Intervention of Electrical Resistance Tomography (ERT) in resolving hydrological problems of a semi arid granite terrain of Southern India     

Rolland Andrade 《Journal of the Geological Society of India》2011,78(4):337-344

Electrical Resistivity Tomography (ERT) has been used in association with several geohydrological, geotechnical and geophysical methods in resolving several site specific problems in hydrological science. Advancement in the field of computers and automation in the field of electronics has jointly resulted in the development of this geophysical innovation which has wide application in groundwater, environmental and engineering problems including monitoring of vadose zone water movement, steam injection etc. In this paper application of ERT in association with geohydrological and other exploration methods in resolving groundwater sustainability problem of a micro-watershed area in semi arid granite terrain is presented as three independent cases. In a hard rock terrain the probability of complexities in understanding the sub-surface lithology and its corresponding hydrological parameters are more. Hence appropriate resistivity survey configuration and suitable inversion of acquired data in congregation with other geo-scientific investigations were carried out to understand the site specific problem. The study demonstrated as 3 independent cases shows the usefulness of the ERT method in hydrological investigations, which is economic, efficient and less time consuming in comparison to the other exploration methods.  相似文献   

Distribution and community structure of estuarine copepods     

Rolland S. Fulton 《Estuaries and Coasts》1984,7(1):38-50

Distribution, abundance, and community structure were studied over a 30 month period in the planktonic copepod community of the estuaries near Beaufort, North Carolina. Many of the copepod species showed a demersal distribution during the day and entered the surface waters at night. Several species were largely confined to vegetated littoral areas during the day. The copepod community showed consistent trends of seasonal abundance and succession of dominant species which differed greatly from those found by previous workers, whose methods were inadequate to sample quantitatively the small, demersal copepods which dominated the community. Copepod abundances were higher than found in previous studies and were correlated with water temperature. Species composition changed from a winter community dominated byCentropages spp., to a spring community dominated byAcartia tonsa, to a summer community jointly dominated byParacalanus crassirostris andOithona spp. Copepods were much more important grazers in these estuaries than previous studies had concluded.  相似文献   

Diffusion-controlled development of silica-undersaturated domains in felsic granulites of the Bohemian Massif (Variscan belt of Central Europe)   总被引：2，自引：0，他引：2  

Lucie Tajčmanová  Jiří Konopásek  James A. D. Connolly 《Contributions to Mineralogy and Petrology》2007,153(2):237-250

Plagioclase rims around metastable kyanite crystals appear during decompression of high-pressure felsic granulites from the high-grade internal zone of the Bohemian Massif (Variscan belt of Central Europe). The development of the plagioclase corona is a manifestation of diffusion-driven transfer of CaO and Na₂O from the surrounding matrix and results in isolation of kyanite grains from the quartz- and K-feldspar-bearing matrix. This process establishes Si-undersaturated conditions along the plagioclase–kyanite interface, which allow crystallization of spinel during low-pressure metamorphism. The process of the plagioclase rim development is modeled thermodynamically assuming local equilibrium. The results combined with textural observations enable estimation of equilibration volume and diffusion length for Na and Ca that extends ∼400–450 and ∼450–550 μm, respectively, around each kyanite crystal. Low estimated bulk diffusion coefficients suggest that the diffusion rate of Ca and Na is controlled by low diffusivity of Al across the plagioclase rim.  相似文献   

The efficiency of kerosene flotation for extraction of chironomid head capsules from lake sediments samples     

Nicolas Rolland  Isabelle Larocque 《Journal of Paleolimnology》2007,37(4):565-572

Kerosene, a grade mineral oil, is commonly used to extract beetles from sediment. Here, the use of kerosene to extract chironomid head capsules was tested on 10 samples from sediment of different lakes, with different organic matter content as measured by loss on ignition, and estimated ages. Our results revealed that this flotation tool is very effective in extracting either full or half chironomid head capsules. The mean extraction efficiency was 89.3 ± 8.0% with an estimated relative abundance error ranging from −1% to 1% for 46 of the 57 identified taxa. Larger chironomids (400–500 μm width), which are often full of sediment particles, have the highest relative abundance error, with a maximum of 4.3% for Corynocera oliveri-type. A canonical correspondence analysis showed that, despite this small bias, samples retrieved with the kerosene flotation do not differ from the whole sample assemblages. These results give us confidence in the use of this flotation technique for chironomid sample preparation.  相似文献   

Solvability and multiquadric analysis as applied to investigations of vertical crustal movements     

Sanford R. Holdahl  Rolland L. Hardy   《Tectonophysics》1979,52(1-4)

A variety of geodetic measurements can be combined, in network fashion, to yield adjusted velocities of elevation change. However, it is not always apparent which network junctions have solvable point velocities. When a velocity surface is desired, it is not always apparent how many coefficients should be used. A solvability algorithm, devised to operate on observation equations, answers these questions, and therefore permits the adjustment process to continue with the assurance that the result will be mathematically justified. Using both the hyperboloid and the reciprocal hyperboloid as quadric forms, multiquadric (MQ) analysis has been applied to leveling and tide gauge data in the vicinity of Puget Sound, to obtain heights corresponding to a selected date, and coefficients which collectively define a velocity surface. The solvability algorithm was used to tell which junctions in the level network had solvable point velocities, and consequently where MQ nodal points should be placed for an optimized solution. Networks of simulated data were also used with the solvability algorithm to help determine data requirements for height—velocity adjustments, and to evaluate the ability of MQ analysis to predict velocities.  相似文献   

Holocene hydrological and vegetation changes in southern France inferred by the study of an alluvial travertine system (Saint-Guilhem-le-Désert, Hérault)     

Adam Ahmed Ali  Paul Roiron  Lucie Chabal  Paul Ambert  Jean Gasco  Joël Andr  Jean-Frdric Terral 《Comptes Rendus Geoscience》2008,340(6):356-366

A geobotanical study of the travertine system of Saint-Guilhem-le-Désert (southern France) was carried out in order to reconstruct the local Holocene environment in a region where the postglacial vegetation history is poorly documented. The travertinisation process has started at ca. 8500 cal. BP, in a landscape dominated by Pinus sylvestris type (probably Pinus nigra sub sp. salzmannii). Around 7000 cal. BP, the travertine system recorded torrential events not evidenced at the regional scale, showing the particularity of the Verdus hydrological regime. More recently, ca. 5100 cal. BP, a lake or a marsh was filled within the Verdus plain, as attested to by sand and silt particles accumulated in the sequence. The present-day vegetation dominated by Quercus ilex, on south facing slopes, was most likely established between the Bronze Age and the Gallo-Roman period correlatively to the decline of Pinus nigra and deciduous Quercus, most probably under human influence.  相似文献   

Βedrock instability of underground storage systems in the Czech Republic,Central Europe     

Lucie Novakova  Milan Broz  Jiri Zaruba  Karel Sosna  Jan Najser  Lenka Rukavickova  Jan Franek  Vladimir Rudajev 《应用地球物理》2016,13(2):315-325

Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH₄), the geological disposal of CO₂, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m^?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure.  相似文献   

A 2000 year midge-based paleotemperature reconstruction from the Canadian Arctic archipelago     

David F. Porinchu  Glen M. MacDonald  Nicolas Rolland 《Journal of Paleolimnology》2009,41(1):177-188

A lake sediment core recovered from Lake V57 on Victoria Island, Nunavut, Canada, spanning the last 2000 years, was analyzed for sub-fossil midge remains and organic-matter content (estimated by loss-on-ignition (LOI)). Significant changes in midge community composition occurred during the last 2000 years, with a distinct midge community appearing after 1600 AD. The chironomid community between 0 and 1600 AD was dominated by Heterotrissocladius, Tanytarsus, Abiskomyia, and Paracladius. At approximately 1600 AD, Heterotrissocladius decreased in relative abundance and taxa such as Corynocera ambigua, C. oliveri, Psectrocladius sordidellus type, and Pentanneurini increased in relative abundance. Previously published midge-based inference models for average July air temperature (AJAT) and summer surface–water temperature (SSWT) were applied to the subfossil midge stratigraphy. The AJAT reconstruction indicates relatively cool conditions existed between 1100 and 1600 AD, with exceptional warming occuring after 1600 AD, as lake productivity inferred from organic-matter content increased concomitantly with midge-inferred AJAT and SSWT. The cooler conditions between 1200 and 1600 AD, and the pattern of warming over recent centuries inferred from Lake V57 is broadly consistent with temperature-sensitive biogenic silica records from other sites in the central Canadian Arctic and the treeline zone to the south suggesting a regionally synchronous response to climate forcing.

David F. PorinchuEmail:

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The use of high-resolution gridded climate data in the development of chironomid-based inference models from remote areas     

Nicolas Rolland  David F. Porinchu  Isabelle Larocque 《Journal of Paleolimnology》2009,41(2):343-348

The development of chironomid-based air temperature inference models in high latitude regions often relies on limited spatial coverage of meteorological data and/or on punctual measurements of water temperature at the time of sampling. The use of simple linear regression to relate air temperature and latitude was until recently the best method to characterize the air temperature gradient along a latitudinal gradient. However, recent studies have used high-resolution gridded climate data to develop new chironomid-based air temperature inference models. This innovative approach has, however, never been further analyzed to test its reliability. This study presents a method using ArcGIS^® to extract air temperatures from a high-resolution global gridded climate data set (New et al. 2002) and to incorporate these new data in a variety of chironomid-based air temperature inference models to test their performance. Results suggest that this method is reliable and produces better estimates of air temperature and will be helpful in the development of further quantitative air temperature inference models in remote areas.  相似文献   

Structural Setting of the Neoarchean Terrains in the Commonwealth Bay Area (143-145°E), Terre Adélie Craton, East Antarctica     

R-P. Mnot  A. Pêcher  Y. Rolland  J-J. Peucat  A. Pelletier  G. Duclaux  S. Guillot 《Gondwana Research》2005,8(1):1-9

Geological maps of East Commonwealth Bay Unit (ECB), (Terre Adélie and Georges V Land, Antarctica) are presented with a summary of the main structural and metamorphic data for the region. The ECB unit was developed during Neoarchean_Paleoproterozoic event (at 2.5-2.42 Ga), with (i) granulite metamorphism at 9±1.5 kbar and 800±50°C in the lower crust section and amphibolite metamorphism (P=5 kbar, T=750°C) at the upper crustal levels; (ii) the lower crustal granulites were uplifted, and suffered local partial melting and retrogression to the amphibolite facies at 550±50°C_5 kbar. Granulites were extruded in the core of a crustal-scale anticlinal fold, but retrogressed only on the rims of the anticline. Crustal-scale folding, along with other structural features resulted from intense NE-SW shortening that prevailed during the Neoarchean orogenic cycle. Strike-slip and extensional motions were only minor components in that process; (iii) top-to-the-East thrusting and nappe piling had (at least locally) occurred under lower amphibolite to greenschist facies conditions. Finally, it seems that (iv) the Paleoproterozoic 1.7 Ga structural imprint may have only affected the rims of the Archean units. The tectonic context observed in the 1.7 Ga Cape Hunter phyllites features mainly an E-W shortening component and vertical extrusion. The eastern (Mertz) and western (Port Martin) parts of the Archean block were reactivated by localized dextral shearing.  相似文献