Evaluation of the origin hypotheses of Pantheon Fossae, central Caloris basin, Mercury     

Christian Klimczak 《Icarus》2010,209(1):262-270

The origin of Pantheon Fossae, a complex structure consisting of radial graben in the center of the Caloris basin, Mercury, has been debated since the structure was first imaged by the MESSENGER spacecraft. Three different formation hypotheses have been suggested, i.e. an origin associated with the Apollodorus impact into a previously domed Caloris basin floor, graben formation as surface expressions of dike intrusions and basin-interior uplift alone. In order to test the scenarios, detailed observations from the currently available imagery were compared to the proposed formation mechanisms. We evaluate these origin hypotheses by means of detailed interpretations of the graben characteristics and patterns, by comparing to radial structures from Earth and Venus, and by mechanical analyses for each formation hypothesis. Results indicate that the formation of Pantheon Fossae as the result of doming in the central part of the Caloris basin is more likely than it having formed in association with a radially symmetric stress field centered at or near the Apollodorus crater, that would have been created by a magma chamber or been superimposed on a pre-existing dome due to impact mechanics.  相似文献   

Volker B?der (1965–2012) in memoriam     

Günter Seeber  Harald Sternberg  Christian Hirt 《Journal of Geodesy》2012,86(11):1077-1078

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Short and zero baseline analysis of GPS L1 C/A, L5Q, GIOVE E1B, and E5aQ signals   总被引：2，自引：1，他引：1  

Peter F. de Bakker  Christian C. J. M. Tiberius  Hans van der Marel  Roel J. P. van Bree 《GPS Solutions》2012,16(1):53-64

Stochastic properties of GNSS range measurements can accurately be estimated using a geometry-free short and zero baseline analysis method. This method is now applied to dual-frequency measurements from a new field campaign. Results are presented for the new GPS L5Q and GIOVE E5aQ wideband signals, in addition to the GPS L1 C/A and GIOVE E1B signals. As expected, the results clearly show the high precision of the new signals, but they also show, rather unexpectedly, significant, slowly changing variations in the pseudorange code measurements that are probably a result of strong multipath interference on the data. Carrier phase measurement noise is assessed on both frequencies, and finally successful mixed GPS-GIOVE double difference ambiguity resolution is demonstrated.  相似文献   

Crop area mapping in West Africa using landscape stratification of MODIS time series and comparison with existing global land products   总被引：6，自引：0，他引：6  

Elodie Vintrou  Annie DesbrosseAgnès Bégué  Sibiry TraoréChristian Baron  Danny Lo Seen 《International Journal of Applied Earth Observation and Geoinformation》2012,14(1):83-93

In Africa, food security early warning systems use satellite-derived data concerning crop conditions and agricultural production. Such systems can be improved if they are provided with a more reliable estimation of the cultivated area at national scale. This paper evaluates the potential of using time series from the MODerate resolution Imaging Spectroradiometer MOD13Q1 (16-day composite of normalized difference vegetation index at 250 m resolution) to extract cultivated areas in the fragmented rural landscapes of Mali. To this end, we first stratified Southern Mali into 13 rural landscapes based on the spatio-temporal variability of NDVI and textural indices, using an object-oriented classification scheme.The accuracy of the resulting map (MODIS_crop) and how it compares with existing coarse-resolution global land products (GLC2000 Africa, GLOBCOVER, MODIS V05 and ECOCLIMAP-II), was then assessed against six crop/non-crop maps derived from SPOT 2.5 m resolution images used as references. For crop areal coverage, the MODIS_crop cultivated map was successful in assessing the overall cultivated area at five out of the six validation sites (less than 6% of the absolute difference), while in terms of crop spatial distribution, the producer accuracy was between 33.1% and 80.8%. This accuracy was linearly correlated with the mean patch size index calculated on the SPOT crop maps (r² = 0.8). Using the Pareto boundary as an accuracy assessment method at the study sites, we showed that (i) 20-40% of the classification crop error was due to the spatial resolution of the MODIS sensor (250 m), and that (ii) compared to MODIS V05, which otherwise performed better than the other existing products, MODIS_crop generally minimized omission-commission errors. A spatial validation of the different products was carried out using SPOT image classifications as reference. In the corresponding error matrices, the fraction of correctly classified pixels for our product was 70%, compared to 58% for MODIS V05, while it ranged between 40% and 51% for the GLC2000, the ECOCLIMAP-II and the GLOBCOVER.  相似文献   

Basin modelling of a lignite‐bearing salt rim syncline: insights into rim syncline evolution and salt diapirism in NW Germany     

Christian Brandes  Lukas Pollok  Carolin Schmidt  Volker Wilde  Jutta Winsemann 《Basin Research》2012,24(6):699-716

The Helmstedt‐Staßfurt salt wall is 70 km long, 6–8 km wide and one of the most important diapiric structures in northern Germany, based on the economically significant lignite‐bearing rim synclines. The analysed Schöningen rim syncline, located on the southwestern side of the Helmstedt‐Staßfurt structure, is 8 km long and 3 km wide. The basin‐fill is up to 366 m thick and characterized by 13 major lignite seams with thicknesses between 0.1 and 30 m. The key objectives of this article were to expand on the classical cross‐section based rim syncline analysis by the use of 3D models and basin simulations. Cross‐sections perpendicular to the basin axis indicate that the basin‐fill has a pronounced lenticular shape. This shape varies from more symmetric in the NW to clearly asymmetric in the SE. Isopach maps imply a two‐fold depocentre evolution. The depocentre migrated over time towards the salt wall and also showed some distinct shifts parallel to the salt wall. The basin modelling part of the study was carried out with the software PetroMod^®, which focused on the burial history of the rim syncline. Modelling results also show the progressive migration of the rim syncline depocentre towards the salt wall. The present‐day asymmetry of the basin‐fill was already developed in the early phases of rim syncline evolution. The extracted geohistory curve shows initial rapid subsidence between 57 and 50 Ma and more moderate subsidence from 50 to 34 Ma. This pattern is interpreted to reflect salt evacuation from the source layer into the salt wall. The initial salt‐withdrawal rate was rapid, but later decreased probably due to depletion of the source layer.  相似文献   

Conditions for deposition of annually laminated sediments in small meromictic lakes: a case study of Lake Suminko (northern Poland)     

Wojciech Tylmann  Kamila Szpakowska  Christian Ohlendorf  Micha? Woszczyk  Bernd Zolitschka 《Journal of Paleolimnology》2012,47(1):55-70

A three-year field study was conducted in Lake Suminko, Poland, to gain an understanding of the limnological variables that influence the formation and spatial extent of annually laminated sediments in the lake. The water body is divided into three depth strata, the mixolimnion, chemocline and monimolimnion, each defined by distinct values of temperature, electrical conductivity and oxygen concentration. Typical for meromictic lakes, the monimolimnion remains perennially anoxic and is rich in dissolved solids and nutrients. The annual pattern of particle flux in Lake Suminko is closely related to biochemical processes in the euphotic zone. During winter months we observed very low accumulation rates of non-carbonaceous matter, while during the rest of the year, three periods of calcite deposition were recorded (April, July–August, and October–November). The periods of high calcite deposition corresponded with algal blooms and oxygen concentration maxima. Two principal factors contribute to meromixis in Lake Suminko: (1) the basin is sheltered, preventing wind mixing, and (2) biochemical processes in the lake associated with high lacustrine productivity. Meromictic conditions must control the formation and preservation of laminated sediments in the lake because preserved laminations occur only in areas where the lake floor lies below monimolimnetic waters.  相似文献   

An integrated socio-environmental framework for glacier hazard management and climate change adaptation: lessons from Lake 513, Cordillera Blanca, Peru   总被引：1，自引：0，他引：1  

Mark Carey  Christian Huggel  Jeffrey Bury  César Portocarrero  Wilfried Haeberli 《Climatic change》2012,112(3-4):733-767

Glacier hazards threaten societies in mountain regions worldwide. Glacial lake outburst floods (GLOFs) pose risks to exposed and vulnerable populations and can be linked in part to long-term post-Little Ice Age climate change because precariously dammed glacial lakes sometimes formed as glaciers generally retreated after the mid-1800s. This paper provides an interdisciplinary and historical analysis of 40?years of glacier hazard management on Mount Hualcán, at glacial Lake 513, and in the city of Carhuaz in Peru’s Cordillera Blanca mountain range. The case study examines attempted hazard zoning, glacial lake evolution and monitoring, and emergency engineering projects to drain Lake 513. It also analyzes the 11 April 2010 Hualcán rock-ice avalanche that triggered a Lake 513 GLOF; we offer both a scientific assessment of the possible role of temperature on slope stability and a GIS spatial analysis of human impacts. Qualitative historical analysis of glacier hazard management since 1970 allows us to identify and explain why certain actions and policies to reduce risk were implemented or omitted. We extrapolate these case-specific variables to generate a broader socio-environmental framework identifying factors that can facilitate or impede disaster risk reduction and climate change adaptation. Facilitating factors are technical capacity, disaster events with visible hazards, institutional support, committed individuals, and international involvement. Impediments include divergent risk perceptions, imposed government policies, institutional instability, knowledge disparities, and invisible hazards. This framework emerges from an empirical analysis of a coupled social-ecological system and offers a holistic approach for integrating disaster risk reduction and climate change adaptation.  相似文献   

Origin of light volatile hydrocarbon gases in mud volcano fluids, Gulf of Cadiz — Evidence for multiple sources and transport mechanisms in active sedimentary wedges     

Marianne Nuzzo  Edward R.C. Hornibrook  Fiona Gill  Christian Hensen  Richard D. Pancost  Matthias Haeckel  Anja Reitz  Florian Scholz  Vitor H. Magalhes  Warner Brückmann  Luis M. Pinheiro 《Chemical Geology》2009,266(3-4):359-372

Widespread mud volcanism across the thick (≤ 14 km) seismically active sedimentary prism of the Gulf of Cadiz is driven by tectonic activity along extensive strike–slip faults and thrusts associated with the accommodation of the Africa–Eurasia convergence and building of the Arc of Gibraltar, respectively. An investigation of eleven active sites located on the Moroccan Margin and in deeper waters across the wedge showed that light volatile hydrocarbon gases vented at the mud volcanoes (MVs) have distinct, mainly thermogenic, origins. Gases of higher and lower thermal maturities are mixed at Ginsburg and Mercator MVs on the Moroccan Margin, probably because high maturity gases that are trapped beneath evaporite deposits are transported upwards at the MVs and mixed with shallower, less mature, thermogenic gases during migration. At all other sites except for the westernmost Porto MV, δ¹³C–CH₄ and δ²H–CH₄ values of ~ − 50‰ and − 200‰, respectively, suggest a common origin for methane; however, the ratio of CH₄/(C₂H₆ + C₃H₈) varies from ~ 10 to > 7000 between sites. Mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply-buried sediments, possibly associated with biodegradation of C₂₊ homologues and secondary methane production at Captain Arutyunov and Carlos Ribeiro MVs. At the deep-water Bonjardim, Olenin and Carlos Ribeiro MVs, generation of C₂₊-enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge. At Porto MV, gases are highly enriched in CH₄ having δ¹³C–CH₄ ~ − 50‰, as at most sites, but markedly lower δ²H–CH₄ values < − 250‰, suggesting that it is not generated by thermal cracking of n-alkanes but rather that it has a deep Archaeal origin. The presence of petroleum-type hydrocarbons is consistent with a thermogenic origin, and at sites where CH₄ is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments ~ 2–4 km deep. These fluids then migrate into shallower, thermally immature muds, driving their mobilization and extrusion at the seafloor. At Porto MV, the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of CH₄.  相似文献   

Electron accepting capacity of dissolved organic matter as determined by reaction with metallic zinc   总被引：2，自引：0，他引：2  

Christian Blodau  Markus Bauer  Simona Regenspurg  Donald Macalady 《Chemical Geology》2009,260(3-4):186-195

Information about the chemical electron accepting capacity (EAC) of dissolved organic matter (DOM) is scarce owing to a lack of applicable methods. We quantified the electron transfer from metallic Zn to natural DOM in batch experiments at DOC concentrations of 10–100 mg-C L^− 1 and related it to spectroscopic information obtained from UV-, synchronous fluorescence, and FTIR- spectroscopy. The electron donating capacity of DOM and pre-reduced DOM was investigated using Fe(CN)₆³⁻ as electron acceptor. Presence of DOM resulted in release of dissolved Zn, consumption of protons, and slower release of hydrogen compared to reaction of metallic Zn with water at pH 6.5. Comparison with reaction stoichiometry confirmed that DOM accepted electrons from metallic Zn. The release of dissolved Zn was dependent on pH, DOC concentration, ionic strength, and organic matter properties. The reaction appeared to be completed within about 24 h and was characterized by pseudo first order kinetics with rate constants of 0.5 to 0.8 h^− 1. EAC per mass unit of carbon ranged from 0.22 mmol g^− 1 C to 12.6 mmol g^− 1 C. Depending on the DOM, a calculated 28–127% of the electrons transferred from metallic Zn to DOM could be subsequently donated to Fe(CN)₆³⁻. EAC decreased with DOC concentration, and increased with aromaticity, carboxyl, and phenolic content of the DOM. The results indicate that an operationally defined EAC of natural DOM can be quantified by reaction with metallic Zn and that DOM properties control the electron transfer. Shortcomings of the method are the coagulation and precipitation of DOM during the experiment and the production of hydrogen and dissolved Zn by reaction of metallic Zn with water, which may influence the determined EAC.  相似文献   

The Skaergaard liquid line of descent revisited   总被引：1，自引：0，他引：1  

Peter Thy  Charles E. Lesher  Christian Tegner 《Contributions to Mineralogy and Petrology》2009,157(6):735-747

There is a fundamental conflict between the suggestion that the iron content of Skaergaard liquids increases during Fe–Ti oxide fractionation and the observation that at the same time oxygen fugacity () drops by two log-units below the fayalite-magnetite-quartz oxygen buffer (FMQ). A new petrographic study of average Skaergaard gabbros shows that the total modal content of Fe–Ti oxides is about 22% in the early LZc and markedly decreases to below 5% in the UZc. Forward modeling based on these modal constraints, as well as experimental results on Skaergaard-related dikes, predicts that fractionation of troctolitic LZa gabbros drives the derivative liquid towards a high-iron content. Strong iron enrichment continues, together with a small decline in silica, during LZb crystallization due to the appearance of augite as a fractionating phase. The fractionation of Fe–Ti oxides in the LZc initially suppresses iron enrichment and reverses the silica trend to one of slight enrichment. However, continued evolution into the UZ produces liquids with maximum UZc FeO* content of 23–25 wt.% and SiO₂ content of 53 wt.% (FeO* is total iron as FeO). The maximum in FeO* is dependent on several factors of which the Fe–Ti oxide mode has the strongest effect. The during crystallization of the LZc is widely thought to have been at, or slightly below, the fayalite-magnetite-quartz oxygen buffer (FMQ). Under closed system evolution, incorporation of ferric iron into augite during formation of the LZb restricts the increase in to about 0.1 log-units above FMQ (=0.1 ΔFMQ). Likewise, crystallization of the LZc through the UZa, involving Fe–Ti oxide minerals, leads to a decline in of less than 0.1 ΔFMQ. Crystallization of the UZb-c gabbros results in oxidation to a maximum of 0.5 ΔFMQ. This behavior can account for the iron-rich character of the UZ gabbros, as well as, the low modal content of Fe–Ti oxides. Thus, evolved Skaergaard liquids are high in iron and contain a modest amount of SiO₂. Our modeling result do not account for a strong drop in through the layered series. Such a drop would require an unacceptably high proportion of Fe–Ti oxides and high-magnetite content in the fractionating assemblage. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献