoda)

The spiriferid brachiopods appeared in the Late Ordovician (Middle Ashgill) in southeastern Asia and then spread throughout the world during the Silurian. The strategies of expansion of the group and the changes in its diversity during this period are discussed here.

Devonian operculate corals (Calceolidae, Cnidaria) from the Massif Armoricain, France

Wright, A.J., Plusquellec, Y. & Gourvennec, R., February 2016. Devonian operculate corals (Calceolidae, Cnidaria) from the Massif Armoricain, France. Alcheringa 40, xxx–xxx. ISSN 0311-5518 The operculate coral Calceola gervillei Bayle, 1878 is described for the first time on the basis of the type material from the Cotentin region of Normandy (North Armorican Domain), from Early Devonian (likely upper Lochkovian to lower Pragian) strata, and is chosen as the type species of the monotypic new genus Gerviphyllum. The new genus is also present in the l’Armorique Formation (lower Pragian) of the Plougastel Peninsula (Central Armorican Domain) as Gerviphyllum sp. cf. G. gervillei. One locality in the upper Emsian (Polygnathus serotinus Conodont Zone) Le Fret Formation, on the northern coast of the Crozon Peninsula, has yielded operculate coral specimens described here as ?Chakeola sp., the first (tentative) record of the genus outside eastern Australia, south China and Vietnam. The operculate coral Calceola collini sp. nov. is described from six localities in the early Middle Devonian (Eifelian: Polygnathus costatus Conodont Zone) Saint-Fiacre Formation of the Plougastel and Crozon Peninsulas (Central Armorican Domain), despite the fact that knowledge of the internal characters, especially of the operculum, of the type species Calceola sandalina is very limited. From an extensive review of published references to Calceola from France, we conclude that only the record of Collin (1929) is valid. Anthony Wright (tony.wright@optusnet.com.au), GeoQuEST Research Centre, School of Earth & Environmental Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia; Yves Plusquellec (yves.plusquellec@univ-brest.fr) and Rémy Gourvennec (remy.gourvennec@univ-brest.fr), Université de Bretagne Occidentale, CNRS-UMR 6538 ‘Domaines océaniques’, Laboratoire de Paléontologie, UFR Sciences et Techniques, 6 avenue Le Gorgeu, CS 98837, F-29283, Brest, France. Received 1.10.2015; revised 8.12.2015; accepted 14.12.2015.

Frasnian rugose and tabulate corals from the eastern Taurus (Kozan region, Turkey)

A section near the Kilgen Lake (Adana Province) has yielded a fauna of rugose and tabulate corals including Disphyllum cf. rugosum (Wedekind, 1922), D. cf. curtum Hill, 1954, Wapitiphyllum sp., Thamnopora sp., and Alveolites sp. This coral assemblage is consistent with the previous Frasnian age assigned to the limestones of the Gümüşali Formation. The rather well-preserved material provides new data on the structure and microstructure of Disphyllum and allows to describe in Thamnopora unusual calicinal morphology (septal ridges, median teeth, and pseudopercula) as well as new structures linked to the lateral increase (basal low wall, apical cul-de-sac).

The genus Verneuilia Hall & Clarke, 1893 (Brachiopoda, Spiriferida)

Abstract The genus Verneuilia, a poorly known spiriferid from the Middle Devonian and Lower Carboniferous, is here redescribed. For the first time a description is provided for some of the internal structures. The systematic position of this aberrant genus, here placed in the superfamily Spiriferacea, is also discussed and two of the assigned species are described in detail.