2014年 25卷 第1期
Sparse sums of Lorentzians can give good approximations to functions consisting of linear combination of piecewise continuous functions. To each Lorentzian, two parameters are assigned: translation and scale. These parameters can be found by using a method for complex frequency detection in the frequency domain. This method is based on an alternating projection scheme between Hankel matrices and finite rank operators, and have the advantage that it can be done in weighted spaces. The weighted spaces can be used to partially revoke the effect of finite band-width filters. Apart from frequency extrapolation the method provides a way of estimating discontinuity locations.
A series of linear stability analysis is carried out on the onset of thermal convection in the presence of spatial variations of viscosity, thermal conductivity and expansivity. We consider the temporal evolution of an infinitesimal perturbation superimposed to a static (motionless) and conductive state in a basally-heated planar layer. From the changes in flow patterns with increasing the amplitudes of temperature dependence of viscosity, we identified the transition into the “stagnant-lid” (ST) regime, where the convection occurs only beneath a thick and stagnant-lid of cold fluid at the top surface. Detailed analysis showed a significant increase of the aspect ratio of convection cells in ST regime induced by the spatial variations in thermal conductivity and/or expansivity: the horizontal length scale of ST convection can be enlarged by up to 50% with 10 times increase of thermal conductivity with depth. We further developed an analytical model of ST convection which successfully reproduced the mechanism of increasing horizontal length scale of ST regime convection cells for given spatial variations in physical properties. Our findings may highlight the essential roles of the spatial variation of thermal conductivity on the convection patterns in the mantle
After the End-Permian mass extinction, ammonoids reached levels of taxonomic diversity higher than in the Changhsingian by the Dienerian Substage of the Induan. However, brachiopods exhibit a prolonged delay in recovery, and their taxonomic diversity had not recovered to Late Permian levels even by the Olenekian. The differential patterns of recovery between these two clades may reflect fundamental differences in physiology and behavior. Brachiopods were benthic organisms that were dependent on specific trophic sources, and their general reduction in size during the Early Triassic may have been a response to a relative paucity of food resources. In contrast, ammonoids were sluggishnektic organisms that utilized a wider range of trophic sources and that suffered no comparable size decrease during the Early Triassic. Brachiopods may have been at a disadvantage also due to vulnerabilities associated with their larval stage, during which they had to locate a suitable substrate for settlement. In contrast, ammonoids had no larval stage and juveniles may have been dispersed widely into favorable habitats. These factors may account for differences in the relative success of ammonoids and brachiopods at high-latitude regions following the End-Permian mass extinction: ammonoids successfully recolonized the Boreal region during the Early Triassic whereas brachiopods did not.
The lower part of Fahdene Formation outcropping in northeastern Tunisia is represented by pelagic sequences and characterized by an important siliciclastic fraction that includes radiolarian and organic-rich beds of Allam Member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam Member is confined to the Microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale deposition. The assemblages can be correlated with the radiolarian biochronozone U.A.10–11 indicating an Early Albian to early Middle Albian in age. Radiolarian assemblages composed of species characteristic of U.A.10 biochronozone (A. montisserei, D. gracilis) are associated with radiolarian taxa belonging to Costata Zone (U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora), which can be correlated with Dercourt Member in the Ionian Zone and Paquier level of the Vocontian Basin (southeast of France). Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa (i.e., Pseudodictyomitrae lodogaensis) compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was diachronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAE1b which is characterized by the widespread of supraregionnally organic-rich beds in the Mediterranean Tethys basins across the Aptian-Albian transition.
The Earliest Triassic Yinkeng Formation is exposed at the well-known Meishan Section, South China, which contains the Global Stratotype of Section and Point (GSSP) for the Permian-Triassic boundary (PTB). It records centimeter-scale rhythmic alternations comprised mainly by marlstone and limestone. Seven types of couplet embedded in five types of bundles were recognized based on occurrence and thickness of the lithologic units, suggesting that their formation was controlled by cyclic processes. The various orders of cycles observed correlate well with other Early Triassic counterparts recorded in South China. Here, we present new cyclostratigraphic results based on lithologic thickness and relative carbonate content of the Yinkeng Formation. Power spectra of carbonate content show that the ratio of major wavelengths recognized throughout the formation is similar to that of the 100 kyr short eccentricity, 33 kyr obliquity, and 21 kyr precession cycles, indicating that astronomical signals are recorded in the Earliest Triassic rhythmic succession. Consistence between pronounced lithologic rhythmicity and sea-level changes obtained from Fischer plots indicates that high-frequency climatic cycles may have driven sea-level changes immediately after the PTB mass extinction. Furthermore, the 4th-order sea-level changes interpreted from the sedimentary record match well with 100 kyr short eccentricity component of carbonate content, reflecting that the 100 kyr short eccentricityinduced climate changes may have likely controlled the deposition of 4th-order sequences recognized from rhythmic successions.
The metamorphosed Early Paleoproterozoic granitoids in the Quanji massif, Northwestern China provide constraints for relationship between the Tarim Craton and North China Craton. Among granitoids batholiths, rocks of the Mohe quartz-diorite show typically adakitic geochemical characteristics, with medium K2O/Na2O ratios (0.56–1.17) and high Sr (519–619 ppm) low Y (9.37–20.40 ppm) and Yb (0.97–1.77 ppm) concentrations. The rocks have εNd(t) values between +2.4 and +4.4 and depleted mantle Nd model ages of 2.43–2.59 Ga. The magmatic zircons have positive εHf(t) values ranging from +0.40 to +7.60 and depleted mantle Hf model ages of 2.43–2.70 Ga, with major peaks at ~2.54 and ~2.65 Ga. The geochemical and Nd-Hf isotopic characteristics indicate that the Mohe quartz-dioritic rocks might be formed by partial melting of high-pressure metamorphosed juvenile crustal rocks in post-orogenic extensional regime in the Early Paleoproterozoic. It suggests that important crustal growth occurred in the Quanji massif and the Tarim Craton at ~2.4 and 2.5–2.7 Ga. The Quanji massif and Tarim Craton might share a similar crustal evolution history with the North China Craton in the Neoarchean.
The Paleoproterozoic (~1.73 Ga) basement rocks from Maddhapara, Bangladesh show a large range of chemical variations including diorite, quartz diorite, monzodiorite, quartz monzonite and granite. These are composed of varying proportions of quartz+plagioclase+K-feldspar+biotite+hornblende±epidote+titanite+magnetite+apatite and zircon. Amphibole and biotite, dominant ferromagnesian minerals, have been analyzed with an electron microprobe. The biotite, Mg-dominant trioctahedral micas, is classified as phlogopitic nature. Relatively high Mg (1.33–1.53 pfu), Mg# (0.52–0.59) and low AlVI (0.13–0.25 pfu) contents in the biotite reflect slightly fractionated magma, which might be a relative indicator for the origin of the parental magma. Biotite is also a very good sensor of oxidation state of the parental magma. Oxygen fugacity of the studied biotites estimate within the QFM and HM buffers and equilibrate at about -12.35 and -12.46, which exhibit the source materials were relatively higher oxidation state during crystallization and related to arc magmatism. Whereas, calcic amphiboles, a parental member of arc-related igneous suite, display consistent oxygen fugacity values (-11.7 to -12.3), low Al# (0.16–0.21) with H2Omelt (5.6 wt.%–9.5 wt.%) suggest their reliability with the typical values of calc-alkaline magma crystallization. The oxygen fugacity of magma is related to its source material, which in turn depends on tectonic setting. Discrimination diagrams and chemical indices of both biotite and amphibole of dioritic rocks reveal calc-alkaline orogenic complexes; mostly I-type suite formed within subduction-related environments. Moreover, igneous micas are used as metallogenic indicator. The biotites with coexisting amphibole compositions show an apparent calc-alkaline trend of differentiation. The study suggests that the trend of oxidized magmas is commonly associated with compressive tectonic and convergent plate boundaries.
To reveal the Jurassic tectonothermal event occurring to the Nyainrong microcontinent which is gripped among the Bangong-Nujiang suture zone, 40Ar/39Ar dating was carried out on the basement orthogneiss and Jurassic granitc gneiss in the microcontinent. In the heating stage, four samples exhibited a flat plateau age, with the value Tp concentrated in the range of 166–176 Ma; isochron age Ti was concentrated in the range of 165–175 Ma, and their corresponding ages were the consistent within allowable range. The ages should be representative of the era of the final deformation of the Amdo gneiss and cooling emplacement of the magmatic rock in the Jurassic. The geochronological studies have shown that the final deformation of microcontinent crystalline basement and the cooling of the Mesozoic large-scale tectonothermal events occurred in late Middle Jurassic. In Middle Jurassic, Nyainrong microcontinent experienced strong tectonic movement. Combining with the geochronological with isotope geochemistry for the microcontinent, the cause of the tectonothermal event should be attributed to the collision between the Nyainrong microcontinent and South Qiangtang Block following the northward subduction of Bangong-Nujiang oceanic crust.
This article aims to study the geomorpometric features of alluvial fans since they act as a small-scale geomorphic unit response to tectonics and climate changes around the Chaka-Qinghai Lake area in the northeastern Tibetan Plateau. We quantitatively extracted geomorphic parameters, such as the surface area and slope of alluvial fans adjacent to the Qinghai Nan Shan and Ela Shan. Alluvial fans in the Chaka Lake partition area, south of the Qinghai Nan Shan, are featured by a small area and short length, but the largest slope. Geomorphic parameters of the alluvial fans in Ela Shan area are intermediate in size, and the alluvial fans in the Qinghai Lake partition area north of Qinghai Nan Shan have the gentlest slope. Together with the regional faulting activity analysis, we suggest that the alluvial fans with the high slopes in the south of Qinghai Nan Shan are mainly controlled by the reverse faulting along the Qinghai Nan Shan faults, and the strike-slip movement of the Ela Shan fault zone plays a weak role. In contrast, due to the lack of active faults, the alluvial fans near the Qinghai Lake area north of the Qinghai Nan Shan only respond to regional erosion, transportation, and deposition processes, thereby forming relatively gentle geomorphic units.
Identification and classification of different seismo-tectonic events with similar characteristics in a region of interest is one of the most important subjects in seismic hazard studies. In this study, linear and nonlinear discriminant analyses have been applied to classify seismic events in the vicinity of Istanbul. The vertical components of the digital velocity seismograms are used for seismic events with magnitude (Md) between 1.8 and 3.0 that occurred between 2001 and 2004. Two, time dependent parameters, complexity and S/P peak amplitude ratio are selected as predictands. Linear, quadratic, diaglinear and diagquadratic discriminant functions are investigated. Accuracy of methods with an additional adjusted quadratic models are 96.6%, 96.6%, 95.5%, 96.6%, and 97.6%, respectively with a various misclassified rate for each class. The performances of models are justified with cross validation and resubstitution error. Although all models remarkably well performed, adjusted quadratic function achieved the best success rate with just 4 misclassified events out of 179, even better compared to complex methods such as, self organizing method, k-means, Gaussion mixture models that applied to same dataset in literature.
Non-uniqueness is always, by nature, the problem we face in inversion processes, and it is caused by the phenomenon of equivalence in field, erroneous, discrete, and finite features in observation and the influence of other sources. Many authors have done lots of researches in this field in order to get more reliable outcomes, and joint inversion is a thriving one where different kinds of data are combined to derive certain information simultaneously or sequentially. One of these studies is that the prior information such as the geological, drilling and seismic data will be used as constraints, while the inversion procedure can be controlled. In this article we use a new method with the goal of better obtaining the three-dimensional density contrast interface. This prior seismic data integrated in the inversion can play a constrained role in the procedure which means that the depth of the Moho interface at the seismic location will be restricted. It thus can provide a credible result. In order to test its effect, this program is applied in a field example―derivation of Moho geometry in Northeast China
The serpentinite blocks of Indikolapelessa, located along an identified litho-tectonic boundary between the Highland Complex (HC) and the Vijayan Complex (VC) of Sri Lanka, have undergone extensive lateralization with metal enrichment. Characteristic serpentinite vegetation with some endemic species was recognized in the soils and supergene deposits develop on serpentinite lithology. This type of geological and ecological relationship forms vegetation covers on serpentinite lithologies which are sharply demarcated from the surrounding metamorphic terrains. The aforesaid “geo-ecological phenomenon” can be used as a tool for geo-vegetation mapping in ultramafic terrains to trace the geological boundaries in landscapes where rock outcrops are virtually absent. We successfully applied the concept of geo-vegetation mapping in order to demarcate the boundary of underlain serpentinite rocks from surrounding non-serpentinite metamorphic rocks (e.g. granitic gneiss). The hypothesis was supported by the geochemical variations of soils/supergene deposits found at serpentinite and non-serpentinite sites, especially immobile elements and some trace elements. Based on whole rock chemistry and soil chemical data obtained, we suggest that the Indikolapelessa serpentinite outcrop, together with the other four serpentinite outcrops, is more likely to represent the Mg-rich mantle fragments at the time of overthrusting of the two crustal blocks of HC and VC during the Pan-African event.
This article aims to analyze the main controlling factors of development, distribution and evolution of the fault systems in the Tarim Basin. Based on the seismic profile interpretation, comprehensive analysis of the drilling and geologic data, six fault systems maybe recognized in the Tarim Basin, they are the foreland fault system of the South Tianshan Mountain, the northern Tarim uplift fault system, North Tarim depression fault system, central fault system, Southwest Tarim fault system, and Southeast Tarim fault system. It is indicated that the main differences exist at the development, evolution and distribution of the fault systems in the Tarim Basin. The sub-fault systems can be recognized according to the differences of the fault development and distribution in the interior of the fault system. It is characterized that the multi-level differential development and distribution of the fault systems exist in the Tarim Basin. The fault belt developed in the Paleozoic strata mainly distribute at the paleo-uplift and paleo-slope in the interior of the Tarim Basin, and the fault belt occurred in the Meso–Cenozoic beds mainly develop at the peripheral foreland depressions. Zonal and segment differential development and distribution of the fault systems also exist in the Tarim Basin. The formation and distribution of the Tarim fault systems is of complex controlling mechanisms. Poly-phase structural movement and tectonic transition controls the multi-phase differential development and distribution of the fault systems in the Tarim Basin. Multi-level differential development and distribution is controlled by multi-level detachment belt and regional unconformities. Zonal and segment differential development and distribution of the Tarim fault systems maybe controlled by pre-existed basement structural texture. The major direction of the fault systems in the Tarim Basin is controlled by the later stage basin-mountain coupling.
The resistivity experimental measurements of core samples drilled from low permeability reservoirs of Ordos Basin, Northwest China, illustrate that the cementation factors are not agminate, but vary from 1.335 to 1.749. This leads to a challenge for the estimation of water and hydrocarbon saturation. Based on the analysis of Purcell equation and assumption that rock resistivity is determined by the parallel connection of numerous capillary resistances, a theoretical expression of cementation factor in terms of porosity and permeability is established. Then, cementation factor can be calculated if the parameters of porosity and permeability are determined. In the field application, porosity can be easily obtained by conventional logs. However, it is a tough challenge to estimate permeability due to the strong heterogeneity of low permeability reservoirs. Thus, the Schlumberger Doll Research (SDR) model derived from NMR logs has been proposed to estimate permeability. Based on the analysis of the theoretical expressions of cementation factor and SDR model, a novel cementation factor prediction model, which is relevant to porosity and logarithmic mean of NMR T2 spectrum (T2lm), is derived. The advantage of this model is that all the input information can be acquired from NMR logs accurately. In order to confirm the credibility of the novel model, the resistivity and corresponding laboratory NMR measurements of 27 core samples are conducted. The credibility of the model is confirmed by comparing the predicted cementation factors with the core analyzed results. The absolute errors for all core samples are lower than 0.071. Once this model is extended to field application, the accuracy of water and hydrocarbon saturation estimation will be significantly improved.
In this study, content and distribution of organic matters (OM) and lipid biomarkers in surface sediments from northern South China Sea (SCS) were identified to reveal the sources and transport of fine-grained sediments. Organic matters and lipid biomarkers exhibited distinct spatial variation in northern SCS. Terrestrial discharge from the Pearl River and some mountainous rivers in southwestern Taiwan may contribute to the relatively high organic matters in the corresponding sea areas. The detection of unsaturated fatty acid homologues suggested the algal and/or bacterial OM contribution to surface sediments. The composites and distribution of lipid biomarkers indicate their mixed sources from terrestrial plants, marine algae and bacterial. Together with the proof of clay mineral composites in the sediments, the results suggested that the currents, including the Guangdong Coastal Current and Kuroshio Current, control the transport and distribution of terrestrial sediment and the sedimentary environment in the northern SCS.
Three cruises were launched in the Pearl River Estuary (PRE) in 2005 to investigate the biogeochemical cycling of nutrients associated with early diagenesis related to degradation of organic matter. Seasonal and spatial variations of pore water nutrient concentrations and profile patterns in sediments were studied. Nutrient fluxes at the sediment-water interface (SWI) were measured by incubation experiments, and we here discussed the accumulation and transformation processes of nutrients at the SWI. The nutrients generally decreased from the Pearl River outlets downstream, indicating anthropogenic influences on the nutrient inputs in the estuary. NO3-N concentration was the highest of the three forms of DIN (dissolved inorganic nitrogen, the sum of NH4-N, NO3-N and NO2-N) in the overlying water, and NH4-N was the main component of DIN in pore water. The gradual increase of NH4-N and the rapid decrease of NO3-N with sediment depth provided the evidence for anaerobic conditions below the SWI. Negative fluxes of NO3-N and positive fluxes of NH4-N were commonly observed, suggesting the denitrification of NO3-N at the SWI. The DIN flux direction suggested that the sediment was the sink of DIN in spring, however, the sediment was generally the source of DIN in summer and winter. PO4-P distribution patterns were distinct while SiO4-Si inconspicuously varied in sediment profiles in different seasons. The flux results indicated that PO4-P mainly diffused from the water column to the sediment while SiO4-Si mainly diffused from the sediment to the water column. Generally, the incubated fluxes were the coupling of diffusion, bioturbation and biochemical reactions, and were relatively accurate in this study.