黔西滇东地区早三叠世早期植物化石研究的新进展     

陈建华  喻建新  黄其胜  宋倩倩  陈斌 《地球科学》2011,36(3):500-510

早三叠世华南地区海相沉积广为发育.陆相沉积仅在海南岛和康滇古陆的东缘零星分布,植物化石非常罕见.报道的植物化石采自黔西滇东陆相岔河剖面宣威组顶部、海陆过渡相密德剖面和土城剖面的卡以头组下部,与晚二叠世晚期宣威组植物化石比较,植物类型单调,保存较破碎,共计14属31种,其中以Annalepis为主的石松纲5种;楔叶纲5种...  相似文献   

Zircon U–Pb and Hf isotopic study of Mesozoic felsic rocks from eastern Zhejiang,South China: Geochemical contrast between the Yangtze and Cathaysia blocks     

Jean Wong  Min Sun  Guangfu Xing  Xian-hua Li  Guochun Zhao  Kenny Wong  Fuyuan Wu 《Gondwana Research》2011,19(1):244-259

The Jiangshan–Shaoxing Fault Zone (JSFZ) in Zhejiang Province has been proposed to represent a suture between the Yangtze and Cathaysia blocks in South China. In this study, in-situ zircon U–Pb and Hf isotopic analysis and whole-rock major- and trace-element measurement of early to middle Cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone. Twelve Cretaceous granitoid bodies were sampled from the NW and SE sides of the fault zone, respectively, with composition ranging from diorite to granite (SiO₂ = 56.2–76.6 wt.%). These granitoids yielded U–Pb ages ranging from 135–100 Ma, with a systematic variation in zircon Hf isotopic compositions (ε_Hf(t) = + 6.9 to –7.0 in the NW side vs. + 1.9 to ? 12.9 in the SE side). The T_DM2 values for the granitoids from the NW side are 0.34 to 1.33 Ga, with two peaks at ca. 876 and 1170 Ma respectively, whereas those from the SE side are 0.70 to 1.62 Ga, with a single peak at ca. 1126 Ma. The Hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the Yangtze and Cathaysia blocks, supporting that the JSFZ is possibly a suture zone between the two blocks. Our results together with the available geological data suggest that the Mesoproterozoic materials are important for both the Yangtze and Cathaysia basement and the Neoproterozoic magmatic activities were important in the Yangtze Block, possibly related to the break-up of the Rodinia supercontinent, but less significant in the Cathaysia Block. This may imply that the two blocks have not completely juxtaposed in the Neoproterozoic.  相似文献   

Geochemical and isotopic (Sr, U) variations of lake waters in the Ol’khon Region, Siberia, Russia: Origin and paleoenvironmental implications     

François Chabaux  Mathieu Granet  Philippe Larqué  Jean Riotte  Eugeni V. Skliarov  Olga Skliarova  Ludmilla Alexeieva  François Risacher 《Comptes Rendus Geoscience》2011,343(7):462-470

The geochemical study of springs and lake waters from the Ol’khon Region, Siberia, confirms the strong chemical variability of these water samples, more particularly regarding their salinity. Such variability does not result from a simple mixing process between surface freshwaters and deeper saline waters. The variability, observed at the scale of a few square kilometers, would preferentially result from a secondary concentration processes (evaporation and/or cryogenesis) of lake waters of variable intensity from one lake to another. The U-disequilibria data suggest that the duration of the secondary process is certainly an important parameter to be considered to account for the variable salinity of these lakes. The data indicate that the lakes, however modest in size, could be as old as several ky, confirming therefore that the lake sedimentary deposits could represent relevant paleoenvironmental recorders for the last thousands years.  相似文献   

Exploratory and Instantaneous Swimming Speeds of Amphidromous Fish School in Shallow-Water Coastal Lagoon Channels     

Patrice Brehmer  Jean Guillard  Pablo I. Caballero Pinzon  Pascal Bach 《Estuaries and Coasts》2011,34(4):739-744

Fish school swimming speeds is essential for ecological and management studies. The multibeam sonar in horizontal beaming provided dynamic echo traces of mobile fish schools. We used two school swimming speed indicators: the average of a series of instantaneous speed values, and the exploratory speed. These swimming speeds were estimated for each fish school observed on the basis of their Euclidian position within the sonar beams. The average ISS values per school ranged from 0.15 m s⁻¹ to 4.46 m s⁻¹, while the ESS values per school were lower, ranging from 0.04 m s⁻¹ to 3.77 m s⁻¹. Multibeam sonar technology makes it possible to measure fish school swimming speeds in their natural habitat at small spatio-temporal scales. This methodology can therefore be used to analyse in situ their movements, and has a wide range of applications in behavioural studies and management purposes.  相似文献   

Estimating baselines for climate change for less developed countries: the case of the Sahel     

Mohammed H.I. Dore  Jean François Lamarche 《Climate Policy》2013,13(2):231-240

Abstract

The UN Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol provide mechanisms for assisting less developed countries that are adversely affected by climate change. Such assistance would need a baseline, which ideally would set a precise date for specific impacts of climate change. This article presents the results of statistical tests that we carried out and, for the African region of the Sahel, finds that for precipitation (affecting food supply), impacts due to climate change can be ‘dated’ to the year 1967, when precipitation fell drastically, affecting the local food supply. Such a statistically robust benchmark would be useful to the Subsidiary Body for Scientific and Technological Advice (SBSTA) of the UNFCCC. The method illustrates how other baselines may be established for the important work of the SBSTA.  相似文献   

Olivine‐rich exposures at Bellicia and Arruntia craters on (4) Vesta from Dawn FC     

Guneshwar Thangjam  Andreas Nathues  Kurt Mengel  Martin Hoffmann  Michael Schäfer  Vishnu Reddy  Edward A. Cloutis  Ulrich Christensen  Holger Sierks  Lucille Le Corre  Jean‐Baptiste Vincent  Christopher T. Russell 《Meteoritics & planetary science》2014,49(10):1831-1850

We present an analysis of olivine‐rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine‐rich materials at these localities as described by Ammannito et al. ( 2013a ) using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various howardite–eucrite–diogenite meteorites, high‐Ca pyroxenes, olivines, and olivine‐orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine‐rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine‐rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine‐rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake 1997 ; Yamaguchi et al. 1997 ). However, it remains unsolved why the olivine‐rich materials are mainly concentrated in the northern hemisphere (approximately 36–42°N, 46–74°E) and are almost absent in the Rheasilvia basin.  相似文献   

Climate change beliefs, concerns, and attitudes toward adaptation and mitigation among farmers in the Midwestern United States     

J. Gordon Arbuckle Jr.  Linda Stalker Prokopy  Tonya Haigh  Jon Hobbs  Tricia Knoot  Cody Knutson  Adam Loy  Amber Saylor Mase  Jean McGuire  Lois Wright Morton  John Tyndall  Melissa Widhalm 《Climatic change》2013,117(4):943-950

A February 2012 survey of almost 5,000 farmers across a region of the U.S. that produces more than half of the nation’s corn and soybean revealed that 66 % of farmers believed climate change is occurring (8 % mostly anthropogenic, 33 % equally human and natural, 25 % mostly natural), while 31 % were uncertain and 3.5 % did not believe that climate change is occurring. Results of initial analyses indicate that farmers’ beliefs about climate change and its causes vary considerably, and the relationships between those beliefs, concern about the potential impacts of climate change, and attitudes toward adaptive and mitigative action differ in systematic ways. Farmers who believed that climate change is occurring and attributable to human activity were significantly more likely to express concern about impacts and support adaptive and mitigative action. On the other hand, farmers who attributed climate change to natural causes, were uncertain about whether it is occurring, or did not believe that it is occurring were less concerned, less supportive of adaptation, and much less likely to support government and individual mitigative action. Results suggest that outreach with farmers should account for these covariances in belief, concerns, and attitudes toward adaptation and mitigation.  相似文献   

Snow accumulation and its moisture origin over Dome Argus, Antarctica   总被引：1，自引：0，他引：1  

Yetang Wang  Harald Sodemann  Shugui Hou  Valérie Masson-Delmotte  Jean Jouzel  Hongxi Pang 《Climate Dynamics》2013,40(3-4):731-742

The spatial and temporal variability of snow accumulation near Dome Argus, Antarctica, is assessed using new snow pit and stake measurement data together with existing snow pit, ice core and automatic weather station records. Snow accumulation rate shows large inter-annual variations, but stable multi-decadal levels over the last seven centuries. Spatial variations in snow accumulation within the space of 50 km of Dome Argus are relatively small, probably thanks to the smooth topography. A comparison of theses accumulation observations with ECMWF reanalyses (ERA-40 and ERA-Interim) suggests ECMWF reanalysis captures the seasonal variations, but underestimates the overall snow accumulation at Dome Argus by ~50 %. The moisture sources for precipitation over Dome Argus are examined by means of a Lagrangian moisture source diagnostic, based on the tracing of specific humidity changes along air parcel trajectories, for the period 2000–2004 using operational ECMWF analysis data. Dome Argus mainly receives moisture from the mid-latitude (46 ± 4°S) South Indian Ocean, with a seasonal latitudinal shift of about 6°. Compared to other central East Antarctic deep ice core sites such as Dome F, Dome C, Vostok, and EPICA Dronning Maud Land, Dome Argus has a more southerly moisture origin, probably due to topographic influences on the moisture transport paths. These results have important implications for the interpretation of future ice cores at Dome Argus.  相似文献   

Estimates of the accuracy of vertically extrapolated forecast errors: Isobaric height and temperature     

H. Jean Thiébaux 《大气与海洋》2013,51(3):219-233

Abstract

Study of vertical extrapolations of the errors in forecast values of pressure‐level heights and temperatures indicates that they do not provide accurate off‐level information. Indeed it appears that, above 850 mb, forecast errors interpolated from observed 1000‐mb values are less accurate than level‐specific monthly mean differences. These results suggest that the de facto function of vertically interpolated single‐level forecast errors, in numerical forecast model updating, is the provision of vertical consistency rather than the injection of time‐specific information – except at the level of observation.  相似文献   

Thermal Conductivity of Argillaceous Rocks: Determination Methodology Using In Situ Heating Tests   总被引：1，自引：1，他引：0  

Benoit Garitte  Antonio Gens  Jean Vaunat  Gilles Armand 《Rock Mechanics and Rock Engineering》2014,47(1):111-129

This study focuses on the characterisation of thermal conductivity for three potential host rocks for radioactive waste disposal. First, the heat conduction process is reviewed on the basis of an analytical solution and key aspects related to anisotropic conduction are discussed. Then the existing information on the three rocks is summarised and a broad uncertainty range of thermal conductivity is estimated based on the mineralogical composition. Procedures to backanalyse the thermal conductivity on the basis of in situ heating tests are assessed and a methodology is put forward. Finally, this methodology is used to estimate the impact of experimental uncertainties and applied to the four in situ heating tests. In the three potential host rocks, a clear influence of the bedding planes was identified and anisotropic heat conduction was shown to be necessary to interpret the observed temperature field. Experimental uncertainties were also shown to induce a larger uncertainty on the anisotropy ratio than on the equivalent thermal conductivity defined as the geometric mean of the thermal conductivity in the three principal directions.  相似文献