2005 Vol. 16, No. 3
Paleontologists search the fossil record for evidence of age, ancient environments, phylogenetic reconstructions and ancient communities. Cenozoic foraminifera preserve evidence for all of these simultaneously from the water column and from at, above and below the sediment/water interface. As our understanding of foraminiferal assemblages and their place in the strata (biofacies) becomes more sophisticated, so are foraminiferal biofacies challenged to contribute to more subtle problems in Cenozoic earth and life history. Progress is described as a series of five “integrations”. (Ⅰ) The quantification of foraminiferal biofacies was an advance on simple presences and absences of species meeting such questions as marine or nonmarine, or shallow or deep. (Ⅱ) Foraminiferal shells carry geochemical signals especially isotopes of oxygen (temperature, ice volume), carbon (nutrition and the carbon cycle), and strontium (seawater ratios through time). (Ⅲ) From modern foraminiferal biology we have lifestyle insights leading to a model of oceans and paleo~oceans called the trophic resource continuum, a valuable way into greenhouse~icehouse comparisons and contrasts. (Ⅳ) Biofacies changes in space and time are sometimes abrupt with little evidence of diachrony, and sometimes gradual. These patterns are clarified in the context of sequence stratigraphy (which they enrich in turn). (Ⅴ) The paleobiological counterpart of sequence stratigraphy is evolutionary paleoecology, reconstructing communities in deep time. The foraminifera are perfectly suited to investigate the possibility (or likelihood) that global environmental shifts have controlled community turnover in the pelagic, neritic and terrestrial realms.
To show paleontological characteristics of the Olenekian~Anisian boundary beds in the Russian Far East, a review of new data on the Upper Olenekian and Lower Anisian biostratigraphy of South Primorye is given on the basis of five sections: Golyi Cape, Petrovka River, Zhitkov Peninsula, Tchernyschew Bay and Atlasov Cape, using new ammonoid, brachiopod and conodont findings. The most representative ammonoid assemblage at the base of the Anisian was discovered in the Ussuriphyllites amurensis Zone (10.6 m thick) of the Atlasov Cape Section: Parasageceras sp. nov., Prionitidae gen. et sp. nov., Ussuriphyllites amurensis (Kiparisova) (dominant), Megaphyllites atlasoviensis Zakharov, Leiophyllites praematurus Kiparisova, Leiophyllites sp., Ussurites sp., Paradanubites sp. indet., Paracrochordiceras sp. nov., Prohungarites popowi Kiparisova, Arctohungarites primoriensis Zakharov, A. solimani (Toula), Salterites sp. indet. (gigantic shell), and Tropigastrites sublachontanus Zakharov. Conodonts Neospathodus cf.homeri (Bender) were found in the lower part of the Ussuriphyllites amurensis Zone of the Atlasov Cape. The Atlasov Cape seems to be one of the very promising sections of the Russian Far East for detailed investigation of the Olenekian~Anisian boundary.
The Carboniferous can be divided into four series in the Dianqiangui basin and its adjacent areas, Southwest China: the Yanguanian series, the Datangian series, the Weiningian series and the Mapingian series. The Maping Formation, traditionally used as the lithostratigraphic unit of the Upper Carboniferous, became an inter~system unit from the Carboniferous to the Permian. Thus, the top part of the Carboniferous and the bottom part of the Permian (Chuanshanian series) constitute a third~order sequence in the Dianqiangui basin and its adjacent areas. In the study area, the Carboniferous system and the Chuanshanian series of the Permian constitute a second~order sequence that can be subdivided into 6 third~order sequences. The bottom boundary of this second~order sequence is an unconformity formed in the principal episode of the Ziyun movement (the second episode), and the top boundary is also an unconformity formed in the principal episode of the Qiangui movement (the second episode). In different paleogeographical backgrounds, the strata from the Carboniferous to the Permian Chuanshanian epoch are marked by different sedimentary features. For example, coal measures and more dolomitic strata are developed in the attached platform; carbonate rocks mainly constitute the isolated platform strata; the inter~platform ditch strata are mainly composed of dark and fine sediments. Therefore, third~order sequences with different architectures of sedimentary~facies succession are formed in different paleogeographical backgrounds. Although the third~order sequences are different in the architecture of sedimentary~succession in space, the processes of their depositional environmental changes due to the third~order relative sea~level changes are simultaneous. Biostratigraphically, the surfaces of the third~order sequences can be correlated and traced in space; the framework of sequence stratigraphy from the Carboniferous to the Chuanshanian epoch of the Permian can be established in the Dianqiangui basin and its adjacent areas in terms of two types of facies~changing surfaces as well as two kinds of diachronism in stratigraphic records. The sequence~stratigraphic subdivisions from the Carboniferous to the Permian Chuanshanian epoch in the study area show that the duration of third~order sequences, formed in the convergent period of Pangea, is more than 10 Ma. This could reflect the elementary feature that the period of sea~level change cycles formed in a relatively quiet period of tectonic action is more than 10 Ma. And this succession shows a marked cyclicity which is supposed to be the low~latitude response to the Gondwanan glaciation in the southern hemisphere.
The major scientific goal of using satellite data for mineral prospecting in the study area was two~fold: (a) mapping geology, faults and fractures that localize ore deposits; (b) recognizing hydrothermally altered rocks by interpreting their spectral signatures. The lithology, properties, and geological relations of the rocks were key to understanding such varied phenomena as convection, melting and transport mechanisms, rock deformation and alteration, the sources of magnetic anomalies, and the hydrothermal circulation and formation of gold deposits. Satellite data were enhanced using the following techniques: band combinations, ratios, directional sharpening filtering, Laplacian transform, spatial convolution, and density slicing. By mapping a larger area, the Paishanlou Gold Mine was discovered to be located within an accommodation zone, with three significant populations of faults having bearings of 95, 145, and 180 degrees. Faults bearing 145 degrees make up the faults of the main shear zone. The faults bearing 180 degrees have large sinistral offsets, typically 1.5 km, and form a synthetic~antithetic set with the faults bearing 145 degrees, which have dextral displacements of tens of meters. In the Landsat ETM+ image composed of bands 7~4~2 RGB, gneiss rocks were clearly seen as red purple, and granitic and plagioclase bodies in pale brown/pink. The strongest alteration signature in the image was found along the detachment fault antiform located closest to the mine and the plutons responsible for the Paishanlou gold mineralization. Satellite image interpretation coupled with field surveys led to the identification of iron mineral composites, hydrothermally altered areas, fractures, and an accommodation zone. These anomalies finally resulted in the discovery of three new gold~mineralized sites.
A stack of records becomes one of the main steps in modern seismic data processing. In the stack procedure, the crucial operation is time correction. Conventional methods, e.g., normal moveout (NMO) and dip moveout (DMO) stacks require a sufficiently accurate macro~velocity model, whereas a multifocusing imaging method does not depend on a macro~velocity model. The multifocusing method proposed by Gelchinsky et al. belongs to a group of methods that can be characterized as macro~model~independent imaging methods. The multifocusing method represents a transformation of 2~D multicoverage reflection data into a simulated zero~offset stack profile. This transformation is based on a completely data~derived spatial stacking operator, and includes stacking large supergathers of seismic traces, each of which can span many CMP gathers. By extending the multifocusing moveout formula to explicitly account for non~zero elevations of the source and receiver, the multifocusing imaging method can yield appropriate results when seismic data are acquired over an irregular topography. In recent years, many applications of multifocusing imaging over an irregular topography have demonstrated its advantages in comparison with conventional CMP processing. This paper illustrates the corresponding formulas for a synthetic data example modeled by the wave equation finite difference method. The result of the synthetic example is very encouraging. By stacking large supergathers and applying multifocusing moveout correction, the reflectors are aligned very well and the S/N is greatly improved. We have also applied multifocusing imaging over an irregular topography to a real data example. The elevation of the data acquisition area varies considerably. Applying multifocusing imaging, a substantial improvement of the simulated section was achieved, compared with a conventional CMP stacked section.
The geothermal waters of south hot spring, small hot spring and Qiaokouba in Chongqing, are all part of the south hot spring geothermal water system. Exploitation has caused a decline in the water levels of the south and small hot springs, which have not flowed naturally for 15 years. Now, bores pump geothermal water to the springs. If the water level drops below the elevation of the rivers, river~water will replenish the geothermal water, destroying this resource. It is therefore an urgent task to model the geothermal water system, to enable sustainable development and continued use of the geothermal water in Qiaokouba. A numerical simulation of the geothermal water system was adopted and a quantitative study on the planning scheme was carried out. A mathematical model was set up to simulate the whole geothermal water system, based on data from the research sites. The model determined the maximum sustainable water yield in Qiaokouba and the two hot springs, and the south hot spring and small hot spring sustainable yields are 1100 m3/d and 700 m3/d from 2006 to 2010, 1300 m3/d and 1000 m3/dfrom 2011 to 2015, and 1500 m3/d and 1200 m3/d from 2016 to 2036. The maximum exploitable yield is 3300 m3/d from 2006 to 2036 in Qiaokouba. The model supplies a basis to adequately exploit and effectively protect the geothermal water resources, and to continue to develop the geothermal water as a tourist attraction in Chongqing
A numerical method was used in order to establish the constitutive relationship of sands under different stress paths. Firstly, based on the numerical method modeling the constitutive law of sands, the elastoplastic constitutive relationship of sand was established for three paths: the constant proportion of principle stress path, the conventional triaxial compression (CTC) path, and the p=constant (TC) path. The yield lines of plastic volumetric strain and plastic generalized shear strain were given. Through visualization, the three dimensional surface of the stress~strain relationship in the whole stress field (p, q) obtained under the three paths was plotted. Also, by comparing the stress~strain surfaces and yield locus of the three stress paths, the differences were found to be obvious, which demonstrates that the influence of the stress paths on constitutive law was not neglected. The numerical modeling method overcame the difficulty of finding an analytical expression for plastic potential. The results simulated the experimental data with an accuracy of 90 % on average, so the constitutive model established in this paper provides an effective constitutive equation for this kind of engineering, reflecting the effect of practical stress paths that occur in sands.
With the rapid development of water facilities, hydroelectric projects, highways and railways in China, beam~anchor reinforcement has been widely used to stabilize slopes in recent years. But the theory for the design of beam~anchor reinforcement is far behind the application. Cross beam~ground anchor reinforcement is a combination of beams and anchors forming a new structure to prevent slope sliding. The forces in the beams are discussed using theoretical analysis and numerical modeling. The Winkler model is used to analyze the beams, and reasonable values of λ, length, spacing and cantilevered length for the beams are determined through a theoretical analysis. A three~dimensional finite element method is adopted to model the interaction of the beams and soils and a structure analysis is applied to treat the beams and to study the stress distribution in external and internal beams. The analytical results show that it is better to satisfy λ ≥ 2π, the spacing between anchors ls should be 1λ<π/2 and cantilever length should be (0.3~0.5) ls for the optimum design. The numerical results show that the same design can be used for all beams in different directions, including the internal and external beams. The application of the analytical method for reinforcement beam analysis is acceptable. It is better to choose a safety coefficient of 1.3 for design based on the analytical method for safety.
Due to complicated rock structure and environment, a prototype test for a tunnel~type anchorage is infeasible. Based on the rock mass parameters from tests, a three~dimensional (3D) elasto~plastic analysis was performed to simulate the influence of the construction procedure of Siduhe bridge with tunnel~type anchorage (TTA) in Hubei Province, China. The surrounding rock and concrete anchorage body were simulated by 8 nodes 3D brick elements. The geostatic state of the complex geometric structure was established with initial data. The in~situ concrete casting of the anchorage body and excavation of the rock mass were simulated by tetrahedral shell elements. The results show that the surrounding rock is in an elastic state under the designed cable force. The numerical overloading analysis indicates that the capacity of the surrounding anchorage is 7 times that of the designed cable force. The failure pattern shows that two anchorage bodies would be pulled out in the end. The maximum shear stress appears 10 m before the back anchorage face. The maximum range influenced by the TTA under ultimate loads is about 16 m.
To understand the forming and tectonic evolution of the South China Sea basin, new data of the structural styles and geochronology were obtained from the Dulong~Song Chay dome, southeastern Yunnan and northern Vietnam. The structural styles were acquired through field investigation and geochronological dating was carried out using zircon SHRIMP Ⅱ U~P and argon isotopic analyses. The South China Sea basin extension occurred firstly at Late Mesozoic to Early Cenozoic, and then at Late Oligocene to Middle Miocene (32~17 Ma). The second stage of extension formed immediately after the first stage, and both extensions have a consistent forming mechanism. New structural analysis and geochronological data do not support the models of “backarc spreading” and “strike~slip faults producing the extension”. Then what mechanism resulted in the extension of South China Sea basin? The data indicate that at least two episodes of major extensional tectonics, i.e., the D1 deformation at 237~228 Ma resulted in the rising and exhumation of the dome, and D2 deformation at 86~78 Ma overprinted and redeformed the dome. Of them, the D2 shows a consistent forming time, extensional direction and tectonic regime among Dulong~Song Chay dome, South China block and the northern margin of the South China Sea basin. Regional geology has proved that the northern margin of the South China Sea basin belongs to the South China block, therefore, we interpreted that the Late Mesozoic to Early Cenozoic extensional tectonics occurred in the northern margin of the South China Sea basin due to the intraplate deformation of the South China block,while the Ailaoshan~Red River sinistral slip strengthened the Cenozoic extension in the South China Sea basin.