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RésuméUne analyse de séries sédimentaires d’âge Crétacé supérieur dans le Sud-Est de la France a été entreprise et intégrée dans un cadre de stratigraphie séquentielle. Les limites Cénomanien–Turonien et la limite Turonien–Coniacien sont marquées par des variations rapides et de fortes amplitudes du niveau marin relatif. La comparaison effectuée avec d’autres bassins mondiaux nous amène à envisager le problème dans un cadre global. On constate : (1) le synchronisme d’événements à haute fréquence dans des contextes géodynamiques différents. (2) les effets de la superposition de cycles eustatiques hiérarchiquement différents, c’est-à-dire la superposition d’oscillations à haute fréquence sur une composante de 3e ordre. Ces observations sont confrontées à deux hypothèses : le glacio-eustatisme et la tectonique à haute fréquence. © Elsevier, Paris. 相似文献
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《Geodinamica Acta》1998,11(1):1-11
In order to debate of the early Paleozoic paleogeography, the repartition of the Hercynian blocks, today scattered around West-Mediterranean Sea. should be known. This is the case for the end of the Paleozoic (Fig. 1), but not for the beginning; Fig. 6 is drawn with the supposed repartition in the middle of the Carboniferous.In Central and Eastern Pyrenees and surrounding areas (Fig. 1), Upper Ordovician beds rest unconformably upon a thick (4–6 km), dominantly pelitic series known as Lower Paleozoic in the Eastern Pyrenees or Seo Formation in the Central Pyrenees. The metamorphic lower part of this series often lies over metagranilic orthogneisses, which are best interpreted as a Precambrian basement, Panafriean-Cadomian in age. By correlation with fossiliferous series of other areas, the Pyrenean Lower Paleozoic should be mainly Cambrian in age (ranging from Uppermost Proterozoic to Lowermost Ordovician).For the purpose of this paper, the complex lithostratigraphic succession of the Lower Paleozoic of the Eastern Pyrenees, with two groups and seven formations, could be summarized (Fig. 2) by a threefold division, from bottom to top: (i) a pelile-greywacke and carbonate unit, with a conspicuous plagioclasic component and a sodic composition (Uppermost Precambrian to Lowermost Cambrian?): (ii) a sandstone-pelite unit, with lithic sandstones, ending with a carbonate level, well developped in the Central Pyrenees (Lower Cambrian?): (iii) a mudstone-siltstone unit (Middle-Upper Cambrian?). Fossiliferous Lower Cambrian beds which outcrop at Terrades (south of the Eastern Pyrenees) could be a remnant of an allochthon unit which can be compared with the nappe-thrusts of the nearby Southern Montagne Noire.The pelite-greywacke and carbonate unit (Fig. 3) occurs only in the South-Eastern Pyrenees as a south to north transgressive platform bordering a basin extending southwards; not far south of Eastern Pyrenees, a volcanism of “intermediate” type supplied in plagioclasic clasts the greywackes and volcanoclastic deposits. Near the base of the sequence, a bimodal volcanism and synsedimentary faults reflect the extensional context of the basin initiation, the geochemistry of which has been related to back-arc setting. An acidic volcanism developped higher in the sequence (tufs and hypovolcanic bodies). Carbonate levels are numerous, particularly in the lower part of the unit. The upper part of the sequence is an oslistostrome made of polygenic intraformational conglomerates fed from the south: it outlines the transition to the next unit.The sandstone-pelite unit (Fig. 4) rests conformably on the previous one in the Eastern Pyrenees, and is unconformable upon the Precambrian basement to the north (North-Pyrenean massifs) and to the west (Central Pyrenees). It is characterized by arkosic lithic sandstones with clear quartz grains: they originated in the erosion of a granitic basement and/or acidic volcanic rocks. Coarseness of the sandstones and thickness (up to 2–4 km) of the unit increase from south-east to north and west. A carbonate upper level, well developped in the Central Pyrenees, can be correlated with Lower Cambrian limestones from the surrounding areas.The mudstone-siltstone unit (Fig. 5) is defined by the prevalence of mm- to cm- scale alternations of argillaceous mud and silt of a flyschoid type, representing a more basinal sedimentation. A carbonate level, the highest in the series, is intercalated in Ihe lower part ot the unit: above this level, deposits are very homogeneous and thiek (about 2 km). A poorly known formation with pelitcs and sandstones caps the muddy-silty unit: it could be Lower Ordovician in age.Thus, the Pyrenean domain shows the same depositional history as West-Mediterranean area: (i) first, a volcano-sedimentary platform or basin occurs, as in Central Spain. Eastern Pyrenees. Sardinia and axial zone of the Montagne Noire, but not further north; (ii) second, a silicoclastic platform spreads out. which becomes carbonated at the end: (iii) third. Ihe basin deepens and receives fine silicoclaslies. This evolution is not fully accounted for in recent synthesis of Pre-hercynian France or Spain, and it should appear useful for a better understanding of the south French Massif Central geological history. 相似文献
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《Geodinamica Acta》1998,11(6):253-270
A recent detailed analysis of southeastern France upper Cretaceous series has evidenced that Cenomanian-Turonian and Turonian-Coniacian boundaries are marked by quick and large amplitude relative sea level changes. Comparisons with other sections in different worldwide basins are coincident with the observations pointed out in southeast France. We establish: (1) high-frequency synchronous events in different geodynamic settings, (2) the superposition of various hierarchically eustatic cycles i.e. the superimposition of high-frequency oscillations on a third-order trend. Two possible mechanisms responsible of these observations are emphasized and discussed: glacio-eustasy versus high-frequency tectonics. 相似文献
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Fossil plants from Upper Jurassic sediments belonging to the Gymnosperms s.l. have been studied in the Manamana massif from the southwestern part of Madagascar. The levels are Upper Oxfordian in age on the basis of the palaeontological content, especially with ammonites. The majority of fossil plants are devoided of organic matter but in some cases collodion peels have been made to present epidermal characters. The cuticle of Brachyphyllum madagascariense nov. sp. has been observed with scanning electron microscope (SEM). This new flora is constituted by Pteridospermales and Coniferales. Fragmentary fronds of Pteridospermales have been collected of Pachypteris sp. A and Pachypteris sp. B. Some epidermal characters are described. Coniferales are represented by leafy stems. The diagnosis of Brachyphyllum madagascariense nov. sp. is given with morphological and epidermal characters. Others conifers have been determined: Brachyphyllum sp. A, Brachyphyllum sp. B, Elatocladus sp., Cupressinocladus sp., Cyparissidium sp.. Araucarites sp. remains are probably isolated fertile scales of a female cone. Complete cones of Conites sp. are also present.Comparisons of the systematic composition are made with other Gondwana floras of the same age from Antarctica, South America, Madagascar, India, South Africa, New Zealand and Australia. This flora shows xerophytic adaptations. With the Filicales described by Appert (1973a, b) from the same localities, it is now the most diverse flora from the Upper Jurassic of Madagascar, despite the lack of Cycadales, Bennettitales and Angiosperms. 相似文献
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