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31.
Benoît Laignel Florence Quesnel Robert Meyer Jean-Jacques Macaire 《Geodinamica Acta》2013,26(4):171-181
RésuméDepuis plus d’un siècle, l’origine autochtone ou allochtone des formations résiduelles à silex (en abrégé RS : résidus à silex) par rapport aux craies a fait l’objet de multiples discussions. Pour répondre à ce problème, un bilan d’altération entre ces deux formations a été effectué. Il repose sur une connaissance précise des âges des craies-mères des RS et sur des comparaisons granulométrique et chimique entre craie et RS. Ces comparaisons s’appuient sur les quantités de silex contenues dans les craies et les RS, sachant que les silex sont reconnus comme autochtones et que leur degré de dissolution est calculé. Les résultats apportent des informations sur l’évolution crétacée du Bassin anglo-parisien, avec la mise en évidence de la craie du Maastrichtien dans le bassin de Paris et la reconstitution des épaisseurs de craie dissoutes. De plus, ils indiquent que la stratigraphie des craies est conservée dans les profils de RS. Ils montrent également que les silex, éléments autochtones des RS, sont faiblement altérés. Les matrices des RS sont, quant à elles, en grande partie allochtones, notamment dans les dix mètres supérieurs de la formation. L’allochtonie diminue avec la profondeur, avec des RS pouvant être considérés comme des résidus d’altération de la craie au sens strict à partir de 20 mètres de profondeur. © Elsevier, Paris 相似文献
32.
Michael M. McGlue Kiram E. Lezzar Andrew S. Cohen James M. Russell Jean-Jacques Tiercelin Anna A. Felton Evelyne Mbede Hudson H. Nkotagu 《Journal of Paleolimnology》2008,40(2):635-653
New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic
evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences
(A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya
Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a
major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions
in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying
sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand
and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal
sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived
desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity.
Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography
created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout
the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water
body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged
aridity. 相似文献
33.
34.
Résumé Les textures des minerais de fer précambriens de type «jaspilite» sont semblables à celles des calcaires. Les éléments texturels suivants sont décrits: 1. orthochems: a) fémicrite, b) matrice siliceuse, c) ciment siliceux; 2. allochems: a) pellets, b) intraclastes, c) oolithes et pisolithes, d) échardes. Les types pétrographiques sont définis par la combinaison des éléments de texture, comme pour la classification des calcaires. Les types de faciès sont caractérisés par une séquence de bancs correspondant à un ou plusieurs types pétrographiques et par certaines structures sédimentaires. Ils forment la base de l'interprétation des conditions de dépôt et de la paléogéographie du bassin.Les transformations épigénétiques sont les suivantes: 1. dessication, fissuration, cimentation et compaction. 2. Cristallisation du gel de silice: a) quartz à cristallisation primaire, calcédonite et quartzine, b) quartz micropolygonal, c) quartz recristallisé. 3. Cristallisation de la poussière d'hématite, migration du fer et cristallisation de la spéculante et de la magnétite. 4. Cristallisation et recristallisation de la sidérite, de la minnesotaïte, de la stilpnomélane, de la riebeckite et du talc. La migration du fer et la cristallisation de la spécularite, de la magnétite et de la sidérite prennent place avant la compaction complète du sédiment et avant ou pendant la cristallisation primaire du quartz. Le quartz recristallisé, la minnesotaïte et peut-être le talc et la stilpnomélane, sont des minéraux tardidiagénétiques. La riebeckite se forme pendant le métamorphisme. Les phénomènes de recristallisation se poursuivent pendant le métamorphisme régional.
Publié avec l'autorisation du Ministre, Ministère des Richesses Naturelles du Québec. 相似文献
Textures of Precambrian cherty ironstones are similar to those of limestones. The following textural elements have been recognized: 1. Orthochems: a) femicrite, b) matrix chert, c) cement chert. 2. Allochems: a) pellets, b) intraclasts, c) oolites and pisolites, d) shards. Textural lithotypes are defined by the combination of the textural elements they contain, analogous to the classification of limestones. Textural faciès consist of beds of one or several lithotypes in characteristic sequence. They commonly contain distinguishing sedimentary structures. Textural facies are the basis of the interpretation of the depositional environment and basin configuration.The following types of epigenetic transformations have been recognized: 1. Dessication, shrinkage, cementation and compaction. 2. Crystallization of silicagel in the following sequence: a) primocrystalline quartz and chalcedony (normal and lengthslow), b) micro-polygonal quartz, c) recrystallized quartz. 3. Crystallization of hematite dust, migration of iron and crystallization of specular hematite and of magnetite. 4. Crystallization and recristallization of siderite, minnesotaite, stilpnomelane, riebeckite and talc. Migration of iron and the recristallization of speculante, magnetite and siderite take place essentially before the complete compaction of the rock and before and during the primo-cristallization of quartz. Recrystallized quartz, minnesotaite, and may be stilpnomelane and talc are essentially late diagenetic minerals. Riebeckite formed during metamorphism. A certain recrystallization occured during regional metamorphism.
Zusammenfassung Texturen der präkambrischen, kieseligen Eisensteine (Jaspilite) sind ähnlich denen von Kalken. Folgende Texturelemente wurden erkannt: 1. Orthocheme: a) Femikrit, b) Quarzmatrix (matrix chert), c) Quarzzement (cement chert). 2. Allocheme: a) Pellets, b) Intraklasten, c) Oolithe und Pisolithe, d) Scherden. Texturelle Lithotypen werden definiert durch die Kombination ihrer Texturelemente, wie in Kalken. Texturelle Fazies bestehen aus einem oder mehreren Lithotypen in regelmäßiger Folge. Sie besitzen oft kennzeichnende Strukturen. Texturfazien sind die Grundlage der Rekonstruktion der Bildungsbedingungen, Umwelt und Paläogeographie der Eisensteine.Folgende Arten epigenetischer Veränderungen wurden unterschieden: 1. Trocknung, Schrumpfung, Zementation und Kompaktion. 2. Kristallisation von Silikagel in der Reihenfolge: a) Primärquarz, Chalzedon und Quarzin, b) Kristallisation von Hämatitstaub, Wanderung von Eisen und Kristallisation von Spekulant und Magnetit. 4. Kristallisation und Rekristallisation von Siderit, Minnesotait, Stilpnomelan, Riebeckit und Talk. Wanderung von Eisen sowie Kristallisation von Spekulant, Magnetit und Siderit erfolgen im wesentlichen während der Kompaktion der Gesteine und vor (z. T. während) der Primärkristallisation von Quarz. Rekristallisierter Quarz, Minnesotait und vielleicht Stilpnomelan und Talk bilden sich weitgehend im spätdiagenetischen Stadium. Regionalmetamorphe Reaktionen führen zur Entstehung von Riebeckit und gelegentlich zu weiterer Kornvergröberung aller Minerale.
( ) : : 1) : ) , ) , ) ; 2) : ), ) , ) , ) . - , . , , , . . . , . : 1) , , , 2) : ) , , ) , , . 4) , , , . , , , , , — — , , , . , - .
Publié avec l'autorisation du Ministre, Ministère des Richesses Naturelles du Québec. 相似文献
35.
Pierre?Souquet Jean-Jacques?Delvolvé Stéphane?BrussetEmail author 《International Journal of Earth Sciences》2003,92(3):316-337
A foreland basin succession has been identified in the Frasnian of the Central Pyrenees. This succession comprises a carbonate-dominated transgressive system which recorded the cratonward migration of the foreland basin subsidence, and siliciclastic depocenters which recorded the progression of the thrust-fold deformation. The foreland basin system has always been maintained in deep-marine environments, i.e., at an underfilled depositional state. It was associated with a thrust wedge which descended toward a deep-marine hinterland, i.e., with a type of orogenic wedge usually related to subduction zones. The Frasnian foreland basin system differs from the one known in the Carboniferous which evolved to overfilled depositional state and was associated with a thrust wedge rising toward a mountainous hinterland. Consequently, the Hercynian orogeny in the Pyrenees seems to result first, from a Frasnian thrusting controlled by a subduction zone located north of the Pyrenees, and second, from a Carboniferous thrusting controlled by the surrection of a frontal thrust belt in the Pyrenees. The association of underfilled foreland basin systems and hinterland-dipping thrust wedges, as exemplified in the Frasnian of the Pyrenees, can be interpreted as illustrative of the initial stages of thrust-wedge growth in deep-marine settings. 相似文献
36.
Correlations and sequence stratigraphic model for Messinian carbonate platforms of the western and central Mediterranean 总被引:1,自引:0,他引:1
Jean-Jacques?CornéeEmail author Jean-Paul?Saint Martin Gilles?Conesa Philippe?Münch Jean-Pierre?André Simona?Saint Martin Stefan?Roger 《International Journal of Earth Sciences》2004,93(4):621-633
Distance correlations of Late Tortonian–Messinian littoral carbonate complexes are proposed from the study of eight platforms in the western and central Mediterranean. Correlations are based on the identification of two major biological sedimentary cycles and of two index surfaces. Surface A is a maximum flooding surface during cycle 1 at around 6.7 Ma. Surface B is a regional marine planation surface at around 5.95 Ma, at the base of cycle 2 (Terminal Carbonate Complex). A general sedimentary model is proposed for the 7–5.6-Ma time-span. The boundary between cycles 1 and 2 is coincident with the onset of the Messinian Salinity Crisis, and appears to be related to major environmental–paleo-oceanographic changes in the Mediterranean, rather than to a major sea-level drop or to climatic change. 相似文献
37.
The Gambia River estuary: A reference point for estuarine fish assemblages studies in West Africa 总被引:3,自引:1,他引:3
Monique Simier Charline Laurent Jean-Marc Ecoutin Jean-Jacques Albaret 《Estuarine, Coastal and Shelf Science》2006,69(3-4):615
The Gambia River is one of the last aquatic ecosystems in West Africa that has not yet been affected by strong environmental changes and human disturbances. In contrast to the neighbouring Casamance and Sine Saloum estuaries, the Gambia estuary is free of major climatic perturbation and remains a “normal” estuary, with a salinity range from freshwater to 39. The present paper aims to study the spatial and seasonal variability of fish assemblages in this estuary in terms of bio-ecological categories and of their relation with some environmental variables. Four surveys were conducted, from June 2001 to April 2002, in order to cover the major hydroclimatic events, at 44 sampling sites along the lower, intermediate and upper zones of the Gambia estuary (up to 220 km). Fish assemblages were sampled using a purse seine net, fish were identified to species level and environmental variables such as water depth, transparency, salinity, temperature and percentage oxygen saturation were measured. The main spatial structure of the fish assemblages and its seasonal changes were first studied using the STATIS-CoA multitable method. The combination of fish assemblages and environmental variables was then analysed using the STATICO method, designed for the simultaneous analysis of paired ecological tables. A total of 67 species were observed, belonging to all bio-ecological categories characterizing West African estuaries. The marine component of the community was largely dominant throughout the estuary, while the freshwater component was permanently observed only in the upstream zone. The main spatial structure was a longitudinal gradient contrasting marine and freshwater affinity assemblages, with strong seasonal variations. The most complete gradient was observed in December, at the beginning of the dry and cool season, while in June, at the end of the dry and warm season, there was the least structured gradient. The role of salinity, always correlated with temperature, was emphasized, while turbidity appeared to be another important factor. Oxygen and depth did not play a major role at the estuary scale. The relative importance of the bio-ecological categories varied according to the season and the distance to sea. Stable fish assemblages were observed in the lower zone at the end of the dry season, in the upper zone during the flood and in the middle zone throughout the year. In some situations, a relative inadequacy between fish assemblages and their environment was noticed. The present study contributes to the definition of the functioning of a “normal” West African estuary, the Gambia estuary, with balanced effects of marine and freshwater influences and the presence of all bio-ecological categories. The Gambia estuary can therefore be considered to be a reference ecosystem for further comparisons with other tropical estuarine ecosystems, subjected to natural or artificial perturbations. 相似文献
38.
Jesús Vidal Solano Francisco A. Paz Moreno Alexander Iriondo Alain Demant Jean-Jacques Cochem 《Comptes Rendus Geoscience》2005,337(16):314
Scattered ignimbritic mesas crop out in the Hermosillo region (Sonora, Mexico). These rocks that have been dated at 12.5 Ma (Middle Miocene) have the petrography and chemical characteristics of comendites. Such a flare-up of peralkaline acidic volcanism, after a long period of subduction-related arc volcanism, emphasises an important change in the source of volcanism. It corresponds to the latest stage of continental extension prior to the marine invasion and the development of spreading centres in the Gulf of California. To cite this article: J. Vidal Solano et al., C. R. Geoscience 337 (2005). 相似文献
39.
Christophe Falgures Jean-Jacques Bahain Carlo Tozzi Giovanni Boschian Jean-Michel Dolo Norbert Mercier Hlne Valladas Yuji Yokoyama 《Quaternary Geochronology》2008,3(4):390-398
The Visogliano shelter, in north-eastern Italy, is an important Middle Pleistocene occupation site where human remains were found together with an archaic lithic industry, including choppers, chopping tools and a few protobifaces. It is of utmost importance to try to document this period, when a second wave of settlement colonised Western Europe, carrying new flaking techniques and tools.Combined ESR/U-series analyses, integrated with biostratigraphical and environmental data, define a chronological frame for the layers from which the artefacts were unearthed. The lower levels, including human remains, can be dated to the 350–500 kyr time span, in agreement with micromammal and stratigraphical studies.These data make Visogliano one of the oldest palaeoanthropological sites in Italy, where human remains are directly associated with protobifaces, choppers and chopping tools. In Western Europe, Visogliano is contemporaneous to the G soil of the Arago Cave, France, with which it shares several similarities in faunal assemblages and radiometric data, and which contains human remains also. These data make Visogliano as one of the oldest sites in Europe where the Acheulian culture is observed. 相似文献
40.
Louis Rousseau Jacques Beauchamp Christophe Falguères Christophe Emblanch Dominique Genty Jean-Jacques Bahain Dominique Blamart 《Comptes Rendus Geoscience》2005,337(15):1348-1354
The isotopic composition of calcite from the stalagmitic floor E of the Lazaret Cave is interpreted as proxy of atmospheric circulation and vegetal cover changes during IOS 5. The variations could indicate change in precipitation sources, which could originate from the Mediterranean Sea during warm periods and from the Atlantic Ocean during colder periods. The variations could be related to vegetal cover and soil type. Tree cover appears to be dominant according to pollen spectra, and organic molecules trapped into calcite (sterols, terpenoids, humic acids). To cite this article: L. Rousseau et al., C. R. Geoscience 337 (2005). 相似文献