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1.
In the northern Apennines, the Palaeozoic basement involved in the Late Oligocene–Middle Miocene nappe stack contains metamorphic units for which hypothetical ages have been assigned on the basis of lithological correlations with the Palaeozoic formations of the Variscan chain in Sardinia. This uncertainty concerning the age poses limitations to reconstructing the Palaeozoic stratigraphy, defining the Alpine and pre‐Alpine histories and correlations with other domains of the Variscan chain. We present the U Pb age of detrital zircon and the 40Ar 39Ar age of metamorphic muscovite for the Calamita Schist and Ortano Porphyroid, two metamorphic units of undetermined Palaeozoic age cropping out in the eastern Elba Island. The radioisotopic data allows us to: (i) define the Early Carboniferous and Middle Ordovician ages for the Calamita Schist and Ortano Porphyroid, respectively, as well as their derivation (flysch deposit and magmatic rocks); (ii) pose some constraints concerning their alpine tectonic and metamorphic histories. These new data generate a more precise reconstruction of the Palaeozoic sequence in the northern Apennines, and they document that the Palaeozoic basement involved in the alpine deformation underwent internal stacking with an inversion of the original sequence. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
The Xing‐Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt that marks the boundary between the North China Block and the Siberian Block. Studies of zircon U Pb ages and Hf isotopic compositions show that four clastic sedimentary rock samples from different parts of the regional stratigraphic sequence were deposited at different ages, none earlier than Mid‐ or Early Silurian. Two sedimentary rocks were deposited during or after the Early Permian. Almost all zircons are of igneous origin. In Silurian and Devonian sediments, zircons show several modal age peaks, and in Permian sediments, zircons show a unimodal age peak. Based on the zircon age distribution of sedimentary rocks versus known ages from exposed rocks of the potential source regions, most of the zircons were derived from the Xing‐Meng Orogen itself. A few came from the South Mongolian microcontinent or the Siberia Block, but none came from the North China Block. The zircons of a biotite‐plagioclase paragneiss in Xilinhot have similar provenance to the sediments and were deposited during or after the Middle Devonian. Similarities between zircon age spectra and events in underlying rocks of sedimentary origin show that the sediments lie at their deposition site north of the Solonker suture zone because north‐dipping subduction and elevation blocked deposition of material from farther afield. Hf isotope compositions show the crustal accretion stages of the provenance areas during the Meso‐ to Neoarchaean, Palaeoproterozoic and Early and Late Palaeozoic. A two‐component mixing calculation based on Hf isotopes shows the large scale of the crustal accretion event of the region. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
In the present paper, we propose a new method for the estimation of the variogram, which combines robustness with efficiency under intrinsic stationary geostatistical processes. The method starts by using a robust estimator to obtain discrete estimates of the variogram and control atypical observations that may exist. When the number of points used in the fit of a model is the same as the number of parameters, ordinary least squares and generalized least squares are asymptotically equivalent. Therefore, the next step is to fit the variogram by ordinary least squares, using just a few discrete estimates. The procedure is then repeated several times with different subsets of points and this produces a sequence of variogram estimates. The final estimate is the median of the multiple estimates of the variogram parameters. The suggested estimator will be called multiple variograms estimator. This procedure assures a global robust estimator, which is more efficient than other robust proposals. Under the assumed dependence structure, we prove that the multiple variograms estimator is consistent and asymptotically normally distributed. A simulation study confirms that the new method has several advantages when compared with other current methods.  相似文献   

4.
正1 Introduction Lithium and its compounds as national strategic resources are extensively used in national defense,industrial and agricultural production.As we know,the salt lakes in the western of China are famous for its high  相似文献   

5.
Crisis? What crisis? Displacing the spatial imaginary of the fiscal state   总被引：1，自引：0，他引：1  
Angus Cameron   《Geoforum》2008,39(3):1145-1154
This paper argues that there is an immanent and evolving relationship between the prevailing form of taxation and the economic geographies of the state. Despite this, the geographic significance of taxation has been obscured by the language in which its historic transformation tends to be couched. Prevailing fiscal systems tend to be presented as essentially static – institutionally and spatially fixed and routinely inscribed within the fixed boundaries and territories of the ‘sovereign’ fiscal state. Any threat to, or change in the nature or geography of the fiscal state tends to be couched in terms of ‘crisis’ – of negative and discontinuous change. This paper contends that these related and essentially conservative discourses of fiscal geography mask the degree to which fiscal spaces are both multiple and continuously evolving. More importantly, it argues, this fluidity and multiplicity does not threaten the stability and viability of state form, but it is an essential process in its maintenance and reproduction. Running counter to the prevailing discourse of the ‘national economy’, the practice of fiscal geography is an under-analysed but key aspect of the historical evolution and transformation of the imagined geographies of economies.  相似文献   

6.
Since a 1921 law the harnessing of the Rhône River from Lyon to the Mediterranean has been directed by a national company composed of the public sector (fromthe valley) as well as of various consumers or distributors of current such as the SNCF or the EDF. This company, the National Company of the Rhône (CNR), was a precursor to the establishment of the TVA in the United States, although it did not begin operations until aftetr the TVA due to prolonged technical negotiations and to the difficulties involved in locating financial support in a period of economic crisis. Even though the utilization of hydraulic power constitutes the prime aim of the CNR, it has also focused on navigation, irration and other agricultural uses from the outset.This article will not further discuss the hydro-electric stations on the Rhône which usually supply more than 22% of French hydro-electric output from thirteen stations now in operation (total power is 2,350 MW and annual average output is 13,000 GWh). This paper will treat the question of the nature and importance of the side effects of the harnessing of the Rhône apart from its essential energy function.  相似文献   

7.
The Triassic?Jurassic (Tr?J) boundary marks a major extinction event, which (~200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr?J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key-species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites?Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites?Pinuspollenites Assemblage, and the Sinemurian Perinopollenites?Cycadopites Assemblage. The Tr?J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio?Ferganoconcha and Waagenoperna?Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio?Ferganoconcha and Waagenoperna?Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine?littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian.  相似文献   

8.
Endo  Shintaro  Shimada  Ryo  Ishikawa  Toshinori  Komine  Tsutomu 《Natural Hazards》2022,110(3):2017-2033

Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.

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9.
Mumbai’s Dharavi slum occupies a plot half the size of Central Park. It is home to one million people, with almost half of residents living in spaces under 10 m2, making it over six times as dense as daytime Manhattan. Using ethnographic fieldwork and online analysis, this article examines slum tourism and the perceptions and experiences of western visitors. Local tour operators emphasize the productivity of the slum, with its annual turnover of $665 million generated from its hutment industries. Its poor sanitation, lack of clean water, squalid conditions and overcrowding are ignored and replaced by a vision of resourcefulness, hard work and diligence. This presentation of the slum as a hive of industry is so successful that visitors overlook, or even deny, its obvious poverty. Dharavi is instead perceived as a manufacturing hub and retail experience; and in some cases even romanticized as a model of contentment and neighbourliness, with western visitors transformed by ‘life-changing’, ‘eye-opening’ and ‘mind-blowing’ experiences. This article concludes that the potential of slum tours as a form of international development is limited, as they enable wealthy middle-class westerners to feel ‘inspired’, ‘uplifted’ and ‘enriched’, but with little understanding of the need for change.  相似文献   

10.
Life was limited for most of Earth's history, remaining at a primitive stage and mostly marine until about 0.55 Ga. In the Paleozoic, life eventually exploded and colonized the continental realm. Why had there been such a long period of delayed evolution of life? Early life was dominated by Archaea and Bacteria,which can survive ionizing radiation better than other organisms. The magnetic field preserves the atmosphere, which is the main shield of UV radiation. We explore the hypothesis that the Cambrian explosion of life could have been enabled by the increase of the magnetic field dipole intensity due to the solidification of the inner core, caused by the cooling of the Earth, and the concomitant decrease with time of the high-energy solar flux since the birth of the solar system. Therefore, the two phenomena could be responsible for the growth and thickening of the atmosphere and the development of land surface life.  相似文献   

11.
Over the last 30 years, a growing body of research has shown that first-order control of the elevation of Earth's surface is exercised by thermal anomalies in the upper asthenosphere. One line of research is to test models and observations of mantle behaviour against the sedimentary record. A second line of research is to use the sedimentary record to further understanding of mantle behaviour. Here this second line of research is adopted: a particular hypothesis of mantle behaviour is tested against the Quaternary sedimentary record of the Thames valley, England. Schoonman et al. (2017) have proposed that a warm finger of mantle material extending from the Icelandic plume underlies southern England at the present day. That warm finger would represent the distal end of the influence of the Icelandic plume in this area, and would have advanced broadly from west to east, causing a progressive tilt of the surface of the Thames valley towards the east. The warm-finger hypothesis is supported by the evidence reviewed here. That evidence consists of two main sets of observations, both sets established beyond reasonable doubt by many researchers over many years. First, there is the progressive increase in elevation westward from the present-day coast of the North Sea of the 2.5–2 Ma shallow-marine Red and Norwich Crags. Second, there is the subsequent Quaternary record of progressive eastward tilting of the Thames valley shown in the river terraces.  相似文献   

12.
Palaeohydraulic estimates have been made using time-tested standard empirical formula involving channel dimensions, especially channel depth, in four Indian Proterozoic fluvial formations. These are the Mesoproterozoic Ramdurg, younger Mesoproterozoic Muchkundi and Neoproterozoic Cave Temple Arenite in Karnataka, and Upper Rewa Sandstone in central India. The basic data came from direct measurement of decompacted thicknesses of completely preserved channel-fills or bedforms, and more commonly of cross-sets. The result, in combination with data derived by others in a similar way from a few other Precambrian fluvial formations helps to provide a new insight into the palaeohydraulics of Precambrian rivers.River gradients appear to have been steeper during the Precambrian; the possibly continuous range of variation in river gradients from alluvial fans to the plains, as a whole shifted to higher values during the Precambrian epoch. The likely reason is a greater possibility of sediment bypassing on vegetation-free land. Concomitant downstream increase in discharge was enhanced in Precambrian rivers due to lack of withdrawal of groundwater through biogenic activity. Precambrian rivers were commonly ephemeral, but downstream the ephemerality index was reduced and some rivers might have been perennial where they debouched into standing bodies of water. The Precambrian river deposits studied generally had smaller width and depth with respect to Phanerozoic and modern rivers, possibly due to unstable substratum causing surface run-off tended to be impelled along multiple independent minor channels.  相似文献   

13.
Arid and Alpine ecosystems are known for extreme environmental changes during the Late Quaternary. We hypothesize that the world's largest Alpine arid ecosystem however, the Alpine Steppes of the Tibetan highlands, remained ecologically stable during the LGM and the mid-Holocene. This hypothesis is tested by distributional range of plant species, plant life forms and rate of endemism. The set of character species has a precipitation gradient between 50 and 350 mm/a, testifying for resilience to precipitation changes. 83% of the species have a wider vertical range than 1000 m used as a proxy for resilience to temperature changes. 30% of the species are endemic with 10 endemic genera, including plate-shaped cushions as a unique plant life form. These findings are in line with palaeo-ecological proxies (δ18O, pollen) allowing the assumption that Alpine Steppes persisted during the LGM with 3 to 4 K lower summer temperatures.During the mid-Holocene, forests could have replaced Alpine Steppes in the upper catchments of the Huang He, Yangtze, Mekong, Salween and Yarlung Zhangbo, but not in the interior basins of the north-western highlands, because the basins were then flooded, suppressing forests and supporting the environmental stability of this arid Alpine grassland biome.  相似文献   

14.
This article explores the constraints and contingencies of contemporary urban governance, with reference to the partial privatization (1999) and partial remunicipalization (2012) of the Berlin Water Company (BWB). It outlines the processes through which this major shift in Berlin politics occurred, showing how the mainstream consensus on privatization was disrupted and alternatives to apparent neoliberal conformity emerged. Dynamics apparent in the BWB case – commercialization, privatization, re-regulation, public contestation and remunicipalization – are indicative of the challenges and opportunities of making policy in and beyond the global norms of neoliberalism. It is argued that this case is important because it reveals something about what we might call the “politics of possibility” within the paradigm of neoliberal urban governance: the continuing potential for change within the constraints of an urban governance configured to the logics and needs of markets. Given this, the paper concludes that local contingencies in urban governance problematize sweeping notions of a post-political condition. However observable post-political strategies and outcomes in Berlin and elsewhere are, researchers should not assume that they are inevitably dominant or universal.  相似文献   

15.
Erosion of complex, rocky coasts has largely been neglected by geologists. Thus, a geo-archaeological study of coastal erosion was required before analysis of the prehistoric settlement pattern could be undertaken. Along the outer, wave-dominated coast of Maine, erosion is episodic, occurring when large storms raise water levels to new heights. Along the inner, tide-dominated coast, erosion occurs more frequently because unconsolidated sediments are exposed at low elevations in bedrock features. The shell midden archaeological sites of the Boothbay, Maine region are situated in the most rapidly eroding areas; therefore, it can be reasoned that localities without cultural deposits were never occupied. On the other hand, coastal erosion is widespread enough to insure that sites have been exposed to discovery by archaeological survey. Settlement pattern analysis of the study area is, therefore, not biased by differential preservation or discovery of archaeological sites.  相似文献   

16.
Extensional-tectonic processes have generated extensive magmatic activity that produced volcanic/plutonic rocks along an E-W-trending belt across north-western Turkey; this belt includes granites and coeval volcanic rocks of the Ala?amdağ volcano-plutonic complex. The petrogenesis of the Early Miocene Ala?amdağ granitic and volcanic rocks are here investigated by means of whole-rock Sr–Nd isotopic data along with field, petrographic and whole-rock geochemical studies. Geological and geochemical data indicate two distinct granite facies having similar mineral assemblages, their major distinguishing characteristic being the presence or absence of porphyritic texture as defined by K-feldspar megacrysts. I-type Ala?amdağ granitic stocks have monzogranitic-granodioritic compositions and contain a number of mafic microgranular enclaves of monzonitic, monzodioritic/monzogabbroic composition. Volcanic rocks occur as intrusions, domes, lava flows, dykes and volcanogenic sedimentary rocks having (first episode) andesitic and dacitic-trachyandesitic, and (second episode) dacitic, rhyolitic and trachytic-trachydacitic compositions. These granitic and volcanic rocks are metaluminous, high-K, and calc-alkaline in character. Chondrite-normalised rare earth element patterns vary only slightly such that all of the igneous rocks of the Ala?amdağ have similar REE patterns. Primitive-mantle-normalised multi-element diagrams show that these granitic and volcanic rocks are strongly enriched in LILE and LREE pattern, high (87Sr/86Sr)i and low ε Nd(t) ratios suggesting Ala?amdağ volcano-plutonic rocks to have been derived from hybrid magma that originated mixing of co-eval lower crustal-derived more felsic magma and enriched subcontinental lithospheric mantle-derived more mafic magmas during extensional processes, and the crustal material was more dominant than the mantle contribution. The Ala?amdağ volcano-plutonic complex rocks may form by retreat of the Hellenic/Aegean subduction zone, coinciding with the early stages of back-arc extension that led to extensive metamorphic core-complex formation.  相似文献   

17.
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18.
A method to predict the enthalpy of formation is based on the parameter HO2-cation (comp) (Vieillard 1982; Vieillard and Tardy 1988a). The calculation of this parameter requires the knowledge of cristallographical and optical properties of minerals (refractive index, molar volume, average distances and shortest bond lengths of cation-oxygens in all sites, existence of hydrogen bonding, presence of a order-disorder in a site of the involved compound). This method has been tested on a great number of minerals and artificial compounds belonging to the system: Li2O-Na2O-K2O-BeO-MgO-CaO-MnO-FeO-Fe2O3-Al2O3-SiO2-H2O (180 minerals) (Vieillard 1994a, b). When several structure refinements of the same mineral are present, several factors such as precision of crystal structure determination, chemical composition, existence of any disorder in a site, presence of hydrogen bonding and estimated standard deviation on bond lengths seem to play an important role in the predication of enthalpy of formation from oxides. Muscovite and natrolite, for which numerous structure refinements are available, are used and discussed in this study.  相似文献   

19.
Steady decline in the percentage of 235U in terrestrial uranium made natural fission impossible after about 1.8 Ga.Fission before 1.8 Ga disturbed the lead isotope system at various places worldwide,su...  相似文献   

20.
Coworking spaces (CWS) and the associated practice of coworking, have emerged in numerous forms and various urban contexts to critically challenge traditional concepts of the workplace and location of creative work, while simultaneously confronting the way in which creative workers interact with and relate to each other as well as with space and to place. Heralded as a solution to increasingly atomised work patterns, CWS are imagined and presented as spaces of serendipitous encounter, spontaneous exchange and collaboration. Nonetheless, little is known about how coworking positively supports workers and how coworking relates to wider urban transformation processes has been largely un-researched. This paper contributes to a critical discussion through empirical analysis of a project aimed at establishing new creative CWS in city-centre locations across SE England. The study adopts a novel approach using Q-methodology. Motivations for coworking and benefits (or dis-benefits) of co-location are assessed, as is the extent to which coworking facilitates interactional effects and wider neighbourhood interactions. In particular, the role of the CWS manager as “mediator” is explored. Coworker benefits relate primarily to peer-interaction and support rather than formal collaboration. While CWS managers play a key connecting role, also ensuring coworker complementarity and compatibility, the coworker profile (motivations, needs, experiences) ultimately influences outcomes. The study cautions against the use of CWS as “quick fix” urban renewal tools, with little indication that the benefits of coworking reach beyond immediate members or that linkages are easily established between coworkers and local (resident or business) communities.  相似文献   

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