5α(H)-cholestan-3α-ol in sediments: Characterization and geochemical significance     

François Mermoud  Fazil O Gülaçar  Armand Buchs 《Geochimica et cosmochimica acta》1985,49(2):459-462

The top five centimeters of sediment collected at the deepest point of Lake Léman (Switzerland), 309 meters below water level, contain concentrations of 5α(H)-cholestan-3α-ol (epicholestanol) up to 10% of the total sterol content. Isobutane chemical ionization mass spectrometry and coinjection with an authentic standard on a SP-1000 glass capillary column were used in order to successfully characterize this epimer of cholestanol.The distribution of this stanol throughout the sediment core studied suggests in situ bacterial production. The change in concentration of epicholestanol with depth is different from those found for other C₂₇ stanols, such as cholestanol or coprostanol. It is probably the result of a change in the bacterial fauna in the most recently deposited sediment, related to the increasing eutrophication of the lake rather than the consequence of its lower stability due to the axial conformation of the OH substituent.  相似文献   

Relative stabilities of cholestadienes calculated by molecular mechanics and semi-empirical methods: application to the acid-catalyzed rearrangement reactions of cholesta-3,5-diene     

Patrick Y. Schüpfer  Fazil O. Gülaar 《Organic Geochemistry》2000,31(12)

The study of geochemical transformations undergone by ‘biological markers’ after their incorporation into sediments is an important field of organic geochemistry. Combined with laboratory simulation experiments, molecular mechanics calculations have been shown to be very useful to establish the reaction pathways, and to predict intermediate components and stable reaction end products, especially in the case of the acid-catalyzed isomerization reactions of steroid and terpenoid hydrocarbons. Many commercially available softwares are able to optimize (minimize) the geometries of molecules and compute some of their thermodynamical data with either molecular mechanics (MM) or semi-empirical methods of quantum chemistry. In order to verify the reliability of these methods, we have computed the relative thermodynamic stabilities of a large number of steradiene isomers with MM3 (Tripos Inc.), MM+ (HYPERCHEM^TM) and MM2 (Chem3D, CambridgeSoft Corp.) empirical force fields, and with AM1 and PM3 (HYPERCHEM^TM) semi-empirical methods. The calculation results of thermodynamic stabilities of steradiene isomers are used to explain the compounds produced by the rearrangement of cholesta-3,5-diene when treated with p-toluenesulfonic acid in acetic acid at 70°C. The end products, namely the spirosteradienes 7–8, obtained by this treatment are the most stable steradiene isomers according to all computational methods. The relative thermodynamic stabilities of cholestadienes are also consistent with the mechanism postulated for the spirosteradiene formation proceeding through a pathway including cholestadienes 2–6 as intermediates.  相似文献   

Macrozoobenthos as an Indicator of the Level of the Trophy and Saprobity of Lake Jarun     

M. Kerovec  V. Tav ar  M. Me&#x;trov 《洁净——土壤、空气、水》1989,17(1):37-45

During complex ecological investigations on Lake Jarun (and neighbouring interstitial underground waters) which took place in 1984 and 1985, macrozoobenthos was also studied. Its qualitative and quantitative composition in a large part depends on the degree of trophy and saprobity of the water. Specially examined were the oligochaetes and chironomids larvae, which besides having a large numerical percentage also occurred with a large number of species. In addition, the representatives of other groups of macroscopic invertebrates were also mentioned, especially those which have a special significance as indicators of a certain degree of trophy and saprobity, and which are important because of their oasis preservation in this ecosystem.  相似文献   

A technique for improving MODIS standard snow products for snow cover monitoring over Eastern Turkey     

Yaşar Tekeli  Ahmet Emre Tekeli 《Arabian Journal of Geosciences》2012,5(2):353-363

Daily snow cover maps at 500 m resolution are available from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on NASA's Terra and Aqua satellites. However, information of the ground can only be obtained during clear sky conditions. In addition, the spectral similarity between clouds and snow in the visible part of the spectrum causes some ambiguities in separation of them. The dynamic behavior of clouds with their tendency to move faster often enables discrimination between cloud and snow, since snow remains relatively stationary. In this study, a daily merging methodology to combine Terra and Aqua based snow maps are proposed, and the benefits of this combination are evaluated. The methodology was tested for Eastern Turkey covering the period from December 2002 to March 2003. Merged maps derived from the standard daily snow maps from Terra (MOD10A1) and Aqua (MYD10A1) reduce the cloud cover present in any one image alone, provide better representation of the surface snow cover, and indicate better agreement with ground snow measurements than when either one is used alone. For “on the ground data date” analyses yielded 31% match ratios for MOD10A1 and MYD10A1, whereas combined images enabled 38%. One- to 2-day temporal window shifting enabled further 7% and 5% improvements in match ratios, respectively. The maximum improvement of 25% was achieved in January of 2003. The proposed methodology provides an easy and effective way to improve snow cover maps with little effort and provides fewer cloud-contaminated images for snow monitoring, for hydrology, and water resource management.  相似文献   

Metamorphic evolution of blueschists of the Altınekin Complex,Konya area,south central Turkey     

Giles T. R. Droop  Muazzez . Karakaya  Yaar Eren  Necati Karakaya 《Geological Journal》2005,40(2):127-153

The Altınekin Complex in south central Turkey forms part of the south‐easterly extension of the Tavşanlı Zone, a Cretaceous subduction complex formed during the closure of the Neo‐Tethys ocean. The protoliths of metamorphic rocks within the Altınekin Complex include peridotites, chromitites, basalts, ferruginous cherts and flysch‐facies impure carbonate sediments. Structurally, the complex consists of a stack of thrust slices, with massive ophiolite tectonically overlying a Cretaceous sediment‐hosted ophiolitic mélange, in turn overlying a sequence of Mesozoic sediments. Rocks within the two lower structural units have undergone blueschist–facies metamorphism. Petrographic, mineral–chemical and thermobarometric studies were undertaken on selected samples of metasedimentary and metabasic rock in order to establish the time relations of deformation and metamorphism and to constrain metamorphic conditions. Microstructures record two phases of plastic deformation, one predating the metamorphic peak, and one postdating it. Estimated peak metamorphic pressures mostly fall in the range 9–11 kbar, corresponding to burial depths of 31–38 km, equivalent to the base of a continental crust of normal thickness. Best‐fit peak metamorphic temperatures range from 375 to 450°C. Metamorphic fluids had high H₂O:CO₂ ratios. Peak metamorphic temperature/depth ratios (T/d values) were low (c. 10–14°C/km), consistent with metamorphism in a subduction zone. Lawsonite‐bearing rocks in the southern part of the ophiolitic mélange record lower peak temperatures and T/d values than epidote blueschists elsewhere in the unit, hinting that the latter may consist of two or more thrust slices with different metamorphic histories. Differences in peak metamorphic conditions also exist between the ophiolitic mélange and the underlying metasediments. Rocks of the Altınekin Complex were subducted to much shallower depths, and experienced higher geothermal gradients, than those of the NW Tavşanlı Zone, possibly indicating dramatic lateral variation in subduction style. Retrograde P–T paths in the Altınekin Complex were strongly decompressive, resulting in localized overprinting of epidote blueschists by greenschist–facies assemblages, and of lawsonite blueschists by pumpellyite–facies assemblages. The observation that the second deformation was associated with decompression is consistent with, but not proof of, exhumation by a process that involved deformation of the hanging‐wall wedge, such as gravitational spreading, corner flow or buoyancy‐driven shallowing of the subduction zone. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Assessing the role of winter grazing in historic land degradation,Mývatnssveit,northeast Iceland     

Ian A. Simpson  Garar Gumundsson  Amanda M. Thomson  Jonathan Cluett 《Geoarchaeology》2004,19(5):471-502

This paper assesses the contribution of historical and traditional winter grazing to long‐term land degradation in northeast Iceland. To do so, indicators of soil erosion from two contrasting historical winter grazing areas, set in a tephrochronological framework, are compared against their temporal and regional land degradation contexts. The observations made indicate distinctive and different landscape responses to historical winter grazing depending on location. In both study areas, there is an accelerated level of wind and water erosion with settlement at ca. A.D. 874 through to A.D. 1477. One of these areas had a subsequent reduction in erosion rates to considerably below the regional average, possibly as a result of adaptive land management; the second, more inherently sensitive area, is now subarctic desert. These findings confirm early land management practices as a major factor in Icelandic land degradation, they contribute to explanations of early settlement success and failure, and highlight the significance of historical approaches in addressing contemporary issues of land degradation and conservation responses. © 2004 Wiley Periodicals, Inc.  相似文献   

Seismotectonic database of Turkey     

Tamer Y. Duman  Tolga Çan  Ömer Emre  F. Tuba Kadirioğlu  Nilay Başarır Baştürk  Tuğbay Kılıç  Selim Arslan  Selim Özalp  Recai F. Kartal  Doğan Kalafat  Ferdane Karakaya  Tuba Eroğlu Azak  Nurcan M. Özel  Semih Ergintav  Sinan Akkar  Yıldız Altınok  Senem Tekin  Ayhan Cingöz  A. İhsan Kurt 《Bulletin of Earthquake Engineering》2018,16(8):3277-3316

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time.  相似文献   

New geomorphological and chronological constraints for glacial deposits in the Rivoli‐Avigliana end‐moraine system and the lower Susa Valley (Western Alps,NW Italy)          下载免费PDF全文

Susan Ivy‐Ochs  Stefania Lucchesi  Paolo Baggio  Gianfranco Fioraso  Franco Gianotti  Giovanni Monegato  Angela A. Graf  Naki Akçar  Marcus Christl  Francesco Carraro  Maria Gabriella Forno  Christian Schlüchter 《第四纪科学杂志》2018,33(5):550-562

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A fuzzy multiple-attribute decision-making modelling for vulnerability analysis on the basis of population information for disaster management     

Z. Zhang  U. Demšar  J. Rantala  K. Virrantaus 《International journal of geographical information science》2014,28(9):1922-1939

Research activity and published literature on the reliability and vulnerability analysis of urban areas for disaster management has grown tremendously in the recent past. Population information has played the most important role during the entire disaster management process. In this article, population information was used as the evaluation criterion, and a fuzzy multiple-attribute decision-making (MADM) approach was used to support a vulnerability analysis of the Helsinki area for disaster management. A kernel density map was produced as a result that showed the vulnerable spatial locations in the event of a disaster. Model results were first validated against the original population information kernel density maps. In the second step, the model was validated by using fuzzy set accuracy assessment and the actual domain knowledge of the rescue experts. This is a novel approach to validation, which makes it possible to see how and if computer decision-making models compare to a real decision-making process in disaster management. The validation results showed that the fuzzy model has produced a reasonably accurate result. By using fuzzy modelling, the number of vulnerable areas was reduced to a reasonable scale and compares to the actual human assessment of these areas, which allows resources to be optimised during the rescue planning and operation.  相似文献   

Geophysical Images of the North Anatolian Fault Zone in the Erzincan Basin, Eastern Turkey, and their Tectonic Implications     

Ümİt Avşar  Erşan Türkoğlu  Martyn Unsworth  İlyas Çağlar  Bülent Kaypak 《Pure and Applied Geophysics》2013,170(3):409-431

The collision between the Arabian and Eurasian plates in eastern Turkey causes the Anatolian block to move westward. The North Anatolian Fault (NAF) is a major strike-slip fault that forms the northern boundary of the Anatolian block, and the Erzincan Basin is the largest sedimentary basin on the NAF. In the last century, two large earthquakes have ruptured the NAF within the Erzincan Basin and caused major damage (M _s = 8.0 in 1939 and M _s = 6.8 in 1992). The seismic hazard in Erzincan from future earthquakes on the NAF is significant because the unconsolidated sedimentary basin can amplify the ground motion during an earthquake. The amount of amplification depends on the thickness and geometry of the basin. Geophysical constraints can be used to image basin depth and predict the amount of seismic amplification. In this study, the basin geometry and fault zone structure were investigated using broadband magnetotelluric (MT) data collected on two profiles crossing the Erzincan Basin. A total of 24 broadband MT stations were acquired with 1–2 km spacing in 2005. Inversion of the MT data with 1D, 2D and 3D algorithms showed that the maximum thickness of the unconsolidated sediments is ~3 km in the Erzincan Basin. The MT resistivity models show that the northern flanks of the basin have a steeper dip than the southern flanks, and the basin deepens towards the east where it has a depth of 3.5 km. The MT models also show that the structure of the NAF may vary from east to west along the Erzincan Basin.  相似文献