2004 Vol. 15, No. 3
Based on the CHAMP Magsat data set, spherical cap harmonic analysis was used to model the magnetic fields over China continent. The data set used in the analysis includes the 15′×15′ gridded values of the CHAMP anomaly fields (latitude φ =25°N to 50°N and longitude λ =78°E to 135°E). The pole of the cap is located at φ =35°N and λ=110°E with half angle of 30°. The maximum index ( K max ) of the model is 30 and the total number of model coefficients is 961, which corresponds to the minimum wavelength at the earth’s surface about 400 km. The root mean square (RMS) deviations between the calculated and observed values are ~ 4 nT for Δ X , ~ 3 nT for Δ Y and ~ 3.5 nT for Δ Z , respectively. Results show that positive anomalies are found mainly at the Tarim basin with ~6~8 nT, the Yangtze platform and North China platform with ~4 nT, and the Songliao basin with ~4-6 nT. In contrast, negative anomaly is mainly located in the Tibet orogenic belt with the amplitude ~ (~6)~(~8) nT. Upward continuation o
The International Stratigraphic Guide defined that all stratified or quasi~stratified rock bodies of the earth crust, including sedimentary, igneous, metamorphic, solidified and unsolidified ones, should be considered as research contents of stratigraphy. Traditional stratigraphy mainly involves strata formed under gravity mechanism, plus a few kinds of bedded volcanic rocks such as lava, pyroclastic rock and volcanic ash, as well as metamorphic sedimentary and volcano~sedimentary rocks. These traditional strata are regarded as Smithian strata in this paper. In modern stratigraphy, mechanism of strata formation includes not only gravity but also thermal (ophiolite), mechanic and tectonic forces (orogenic mélange and tectonite). In these above~mentioned non~gravitative conditions, the strata, formed complying with their own mechanisms but not with the law of superposition of Smithian stratigraphy, are called non~Smithian strata here. In mélange regions from orogenic belt, formations of non~Smithian strata could be classified into subduct~scrape~match, subduct~return~match, and subduct overthrust types.
The continuous wavelet transform (CWT) analysis reveals the instantaneous variability of the foraminiferal δ18O and δ13C of Site 1143 for the past 5 Ma at the eccentricity, obliquity and precession bands. The cross CWT analysis further demonstrates nonstationary phases of the benthic -δ18O relative to ETP at the three primary Milankovitch bands in the last 5 Ma. The instantaneous phases between benthic -δ18O and δ13C at the precession band display a prominent 128 ka period, probably the cyclicity of the nonstationary climate close to the eccentricity. To explain these nonstationary phases, it is desirable to introduce a nonlinear response model to the global climate system, in which the output has a prominent cycle around 100 ka to match the 128 ka cycle of the instantaneous phase of the δ13C and -δ18O on the precession band.
Sewage sludge ash (SSA), the waste generated in sewage sludge incineration, was obtained from Wuhan Sewage Treatment Plant and used as a lowcost sorbent for removing Cu (Ⅱ) from wastewaters. The sorbent was first modified with 5 % sulfuric acid to increase its sorption capacity. The specific surface area, porosity, cationexchange capacity (CEC) and pH ZPC of the sorbent were measured. Batch experiments were made to study the effect of contact time, solution pH value and temperature on sorption. Both Langmuir and Freundlich models well described the Cu(Ⅱ) sorption process, with correlation coefficient (R2) values of 0.993 4 and 0.989 9 respectively. And the sorption process follows the Lagergren first order kinetic model. The equilibrium sorption capacity of acidified SSA to Cu(Ⅱ)is estimated to be 7.78 mg/g under optimal conditions.
In recent years, China has suffered serious geological disasters, most of slope movements due to complex geology, geomorphology, unusual weather conditions, and large~scale land explorations during high speed economic development. According to geological hazard investigations organized by the Ministry of Land and Resources of China, there are 400 towns and more than 10 000 villages under the threatening of those landslide hazards. This paper presents the overview landslide hazard assessment in terms of GIS, which aims to evaluate the overview geohazard potentials, vulnerabilities of lives and land resources, and risks in conterminous China on the scale of 1∶6 000 000. This is the first overview landslide hazard potential map of China.
In the Karamay oilfield located on the northwestern margin of Junggar basin, Xinjiang, China, a large area of the Karamay Formation is exposed at outcrop in the northeast of the oilfield, a consequence of thrusting. The Middle Triassic Karamay Formation in the outcrop area is a type of terrestrial third order sequence, bounded by two easily recognizable sequence boundaries: a regional surface of angular unconformity (SB1) at the base and a regional unconformity (SB2) at the top. Within the Karamay Formation, two lacustrine expansion events can be recognized and be used to identify both the initial and the maximum lacustrine flooding surfaces. The two lacustrine flooding surfaces serve as references for the classification of this third order sequence—Karamay Formation into the following three sedimentary successions: a lower lowstand systems tract (LST), a middle lacustrine expanding systems tract (EST), and an upper highstand systems tract (HST). Different systems tracts are composed of different depositional system assemblages. In this paper, each depositional system is described in detail. The lowstand systems tract in the study area is characterized by incised valleys. At the base and on the margin of the incised valleys occur alluvial fan depositional systems, and in the upper and distal parts of the alluvial fan, low sinuosity river depositional systems. The lacustrine expanding systems tract consists of a lacustrine depositional system and a lacustrine delta depositional system, overlying the lower incised valley fills. The highstand systems tract is filled by a widespread lacustrine braided delta depositional system. The analysis of sequence stratigraphy in this paper serves the description of the spatial distribution of the reservoir. The depositional system analysis serves the description of the reservoir types. Field investigations of oil sandstone and oil seepage show that the Karamay Formation is composed of several types of reservoirs. However, two types of high quality reservoir occur both in the upper interval of the lowstand systems tract and in the lacustrine expanding systems tract: gravelly low sinuosity channel in the distal fans and sandy-gravelly distributary channel in the lacustrine delta plain.
The origin and distribution of formation overpressure have effect not only on hydrocarbon migration and accumulation, but also on technique of drilling well. The study and prediction of overpressure are very important in basin analysis. At present, overpressure is mostly predicted by stack velocity. The process in calculating inter velocity from stack velocity is very complex and inevitably leads to errors. Especially, this method is not available in the case that structural compression contribution to overpressure occurred. This paper introduces a new method, impedance inversion, to predict overpressure, and the principle is discussed. This method is used to predict the overpressure in Kuqa depression, Tarim basin and as a result, the absolute errors are less than 0.1, and relative errors are less than 5 % for predicted fluid pressure coefficients to the drill stem test (DST) measurements. It suggests that this method can be widely used to predict overpressure in foreland basins.
“Three component” method consists of three close connected aspects: geological anomaly, diversity of mineralization and mineral deposit spectrum. All these three concepts are not new separately, but it is a new approach to combine these three aspects in one single concept for quantitative mineral resources prediction and assessment and it is also the first time to conduct a more detailed study in each aspect. Investigation and clarification of geological anomalies, diversity of mineralization and spectrum of mineral deposits are realized by digitization and quantification of ore~forming controlling factors, ore~existing symbols or marks, characteristics of mineralization and regulation of ore~genesis and laws of distribution. These procedures lead to construction of a “digital model” for mineral resources prediction and assessment.
New structural and petrological data unveil a very complicated ductile deformation history of the Xiongdian Suhe HP metamorphic unit, north western Dabie Shan, central China. The fine grained symplectic amphibolite facies assemblage and coronal structure enveloping eclogite facies garnet, omphacite and phengite etc., representing strain free decompression and retrogressive metamorphism, are considered as the main criteria to distinguish between the early stage deformation under HP metamorphic conditions related to the continental deep subduction and collision, and the late stage deformation under amphibolite to greenschist facies conditions occurred in the post eclogite exhumation processes. Two late stages of widely developed, sequential ductile deformations D3 and D4, are recognized on the basis of penetrative fabrics and mineral aggregates in the Xiongdian Suhe HP metamorphic unit, which shows clear, regionally, consistent overprinting relationships. D3 fabrics are best preserved in the Suhe tract of low post D3 deformation intensity and characterized by steeply dipping layered mylonitic amphibolites associated with doubly vergent folds. They are attributed to a phase of tectonism linked to the initial exhumation of the HP rocks and involved crustal shortening with the development of upright structures and the widespread emplacement of garnet bearing granites and felsic dikes. D4 structures are attributed to the main episode of ductile extension (D 1 4) with a gently dipping foliation to the north and common intrafolial, recumbent folds in the Xiongdian tract, followed by normal sense top to the north ductile shearing (D24) along an important tectonic boundary, the so~called Majiawa~Hexiwan fault (MHF), the westward continuation of the Balifan~Mozitan~Xiaotian fault (BMXF) of the northern Dabie Shan. It is indicated that the two stages of ductile deformation observed in the Xiongdian Suhe HP metamorphic unit, reflecting the post eclogite compressional or extrusion wedge formation, the subhorizontal ductile extension and crustal thinning as well as the top to the north shearing along the high angle ductile shear zones responsible for exhumation of the HP unit as a coherent slab, are consistent with those recognized in the Dabie Sulu UHP and HP metamorphic belts, suggesting that they were closely associated in time and space. The Xiongdian~Suhe HP metamorphic unit thus forms part of the Triassic (250~230 Ma) collision orogenic belt, and can not connect with the South Altun~North Qaidam~North Qinling UHP metamorphic belt formed during the Early Paleozoic (500~400 Ma)
Modeling landscape with high resolution digital elevation model (DEM) in a geographic information system can provide essential morphological and structural information for modeling surface processes such as geomorphologic process and water systems. This paper introduces several DEM~based spatial analysis processes applied to characterize spatial distribution and their interactions of ground and surface water systems in the Greater Toronto Area (GTA),Canada.The stream networks and drainage basin systems were derived from the DEM with 30 m resolution and the regularities of the surface stream and drainage patterns were modeled from a statistical/multifractal point of view. Together with the elevation and slope of topography, other attributes defined from modeling the stream system, and drainage networks were used to associate geological, hydrological and topographical features to water flow in river systems and the spatial locations of artesian aquifers in the study area. Stream flow data derived from daily flow measurements recorded at river gauging stations for multi~year period were decomposed into “drainage~area dependent” and “drainage~area independent” flow components by two~step ”frequency” and “spatial” analysis processes. The latter component was further demonstrated to relate most likely to the ground water discharge. An independent analysis was conducted to model the distribution of aquifers with information derived from the records of water wells. The focus was given on quantification of the likelihood of ground water discharge to river and ponds through flowing wells, springs and seepages. It has been shown that the Oak Ridges Moraine (ORM) is a unique glacial deposit that serves as a recharge layer and that the aquifers in the ORM underlain by Hilton Tills and later deposits exposed near the steep slope zone of the ridges of ORM provide significant discharge to the surface water systems (river flow and ponds) through flowing wells, springs and seepages. Various statistics (cross~ and auto~ correlation coefficients, fractal R/S exponent) were used in conjunction with GIS to demonstrate the influence of land types, topography and geometry of drainage basins on short and long term persistence of river flows as well as responding time to precipitation events. The current study has provided not only insight in understanding the interaction of water systems in the GTA, but also a base for further establishment of an on~line GIS system for predicting spatial temporal changes of river flow and groundwater level in the GTA.
To lower the CO2 risk for hydrocarbon exploration in the west continental shelf of Yinggehai basin, South China Sea, we do attempt not only to know the CO2 origins, but also to make an understanding of the degassing processes from the mantle and crust. Based on the stable carbon isotope ratios of CO2 alone, the organic and inorganic CO2 can be successively distinguished, but the formation conditions and mixing processes for inorganic CO2 are still not clear. The relationships between lg［R(=3He/4He)/Ra(=1.386×10-6)] and CO2 content (%), CO2/3He and δ13CCO2 have been employed, respectively, to obtain that the CO2 gases in the reservoirs can be classified into three categories: (1) organic CO2 with very low contents but contaminated by mantle~derived helium; (2) inorganic CO2 gases with lower to higher contents being mixtures of crustal CO2 with mantle derived CO2, the mantle contributed percentage being in the range of 0 % ~ 27 %, and (3) mainly crust~derived inorganic CO2 gases being characterized by high contents (more than 50 %) and indicating the crustal addition by metamorphism of rich in carbon rocks in basement. Nevertheless, some CO2/3He ratios of organic CO2 fall into the range 108-1010, which made us inquire whether the CO2/3He=(1-10)×109 can be the unique signature of magmatic CO2 or not. All the observation of plutonic activities, fluid inclusion measurements in gas reservoirs, pre~stack depth/time seismic sections and the satellite infrared remote photography taken from Yinggehai basin, South China Sea, during Chichi earthquake in Taiwan on September 21, 1999, supports that the degassing processes are in a discontinuous mode, which may be triggered by igneous intrusion or extrusion, or earthquakes. In the central diapir zone of the basin, at least 3 to 4 orders of discharge of across~formational thermal fluid flows through fractures can be determined in different scales. The mantle degassing process may have a strong effect on overpressured system forming and outgassing in crust. However, it is very difficult to estimate the transferring rates for a special fractured zone at a specific time interval.
Increasing world class, high grade, and metals enriched supergene manganese ore deposits have been discovered in the last two decades, making them more and more economically important. However, data on the timing and duration of their formation are sparse, mainly due to the difficulties extracting datable minerals suited to traditional radiometric dating methods. Hollandite, cryptomelane, coronadite, todorokite, and manjiroite are common manganese oxide minerals in supergene environments. These minerals host potassium of variable amounts from 0.1 wt% to 5.0 wt% in their structural sites. This geochemical property provides possibility to date supergene manganese ores by using K-Ar and 40Ar/39Ar methods. In this study, we perform 40Ar/39Ar dating on a 7.1cm thick botryoidal manganese nodule from an ancient weathering profile at Mount Tabor, central Queensland, Australia. Laser microprobe incremental analyses of distinct growth bands, from the inner core through the intermediate bands to the outermost crusts of the nodule, have yielded high quality 40Ar/39Ar ages at 27.3 Ma, 20.9 Ma, 19.2 Ma, and 16.1 Ma,respectively. The age results permit preliminary estimates on the average growth rates of the nodule varying from 4.7×10-3mm/ka to 7.6×10-3mm/ka to 9.0×10-3mm/ka, from the core to the rim. Results of this study are of significance in our understanding of the mode, mechanism, process, and climatic conditions in the formation of supergene manganese ore deposits