Les climats du paléogène franÇais reconstitués par les argiles néoformées et les microflores     

Sittler  Claude  Millot  Georges 《International Journal of Earth Sciences》1964,54(1):333-343

Résumé Des argiles néoformées ou authigènes se présentent au cours de la sédimentation du Paléogène. Tel est le cas dans trois séries sédimentaires étudiées. On trouve l'attapulgite dans les terrains de la limite du Crétacé et du Tertiaire au Languedoc, l'attapulgite et la montmorillonite à l'Eocène inférieur et à l'Oligocène moyen en Provence, la sépiolite à l'Oligocène supérieur en Bresse. Ces minéraux argileux sont interprétés comme néoformés dans des milieux à caractère alcalin, déposant aussi des carbonates et des silex. Ceci nécessite des bassins de sédimentation confinés, riches en solutions de silice, de magnésie et de chaux. Ces solutions sont le produit du lessivage des continents sous des climats fortement hydrolysants, tels que les climats humides et chauds à caractère tropical plus ou moins accusé. Or, l'analyse pollinique de ces mÊmes niveaux et la reconstitution des flores que l'on peut en déduire, confirment l'existence de ces climats subtropicaux ou méditerranéens à affinités tropicales, dont nous ont parlé par ailleurs les paléobotanistes. On remarque que ces climats ont des effets différents pendant les périodes d'agitation tectonique et pendant les périodes de calme où les actions dissolvantes se prolongent. Ce type de climat s'est maintenu depuis le Crétacé supérieur jusqu'à l'Oligocène supérieur.

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In the Tertiary basins of Provence, Languedoc and Bresse, the neoformation of clay minerals (attapulgit, sepiolit and montmorillonit) indicates warm tropical climates with humid and dry seasons. The palynological studies of these sediments attest the tropical character of the flora during Eocene and Oligocene time.

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Zusammenfassung Neubildungen von Tonmineralien werden in verschiedenen paläogenen Sedimentationsräumen festgestellt; so z.B.: Attapulgit an der Grenze Kreide-Tertiär des Languedoc, Attapulgit und Montmorillonit während des unteren Eozäns und mittleren Oligozäns in der Provence, Sepiolit im oberen Oligozän der Bresse. Es wird angenommen, da\ diese Tone in einem alkalischen Milieu entstanden sind, in dem gleichzeitig Karbonate und Kieselsäure ausgefällt wurden. Dies ist nur in geschlossenen Sedimentationsbecken, unter Einflu\ Si-, Mg- und Ca-haltiger Lösungen möglich. Diese Lösungen sind durch Auslaugung auf dem Festland unter stark hydrolysierendem Klimaeinflu\ entstanden, wie z. B. bei feucht-warmem Klima mit mehr oder minder ausgeprägt tropischem Charakter. Die Pollenanalyse dieser Schichten und das Pflanzenbild das sie widerspiegelt, lassen ebenfalls auf subtropisches bis mediterranes Klima mit tropischen Einschlägen schlie\en. ähnliches haben die Paläobotaniker an Hand der Makrofossilien festgestellt. Doch die Klimaverhältnisse wirken sich verschieden aus, je nachdem es sich um einen tektonisch unruhigen oder einen ruhigen Zeitabschnitt handelt. Während letzterem halten die Lösungsprozesse, d. h. die chemischen Vorbedingungen für die Ton-Neubildungen, länger an. Dieser Klimatyp bestand von der Oberkreide bis zum obersten Oligozän.

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The growth of the continent through geological time studied by Nd isotope analysis of shales   总被引：2，自引：0，他引：2  

Claude J. Allègre  Dominique Rousseau 《Earth and Planetary Science Letters》1984,67(1):19-34

We determined the Nd isotopic composition and the Sm/Nd ratios in a series of Australian shales ranging from 0.2 Gy to 3.3 Gy. The first result of this study is the constancy of the Sm/Nd ratio in these shales, as in granitoids. Secondly, the initial (¹⁴³Nd/¹⁴⁴Nd) ratio gives a regular curve decreasing through geological time. Both results confirm that shales are representative samples of the continental crust, when insoluble elements, like REE, are studied.We calculated their Nd model ages of crustal differentiation. The model ages regularly decrease with the stratigraphic ages and after 2 Gy, the curve flattens and tends to an asymptotic value at around 1.8 Gy. The significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin.From these results, we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas. We propose that the results obtained here are representative of the whole Gondwana continent.Having studied the case of the Australian shales, we try to extend our study. First we applied our quantitative approach to the recent results obtained by O'Nions et al. on North Atlantic provinces. The continental growth curves obtained by our inversion procedure are quite distinct from the Australian shales showing the regional character of shales.With these two cases studied we try to compare our results with the already developed model for continental growth. The consideration of the surface conservative versus surface non-conservative models clearly show the non-uniqueness of the geological interpretation of the growth curve. On the other hand, we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the Hurley-Rand province age curve. Such recycling increases with time in agreement with the data obtained on Nd and Sr initial ratios on granitoids.  相似文献   

The Palung granite (Himalaya); high-resolution UPb systematics in zircon and monazite     

Urs Schärer  Claude J. Allègre 《Earth and Planetary Science Letters》1983,63(3):423-432

UPb analyses of fractions of zircon and monazite (3–8 grains each) and of single zircon grains resolve a lower Ordovician age of 470 ±4m.y. for the Palung granite which occurs in the High Himalayan nappes south of Kathmandu. Its thrusting during the Alpine orogeny under lower greenschist facies conditions did not affect the UPb systems in zircon and monazite. The granite crystallized from a magma which was mainly generated by anatexis of Precambrian continental crust. The magma was heterogeneous with respect to primary ages and/or metamorphic histories of the magma source rocks. This indicates either a derivation from (meta-) sediments or an intense mixing of different crustally derived magmas. The genesis of the Palung granite is possibly related to an orogeny which affected the Indian shield in lower Palaeozoic times. The detected inherited radiogenic lead in the Palung zircons occurs in perfectly homogeneous, transparent crystals; i.e. this radiogenic (“excess”) lead is not related to the presence of old, microscopically visible, overgrown zircon cores. The minimum ages of the inherited lead components range from about 800 to 1700 m.y.  相似文献   

Destabilization of a 650 km chemical boundary layer and its bearing on the evolution of the continental crust     

Claude T. Herzberg  Randall D. Forsythe 《Physics of the Earth and Planetary Interiors》1983,32(4):352-360

A mechanism for the production of a chemical change in the mantle, from primordial silicate compositions above the 650 km discontinuity to differentiated compositions below, is reviewed. Some consequences of this are the stabilization of two layer convection with a temperature contrast between the anhydrous mantle solidus and the geotherm which, at 650 km depth, is lower than any other location in the mantle. With thermal contributions from the concentration of the heat producing elements U, Th and K below the 650 km mantle boundary layer and the higher geotherms in the past, widespread or catastrophic melting may have taken place at this location. An episodic breach of this boundary layer by extensive heat and mass transport may have periodically destroyed any simple two-layer convection geometry in the mantle. Such episodic injections of mass and energy into the upper mantle from below may have been the mechanism responsible for episodes of enhanced surface tectonism and thermal activity which appear to be recorded in apparent polar wandering paths and radiometric ages of continental rocks.  相似文献   

Geochemistry of the Mesozoic bedded cherts of Central Baja California (Vizcaino-Cedros-San Benito): implications for paleogeographic reconstruction of an old oceanic basin     

Claude Rangin  Michel Steinberg  Chantal Bonnot-Courtois 《Earth and Planetary Science Letters》1981,54(2):313-322

In central Baja California (Vizcaino Peninsula, and Cedros and San Benito Islands) two distinct radiolarian bedded chert sequences of late Triassic and late Jurassic/lowermost Cretaceous age, can be differentiated on lithostratigraphic and geochemical criteria.These bedded chert sequences are part of the conformable sedimentary cover of more or less dismembered ophiolites, which are overthrusted by the San Andrès-Cedros volcanic arc system of middle late Jurassic age.Major and trace elements permit paleogeographic zonation of the late Jurassic/lowermost Cretaceous radiolarites lying conformably upon ophiolites considered as fragments of an oceanic basin floor which developed westward of the San Andrès volcanic arc. Progressive accretion of this oceanic basin floor, along the continental margin is supported by the fact that the more distal radiolarian chert sequences belong to the lowermost structural units of this area.  相似文献   

Spatio‐temporal variations in demersal fish assemblages and diversity in the northern Gulf of St. Lawrence (Canada)          下载免费PDF全文

Hacène Tamdrari  Jean‐Claude Brêthes  Diane Archambault 《Marine Ecology》2015,36(3):557-571

Species diversity is generally considered one of the key factors of ecosystem resilience in response to anthropogenic pressures, including fishing. In this context, the spatial and temporal changes in demersal fish assemblages and species diversity were investigated in the northern Gulf of St. Lawrence (Canada), over a 20‐year period (1990–2010). Data were obtained from the summer research survey conducted by the Department of Fisheries and Oceans, and include commercial and non‐commercial species. The study covers the period of groundfish fishery collapse, the moratorium period, and the post‐moratorium period, and reflects various modifications in management. Multivariate statistical methods revealed two communities. A coastal community corresponds to strata located above 200 m depth and a deeper community located in the deep channels. Interannual differences in the composition of fish assemblages were observed and are mainly due to the changes in the relative biomass of some dominant species. Three diversity indices (Shannon–Wiener, Simpson's Index of Diversity and Motomura's constant) indicate a slight but significant increase of the diversity over time. This trend is due to the increase of the relative biomass of low‐rank species, which may have been favoured by the prohibition of groundfish trawling after 1997 in that region. The geographical distribution of the Shannon–Wiener index also shows temporal dynamics reflecting the biomass distribution of dominant demersal species.  相似文献   

Short‐term forecasting with a multi‐level spectral primitive equation model part II ‐ Hemispheric prognoses and verification     

Roger Daley  Claude Girard  John Henderson  Ian Simmonds 《大气与海洋》2013,51(2):117-134

The spectral global baroclinic primitive equation model described in Part I of this paper has been extensively tested. The model has been run daily from operational analyses for over a year. From this large sample of forecasts, verification statistics have been collected and compared with similar statistics collected from three competitive grid‐point models. The spectral model is also compared with the grid‐point models in a synoptic case study.

A second case study demonstrates the effect of horizontal resolution and physical effects on spectral model forecasts. The results of these experiments demonstrate that the spectral model is highly competitive with other models, in terms of both accuracy and computational efficiency. On 18 February 1976 the spectral model became the operational Canadian large‐scale forecast model.  相似文献   

Atmospheric response to the North Atlantic Ocean variability on seasonal to decadal time scales   总被引：1，自引：1，他引：0  

Guillaume Gastineau  Fabio D’Andrea  Claude Frankignoul 《Climate Dynamics》2013,40(9-10):2311-2330

The NCEP twentieth century reanalyis and a 500-year control simulation with the IPSL-CM5 climate model are used to assess the influence of ocean-atmosphere coupling in the North Atlantic region at seasonal to decadal time scales. At the seasonal scale, the air-sea interaction patterns are similar in the model and observations. In both, a statistically significant summer sea surface temperature (SST) anomaly with a horseshoe shape leads an atmospheric signal that resembles the North Atlantic Oscillation (NAO) during the winter. The air-sea interactions in the model thus seem realistic, although the amplitude of the atmospheric signal is half that observed, and it is detected throughout the cold season, while it is significant only in late fall and early winter in the observations. In both model and observations, the North Atlantic horseshoe SST anomaly pattern is in part generated by the spring and summer internal atmospheric variability. In the model, the influence of the ocean dynamics can be assessed and is found to contribute to the SST anomaly, in particular at the decadal scale. Indeed, the North Atlantic SST anomalies that follow an intensification of the Atlantic meridional overturning circulation (AMOC) by about 9 years, or an intensification of a clockwise intergyre gyre in the Atlantic Ocean by 6 years, resemble the horseshoe pattern, and are also similar to the model Atlantic Multidecadal Oscillation (AMO). As the AMOC is shown to have a significant impact on the winter NAO, most strongly when it leads by 9 years, the decadal interactions in the model are consistent with the seasonal analysis. In the observations, there is also a strong correlation between the AMO and the SST horseshoe pattern that influences the NAO. The analogy with the coupled model suggests that the natural variability of the AMOC and the gyre circulation might influence the climate of the North Atlantic region at the decadal scale.  相似文献