Fish remains (Elasmobranchii, Actinopterygii) from the Late Cretaceous of the Benue Trough, Nigeria

International audienceSelachian and ray-finned fish remains from various Late Cretaceous localities of Nigeria are described. Each locality has yielded only a very few specimens and the diversity is therefore very low. However, some taxa are recorded for the first time in Africa. The Ashaka locality in the Upper Benue Trough (northeastern Nigeria) has yielded a small but interesting late Cenomanian assemblage of microremains, including teeth of ''Carcharias'' amonensis, Rhombopterygia zaborskii sp. nov., Hamrabatis sp., ''Stephanodus'' sp., and a possible ionoscopiform. A large prearticular dentition coming from the early Turonian beds of this locality is assigned to the large pycnodontiform Acrotemnus, a poorly known genus here regarded as a senior synonym of Macropycnodon. In the Lower Benue Trough (southeastern Nigeria), several localities ranging in age from the late Cenomanian to the early Maastrichtian have yielded various widespread taxa such as Ptychodus, Scapanorhynchus, Squalicorax, Vidalamiinae indet., cf. Protosphyraena, and Eodiaphyodus. The seaway that occupied the Benue Trough during transgressive episodes (late Cenomanian-early Turonian and Maastrichtian) created opportunities for the dispersal of many marine fish taxa into new areas, such as the proto-South Atlantic

A Miocene tectonic inversion in the Ionian Sea (Central Mediterranean): evidence from multi-channel seismic data

It is widely accepted that the Central and Eastern Mediterranean are remnants of the Neo-Tethys. However, the orientation and timing of spreading of this domain remain controversial. Here, we present time migrated and pre-stack depth migrated NW-SE oriented Archimede (1997) lines together with the PrisMed01 (1993) profile to constrain the evolution of the Ionian basin. Our interpretation allows us to identify a large-scale set of SW-NE striking reverse faults beneath the Ionian Abyssal Plain. These primarily NW vergent faults are characterized by a spacing comprised between 10 to 20 km and a dip ranging from 60 to 65{degree sign}. Following very recent paleogeographic reconstructions, we propose that the set of N{degree sign}55 features initially formed as normal faults during the NW-SE trending seafloor spreading of the Ionian basin after its late Triassic-early Jurassic rifting. Based on geometric comparisons with the intraplate deformation observed beneath the Central Indian Ocean, we show that the inherited oceanic normal faults were reactivated under compression as reverse faults. Well-developed Tortonian syntectonic basins developed NW of the major faults and the base of the Messinian evaporites (Mobile Unit) is slightly folded by the activity of the faults. We show that 3-4 km of total shortening occurs over a 80 km wide area beneath the Ionian Abyssal Plain, resulting in a bulk shortening of 3.5-5 %. We propose a link between the Tortonian-early Messinian inversion of the fault pattern and a plate tectonic reorganization prior to the main phase of back-arc opening of the Tyrrhenian domain

Levantine basin and Cyprus arc : structural and sedimentary process along sub-marine plate boundaries

La convergence des plaques eurasienne et africaine s est réalisée, depuis le Crétacé, par une succession de subductions et de zones de pré-collision qui témoignent d un processus de fermeture de la Méditerranée. L arc de Chypre est le segment le plus oriental de ce système de convergence méditerranéen qui se complique par le mouvement vers l Ouest de la microplaque anatolienne. Ce mouvement génère en Méditerranée Orientale et particulièrement le long de l Arc de Chypre, un régime tectonique complexe. Au cours d une campagne de géophysique marine réalisée en 2003 (campagne BLAC, N/O Le Suroît), près de 20000 km2 ont été cartographiés aboutissant à une couverture quasi-complète du segment oriental de l arc de Chypre depuis les monts Hecataeus jusqu aux abords de la marge syrienne. Les données suivantes ont été acquises de façon simultanée et continue : bathymétrie multifaisceaux et imagerie acoustique grâce au sondeur multifaisceaux Simrad EM300, sismique réflexion 6-traces, sondeur de sédiments (CHIRP), gravimétrie et magnétisme. Ce travail fournit une analyse structurale et morphologique du segment le plus oriental de l arc de Chypre ainsi qu un examen détaillé des instabilités gravitaires sur la marge syrienne et les différentes activités halo/argilocinèse au sein des bassins avoisinants de l arc de Chypre.The convergence of Eurasian and African plates started since the Cretaceous by a succession of subduction and pre-collision zones that witness a closure process of the Mediterranean. The Cyprus Arc is the easternmost segment of this Mediterranean convergence system which got complicated with the westward extrusion of the Anatolian microplate. This movement generates in the Eastern Mediterranean and in particularly along the Cyprus Arc a complex tectonic regime. During the research cruise BLAC in 2003 onboard the R/V Le Suroît, 20.000 sq Km of seafloor has been mapped including the easternmost segment of Cyprus Arc and going from Hecataeus Seamount till the Syrian margins. The following data have been acquired continuously and in a simultaneous way: Multibeam bathymetry and backscatter imagery with the multibeam echousounder EM300, 6-traces seismic reflection, subbottom sediment echousounder (CHIRP), gravity and magnetic data. This manuscript gives structural and morphological analysis of the easternmost segment of the Cyprus Arc as well as a detailed study of gravity induced instabilities on the Syrian margin and the different mud and salt activities in the adjacent basins of the Cyprus Arc.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Étude biocénotique et qualité des eaux de quatre cours d'eau côtiers libanais Nahr Ibrahim, Nahr el Kalb, Nahr Antélias et Nahr Beyrouth (biologie et écologie de Capoeta damascina Günther 1868 (poisson, cyprinidae))

Quatre cours d'eau libanais ont fait l'objet d'une étude écologique basée sur des observations, des recherches et des mesures physico-chimiques et biologiques afin d'évaluer la qualité des eaux de ces hydrosystèmes continentaux. Les barrages sur Nahr Ibrahim n'ont pas d'effet notoire sur la qualité des eaux. Nahr el Kalb possède un régime d'écoulement temporaire dans son cours moyen. Les communautés zoologiques sont plus pauvres que celles du Nahr Ibrahim. Nahr Antélias est pollué sur tout son cours, les rejets d'eaux usées aggravant cette pollution. Le genre Physa caractérise ce cours d'eau. Dans le Nahr Beyrouth les indices biotiques possèdent des valeurs assez grandes. Le cours inférieur est un égout en basses eaux, avec des espèces faunistiques et floristiques caractéristiques des eaux polluées. Capoeta damascina, est un poisson phytophage, qui se nourri de diatomées (Navicula et Synedra) et de l'algue Rhizoclonium. L'étude du cycle sexuel de C. damascina montre l'apparition d'un dimorphisme sexuel, et un sex-ratio supérieur à 1.The ecology of 4 rivers in Lebanon, Nahr Ibrahim, Nar el Kalb, Nahr Antelias and Nahr Beirut has been studied based on systematic observations and on the study of physico-chemical and biological parameters in order to evaluate their ecological status and characterize any anthropological impacts. Dams on Nahr Ibrahim have no measurable effect on the ecosystem. Nahr el Kalb possesses a temporary flow in its middle section. The zoological communities appear to be poorer than that of Nahr Ibrahim. Nahr Antelias is polluted throughout mainly as a result of discharges from the village of Antelias. The river is characterized by the presence of the mollusca Physa. In Nahr Beirut, the biotic indices are high. The lower section of the river, transforms into a sewer in periods of low water flow as evidenced by fauna and flora characteristic of such waters. Capoeta damascina in these waters is a phytophagous fish and diatoms ( Navicula & Synedra) with the algae Rhizoclonium are its major dietary source. The fish shows sexual dimorphism with the sex ratio higher than 1.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Morphodynamique à multi-échelles du trait de côte (prisme sableux) du golfe du Lion depuis le dernier optimum climatique

La problématique du trait de côte revient constamment dans les problèmes environnementaux littoraux. Depuis 6000 ans, le trait de côte s est déplacé. Le golfe du Lion (mer Méditerranée) constitue un laboratoire naturel exceptionnel pour l étude de la migration du trait de côte en milieu microtidal, de par les présences de lagunes en arrière du cordon et de barres subtidales sur l avant-côte. Les lagunes sont des milieux où l enregistrement sédimentaire est bien préservé, permettant de reconstruire l évolution de la lagune et la construction de la barrière littorale. Le premier objectif de ce travail est de caractériser l évolution de la lagune de Thau et du lido de Sète à travers l étude du remplissage sédimentaire. Utilisant les techniques de sismique réflexion et de carottages sédimentaires, trois unités principales ont été décrites. Leur analyse et les datations obtenues ont permis de reconstruire les principales étapes de l édification de la lagune. Les littoraux présentant deux barres sédimentaires ont été largement observés en milieux méso- et macrotidaux. Leur étude en milieu microtidal étant moins fréquente, le système à deux barres festonnées de Leucate-Plage a donc été observé depuis 2000. Le second objectif de ce travail est de proposer un modèle conceptuel d évolution basé sur la morphodynamique de ce système, à partir de suivis géophysiques et hydrodynamiques. Ce modèle, basé sur différentes séquences évolutives observées, a nécessité la création de nouveaux états de plage incluables dans les classifications usuelles. Il met en évidence l importance de la hauteur significative et de l incidence de la houle dans les changements morphologiques des systèmes.Problems in coastal environments are often linked to the position of the shoreline, which has moved for 6000 years. Gulf of Lion (Mediterranean Sea) is an exceptional natural laboratory for morphodynamical studies of the shoreline in microtidal environment, using the existence of coastal lagoons behind the barrier island and subtidal sandbars on the shoreface.Lagoons are environments where the sedimentary infill is well preserved. The sedimentary record can be used for the paleo-reconstruction of the lagoon and of the sandy barrier. The first goal of this work is to characterize the evolution of Thau lagoon and Sète sandy barrier from the sedimentary infill. Using data of seismic reflexion and sedimentary cores, three mains units have been described. The main steps of the lagoon edification have been reconstructed using the analyses and the datation of the sedimentary samples.Coast showing systems with two sandbars have been observed in meso- and macrotidal environments. Their study in microtidal environment is less abundant, that s why the system of Leucate Beach has been studied since 2000. The second goal of this work is to propose a conceptual modeling based on the morphodynamics of the system, from geophysical and hydrodynamical data. This model is based on morphodynamic observed sequences, it is necessary to create two beach states which can be included in the usual classification. It shows the role of the significant wave height and the incidence of the waves in the morphodynamics of the system.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF