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41.
P. TEILHARD DE CHARDIN 《地质学报》1934,(1)
I had recently an opportunity for observing, along the western border of the northern Hoshan (Central Shansi), at the base of the Palaeozoic, a particularly clear section, in which several interesting features seem to be worth mentioning. This section, illustrated in the text-figure 1, was taken at the entrance 相似文献
42.
This paper describes a low-cost device for measuring the three-dimensional morphology of a gully headwall. The device was designed to operate in a gully system with the following characteristics: overhanging banks caused by a thick, dense root mat; retreat of the underlying unconsolidated sediments through small slab failures, leading to a considerable variation in retreat rate at each point on the headwall; and changes in the orientation of the headwall owing to changes in sediment properties and the topographical and hydrological controls of gully growth. The device is used to measure a series of closely spaced vertical profiles of the headwall, and the collected data are combined to draw a contour map showing the distance from the plane of the instrument to the headwall. Comparing maps for sequential times enables retreat rates for the diffferent proportions of the headwall to be quantified. 相似文献
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Abstract The whole of a basin responds to a precipitate on event. The resulting flood wave introduces a complex pattern of interrelated processes which occur in the vegetation, soil, bedrock, human facilities, channel and in the different parts of the basin. The main advantage of field experiments is that it becomes possible to exclude several governing factors or sources and to control others by the experimental design. In a small brook near Trier (Germany), artificial flood events are created. In-channel transport processes of sediment are investigated without taking into account the interference of soil erosion and runoff. It is demonstrated that kinematic waves-describing the translation of flow with limited hydraulic dispersion or diffusion-also occur in small basins. The kinematic waves-travelling only a few hundred meters-have a large impact on the relationship between the hydrograph and dissolved or particle-bound substances. Consequently, classifications and simple mixing models between those components are impeded. 相似文献
45.
JACQUES CALLEDE JEAN LOUP GUYOT JOSYANE RONCHAIL MICHEL MOLINIER EURIDES DE OLIVEIRA 《水文科学杂志》2013,58(2):321-333
Résumé Effectuées dans le cadre du Projet Hidrologia e geoquímica na Bacia Amazönica (HiBAm), les nouvelles mesures de débit à Obidos ont amélioré la connaissance des caractéristiques hydrologiques de l'Amazone à cette station qui contrâle les plus forts débits du monde. Une nouvelle méthode de correction détermine les débits journaliers avec une précision de ±3.0%. La reconstitution des périodes manquantes, avec les observations faites à Manaus, permet de disposer d'une chronologie de près d'un siècle. Avec cet échantillon commençant en 1902, le module interannuel de l'Amazone à Obidos est de 163 000 m3 s?1, avec un coefficient d'irrégularité extrêmement faible (K3 = 1.28). L'étiage décennal (78 000 m3 s?1) est de même grandeur que la crue centenaire du Congo à Brazzaville. La crue décennale est estimée à 260 000 m3 s?1. Le Bilan hydrologique indique un déficit d'écoulement de 1193 mm, qui peut être assimilé à l'évapotranspiration réelle. En conclusion, l'Amazone est bien le fleuve le plus puissant et le plus régulier de la planète. 相似文献
46.
GIORGIO BASILICI PEDRO HENRIQUE VIEIRA DE LUCA ELSON PAIVA OLIVEIRA 《Sedimentology》2012,59(5):1613-1639
Open‐coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open‐coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north‐eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave‐dominated or tide‐dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic hummocky cross‐stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky cross‐stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair‐weather wave base. However, in this model of an open‐coast tidal flat, hummocky cross‐stratification beds were found in very shallow waters above the fair‐weather wave base. Indeed, this depositional environment was characterized by: (i) fair‐weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these hummocky cross‐stratification deposits. 相似文献
47.
DARIO HARAZIM BAS VAN DE SCHOOTBRUGGE KATRIN SORICHTER JENS FIEBIG ANDRIES WEUG GUILLAUME SUAN WOLFGANG OSCHMANN 《Sedimentology》2013,60(2):359-390
In order to constrain spatial variability in watermass conditions within the European Epicontinental Seaway prior to, during and after the Toarcian Oceanic Anoxic Event, carbon (δ13Cbel, δ13Ccarb) and oxygen (δ18Obel, δ18Ocarb) isotope records were obtained from three sections in the Grands Causses Basin (southern France). These data were then compared with similar records along a north–south transect across the European Epicontinental Seaway. As the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes, an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite. Intra‐rostral carbon and oxygen‐isotope data from six belemnite specimens belonging to the genus Passaloteuthis were collected. Intra‐rostral carbon‐isotopes are influenced by vital effects, whereas oxygen‐isotopes reflect relative changes in temperature and salinity. Palaeotemperatures calculated from δ18Obel‐isotope records from the Grands Causses Basin confirm relatively low temperatures throughout the Late Pliensbachian. Similar cool water conditions have previously been shown in Germany, England, Spain and Portugal. A temperature increase of up to 6 °C is observed across the Pliensbachian–Toarcian boundary. A pronounced negative shift of at least ?3‰ (Vienna‐Pee Dee Belemnite) is recorded in bulk carbonate carbon during the lower Harpoceras serpentinum zone, typical of the Toarcian Oceanic Anoxic Event. Before and after the Toarcian Oceanic Anoxic Event, a good correlation between δ13Ccarb and δ13Cbel exists, indicating well‐ventilated bottom‐waters and normal marine conditions. Instead, data for the Toarcian Oceanic Anoxic Event indicate the development of a strong north–south gradient in salinity stratification and surface‐water productivity for the Western Tethyan realm. This study thus lends further support to a pronounced regional overprint on carbon and oxygen‐isotope records in epicontinental seaways. 相似文献
48.
Abstract Mineralogical and geochemical evidence indicates that partial melting and desulphidation have occurred in the Big Bell gold deposit. Decarbonation may also have occurred, to account for the lack of a carbonate alteration halo; this is compatible with the present data, but difficult to test. The Big Bell deposit consists of auriferous sulphide-bearing (‘lode’;) schists with muscovite and K-feldspar, and surrounding biotite schists, all derived by intense premetamorphic alteration of rocks of mafic composition. Assemblages which include cordierite-sillimanite-K-feldspar-garnet-biotite-quartz suggest peak metamorphic conditions of 4–5 kbar, and 650–700° C, based on phase relations, geobaro-meters and garnet-biotite Fe-Mg exchange partitioning. Partial melting occurred at peak metamorphism, particularly in the altered mafic rocks in and around the deposit, and its occurrence may have been essential to the preservation of the deposit. Melting greatly limited the importance of devolatilization reactions, resulting in negligible aqueous fluids and no means of removing appreciable gold. Minor gold loss may have accompanied desulphidation. A diversity of complex metamorphic assemblages occurs around the mine, compared to the assemblages developed regionally; variable bulk rock composition influences this contrast, but there is no evidence of higher metamorphic grades at the mine, nor that this might have been the prime control on the different assemblages in this narrow belt. It is suggested that the Big Bell and Hemlo deposits are the higher metamorphic grade equivalents of the more abundant greenschist facies gold deposits within Archaean greenstone belts. This interpretation is favoured by the host rock setting and geochemical characteristics of Big Bell. Alternative models that suggest that this class of deposit is a new type must account for the absence of high-grade equivalents of the greenschist facies deposits and also the lack of low-grade equivalents of the Big Bell/Hemlo type. Archaean gold deposits in high-grade metamorphic terrains have undergone a series of processes that are not recorded in the more typical gold deposits of the greenschist facies. 相似文献
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