Characterization of seafloor pockmark seepage of hydrocarbons employing fractal: A case study from the western continental margin of India     

Sumanta Dandapath  Bishwajit Chakraborty  Nicolas Maslov  Siddaiah M. Karisiddaiah  Dhrupad Ghosh  William Fernandes  Andrew Menezes 《Marine and Petroleum Geology》2012,29(1):115-128

Here we apply quantitative technique to describe the seafloor seepages based on the multi-beam backscatter and bathymetric investigations to characterize the pockmark morphology. The variable seafloor backscatter strength for coarser seafloor sediments are related to the diagenesis derived from biodegraded seepages. In this regard, box counting method is used to estimate ‘fractal dimension’ for backscatter imagery data of 398 blocks. These blocks are further sub-grouped into six classes depending on the spread of pockmark related seepages. The study area lies 102 km west off Marmagao along the central west coast of India which contains pre-dominantly (70%) gas-charged sediments. Comparison between the estimated self-similar fractals reveals that there is approximately 97% correlation between the box (D_box) and information (D_info) dimensions. Box dimension–derived fractal dimension values, suggest that the seepages are more along the fault trace in deeper waters, in comparison to sparsely distributed shallow water seepages. Besides, this poor seepage is confined within the smooth to moderately rough seafloor. It is established that the high backscatter strength along the upper slope of the pockmark region having higher fractal dimensions reflects multifractal behavior of seepage distribution. Entire area indicates patchy seepage patterns as supported by estimated fractal values showing intermittent fluctuations, which emphasizes non-linear behavior. Estimated self organizing criticality (SOC) parameters for six representative blocks reveal that the nature of pockmark, fault trace, sediment nature coupled with slumping of pockmark’s wall, sediment movement due to bottom currents are controlling the dynamic balance in the area seepage system. Further, our study emphasizing the multifractal behavior of seepage blocks, clearly depicts the drift in the seepage pattern.  相似文献   

Oxygen and organic carbon fluxes in sediments of the Bay of Biscay     

Aurélia Mouret  Pierre Anschutz  Bruno Deflandre  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Henri Etcheber  Jean-Marie Jouanneau  Antoine Grémare  Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540

The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O₂ consumption and POC burial rates. Benthic O₂ distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O₂ consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O₂ fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O₂ profiles. The rupture in the gradient of O₂ microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O₂ fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O₂ fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O₂ penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.  相似文献   

Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific and Baltic‐Skagerrak region: calibration as an annual density proxy and first evidence of pseudo‐cryptic speciation     

Kenneth Neil Mertens  Manuel Bringué  Nicolas Van Nieuwenhove  Yoshihito Takano  Vera Pospelova  Andre Rochon  Anne De Vernal  Taoufik Radi  Barrie Dale  R. Timothy Patterson  Kaarina Weckström  Elinor Andrén  Stephen Louwye  Kazumi Matsuoka 《第四纪科学杂志》2012,27(7):734-744

Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparède et Lachmann) Bütschli in surface sediments from the North Pacific was investigated. The average process length showed a significant inverse relation to annual seawater density: σ_{t annual} = ?0.8674 × average process length + 1029.3 (R² = 0.84), with a standard error of 0.78 kg m^?3. A sediment trap study from Effingham Inlet in British Columbia revealed the same relationship between average process length and local seawater density variations. In the Baltic–Skagerrak region, the average process length variation was related significantly to annual seawater density: σ_{t annual} = 3.5457 × average process length ? 993.28 (R² = 0.86), with a standard error of 3.09 kg m^?3. These calibrations cannot be reconciled, which accentuates the regional character of the calibrations. This can be related to variations in molecular data (small subunit, long subunit and internal transcribed spacer sequences), which show the presence of several genotypes and the occurrence of pseudo‐cryptic speciation within this species. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Test of the vibrational modelling for the λ-type transitions: Application to the α-β quartz transition     

Joëlle Castex  Michel Madon 《Physics and Chemistry of Minerals》1995,22(1):1-10

Vibrational modelling is at the present time the only known way to predict the heat capacities of the Earth's mantle minerals at high-pressure and high-temperature. To test the validity of this method for λ-type transitions, we have applied it to the α-β quartz transition (T ₀=846±1 K). Raman spectra of quartz were recorded up to 900 K. Measured frequency shifts of the α-quartz Raman modes were then used in conjunction with available high-pressure Raman data to calculate intrinsic mode anharmonicity, through the parameter a _i=(?Lnv_i/?T)_v. Vibrational modelling of the heat capacity at constant volume, Cv, and at constant pressure, Cp, including anharmonic corrections deduced from the a _i parameters, are compared to experimental data. Taking into account the soft-mode associated to the α-β quartz transition, the model reproduces the excess of Cp related to the transition. Then, this study confirms that detecting a soft-mode from vibrational data allows one to predict λ-type transitions. However, when modelling the thermodynamic properties, the contribution of a soft-mode cannot be established from spectroscopic data. Therefore, one needs first to determine this contribution in order to predict the heat capacities of Earth's mantle minerals displaying λ-type transitions. In α-quartz, this contribution has been determined as 0.007% of the total number of the optic modes in the model of the density of states.  相似文献   

Cumulating processes at the crust-mantle transition zone inferred from Permian mafic-ultramafic xenoliths (Puy Beaunit,France)     

Julien Berger  Olivier Féménias  Nicolas Coussaert  Jean-Claude C. Mercier  Daniel Demaiffe 《Contributions to Mineralogy and Petrology》2007,153(5):557-575

Ultramafic and mafic xenoliths of magmatic origin, sampled in the Beaunit vent (northern French Massif Central), derive from the Permian (257 Ma) Beaunit layered complex (BLC) that was emplaced at the crust-mantle transition zone (∼1 GPa). These plutonic xenoliths are linked to a single fractional crystallisation process in four steps: peridotitic cumulates; websteritic cumulates; Al-rich mafic cumulates (plagioclase, pyroxenes, garnet, amphibole and spinel) and finally low-Al mafic cumulates. This sequence of cumulates can be related to the compositional evolution of hydrous Mg basaltic magma that evolved to high-Al basalt and finally to andesitic basalt. Sr and Nd isotopic compositions confirm the co-genetic character of the various magmatic xenoliths and argue for an enriched upper mantle source comparable to present mantle wedges above subduction zones. LILE, LREE and Pb enrichment are a common feature of all xenoliths and argue for an enriched sub-alkaline transitional parental magma. The existence of a Permian magma chamber at 30 km depth suggests that the low-velocity zone observed locally beneath the Moho probably does not represent an anomalous mantle but rather a sequence of mafic/ultramafic cumulates with densities close to those of mantle rocks.  相似文献   

Earthquakes in Switzerland and surrounding regions during 2006     

Manfred Baer  Nicolas Deichmann  Jochen Braunmiller  John Clinton  Stephan Husen  Donat Fäh  Domenico Giardini  Philipp Kästli  Urs Kradolfer  Stefan Wiemer 《Swiss Journal of Geoscience》2007,100(3):517-528

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2006. During this period, 572 earthquakes and 91 quarry blasts were detected and located in the region under consideration. Of these earthquakes, two occurred in conjunction with the construction of the new Gotthard railway tunnel and 165 were induced artificially by the stimulation of a proposed geothermal reservoir beneath the city of Basel. With 20 events with M _L ≥ 2.5, five of which were artificially induced, the seismic activity in the year 2006 was far below the average over the previous 31 years. Nevertheless, six events were felt by the public, most prominently the strongest of the induced Basel events (M _L 3.4), which caused some non-structural building damage. Noteworthy are also the two earthquakes near Cortaillod (M _L 3.2), on the shore of Lake Neuchatel, and in Val Mora (M _L 3.5), between the Engadin and Val Müstair, as well as the 42 aftershocks of the M _L 4.9 Vallorcine earthquake, between Martigny and Chamonix, of September 2005. Editorial handling: Stefan Bucher  相似文献   

Transport and deposition of suspended particles in saturated porous media: hydrodynamic effect   总被引：1，自引：1，他引：1  

Nasre-Dine Ahfir  Hua Qing Wang  Ahmed Benamar  Adbellah Alem  Nicolas Massei  Jean-Paul Dupont 《Hydrogeology Journal》2007,15(4):659-668

A laboratory study was undertaken to determine the transport and deposition rate of suspended particles in columns of saturated porous media (gravel and glass beads), where the porous media were subjected to steady-state flow. Silt particles with a mode of 14 μm diameter (used as the suspended particles) and fluorescein (as the conservative tracer) were injected into the columns in short pulses. The breakthrough curves were competently described with the analytical solution of a convection–dispersion equation with a first-order deposition rate. The experiments were performed using different flow rates. The suspended particle size distribution, the porous media, and the flow rates themselves were the main factors retained in this study to investigate the mechanisms governing the transport and deposition kinetics in detail. The results showed the existence of a flow rate, beyond which suspended particles travel faster than the conservative tracer. A decrease of the deposition rate of suspended particles beyond a critical flow velocity was also observed. Such behaviour led to consideration of the couple hydrodynamic-gravity forces at high flow rates. As the hydrodynamic force increases, particle deposition rates are reduced due to the effect of hydrodynamic forces inhibiting the deposition.  相似文献   

Confronting climate change: Critical issues for New Zealand     

Nicolas J. Cullen 《New Zealand geographer》2007,63(3):227-228

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Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation,southern England)     

Jean-Fran?ois?DeconinckEmail author  Stephen?P.?Hesselbo  Nicolas?Debuisser  Olivier?Averbuch  Fran?ois?Baudin  Julian?Bessa 《International Journal of Earth Sciences》2003,92(2):255-266

We present a dataset including clay mineralogy, gamma-ray spectrometry, organic matter content and magnetic susceptibility of the Hettangian to lowest Sinemurian successions of Dorset and Somerset, southern UK (Blue Lias Formation, Bristol Channel and Wessex basins). In both areas, the clay assemblages comprise predominantly detrital illite, kaolinite and illite/smectite mixed layers. Clays probably originated from the erosion of the Hercynian massifs, the relative proportions of kaolinite and illite being modulated by arid-humid climatic fluctuations. The organic matter (OM) content (types II to IV) ranges up to 12% in both areas. A clear stratigraphical trend in clay mineral assemblages is apparent in Somerset, whereas in Dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long-term evolution. Correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata Zone of the Dorset succession. As expected, the kaolinite/illite ratio correlates with the Th/K ratio deduced from gamma-ray spectrometry. However, significant departures from the correlation occur in OM-rich intervals, suggesting that Th may be partly adsorbed on to OM particles. Surprisingly, high magnetic susceptibility correlates with abundant kaolinite, not with Fe-rich clays, indicating either that kaolinite is accompanied by a soil-inherited magnetisable phase (possibly iron oxide) or that illite-rich rocks are more strongly diluted by carbonate than are kaolinite-rich strata.  相似文献   

Single GPS receiver time-relative positioning with loop misclosure corrections     

Nicolas Balard  Rock Santerre  Marc Cocard  Stéphanie Bourgon 《GPS Solutions》2006,10(1):56-62

Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about 40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under 20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the horizontal components and 29 cm for the vertical component with dual frequency data.  相似文献