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   

Experimental study of the coastal thermocline height variations caused by an impulsively applied wind of limited along-shore extent     

Dal S. Lee  Dominique P. Renouard 《Dynamics of Atmospheres and Oceans》1983,7(3):129-145

On the large rotating platform of Grenoble's University, a channel (8×2×0.6 m) has been built, equipped with a wind entrainment simulation effects mechanism. With a local wind, acting over a two-layered ocean, upwelling or downwelling patterns are induced, which are Kelvin-type height variations of the interface; propagating so that, in the northern hemisphere, they leave the coastline to the right of their direction of propagation, and having a profile exponentially decreasing from the coastline towards the open sea. The agreement between these observations and the recently proposed model of Crepon and Richez (1982) is very good at some distance from the excitation zone.However, this model, for its application, is limited to the situation in which the Ekman layer is of the same order of magnitude as the upper layer. Otherwise the oceanographic observations, as well as our observations, show a cross-shore current in the intermediate layer. Near the boundaries of the excitation zone (i.e., the wind zone), such a current is responsible for vortices which cause local upwelling. The model does not account for such local upwelling which is superimposed on the Kelvin-type height variation of the thermocline. These vortices may be explained by consideration of variations of relative vorticity. The experiments also show that a wind perpendicular to the coast may also induce upwelling or downwelling.  相似文献   

Using a decadal diatom sediment trap record to unravel seasonal processes important for the formation of the sedimentary diatom signal     

Dominique Béatrice Maier  Veronika Gälman  Ingemar Renberg  Christian Bigler 《Journal of Paleolimnology》2018,60(2):133-152

Sediment trap studies and high frequency monitoring are of great importance to develop a deeper understanding of how seasonal environmental processes are imprinted in sediment signal formation. We collected whole year diatom assemblages from 2002 to 2014 with a sequential sediment trap from a varved boreal lake (Nylandssjön, Sweden) together with environmental and limnological parameters, and compared them with the corresponding diatom record of the annual laminated sediment. Our data set indicates a large year-to-year variability of diatom succession and abundance patterns, which is well reflected in the varved sediments. Specifically, Cyclotella glomerata dominated the annual sediment trap record (as well as in the corresponding sediment varves) in years with warmer air temperatures in March/April, and Asterionella formosa dominated the annual sediment assemblages as a consequence of years characterized by higher runoff before lake over-turn. Years succeeding forest clearance in the lake catchment showed marked increase in diatom and sediment flux. The DCA scores of the yearly diatom trap assemblages clearly resemble the lake’s thermal structure, which indicates that the relative abundance of major taxa seems primarily controlled by the timing of seasonal environmental events, such as above-average winter air temperature and/or autumn runoff and the current thermal structure of the lake. The high seasonal variability between environmental drivers in combination with the physical limnology leaves us with several possible scenarios leading to either an A. formosa versus C. glomerata dominated annual diatom sediment signal. With this study we highlight that short-term environmental events and seasonal limnological conditions are of major importance for interpreting annual sediment signals.  相似文献   

Herschel SPIRE fourier transform spectrometer: calibration of its bright-source mode     

Nanyao Lu  Edward T. Polehampton  Bruce M. Swinyard  Dominique Benielli  Trevor Fulton  Rosalind Hopwood  Peter Imhof  Tanya Lim  Nicola Marchili  David A. Naylor  Bernhard Schulz  Sunil Sidher  Ivan Valtchanov 《Experimental Astronomy》2014,37(2):239-252

The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two detector setting modes: (a) a nominal mode, which is optimized for observing moderately bright to faint astronomical targets, and (b) a bright-source mode recommended for sources significantly brighter than 500 Jy, within the SPIRE FTS bandwidth of 446.7–1544 GHz (or 194–671 microns in wavelength), which employs a reduced detector responsivity and out-of-phase analog signal amplifier/demodulator. We address in detail the calibration issues unique to the bright-source mode, describe the integration of the bright-mode data processing into the existing pipeline for the nominal mode, and show that the flux calibration accuracy of the bright-source mode is generally within 2 % of that of the nominal mode, and that the bright-source mode is 3 to 4 times less sensitive than the nominal mode.  相似文献   

Herschel SPIRE FTS spectral mapping calibration     

Dominique Benielli  Edward Polehampton  Rosalind Hopwood  Ana Belén Griñón Marín  Trevor Fulton  Peter Imhof  Tanya Lim  Nanyao Lu  Gibion Makiwa  Nicola Marchili  David Naylor  Locke Spencer  Bruce Swinyard  Ivan Valtchanov  Matthijs van der Wiel 《Experimental Astronomy》2014,37(2):357-367

The Herschel SPIRE Fourier transform spectrometer (FTS) performs spectral imaging in the 447–1546 GHz band. It can observe in three spatial sampling modes: sparse mode, with a single pointing on sky, or intermediate or full modes with 1 and 1/2 beam spacing, respectively. In this paper, we investigate the uncertainty and repeatability for fully sampled FTS mapping observations. The repeatability is characterised using nine observations of the Orion Bar. Metrics are derived based on the ratio of the measured intensity in each observation compared to that in the combined spectral cube from all observations. The mean relative deviation is determined to be within 2 %, and the pixel-by-pixel scatter is ～ 7 %. The scatter increases towards the edges of the maps. The uncertainty in the frequency scale is also studied, and the spread in the line centre velocity across the maps is found to be ～ 15 km s ^{? 1}. Other causes of uncertainty are also discussed including the effect of pointing and the additive uncertainty in the continuum.  相似文献   

Changes in temperature and temperature gradients in the French Northern Alps during the last century     

M. Dominique Dumas 《Theoretical and Applied Climatology》2013,111(1-2):223-233

In mountain environments, local factors such as topography or exposure to the sun influence the spatial distribution of temperatures. It is therefore difficult to characterise the global evolution of temperatures over several decades. Such local effects can either accentuate or attenuate thermal contrasts between neighbouring areas. The present study uses two regional thermal indicators—thermal gradients and temperatures reduced to sea level—to monitor the monthly evolution of minimum and maximum temperatures in the French Northern Alps. Measures were calculated for the period extending from 1960 to 2007 based on data from 92 measuring stations. Temperature gradients were computed and further used to monitor the altitudinal evolution of temperatures. A characteristic regional temperature was determined for the whole of the French Northern Alps based on temperatures reduced to sea level, and changes in temperatures since 1960 were assessed. Multiple linear regression models made it possible to extend measurements over a longer period and to make enhanced calculations of temperature changes in the mountains since 1885. This is the first study to examine temperature changes in the French Northern Alps over such an extended period. Gradient data suggest that over the last 50 years, temperatures have changed at all altitudes. In addition, the evaluation of the temperature rise over 100 years reveals that minimal and maximal monthly temperatures trends are only significant a few months of the year.  相似文献   

The mantle rotation pole position. A solar component     

Fernando Lopes  Jean-Louis Le Mouël  Dominique Gibert 《Comptes Rendus Geoscience》2017,349(4):159-164

The direction of the Earth's rotation axis with respect to the mantle has been studied for more than a century. The time variation of this direction is generally considered to be the sum of three components: the annual wobble, forced by the atmosphere, the Chandler wobble, a free oscillation with a period of 435 days, and the so-called drift of the mean pole. In the present paper, applying the singular spectrum analysis (SSA) technique, we uncover two more components, with smaller amplitude than the three first ones, but well identified, periodic with periods of 11 and 5.5 years, respectively, undoubtedly linked to solar activity. We interpret them tentatively as the result of an exchange of kinetic angular momentum between the atmosphere, in which a flow would be generated by solar activity, and the mantle. The order of magnitude of the required mean winds in the atmosphere computed in the frame of a schematic model is 1 ms^?1, compatible with the observed values of the meridional mean circulation.  相似文献   

Exploring the past through lynchet landscapes in the Vosges Mountains and the Lorraine Plateau (France)     

Benjamin Keller  Robin Vincent  Dominique Schwartz  Damien Ertlen 《Geoarchaeology》2024,39(3):300-319

Lynchets are ridges formed by erosion and sediment accumulation downstream of agricultural plots and offer valuable insights into past agricultural activity. These microtopographies cover vast areas and serve as indicators of historical changes in land use. As a result, their ubiquity across Europe makes them particularly interesting. In this study, we propose a geoarchaeological approach to analyze six lynchets, four in the Vosges Mountains and two on the Lorraine Plateau (France). The lynchets can be considered soil archives with no stratigraphic organization or chronological sequence from bottom to top, making it difficult to determine the age of the lynchets and identify changes in land use over time. To this end, we propose the analysis of historical and geo-historical archives combined with the “pedosedimentary” archives of lynchets through charcoal identification and dating combined with near-infrared spectroscopy to determine the age, vegetation, and past land use changes associated with lynchet landscapes. By combining these multiple data sources, we are better able to show the chronological development of these ancient agricultural systems and uncover valuable information on landscape history. Charcoal dating suggests a higher frequency of fires from the Middle Ages. The dating aligns with the regional dynamics of anthropogenic fires, indicating a potential use of fire for cultural purposes. We also demonstrate the difficulty of extrapolating the dating of a lynchet to the entire lynchet system. Our results highlight the difficulties of interpreting the formation and dating of lynchets and the lynchet system on the sole basis of charcoal analysis. However, we highlight the value of applying pedoanthracology to lynchets to determine the dynamics of land use change in former fields.  相似文献   

Sub-Micrometre Resolution FIB-SEM-based ToF-SIMS Used to Map Geochemical Zoning in Four Zircon Reference Materials     

Ryan North  Lloyd T. White  Mitchell Nancarrow  Anthony Dosseto  Dominique Tanner 《Geostandards and Geoanalytical Research》2023,47(1):125-142

Zircon geochemistry can vary over micrometre scales; therefore, natural reference materials need to be well characterised before being used to calculate trace element mass fractions in unmeasured samples. Moreover, reference material homogeneity needs to be ensured with the accelerating rate of geoanalytical developments to map mineral chemistry at increasingly finer scales. Here, we investigate trace element zoning in four widely used zircon reference materials: 91500, Mud Tank, Temora and Plešovice, as well as zircon crystals from the Mount Dromedary/Gulaga Igneous Complex, Australia. Sub-micrometre resolution focused ion beam scanning electron microscope (FIB-SEM) based time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 5 μm resolution LA-ICP-MS mapping show that trace elements are zoned in all reference materials, though 91500 exhibited the least zonation. We demonstrate that FIB-SEM-based ToF-SIMS can rapidly resolve variations in trace elements (e.g., U, Th, Sc, Y, Gd, Dy, Yb and Li) at sensitivities down to the μg g^-1 level with a spatial resolution of 195 nm for areas 100 × 85 μm to 959 × 828 μm. Zircon 91500 is recommended for future quantitative analyses provided that (1) the spatial distribution of elements is imaged before analysis of unknown samples and (2) it is used in conjunction with a doped glass as the primary reference material.  相似文献