Jean-Georges Casier

Les ostracodes au passage Eifelien/Givetien a Glageon (Avesnois, France)

Fifty-six ostracod species are recognized in the Hanonet Formation (Upper Eifelian) and in the lowermost Trois-FontainesFormation (Lower Givetian) of the Glageon Quarry (Southern border of the Dinant Basin, Avesnois, Northern France). The ostracods belong to the Eifel ecotype sensu Becker (in Bandel & Becker, 1975) and two assemblages are recognized: 1. assemblage III characterizes a relatively quiet marine environment below wave base on the mid-ramp setting (Hanonet Formation); 2. assemblage II characterizes a shallow marine environment above wave base on the inner-ramp (lower part of the Trois-Fontaines Formation). Comparatively with other outcrops from the Southern border of the Dinant Basin, the sea level fluctuations were of very low amplitude near the Eifelian/Givetian boundary at Glageon. The study of sediments in Glageon is consistent with the data from ostracods.

Ostracods, organic matter and anoxic events associated with the Frasnian/Famennian boundary in the Schmidt quarry (Germany)

Abstract The distribution of ostracods across the Frasnian/Famennian boundary in the Schmidt quarry is documented and all the benthonic species figured. Eighty per cent of the Frasnian ostracods disappeared close to this boundary, and all myodocopid species (Entomozoacea and Cypridinacea) were exterminated. The recovery in the Famennian seems to have been slow and gradual, and twelve lazarus species have been identified. These benthonic ostracods probably survived the Late Frasnian anoxic event sheltered in shallower marine environments. A strong relationship exists in the Schmidt quarry between fluctuations of the oxygen content of the bottom waters as displayed by the ostracod distribution, and the total organic carbon contents measured by the Rock-Eval Pyrolysis. Two new species are erected: Ampuloides kellerwaldensis nov. sp. and Acratia badwildungensis nov. sp.

Ostracods Late Devonian mass extinction : the Schmidt quarry parastratotype (Kellerwald, Germany)

Abstract Sixty-eight ostracod species have been recognized (the benthonic one for the first time) close to the Frasnian/Famennian boundary in the Schmidt quarry parastratotype. In the Late Frasnian, ostracods belong to an assemblage of the Eifelian ecotype and to the Myodocopid ecotype. In the base of the Famennian, they belong exclusively to the Eifelian ecotype. The oxygen content of the bottom waters during the deposition of the Upper Kellwasser horizon was highly unstable whereas this horizon was known to be anoxic. The Late Devonian mass extinction, probably the second in order of magnitude during the Phanerozoic, took place in the last 5 cm of the Upper Kellwasser horizon. Twelve ostracod species recognized in the Schmidt quarry survived this exvent.

Ostracods from the late Frasnian of the Neuville railway section (Dinant Synclinorium, Belgium) : relation to the Kellwasser Event

Ostracods from the upper part of the Valisettes Formation (Frasnian), from the Matagne Formation (Idem) and from the base of the Senzeille Formation (Famennian) exposed in the Neuville railway section (southern side of the Philippeville Massif within the Dinant Synclinorium) have been studied in order to advance the knowledge of the late Devonian mass extinction. The ostracod assemblage present in the upper part of the Valisettes Formation belongs to the Eifelian ecotype, and is dominated by filter-feeding metacopid ostracods indicative of an hypoxic trend related to an increase in the water depth. The overlying Matagne Formation is characterised by opportunistic species belonging to the myodocopid ecotype indicative of more severe hypoxic water conditions. The ostracod assemblage recognised in the base of the Matagne Formation is comparable to the assemblage found in the Upper Kellwasser Horizon of the Schmidt quarry parastratotype (Kellerwald, Germany), and the sartenaeri, splendens and sigmoidale Zones of the biozonation on entomozoid ostracods are also recognised. The splendens Zone -- sigmoidale Zone transition which corresponds to an important change in the entomozoid fauna in relation to the late Devonian mass extinction must be fixed definitively into the late Frasnian. Only Palaeophilomedes neuvillensis CASIER, 1988, and Ovatoquasillites avesnellensis (LETHIERS, 1973) survived the extinction in the Neuville railway section. P. neuvillensis is perhaps the sole true nekto-planktonic myodocopid present in the section, and the pre-adapted Lazarus species O. avesnellensis is known to have lived in very shallow marine and semi-restricted environments. We can conclude that the surface waters and the shallow marine environments were probably not disturbed during the late Devonian mass extinction. A figure, summarises the succession of events at the Frasnian -- Famennian transition on the southern border of the Philippeville Massif.

Ostracods from the Frasnian/Famennian transition beds in the Lijiaping section (Hunan, southern China)

Abstract Ostracods are highly abundant but poorly diversified in the Frasnian/Famennian (F/F) transition beds in the Lijiaping section of Hunan Province, southern China. Sixteen species have been recognized, and the fauna is distinctly dominated by Kloedenellacea, and by the genus Famenella 1953. This assemblage represents probably the first evidence from Hunan, of an ostracod fauna recovering from the Late Devonian mass extinction event.

Autopsie d'une extinction biologique. Un exemple: la crise de la limite frasnien-famennien (364 ma)

Abstract Without studying the causes of the F/F boundary mass extinction, the precise analysis of ostracod species shows evolutionary process only discernable at the global scale. About 75% of all neritic species disappeared in the Uppermost Frasnian in all studied regions of the world. Others survived, with some geographic changes, owing to littoral refuges (Lazarus eflect). Deep benthic ostracods seem almost untouched by this event. We show that new post-event species resulted from allopatric speciations by migration between neritic provinces or along continental slopes towards deeper environments. During the event surviving lineages show a continuous gradation from unscathed species to chronocline species, to phyletic subspeciations or speciations (= pseudo extinctions) and even to new genera. The durability of lineages is controlled by the migration of populations.

Ecology of Devonian ostracods: application to the Frasnian/Famennian boundary bioevent in the type region (Dinant Synclinorium, Belgium)

Three mega-assemblages and six assemblages of ostracods numbered 0 to V are recognised in the Devonian. They are indicative of lagoonal environments, semi-restricted environments and marine environments above and below fair-weather wave-base or storm wave-base. The water energy, the oxygenation and the temperature of marine waters seem to be the most important factors controlling the distribution of ostracods in the Devonian. These ostracod assemblages and mega-assemblages are also recognised in the Silurian and the Carboniferous. The ecological study of ostracods in the southern border of the Dinant Synclinorium, the type region for the definition of the Frasnian and Famennian stages, proves that the Late Devonian mass extinction is related to a period of hypoxy of marine waters followed and probably linked to a regression close to their boundary. The hypoxy is marked by the occurrence of the Myodocopid Mega-Assemblage, and its acme corresponds to the splendens Zone/sigmoidale Zone boundary of the parachronology based on Entomozoid ostracods. The sea-level fall is attested by the occurrence of ostracods indicative of semi-restricted water conditions in several sections, and particularly at Sinsin where stacked valves due to very small waves related to the lap are observed. Thus, the study of ostracods shows that intrinsic factors linked to the global tectonic regime are the most important factors explaining the Late Devonian mass extinction. The Frasnian/Famennian historic boundary of Gosselet (Annales de la Société géologique du Nord, 4, 303–320, 1877) corresponding to the recovery of the mega-fauna after the acme of this mass extinction marks in reality the return to true marine water conditions after the semi-restricted marine episode. The Matagne Fm, the Senzeille Fm and the position of the F/F boundary in the Synclinorium of Dinant are discussed.

The recovery of the ostracod fauna after the Late Devonian mass extinction : The Devils Gate Pass section example (Nevada, USA)

The recovery of the ostracod fauna is rapid after the Late Devonian mass extinction in the Devils Gate Pass section and fifty-nine species have been recognised in the Early Famennian. Forty-five appear for the first time, whereas fourteen others are known from the Late Frasnian (= lazarus species). The ostracod distribution in the Early Famennian at Devils Gate is greatly influenced by regional sedimentological factors principally induced by a drastic sea-level eustatic fall.

Micronewsomites et decoranewsomites, deux nouveaux genres d'ostracodes dévoniens

Resume Deux genres devoniens nouveaux appartenant a la famille Pachydomellidae sont fondes : Decoranewsomites (espece-type : Newsomites multicavus Rozhdestvenskaya, 1972 ) et Micronewsomites (espece-type : Newsomites natus Rozhdestvenskaya, 1972 ). La diagnose du genre Newsomites est emendee. Microcheilinella notabilis umbonata Polenova, 1960 , Newsomites notabilis kusnezkiensis Polenova, 1968 , et Newsomites notabilis arcticus Polenova, 1974 qui appartiennent au nouveau genre Micronewsomites, sont eleves au rang specifique.

Ostracods and rock facies across the Emsian/Eifelian boundary at Couvin (Dinant Synclinorium, Belgium)

A moderately rich ostracod fauna is reported from the upper part of the St. Joseph Formation (Fm), the Eau Noire Fm and the lower part of the Couvin Fm in the Eau Noire section located nearby Couvin. The section that crosses the Emsian/Eifelian boundary belongs entirely to the Couvinian historical stage. The ostracod fauna observed appertains to the Eifelian Mega-Assemblage and is indicative, in the Eau Noire Fm and in the Couvin Fm, of continuous shallow open-marine environments close to the fair-weather wave-base. The sampling and the number of ostracods extracted from the St. Joseph Fm are not sufficient to make environmental inferences and the study does not demonstrate an abnormal change in the ostracod fauna neither in relation with the Eau Noire Fm/Couvin Fm boundary, nor in relation with the Emsian/Eifelian boundary. The ostracods present near the Emsian/Eifelian boundary are mentioned for the first time in the southern border of the Dinant Synclinorium and they display close relations with the Eifel Mountains (Germany) and the Holy Cross Mountains (Poland).