Florentin Paris

A global chitinozoa biozonation for the Silurian.

A global Chitinozoan biozonation for the Silurian Period is proposed. Each biozone is an interval range defined by the first occurrence of an index species, selected from well-defined species with a relatively short biostratigraphic range. To be included in the scheme, index species must have been recorded from at least two major Silurian palaeocontinents where usable Chitinozoa assemblages have been studied, that is, Avalonia—Baltica (which had already undergone collision by the Silurian), Laurentia, Gondwana and Southern China. Seventeen biozones are identified with seven in the Llandovery: the fragilis, postrobusta, electa, maennili, alargada, dolioliformis and longicollis biozones; four in the Wenlock: the margaritana, cingulata, pachycephala and lycoperdoides biozones; three in the Ludlow: the elongata, philipi and barrandei biozones; and three in the Přidoli: the kosovensis, elegans and superba biozones. Chronostratigraphic calibration is partly provided by reference to the range of the appropriate Chitinozoa index species in the global stratotype sections and points (GSSP) of the Silurian series, e.g. in Bohemia (Czech Republic) for the Přidoli and the Welsh Borderland in England for the Ludlow and part of the Wenlock. When this information was not available, independent biostratigraphic control was provided by calibration with graptolite biozones or in a few cases, conodont or trilobite biozonal schemes. The index and most characteristic species of each biozone are illustrated and their total stratigraphie range provided.

Ludlovian, Pridolian and Lochkovianin la Meignanne (Massif Armoricain): Biostratigraphy and correlations based on Bivalvia and Chitinozoa

Abstract Black carbonate rocks («ampelitic limestones)exposed in la Meignanne, NW of Angers, Massif Armoricain, as tectonic lenses within a complex tectonic structure of grey Pragian limestones are assigned from Bivalvia and Chitinozoa to the Upper Silurian and Lowermost Devonian. Biostratigraphical and paleoecological analyses show that the Silurian-Devonian boundary in this area is developed in offshore facies and that it may be correlated directly with the international stratotype of the Prague Basin (Barrandian, Bohemia). Paleogeographical communication between the two areas is indicated by 28 species of bivalves in common from two Pridolian assemblages (with Cheiopteria bridgei and with Snoopyia insolita) and one Lochkovian (with Antipleura bohemica). Stratigraphical correlation with the Prague Basin is also based on the chitinozoan zonal index species for the Uppermost Pridolian (Urnochitina urna) and Lowermost Lochkovian (Eisenackitina bohemica). A Lochkovian age is further supported by the discovery of Monograptus uniformis uniformis in the assemblage with Antipleura bohemica. A Ludlovian age is indicated by the occurence of «Hemicadium elevatum and an abundance of the ostracode Entomozoe (Richteria) migrans, which is an index species for the Middle Ludlovian in Bohemia.

Palynological dating (acritarchs and chitinozoans) of Lower Paleozoic phyllites from the Black Forest/southwestern Germany

Abstract The Black Forest (southwestern Germany) comprises two phyllite-bearing low-grade metasedimentary units, which are separated by the Central Schwarzwald Gneiss Complex. Both zones have been subjected to palynological investigation. In the north, the phyllites of the zone of Baden-Baden—Gaggenau, until now believed to be unfossiliferous, yielded a poorly preserved acritarch assemblage, indicating an age ranging from the Upper Cambrian to the Lower Ordovician. These phyllites may be equivalent to the Ville slates of the Vosges mountains (eastern France). In the south, the phyllites of the zone of Badenweiler—Lenzkirch contain chitinozoans of Silurian age.

Contribution of morphometrics to the systematics of the Ordovician genus Neseuretus (Calymenidae, Trilobita) from the Armorican massif, France.

Abstract The genus Neseuretus Hicks, 1873 is the most abundant trilobite of the Ordovician siltite succession of the Andouillé and Traveusot Formations in the French Armorican massif. The systematics of some species of Neseuretus is still unclear. Armorican and Iberian domains formed part of a distinctive paleobiogeographical province in the Ordovician and, while five Neseuretus species were defined in Iberia that follow each other through time, from the Middle to the Upper Ordovician, only one Neseuretus species, N. tristani, has been identified in the Armorican massif so far. The discovery of new fossil deposits in the Ménez-Belair syncline has led to the identification and re-description of three Neseuretus taxa: Neseuretus avus Hamman, 1977 from the early-middle Darriwilian, Neseuretus tristani (Brongniart in Desmarest, 1817) from the late–middle Darriwilian to late Darriwilian and Neseuretus tardus (Hammann, 1983) from the Darriwilian–Sandbian boundary and early Sandbian. Morphological characters of the cephalon and pygidium were determined that can definitively distinguish the three identified taxa. These results stem from both traditional and geometric (outline and landmark-based) morphometric analyses. The three taxa follow each other through time and constitute a morphological sequence that contributes to improving the stratigraphy of the Middle and Upper Ordovician.