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Utilisant une méthode rapide et précise, l'eau combinée (H2 O+) a été dosée dans les standrds géochimiques de l'ANRT et du CRPG. 相似文献
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ROBERT W. DALRYMPLE R. JOHN KNIGHT BRIAN A. ZAITLIN GERARD V. MIDDLETON 《Sedimentology》1990,37(4):577-612
The 40-km-long, Cobequid Bay—Salmon River estuary has a maximum tidal range of 16·3 m and experiences limited wave action. Sediment, which is derived primarily from areas seaward of the estuary, is accumulating faster than the high-tide elevation is rising, and the system is progradational. The deposits consist of an axial belt of sands, which is flanked by mudflats and salt marshes in the inner half of the estuary where a funnel-shaped geometry is developed, and by erosional or non-depositional foreshores in the outer half where the system is confined by the valley walls. The axial sands are divisible into three facies zones: zone 1—elongate, tidal sand bars at the seaward end; zone 2—sand flats with a braided channel pattern; zone 3—the inner, single-channel, tidal—fluvial transition. Tidal current speeds reach a maximum in zone 2, but grain sizes decrease headward (from medium and coarse sand in zone 1, to fine and very fine sand in zones 2 and 3) because the headward termination of the major flood channels prevents the coarse, traction population from entering the inner part of the estuary. Longitudinal progradation will produce a 20-m-thick, upward-fining succession, the lower 1/2–2/3 of which will consist of cross-bedded, medium to coarse sand deposited on the zone 1 sand bars. The ebb-dominated portion of this unit will be finer grained than the flood-dominated part, and will contain trough crossbedding produced by 3-D megaripples; the flood-dominated areas, by contrast, will consist mainly of compound cross-bedding created by sandwaves with superimposed megaripples. Headward migration of swatchways (oblique channels that link the ebb- and flood-dominated areas) will create packages of ebb cross-bedding that is orientated at a high angle to the long axis of the estuary and that contains headwardinclined, lateral-accretion surfaces. The overlying fine and very fine sands of zones 2 and 3 will be composed mainly of upper-flow-regime parallel lamination. The succession will be capped by a 4-m-thick unit of mixed flat, mudflat and salt marsh sediments. A review of other macrotidal estuaries with tidal ranges greater than 10 m suggests that the major elements of the model have general applicability. 相似文献
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A discussion is given of the requirements, the advantages and the methods to be considered in attempting the quantitative interpretation of gravity or magnetic fields from computed maps of the vertically derived field. The transform which is used here is the first vertical derivative (or vertical gradient) with or without downward continuation, but the computed maps are in fact obtained by a controllable Fourier method in which two kinds of operations can be simultaneously performed in complete independance: on one hand the separation of any part of the data by frequency cut-off, and on the other hand the transformation by vertical derivation or continuation of the part which is retained. Taking as raw data either actual surveys or artificially constructed maps, it is first shown how separated and transformed maps of this type can be efficiently obtained under quite flexible conditions, using a special computer program. It is further seen that for correctly controlled filterings the accuracy of the computed maps actually permits to take them as the basis for quantitative interpretation. To effect this, any one of the conventional methods which make use of equivalent model computations may in the first place be adapted to the interpretation of gradients, with the benefits, however, of an enhanced lateral separation of the anomalies and of a large attenuation of the regional effects. Particularly, the delineation of horizontal contours for even fairly complex models can often be made directly in a sufficiently safe way on the anomalies as they show on the vertical gradient maps. This greatly accelerates the process of determining equivalent model bodies. More special methods of interpretation can also be designed by taking into account first the fact that the vertical derivation of the field amounts to an operation of separation on the field's sources themselves, and in addition the availability of the frequency form of the information as a result of using a Fourier method of transform computation. Trial utilisations of various such interpretation processes of either the conventional or the less conventional type, are presented especially in connection with an interpretation study on transformed maps of parts of an offshore aeromagnetic survey (English Channel). 相似文献
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Various methods have been used to study soil redistribution in the Loam Belt of Belgium. These methods have had contrasting levels of spatial coverage and time-scale. Ideally, a technique to assess soil redistribution patterns should provide the determination of dense networks of X, Y and Z terrain coordinates (digital elevation models) at different time intervals. Sequential stereoscopic aerial photographs contain this information, which can be extracted with standard photogrammetric techniques. In this study, aerial photographs taken by the National Geographic Institute of Belgium in 1947 and 1991 were used to determine the soil redistribution pattern between these years. This was done by overlaying the two digital elevation models and subtracting the corresponding Z coordinate values (heights). The results indicate that most severe surface lowering occurs on the top of the hillslope and on the hillslope convexities. Important deposition occurs on the lowermost parts of the hillslope, in most hillslope concavities and in the topographically defined concentration line. The observed pattern differs markedly from that expected from water erosion processes, and suggests that the soil redistribution is dominated by tillage operations. 相似文献
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LIONEL VISSET GERARD HAURAY 《Boreas: An International Journal of Quaternary Research》1988,17(3):329-331
Since 1980 the authors have been using a mechanized Gik corer for coring in marshlands and peat bogs. Final modifications to the equipment are described and shown in photographs and drawings. 相似文献