bluuebunny/crossref_metadata_2025 huggingface dataset:
New data on the flora and fauna from the ?uppermost Carboniferous-Lower Permian of Buxieres-les-Mines, Bourbon l'Archambault Basin (Allier, France); a preliminary report
Authors: Steyer J. Sebastien , Escuillie Francois , Pouillon Jean-Marc , Broutin Jean , Debriette Pierre , Freytet Pierre , Gand Georges , Poplin Cecile , Rage Jean-Claude , Rival Jacques , Schneider Joerg W. , Stamberg Stanislav , Werneburg Ralf , Cuny Gilles
Published: June 2005

New fossils from the ?uppermost Carboniferous-Lower Permian have been found at Buxieres-les-Mines (Massif central, France). In this preliminary article we report on algae, stromatolites, palynomorphs, macroflora, ostracods, insects, elasmobranchs, acanthodians, actinopterygians and amphibians. Elasmobranchs and amphibians are diversified compared with those of other European localities. Most taxa indicate lacustrine deposits and an Asselian age, and permit us to address the question of the palaeoecosystem evolution of the Bourbon-l'Archambault Basin, during the Lower Permian.
Des boules de bousiers fossiles et leurs terriers dans les sites a Australopitheques du Pliocene tchadien
Authors: Duringer Philippe , Brunet Michel , Cambefort Yves , Beauvilain Alain , Mackaye Hassane Taisso , Vignaud Patrick , Schuster Mathieu
Published: June 2005

The structures under study belong to the Pliocene continental formation of the palaeo-lake Chad system. This formation is famous for the discovery, in 1995, of the first australopithecine from Chad associated with a rich fauna of mammals, birds, reptiles and fishes. The analysis of this fauna and the interpretation of the depositional environment reveal a landscape of gallery forest, savannah grasslands, and ephemeral rivers interrupted by lacustrine episodes. The sandstone facies contains sandstone balls of 4 to 12 centimetres in diameter, lightly flattened at the poles. These structures are characterized by an external husk or crust and by a centimetric cavity in the upper part of the ball. Between the husk and the cavity, there exists a number of concave laminae, similar to those of a bulb, whose concavity is directed toward the upper cavity. These balls are associated with a vast metre-scale gallery network. This sandstone balls are interpreted as fossil brood-balls of dung beetles (Coleoptera, Scarabaeidae). Comparisons between these structures and the brood-balls of modern Scarabaeidae reveal great similarity, especially in the external husk, the concave internal laminae, and the chamber for the larva in the upper part of the structures.
Les oeufs de dinosaures du Cretace superieur du bassin de Villeveyrac-Meze (Herault, France); description d'une nouvelle ooespece de Prismatoolithus
Authors: Garcia Geraldine , Feist Monique , Cabot Alain , Valentin Xavier , Vianey-Liaud Monique
Published: June 2005

The dinosaurian eggshell localities, found recently in the Villeveyrac-Meze basin allow to precise the datation of the continental levels overlaying the Villeveyrac Campanian series. They also provide information on the oospecies diversity in the Campano-Maastrichtian of southern France. Seven Megaloolithidae species which are already known in the Aix basin have been identified as well as a new prismatoolithid species, Prismatoolithus caboti.
Modification of the original stratigraphic distribution of Globigerina hillebrandti Orue-Etxebarria, 1985 and its inclusion in another genus; one more planktonic foraminifer species surviving the mass extinction of the K/T boundary
Authors: Orue-Etxebarria Xabier , Apellaniz Estibaliz
Published: June 2005

The detailed study of K/T sections in western Pyrenees, SE of the Iberian Peninsula and Tunisia demonstrate that Hedbergella hillebrandti previously thought to be restricted to the Lower Paleocene also occurs from the Upper Maastrichtian. This species originally attributed to the genus Globigerina is transferred in Hedbergella and is one of the planktonic foraminifers surviving the mass extinction of the K/T boundary.
Mode d'empilement et distorsion de sequences genetiques en milieu marin restreint; facies et architecture des depots hettangiens du sud-ouest du bassin de Paris
Authors: Merzeraud Gilles , Rauscher Raymond , Hoffert Michel , Verdier Francois
Published: June 2005

In the southwestern part of the Paris Basin (Sologne region), dolomite and limestone deposits of Hettangian age represent an excellent cover for a thick sandstone reservoir, which is being worked by "Gaz de France" for natural gas storage in underground aquifers. The "genetic sequences" of these shallow marine deposits and their stacking patterns are associated with two orders of relative sea-level fluctuations. The thinnest genetic sequences are arranged in transgressive/regressive hemicycles that include distinct facies assemblages. The facies changes are related to rapid palaeogeographic variations that occur during the onset of each genetic sequence. On a different scale, the stacked genetic sequences are organized into three geometric patterns, which are related to long-term eustatic fluctuations (eg. aggradational, retrogradational, and progradational patterns). For each of these stacked geometries, the partitioning of sediment volumes, the degree of symmetry, and the two-dimensional architecture of the genetic sequences had been modified through time. These changes are related to the effects of two superimposed short-term and long-term sea-level oscillations that distort the stratigraphic record.
Les glissements rocheux du versant sud du Layens (Vallee d'Aspe, Pyrenees occidentales)
Authors: Fabre Richard , Desreumaux Christian , Lebourg Thomas
Published: June 2005

Detailed geological surveys carried out recently on the Layens have permitted to redefine the lithostratigraphy and to establish the structure of its south slope where several rockslides have been precisely located. This south slope is composed of a carbonaceous Mesozoic series ranging from the Triassic up to the Lower Cretaceous which is located on the reverse flank of a large overfolded north north-eastern syncline. The lithological and structural heritage, together with its special geodynamic setting, generate many brittle zones which favour the mechanical instability of the slope. On this basis the morphostructural position of the rockslides has been established, some of which are unstable while others are stable. Two stages in the evolution of the rockslides have been deduced from the geomorphology and mapping. These field observations have enabled us to distinguish three different rockslides (A, B, C) which are either deep or superficial. The analysis of the causes of their instability have been considered by taking into account the orientation of the major mechanical discontinuities, inherited from the structural context, as well as the sensitivity to the slipping of Triassic clay formations. The natural causes of the destabilization of the south slope of the Layens have been established for the most active rockslide : the geological surveys permit an evaluation of the volume and the total displacements.
Utilisation du 10 Be cosmogenique produit in-situ pour l'etude de la dynamique et de l'evolution des sols en milieux lateritiques
Authors: Braucher Regis , Siame Lionel , Bourles Didier , Colin Fabrice
Published: June 2005

In situ-produced cosmonuclides result from nuclear reactions between cosmic-rays derived particles and the elements constituting the Earth's surface material. Cosmogenic 10 Be (T1/2 = 1,5Ma) and 26 Al (T1/2 = 0.73 Ma) produced within the quartz mineral fraction of surficial rocks have been used to quantitatively study the emplacement and development of laterites. Depth distributions of in situ-produced 10 Be along quartz veins and soil profiles permit: (1) to clarify mechanisms involved in soil formation and landform evolutions, (2) to quantify burial or denudation rates. Lateral variations of the in situ-produced 10 Be concentration along stone-lines allow to determine whether the stone-line constituting material has an allochthonous or an autochthonous origin, and, in the latter case, to estimate the lateral displacement rates.
Les lahars; depots, origines et dynamique
Authors: Lavigne Frank , Thouret Jean-Claude
Published: June 2005

A lahar is a flowing mixture of rock debris and water (other than normal streamflow) from a volcano, which encompasses a continuum from debris flows (sediment concentration > or =60% per volume) to hyperconcentrated streamflows (sediment concentration from 20 to 60% per volume). Debris flow deposits are poorly sorted and massive with abundant clasts. Lahars can be either syn-eruptive, post-eruptive or have a non-eruptive origin. Four types of lahars can be generated during an eruption, based on distinct sources of water (i.e. ice, snow, crater lake, river, and rain) that allow the sediments to be removed and incorporated in the lahar (e.g., Mount St.-Helens in 1980, Nevado del Ruiz in 1985). Post-eruptive lahars, which are rain-triggered, occur during several years after an eruption (e.g., still occurring at Pinatubo). Non-eruptive lahars are flows generated on volcanoes without eruptive activity, particularly in the case of a debris avalanche or a lake outburst (e.g., Kelud or Ruapehu). Lahars flow as pulses, whose velocity and discharge are much higher than those of streamflows, including catchments similar in size. Sediment transport capacity of lahars is exceptional, owing to buoyancy, dispersive pressure, and to the amount of cohesive clay and silt. However, the finding of recent experimental works indicates that even clay-rich lahar mixtures have little true cohesion. Therefore, the typical classification of lahars into "cohesive" and "non cohesive" seems to be inappropriate at present. Besides, past work on lahar mechanics used models based on the Bagnold's or the Bingham's theories. Recent advances in experimentation show that a lahar has specific rheological properties: it moves as a surge or series of surges, driven by gravity, by porosity fluctuation, and by pore fluid pressures, in accordance with the Coulomb grain flow model. Grain size distribution and sorting control pore pressure distribution. Lahar mechanics depend on much more than steady-state rheology, because lahars are highly unsteady and typically heterogeneous flows. Lahar can show a succession of debris flow phases, hyperconcentrated flow phases, and sometimes transient streamflow phases. Therefore, some fluids-mechanics concepts and terminology, such as "viscous", "laminar" or "non-Newtonian" are inappropriate to describe the mechanical properties of lahars. Processes of deposition are complex and poorly known. Interpretation of massive and unsorted lahar deposits commonly ascribe the deposition regime to a freezing en masse process. However, recent laboratory experiments highlight that debris-flow deposits may result from incremental deposition processes.
Caracteres structuraux et dynamiques d'un bassin en transtension; la plate-forme tunisienne a l'Ypresien terminal
Authors: Gourmelen Claude , Rigane Adel , Broquet Paul , Truillet Rene , Aite Mohamed Ouramdane
Published: June 2005

In Tunisia, Ypresian carbonate deposits occur on a platform preserving vestige of an inherited fault network. The fault network delineates blocks of different sizes accounting for the platform morphology and in turn for variation in thickness of the Ypresian sequence. The nummulitic limestone carapace of the Ypresian sequence is fractured by faults and joints of various orientations which are systematically sealed by marly beds of early Lutetian age. This indicates that the fault network was reactivated during late Ypresian. Geometric and kinematic study indicates that this strike slip late reactivation is accomodated by normal fault. These structures originated in soft sediment undergoing diagenesis. Depending on bed competency, both ductile and brittle deformation features were recognized in the fault. This superficial tectonic event represents, a recent reactivation of ancient fractures cartographically located on the boundaries of late Ypresian megablocks. Kinematic study of the deformation within and along the boundaries of one of these blocks, (Ousseltia block), indicates a late Ypresian, early Lutetian strike-slip distensive faulting dynamic. Stress-field orientation indicates a rapid re-orientation in time from a predominantly NW-SE extensional tectonic to a NE-SW extensional event. Stratigraphic dating of that tectonical crisis coincides with a turbulent period of relative motions between Europe and Africa.
La desilicification des silex des formations residuelles a silex de l'ouest du bassin de Paris
Authors: Laignel Benoit , Meyer Robert
Published: June 2005

In NW Europe, chalk areas are generally covered with clay-with-flints (CWF). These formations are made of flints with a clayey or silty-clayey matrix. In the literature devoted to CWF, the flint dissolution during the weathering of chalk was poorly studied. In this study, we provide an estimation of this phenomenon in the western Paris Basin, by comparisons between the flints of CWF and those of chalks based on mineralogy, size, cortex and surface cavities of flints. Our results show that the mineralogy and thickness of flints have not been affected by the weathering. Only the volumes of cortex and surface cavities have increased. These two parametres allow us to quantify the flint dissolution. Flint dissolution is low: the amount of dissolved silica in flints varies between 0.9 and 7.3%. These low values show that weathering of chalk who has led to the creation of CWF has not reached the intensity of a lateritic type weathering, as is the case in the ferralitic soil.
Morphodynamique fluviale et neotectonique dans la vallee de l'Oise (Bassin parisien, France)
Authors: Larue Jean-Pierre
Published: June 2005

To show the impact of neotectonics on fluvial morphodynamics, the author presents a geomorphological study of the Oise valley where it crosses the Pays de Bray anticline, and of the gullies and the dry valleys of the Pays de Thelle. The analysis of alluvial and colluvial forms and formations makes it possible to reconstruct the longitudinal profiles of successive river beds, from the valley heads to the Oise valley and thus to reveal anomalies. Tectonics control fluvial dynamics, but impacts are only observed if the climatic conditions are favourable: hence it can be deduced that the gullies were formed during the wet Subboreal period.
Influence of mineralogy and moisture content on plasticity and induced anisotropic damage of a claystone; application to nuclear waste disposals
Authors: Chiarelli Anne-Sophie , Ledesert Beatrice , Sibai Malek , Karami Mohammed , Hoteit Nasser
Published: June 2005

The influence of mineralogy and moisture content on mechanical behaviour of a claystone rock is studied by the way of uniaxial and triaxial compression tests and microscopic observations. Some parameters characteristic of phenomena like plasticity and induced anisotropic damage are discussed as a function of these two factors. Rock behaviour becomes more brittle when calcite content grows or when clay or moisture content decreases. At the microlevel, plasticity is induced by slip of clay sheets and induced anisotropic damage appears by growth of oriented microcracks at the interface between grains and matrix.
Sedimentological and diagenetical conditions of the impact level of the Cretaceous/Tertiary boundary in Tunisia; no anoxia required
Authors: Tribovillard Nicolas , Dupuis Christian , Robin Eric
Published: June 2005

The Ain Settara section (Kalaat-Senan area, Tunisia) shows a well-exposed and expanded Cretaceous/Tertiary (K/T) boundary that can be divided into several units of contrasted lithologies. The bolide impact level is identified thanks to the occurrence of a peak of iridium and Ni-rich spinel abundance. The impact level is a jarosite nodule-rich horizon upon which the emphasis is placed: the jarosite nodules, initially present as pyrite nodules, may be interpreted as reflecting reducing depositional conditions at the K/T boundary. Trace metal geochemistry indicates that depositional conditions were not reducing and that the nodules must not have formed during earliest diagenesis. Consequently, water column-scaled anoxia cannot be put forward to account for the mass extinctions observed at the K/T boundary at Ain Settara.
Contribution de la photogrammetrie numerique a l'etude spatio-temporelle de versants instables; l'exemple du glissement de terrain de Super-Sauze (Alpes-de-Haute-Provence, France)
Authors: Weber Dominique , Herrmann Agnes
Published: June 2005

Recent developments in image processing and digital photogrammetry offer to the geomorphologists increasingly accessible and effective tools for the spatio-temporal knowledge of landslides. These techniques were used to reconstitute the historical evolution of a complex flow slide occurring in the "Terres Noires" of the Barcelonnette basin. The lithological and morphological environment of the studied site is characteristic of the whole southern French Prealps where are largely present Jurassic marly formations. Six digital elevation models (D.E.M.) generated from stereoscopic couples of aerial photography, but also various ortho-images and perspective views, allow to follow the morphological evolution of the unstable slope since the years 1950's -- before the releasing of the landslide -- until our days. Besides multitemporal descriptions of the landscape and of the morphological processes occurred on this site, the implemented method appears particularly useful for the quantitative analysis of the instabilities. It appears notably as a powerful tool for the 3-D reconstruction of the landslide geometry and by the same occasion for the calculation of its volume.
Structural evolution of the early Miocene in the eastern Betic internal-external zone boundary (SE Spain)
Authors: Tent-Manclu Jose Enrique , Martin-Martin Manuel , Martin-Perez Jose Antonio , Serrano Francisco
Published: June 2005

The Internal-External Zone boundary (IEZB) in the eastern Betic Cordillera partially coincides with the Cadiz-Alicante Accident, mainly a major transcurrent fault of N060E direction. The study of an area located along the IEZB at a point where it separates from the Cadiz-Alicante accident has provided details concerning the geodynamic evolution of the cordillera at the moment of its structuration. Here the Internal Zone, consists of rocks assigned to the Malaguide Complex, dating its last sedimentation to the Aquitanian, and deposits assigned to the Vinuela Group (early-middle Burdigalian). The nappes of the Internal Zone were emplaced during the latest Aquitanian and the Vinuela Group (here the El Nino Formation) sealed it but was afterwards affected by the collision with the External Zone. On the other side of the boundary, the External Zone comprises two tectonic units: the Penarrubia Unit (late Cretaceous-middle Burdigalian), which is made up mainly of limestones and marls, and the El Frances Chaotic Complex composed by a set of different lithologies, all from the External Zone in a marly matrix that could be interpreted as a collisional melange formed in the early-middle Burdigalian. The contact between the two domains corresponds to a backthrust of the External Zone over the Internal Zone which occurred in the middle Burdigalian. The deposits sealing the IEZB are dated by calcareous nannofossils and planktonic foraminifera as late Burdigalian, and comprise clasts from both domains.
La succession lithostratigraphique du bloc de Banda dans la region de Kolonodale (Sulawesi central, Indonesie)
Authors: Villeneuve Michel , Cornee Jean-Jacques , Gunawan Wahyu , Martini Rossana , Tronchetti Guy , Janin Marie-Christine , Saint-Marc Pierre , Zaninetti Louisette
Published: June 2005

Sulawesi island is the convergence area of the Eurasian, the Pacific and the Australian plates. Villeneuve et al. demonstrated, from both lithostratigraphic and tectonic studies, that east and southeast Sulawesi was composed of two major continental blocks. - The "Banda block", including also Buru, Seram and Sinta Ridge, collided with the Asian volcanic arc of west Sulawesi during Oligocene times, then was dismembered during the Late Neogene Banda sea opening. - The Banggai-Sula block which was drifted from Irian Jaya and collided with the Banda block during Mid-Late Pliocene times. One of the fragments of the Banda block is in East Sulawesi, corresponding to the ophiolitic zone. There, in the Kolonodale area, it is possible to reconstruct the sedimentary succession under the ophiolite, despite intensive deformations. Over several years the stratigraphic framework of this area was detailed, following general mapping, and it is now possible, by including unpublished data concerning Cainozoic rocks, to reconstruct the Mesozoic-Cainozoic succession. Reconstructing the succession was possible by joint structural, stratigraphic and palaeoenvironmental studies. An example of structural cross-sections around the Kolonodale gulf is given on figure 4, from which local successions were built. We can now propose the general succession.
Influence of paleoenvironment and radiolytic alteration on the geochemistry of organic matter from Autunian shales of the Lodeve uranium deposit, France
Authors: Schlepp Laurence , Landais Patrick , Elie Marcel , Faure Pierre
Published: June 2005

Thirty-three samples of shales from the Lodeve Permian uranium deposit were examined by different analytical techniques. Samples were analyzed by Rock-Eval pyrolysis and by gas chromatography-mass spectrometry after extraction and fractionation. The determination of uranium content was carried out by atomic emission spectrometry. The composition of the organic extracts allows two groups of shales to be distinguished: the first one is marked by a high proportion of aliphatic hydrocarbons and the second by the predominance of aromatic compounds. These two groups exhibit distinctive biomarker characteristics. One group is characterized by (1) pristane/phytane ratios higher than 1, (2) distributions of terpanes dominated by the tricyclic terpanes and (3) the predominance of C 29 and C 28 steranes. The second group is marked by (1) pristane/phytane ratios lower than 1, (2) the predominance of the pentacyclic terpanes over the tricyclic terpanes and (3) the predominance of C 27 and C 29 steranes. It is suggested that the differences observed are mainly related to different depositional environments, although the uranium content may also influence some parameters such as the hydrogen index and the extraction yield.
The evolution of the Massif Central Rift; spatio-temporal distribution of the volcanism
Authors: Michon Laurent , Merle Olivier
Published: June 2005

The Massif Central area is the largest magmatic province of the West-European Rift system. The spatial-temporal distribution of Tertiary-Quaternary volcanism in the Massif Central, France, shows that three magmatic phases can be defined, each of them characterized by different volumes and different locations. The first event, termed the pre-rift magmatic event, is very scarce and restricted to the north of the Massif Central. It is suggested that this could result from lithospheric bending of the European lithosphere ahead of the incipient Alpine chain during the Paleocene. The second event, termed the rift-related magmatic event, is located in the north of the Massif Central only and is spatially connected with zones of high crustal thinning (i.e. the Limagne graben). It immediately follows Oligocene graben formation and associated sedimentation, and is represented by more than 200 scattered monogenic edifices. This second event can be attributed to partial melting as a consequence of lithospheric thinning that affected the north of the Massif Central during the rifting event. The lack of volcanism in the south during the same period of time is probably related to the very slight lithospheric thinning during the Oligocene. The third event, termed the major magmatic event, started first in the south in the upper Miocene at about 15 Ma, well after the end of the sedimentation. It is unrelated to any extensional event. This major magmatic event reached the north of the Massif Central at about 3.5 Ma, following a pause in volcanism of about 6 Ma after the rift-related magmatic event. These two episodes of the major magmatic event are spatially and temporally associated with the two main periods of uplift, suggesting a common origin for volcanism and uplift processes. The major magmatic event can be attributed to late thermal erosion of the base of the lithosphere above a mantle diapir, as suggested by seismic tomography data. This general magmatic evolution drawn from data at the Massif Central scale may apply to the Eger graben as well, as the three magmatic events described in this study (pre-rift magmatic event, rifting event and post-Miocene volcanic event) are also reported in the literature. This suggests that a single cause should explain the formation of the entire western European rift surrounding the Alpine mountain belt.
Melting of lower continental crust in a young post-collision setting; a geochemical study of Plio-Quaternary acidic magmatism from central Sulawesi (Indonesia)
Authors: Polve Mireille , Maury Rene C. , Vidal Philippe , Priadi Bambang , Bellon Herve , Soeria-Atmadja Rubini , Joron Jean-Louis , Cotten Joseph
Published: June 2005

Acidic potassic calc-alkaline (CAK) magmas have been emplaced in the central part of the western arm of Sulawesi from 6.5 to 0.6 Ma, mostly as peraluminous dacites, rhyolites and granites. They overlay or crosscut a high-grade metamorphic basement including lower crustal garnet peridotites and granulites, the latter showing evidences for incipient melting during rapid uplift. Major and trace element data coupled with a Sr, Nd and Pb isotopic study of the CAK magmas and their lower crustal basement rocks demonstrate that they share a number of common features, including radiogenic Sr and Pb and unradiogenic Nd signatures, consistent with those of Australian granulites and Indian Ocean sediments. We propose that the CAK magmas derived from the anatexis of lower crustal rocks of Australian origin (the Banggai-Sula microcontinent) during the phase of uplift which followed their collision with the Sundaland margin (the western arm of Sulawesi) during the Middle Miocene, and possibly the breakoff of the subducted Molucca Sea slab.
The Lias/Dogger boundary in Iberia; Betic and Iberian cordilleras and Lusitanian Basin
Authors: Sandoval Jose , Henriques Maria Helena , Ureta Soledad , Goy Antonio , Rivas Pascual
Published: June 2005

In this paper we present a synthesis on the Toarcian/Aalenian (Lias/Dogger) boundary in the Iberian Peninsula. We have selected in each domain the most representative areas and sections in which this boundary is represented: Fuentelsaz and Moyuela sections in the Iberian Cordillera, Sierra de Ricote and Cerro Mendez in the Betic Cordillera, and Sao Giao in the Lusitanian Basin. In these areas the succession across the Toarcian/Aalenian boundary is represented mainly by pelagic grey marl-marly limestone rhythmites, which contain abundant and characteristic ammonites. The standard ammonite zones of Aalensis (Mactra, Aalensis and Buckmani Subzones) for the uppermost Upper Toarcian, and Opalinum (Opalinum and Comptum Subzones) in the Lower Aalenian are recognised and characterised. Although the ammonite assemblages of the Betic Cordillera are typical of the Mediterranean province, and the Iberian and Lusitanian basins constitute a Sub-Mediterranean one, the ammonite assemblages are similar in the three basins, with the only significant difference being that phylloceratids and lytoceratids are abundant in the Betic domain and are scarcer in the other basins.
Nature des sources des composants andesitiques des Gres du Champsaur et des Gres de Taveyannaz; implications dans l'evolution des Alpes occidentales au Paleogene
Authors: Boyet Maud , Lapierre Henriette , Tardy Marc , Bosch Delphine , Maury Rene
Published: June 2005

Paleogene magmatism is widespread in the western Alps and its origin is still a matter of debate. It consists of calc-alkaline and shoshonitic suites with mainly granodioritic intrusions in the Internal Zone (northern Italy), andesitic volcanism in the Delphino-Helvetic Zone (French-Swiss domain) and the Esterellite intrusions in Provence. In the External Alpine Zone, the Taveyannaz Sandstones and the Champsaur Sandstones preserve andesitic pebbles and mineral fragments dated at 32 Ma. On the basis of trace-element and isotopic geochemistry (Sr, Nd, Pb and O) of mineral separates (amphibole, pyroxene and plagioclase) and andesitic clasts, we characterise the nature of magmatic source(s) and compare the isotopic compositions of the andesites with those of well known Paleogene igneous suites.
Interet de l'etude du cycle biogeochimique du silicium pour interpreter la dynamique des sols tropicaux
Authors: Meunier Jean-Dominique , Alexandre Anne , Colin Fabrice , Braun Jean-Jacques
Published: June 2005

Recent studies on the biogeochemical cycle of silica put new constraints into models of genesis and evolution of silica in tropical environments. The role of plants in weathering mass balances are illustrated by phytolith studies. In Dimonika (Congo) latosols, dissolved silica originates mainly from the dissolution of phytoliths rather than from the dissolution of non-biogenic silicates. In andosols from La Reunion island (Indian Ocean), a 15 cm thick, biogenic silica accumulation formed within 4000 years from bamboo forests fires. The turn-over of silica by plants must therefore be taken into account in studies of weathering rates. Weathering rates of trachytic ash layers in La Reunion island show that all the primary minerals are destroyed and that 50% of amorphous secondary Al/Si products are transformed into halloysite. Theses rates, which are faster than the ones obtained in the Hawaii islands, may strongly influence the turn-over of carbon in soils. Besides, phytoliths preserved from dissolution may help to decipher the records of environmental changes in soils. In Salitre (Brazil), the phytolith distribution has been calibrated with charcoal and pollens. The age of phytoliths, which increases with depth, allow to trace the savanna/forest changes.
Tectonic evolution of the Cevennes para-autochthonous domain of the Hercynian French Massif Central and its bearing on ore deposits formation
Authors: Faure Michel , Charonnat Xavier , Chauvet Alain , Chen Yan , Talbot Jean-Yves , Martelet Guillaume , Courrioux Gabriel , Monie Patrick , Milesi Jean-Pierre
Published: June 2005

The Cevennes area belongs to the para-autochthonous domain of the Hercynian Belt of the French Massif Central. Three lithological series, namely: sandstone-pelite, black micaschist and gneiss-micaschist, are identified. They form an imbrication of five tectonic units which overthrust the unmetamorphosed Viganais Paleozoic units to the south and the gneissic Mamejean Unit to the north. The structural, metamorphic and magmatic evolution of the Cevennes area is characterized by three events, namely: (1) southward shearing coeval to a MP/MT metamorphism dated around 340 Ma; (2) post nappe anatexis (T<750 degrees C, P>5 kb); (3) Namurian (ca 315 Ma) E-W extensional tectonics and plutonism. The structure of the Mt-Lozere-Borne granitic complex is constrained by new AMS and gravimetric data. The plutons are the driving power of the hydrothermal convective circulations responsible for an early deposition of diffuse arsenopyrite in the thermal aureole. Gold bearing sulfides are afterwards concentrated in quartz veins along brittle normal and wrench faults around the granite. Lastly, ore bearing quartz pebbles are sedimented in the Stephanian Ales coal basin.
Les vallees fossiles de la baie de la Vilaine; nature et evolution du prisme sedimentaire cotier du Pleistocene armoricain
Authors: Proust Jean-Noel , Menier David , Guillocheau Francois , Guennoc Pol , Bonnet Stephane , Rouby Delphine , Le Corre C.
Published: June 2005

The study of a dense network of high resolution seismic profiles in the bay of Vilaine, INSU-CNRS cruise Geovill, have led to the characterization of the architecture of the sediment wedge preserved between the coast and the 50 m isobath. This wedge lies on a substratum composed of three seismic units, U1, U2 and U3 respectively attributed to metamorphic and magmatic rocks, Lutetian and Ypresian sandy carbonates and post-Eocene sediments. The coastal sediment wedge comprises three major units. A basal unit (U4), dated around 600 to 300 ky BP, interpreted as braided river sandy conglomerates. A median unit (U5) corresponding to estuarine and fluvial sandstones and clays that give way to the west to mouth bar sandstones. A sommital unit (U6) attributed to marine argillites and barrier island sandstones dated from 8110+ or -200 years at the base. These three units are bounded by two major surfaces: an unconformity between U4 and U5 and a marine (wave and tidal) ravinement surface between U5 and U6. The unconformity is interpreted as a sequence boundary between two depositional sequences: a lower one with U4 seismic unit and a topmost one with U5 and U6 seismic units. Based on the available datations, the lower sequence is attributed to the Saalian and/or Elsterian glacial cycles and, the upper sequence to the Weichselian (lowstand systems tract) and to the Holocene marine transgression (transgressive systems tract). The passage from one sequence to the other corresponds however to a drastic shift in the paleoflow directions (60 degrees ) in the Bay of Vilaine closely related to the main faults orientations. The tectonic activity in Brittany during the Pleistocene, linked to intraplate stress, seems to exert a control on sediment architecture in the coastal wedge. Indeed, the tilt of the Armorican Massif during that period has caused a complete rejuvenation of the fluvial profiles in land and the separation of the paleo-Vilaine from the Paleo-Loire river courses.
The Pre-Pan-African rifting of Saghro (Anti-Atlas, Morocco): example of the middle Neoproterozoic Basin of Boumalne
Authors: Fekkak Abdelilah , Pouclet André , Badra Lakhlifi
Published: June 2005

In the Anti-Atlas, the Boumalne basin includes 3,000 m of Middle Neoproterozoic sediments. It consists of turbiditic deposits folded during the major Pan-African event ca 685 Ma. A syn-sedimentary basaltic pile of lava flows is interbedded in the upper part of the lower formation. These lavas show an initial rift tholeiite (IRT) chemical signature. Petrographical analysis of sediments and typology of detrital zircons indicate a continental margin sedimentation, without any volcano-sedimentary supply from a close volcanic arc. It is concluded that the Boumalne Basin formed in a continental passive margin evolving from an intracontinental rift. This interpretation differs clearly from that of a back-arc basin which is commonly accepted. Hence, the opening of this basin is related to the pre-Pan-African Saghro rift synchronous to the Central Anti-Atlas oceanization, and not to the demise of this oceanic domain along an active margin.
How does the Alpine belt end between Spain and Morocco ?
Authors: Michard André , Chalouan Ahmed , Feinberg Hugues , Goffé Bruno , Montigny Raymond
Published: June 2005

The Betic-Rif arcuate mountain belt (southern Spain, northern Morocco) has been interpreted as a symmetrical collisional orogen, partly collapsed through convective removal of its lithospheric mantle root, or else as resulting of the African plate subduction beneath Iberia, with further extension due either to slab break-off or to slab retreat. In both cases, the Betic-Rif orogen would show little continuity with the western Alps. However, it can be recognized in this belt a composite orocline which includes a deformed, exotic terrane, i.e. the Alboran Terrane, thrust through oceanic/transitional crust-floored units onto two distinct plates, i.e. the Iberian and African plates. During the Jurassic-Early Cretaceous, the yet undeformed Alboran Terrane was part of a larger, Alkapeca microcontinent bounded by two arms of the Tethyan-African oceanic domain, alike the Sesia-Margna Austroalpine block further to the northeast. Blueschist- and eclogite-facies metamorphism affected the Alkapeka northern margin and adjacent oceanic crust during the Late Cretaceous-Eocene interval. This testifies the occurrence of a SE-dipping subduction zone which is regarded as the SW projection of the western Alps subduction zone. During the late Eocene-Oligocene, the Alkapeca-Iberia collision triggered back-thrust tectonics, then NW-dipping subduction of the African margin beneath the Alboran Terrane. This Maghrebian-Apenninic subduction resulted in the Mediterranean basin opening, and drifting of the deformed Alkapeca fragments through slab roll back process and back-arc extension, as reported in several publications. In the Gibraltar area, the western tip of the Apenninic-Maghrebian subduction merges with that of the Alpine-Betic subduction zone, and their Neogene roll back resulted in the Alboran Terrane collage astride the Azores-Gibraltar transpressive plate boundary. Therefore, the Betic-Rif belt appears as an asymmetrical, subduction/collision orogen formed through a protracted evolution straightfully related to the Alpine-Apenninic mountain building.
The island of Maupiti : the oldest emergent volcano in the Society hot spot chain (French Polynesia)
Authors: Blais Sylvain , Guille Gérard , Guillou Hervé , Chauvel Catherine , Maury Rene C. , Pernet Gilles , Cotten Joseph
Published: June 2005

The island of Maupiti is the top of an eroded volcanic shield surrounded by a large lagoon and coral reef. The most important part of this shield is made up of alkali basaltic lavas grading upward into hawaiitic flows. The shield-building event is dated at ca. 4.51 ± 0.04 Ma. A few mugearitic and benmoreitic late dykes were emplaced at 4.21 ± 0.04 Ma. These chronological data are consistent with a Pacific plate motion of 11 cm/year with respect to a fixed Society plume. The Maupiti lava series results from the effects of fractional crystallisation of a parental alkali basalt magma displaying a prominent EM II isotopic and trace element signature, in many ways similar to that of the youngest Society hot spot lavas. This feature suggests that the geochemical signature of the Society plume did not change through time.
Sea-level changes and ammonite faunal turnover during the Lias/Dogger transition in the western Tethys
Authors: Sandoval José , O’Dogherty Luis , Vera Juan Antonio , Guex Jean
Published: June 2005

The aim of this paper was to investigate the possible connections between ammonite faunal turnover and the eustatic events recorded in Tethyan sequences during the middle Toarcian/early Bajocian time interval. For this we have analysed the biostratigraphic ranges, at the subzone level, of approximately 600 ammonite species belonging to 160 genera from several selected sections of the western Tethys (Mediterranean and Submediterranean provinces). The analysis of taxon ranges enabled us to plot curves for ammonite faunal turnovers, inter-subzonal distance, and diversity. Comparing the mentioned curves with Tethyan sequences [Hardenbol et al., 1998], we find that sea-level changes correlate well with origination and extinction events and faunal diversity. Most of the faunal turnovers correlate with stratigraphic events. Extinction events with their corresponding decrease in diversity correlate with regressive intervals and with major or minor sequence boundaries. Origination events and their corresponding increase in diversity were clearly connected with transgressions in Tethyan sequences. In several cases, the major sequence boundary and the subsequent transgressive phase correlate with major ammonite faunal turnover, whereas minor or medium sequence boundaries generally gave rise to minor or medium turnovers.
Role of an extension of pre-Quaternary age for the evolution of the carbonate massifs in the occidental Betic Cordillera: The case of the Yunquera-Nieves massif (southern Spain)
Authors: Pistre Séverin , Liñán Cristina , Andreo Bartolomé , Carrasco Francisco , Drogue Claude , Martin-Algarra Agustín
Published: June 2005

A simultaneous analysis of the fracture geometry and paleo-stress fields of the karstic Yunquera-Nieves massif i n southern Spain (Málaga Province) has been carried out with microtectonic stations. It reveals polyphased t ec -tonics linked to the structural position of this carbonate domain in the western Betic Cordillera.

Among the tectonic regimes described in this domain appears a distensive stage with a radial trend probably of post-Tortonian to Quaternary age. Todate, it has seldom been described and is absent from geodynamic models though it seems to have had a regional importance. Furthermore, it played a major role for the acquisition of the hydrodynamic properties of t he aquifer and its karstogenesis. This stage opened all fractures and allowed t he development of karstic drains with NW-SE and N-S directions. Finally, the karstic network was shaped by more recent climatic and tectonic events.
Trapping and mobilisation of arsenic and lead in former mine tailings –Environmental conditions effects
Authors: Courtin-Nomade Alexandra , Neel Catherine , Bril Hubert , Davranche Mélanie
Published: June 2005

Tailings of two former mines located in the French Massif Central (La Petite Faye in Creuse Dpt. and Enguialès in Aveyron Dpt.) were studied in order to forecast the mobility of arsenic and others metallic trace elements (MTE) resulting from sulphides oxidation. Arsenic and MTE could potentially be toxic as a contamination in the sediments, soils, waters…The formation of new products resulting from the alteration processes is especially interesting because of the abilities of these products to trap these metals or metalloids. We have focussed our study on the alteration products in order to determine their role in the immobilisation of arsenic and others MTE. The two selected sites present closed Eh-pH conditions (acidic and oxidant). Nevertheless La Petite Faye site display less leaching than in the site of Enguialès due to its layout: the tailings in the former site are disposed in a settling basin whereas in the latter one, they are spread out on a steep slope. After a chemical and mineralogical characterisation of the tailings, we have estimated according to the Eh-pH conditions the solubilities of the various secondary products. In both sites, the hydrochemical study (for la Petite Faye) and laboratory experiments (for Enguialès) highlight the presence of mineralogical products with low solubility in the current geochemical conditions. At la Petite Faye, scorodite and beudantite mainly ensure an efficient trapping of As and Pb. These two minerals are stable for acidic and oxidant conditions, even if scorodite is more sensitive to pH variations and could transform into goethite. The low As (< 0,1 mg.L−1) and Pb (under detection limit) concentrations measured in the water table along the six-months hydrological study confirm this previous result. In Enguialès, high quantities of As are trapped in amorphous products (Fe/As ~ 1.7). Subsequently As is more easily remobilised and is trapped secondarily by goethite, hematite or jarosite but in few quantities in comparison with those observed in amorphous products (1.4 wt.% < As < 3.5 wt.%). This releasing is highlighted by the leaching experiments, which indicate a significant remobilisation of As issued from amorphous products. However, in current conditions, the properties of the iron oxyhydroxides or of the iron sulphate ensure an efficient As trapping.

The different behaviours of the trapping of As and Pb in the two sites are mainly explained by the hydrological context, the tailings layout, their granulometry and the cristallinity of the secondary products.
Evidence of flexural extension of the Rif foreland: The Rharb-Mamora basin (northern Morocco)
Authors: Zouhri Lahcen , Lamouroux Christian , Vachard Daniel , Pique Alain
Published: June 2005

The Rharb-Mamora basin is the foreland of the Rif Cordillera (orogenic belt). The Mamora area (northern Morocco) is located at the southern border of the Rharb basin and intercalated between the Alpine Rif Mountains to the north and the Hercynian Moroccan Meseta domain to the south.

Analysis and interpretation of seismic lines, hydrogeological and oil wells, have allowed to precise the major structural elements of the Mamora area, which is covered by late Neogene sediments.

The structure of the area is controlled by faults that also affect the Paleozoic basement. The NE-SW and NW-SE trending faults induce the palaeogeographical evolution and control, the facies distribution and the thickness variations. The most important or relevant structural feature of the Mamora area is the Kenitra-Sidi-Slimane fault (K2SF) [Zouhri et al., 2001]. This fault N110oE trending is south of the Rif Alpine thrust front and is marked by a progressive deepening of its northern compartment, at least since Cretaceous time. Thus the Mamora appears as a hinge between the Rharb Basin and the Moroccan Meseta from Cretaceous to Neogene time.
Prominent facies from the Lower/Middle Cambrian of the Dead Sea area (Jordan) and their palaeodepositional significance
Authors: Elicki Olaf , Schneider Jörg , Shinaq Rafie
Published: June 2005

New carbonate facies types are reported from the Cambrian Burj Fm. (Bilbilian) of the southern Dead Sea area (Jordan). They indicate the existence of a large low energy lagoon, with restricted water circulation and higher salinity, behind a high energy oolite shoal or shoal complex (back-barrier system). The transition between shoal and lagoon is marked by the interfingering of sediments from both environments, caused by washover events from the shoal into the lagoon behind. The lagoon itself was characterized by a low sedimentation rate and entire bioturbation. In a shoreward direction, the lagoonal facies changed into a microbial-dominated tidal or sabkha flat environment from which sediments were periodically reworked and redeposited into the lagoon. Comparison of our results with investigations of subsurface Cambrian deposits in southeastern and northern Jordan shows that lagoonal environments were the predominant carbonate production centres in this area during the short marine phase in the Cambrian of the Dead Sea area.