2013 Vol. 24, No. 3
Combined with field studies, microscopic observations, and EBSD fabric analysis, we defined a possible Early Cretaceous metamorphic core complex (MCC) in the Wulian (sic) area along the Sulu (sic) orogenic belt in eastern China. The MCC is of typical Cordilleran type with five elements: (1) a master detachment fault and sheared rocks beneath it, a lower plate of crystalline rocks with (2) middle crust metamorphic rocks, (3) syn-kinematic plutons, (4) an upper plate of weakly deformed Proterozoic metamorphic rocks, and (5) Cretaceous volcanic-sedimentary rocks in the supradetachment basin. Some postkinematic incursions cut across the master detachment fault zone and two plates. In the upper plate, Zhucheng (sic) Basin basement consists of the Proterozoic Fenzishan (sic) Group, Alining period granite (762-834 Ma). The supradetachment basin above the Proterozoic rocks is filled with the Early Cretaceous Laiyang (sic) (similar to 135-125 Ma) and Qingshan (sic) groups (120-105 Ma), as well as the Late Cretaceous Wangshi (sic) Group (85-65 Ma). The detachment fault zone is developed at the base and margin of the superposed basin. Pseudotachylite and micro breccia layers located at the top of the detachment fault. Stretching lineation and foliation are well developed in the ductile shear belt in the detachment faults. The stretching lineation indicates a transport direction of nearly east to west on the whole, while the foliations trend WNW, WSW, and SE. Protomylonite, mylonite, and ultramylonite are universally developed in the faults, transitioning to mylonitic gneiss, and finally to gneiss downward. Microstructure and quartz preferred orientation show that the mylonites formed at high greenschist facies to low greenschist facies as a whole. The footwall metamorphic rock series of the Wulian MCC are chiefly UHP (ultrahigh pressure) metamorphic rocks. Syntectonic rocks developed simultaneously with the Wulian MCC detachment and extension. Geological research has demonstrated that the MCC is associated with small-scale intrusive rocks developing in the vicinity of the detachment faults, for instance, dike. Geochronology results indicate that the denudation of the Wulian MCC occurred at about 135-122 Ma. Its development and exhumation was irrelevant to the Sulu UHP metamorphism zone rapid exhumation during Triassic Period but resulted from the crustal extension of North China Craton and adjacent area.
Clay mineralogy and bulk mineral composition of Tertiary sediments in Qaidam were investigated using X-ray diffraction (XRD) and scanning electron microscopy in order to better understand regional climate change resulting from uplift of the Northeast Tibetan Plateau. Climate change in Qaidam since similar to 53.5 Ma could be divided into four stages: a warm and seasonally arid climate between similar to 53.5 and 40 Ma, a cold and arid climate from similar to 40 to 26 Ma, a warm and humid climate between similar to 26 and 13.5 Ma, and a much colder and arid climate from similar to 13.5 to 2.5 Ma, respectively. The Mite crystallinity and sedimentary facies suggested that uplift events took place around >52-50, similar to 40-38, similar to 26-15, similar to 10-8, and <5 Ma in the Qaidam region, respectively. The climate in Qaidam Basin could have been controlled by global climate prior to 13.5 Ma. As the Tibetan Plateau reached a significant elevation by similar to 13.5 Ma, and the climate cycles of the East Asian monsoon might add additional influence.
The occurrence of hydrocarbon migration in petroliferous basins depends on the balance of driving force and resistance of carriers, which restricts mostly the quantity and positions of hydrocarbon accumulation. The driving forces of hydrocarbon migration have been quantitatively studied, whereas the migration pathways and carriers were only qualitatively discussed up to now. Establishing a compound hydrocarbon carrier system and quantitatively characterizing its transport capability are significant for understanding the dynamic process of hydrocarbon migration and revealing the hydrocarbon accumulation characteristics. It has become an innovatory trend and also a difficult topic in study of hydrocarbon migration. In this article, a method is described for using displacement pressure to quantitatively characterize the transport capability of the compound carrier system, which composed of sandstone carriers, unconformities and faults. When the weathered and leached zone rarely developed, the basal conglomerate or transgressive sandstone of unconformities can be treated as part of sandstone carriers. An empirical relationship among core porosity, air permeability, and the pore aperture radius corresponding to a mercury saturation of 10% (r(10)) can be obtained by multiple regression. Using porosity and permeability inversed by seismic data, the displacement pressure of sandstone carriers can be calculated by the empirical relationship and Washburn Equation. Displacement pressure of fault plane can be estimated by the regression formula between fault opening index (FOI) and hydrocarbon column height it can support. This method is applied in the eastern part of south slope in Dongying (sic) depression, Bohai (sic) Bay Basin, China, to quantitatively characterize the transport capability of the compound carrier system of Shahejie (sic) Formation. The results have good agreement with data from drilling wells. This method may be a step further in study of compound hydrocarbon carrier system in petroliferous basins. It may provide the basis of coupling expulsion quantity, migration driving force and hydrocarbon carrier system to simulate hydrocarbon migration and accumulation. Therefore this will help predict hydrocarbon migration pathways and the locations of hydrocarbon accumulation.
This study was undertaken to establish an evaluation method for buried dissolution of carbonate reservoir in the Tahe (sic) Oilfield. Because of the difficulty in tracing the dissolution in geologic record, the precipitation is taken as a useful indicator to presume the dissolution reversed. The fluid inclusions data is a useful tool to identify the precipitation. On the basis of the principle that the temperature data of fluid inclusions captured in the calcite fillings of caves and cracks can reflect the fluid activity time, a total of 256 fluid inclusions samples in 12 drills were collected and analyzed to study their forming time in buried environment in the Tahe Oilfield, Tarim Basin, NW China. Results show that the temperature data of fluid inclusions captured by Ordovician cave and crack fillings accumulated in six intervals, which indicated six stages of fluid activity in the area of study. Meanwhile, it is clear that a different number of temperature intervals was captured in different wells, representing a different number of precipitation distributed in space. According to this conclusion, the buried precipitation trend in late Himalayan stage (the sixth stage) was supposed in space and its effectiveness has been approved by the chemical thermodynamics method. This method was also used in all of the other five stages of fluid activity and the comprehensive trend of the buried precipitation in space for Ordovician strata was evaluated. It shows that more temperature intervals were captured in the southwestern region (wells S76, S79, S65 and S75) and the eastern region (well S69) in the area of study, indicating intensive precipitation and weak dissolution in this area. This evaluation method for buried dissolution is a new attempt and may have important implications for further petroleum exploration in the Tarim Basin.
Carboniferous source rocks identified by drilling in Santanghu (sic) Basin were evaluated for their source potential, employing organic geochemistry and RockEval pyrolysis. The organic matter origin and depositional environment of these samples were also determined through biomarker analysis. Most of the Carboniferous source rocks in Santanghu Basin are characterised by high values of total organic carbon (TOC) content and high extractable organic matter content and hydrocarbon yields, indicating that they are organic-rich source rocks with high oil generative potential. The organic matter is predominantly Type I and Type II kerogen with a minor contribution of Type III kerogen, as demonstrated by its pyrolysis parameters and carbon isotope values. According to Ro (%) and T-max values, most of the studied samples are at early- to middle-thermal mature stage; only a few of the samples are at a highly mature stage (past peak oil generation). The biomarker analysis reveals a dominance of algal/bacterial organic matter input, with a minor contribution of land plant material. Pr/Ph ratio supports a suboxic depositional condition, consistent with a neritic or marine-continental alternating environment proposed by predecessor.
In this article, an appropriate strategy for registration of correspondent points in the stereo-pairs of Chang’E-1 lunar mission has been introduced. It consists of area-based method and feature-based method as two steps. Firstly, one subimage was extracted from nadir image as reference image. Making use of area-based method, another subimage which is called target image can be obtained from backward or forward image overlapping the same region of lunar surface with reference image. Secondly, feature points of each subimage can be extracted by SIFT (scale invariant feature transform) algorithm. Lastly, for each feature point given in reference image, the position of correspondence in target image can be estimated according to the parameters of Chang’E-1 lunar orbiter. In contrast to standard SIFT matching algorithm, the method proposed in this article can narrow the search space and accelerate the speed of computation while achieving reduction of the percentage of false registration.
Although Pleistocene red paleosols are widely distributed in South China, paleoenvironmental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower (higher) chi but higher (lower) values of HIRM (hard isothermal remanent magnetization) and SIRM (saturation isothermal remanent magnetization)/chi has tight relationship with the intensity of pedogenesis, especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP (superparamagnetic)/SD (single domain) ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to the extremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon: (1) the most effective since the Middle Pleistocene; (2) moderately effective since 270 ka or so; (3) least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.
Denizli graben (DG) is bounded in the NE by the Pamukkale fault zone and in the SW by the Babadag-Honaz fault zone. The Babadag and Honaz fault zones are generally made up as nearly E-W directed two segments. The Pamukkale fault also contains many overlapping segments in the Denizli area along the NE margin of the graben. The DG contains an NW-SE trending horst (Karakova) controlled by normal faults with oppositely dipping high angles and that truncate the Plio-Quaternary rock units. The faults that bound the DG are likely to have been initiated during the Early to Late Miocene and appear to be active today. The faults of the DG are active and the potential energy that accumulates in them is easily conducted to the other faults that they come in contact with. This signifies that a movement in one of the faults forming the grabens in the Denizli region affects the other structures as well. Earthquakes in the Buldan region usually occur 2-3 years after seismical movements occur in the Denizli Basin. The Buldan region is a ridge between DG and Alasehir graben (ALG). Based on the fact that DG in its south and ALG in its north move seismically, there is a probability that a break would appear in the Buldan region in the near future.
This project studies marine terraces in western Messenia, southwestern Peloponnese, Greece, to propose a model of neotectonic configuration and paleogeographic evolution of western Messenia during the Quaternary. GIS analysis of topographic data and geological mapping revealed flanks of raised terraces created on Quaternary marine deposits. Luminescence ages of sediments from the three westernmost marine terraces tend to be consistent OIS-5, OIS-7 and OIS-9, respectively, thus agreeing with the three latest warm stages of the Pleistocene. Moreover, the type and the extent of deformation of the dated marine terraces allowed us to reflect on the neotectonic configuration of western Messenia as well as to conclude that progressive differential uplift over the last 300 ka has induced a dome-like structure to the upper crust of western Messenia.
High-precision, clay sediment oxygen and hydrogen isotopes analyses of Pleistocene-Holocene deep-sea sediments from the Bay of Bengal (BOB) are presented for the first time. Our study shows that the major source of sediments in the study area, since the last similar to 25 000 years, is likely to be the Higher Himalayan crystalline rocks. Further, the study of these stable isotope data displays the variation of southwest monsoon (SWM) in the BOB region since the last similar to 25 000 years and the cause behind the variation has been interpreted. The delta O-18 values of the clay sediments are compared with delta O-18 values of the BOB seawater. This comparison shows that the clay sediment delta O-18 values of the studied sediment cores temporally vary along with the changes in strength of the SWM. Based on the changes in the clay sediment delta O-18 values of the studied sediment, we evaluate the variance in the SWM since the last 25 000 years in the BOB. Our results are consistent with previous work in the region based on other proxies. To evaluate the factors influencing the intensity of the SWM since the last glacial maxima, we conducted comparative analyses of the studied clay sediment delta O-18 values with delta O-18 values in the Greenland ice cores (GISP2) and Tibetan ice cores (Guliya). The results from this comparative study show that large-scale changes in the intensity of the SWM since 25 000 years are affected by the climate oscillations of the Northern Hemisphere, but rapid and abrupt fluctuations in the SWM seem to be controlled by the amount of snow cover in the Tibetan Plateau.
Guizhou (sic) Province, Southwest China, is rich in coalbed methane (CBM) resources, wherein its geological structure is complicated. We discuss the occurrence characteristics of CBM based on CBM borehole test data and geological setting. In combination with the analysis of the regional tectonics, macro- and micro-scopic geological structures and pore size distributions, the structural controls on CBM reservoirs were further discussed from the aspects involving tectonic evolution, structural features, and deformation of coal. The results show that the CBM enrichment was mainly controlled by the regional tectonic subsidence and weak structural deformation on coal reservoirs after coal formation. The Yangmeishu (sic) syncline and topography are the main controlling factors to the current distribution pattern of CBM, which is higher in the north than the south and trending toward the NE direction. Normal faults and fractures can be divided into open, closed, and occluded types. The open type reduces both gas content and methane concentration of nearby coal seams. The closed type causes the decrease of gas content, while methane concentration is still high. The occluded type fail to reduces gas content, and even results in the enrichment of CBM in small areas near fault. Moderate brittle deformation can improve the pore structure and development of structural fracture of coal reservoir. Cataclastic structural coals with well-developed fractures and relatively uniformly distributed pore structures are common in the Faer (sic) coal mine, which are favorable for the production of CBM.
Coal is the primary energy resource in China. Thousands of underground coal mines are operating in China and cause severe land subsidence, leading to many environmental and engineering problems. Huainan (sic) coal mine is the largest coal mining area in East China. Surface subsidence associated with Huainan coal mining activities has been monitoring by DInSAR (differential synthetic aperture radar) techniques in this study. Four ASAR (advanced SAR) pairs from 2009 to 2010 are selected to perform 2-pass DInSAR processing with spatial and temporal baselines suitable for subsidence monitoring. The subsidence maps generated from these pairs show that the extension of subsidence is consistent with the field observation. Quantitative measurements indicated that the magnitudes of subsidence are increased with the development of underground coal mining exploitation. This study demonstrates that DInSAR technique is effective for surface subsidence monitoring in coal mining area. Limitations and recommendations both in the adopted method and auxiliary data are also discussed.
A total of 80 weathering pits (gnammas), located on granite surfaces of Qing Mountain (sic), Hexigten (sic) Global Geopark, Inner Mongolia, were identified and measured in terms of dimensional and orientational features. This article attempts to extract characteristics of the weathering pits by descriptive statistics and orientation rose diagrams, investigate the multi-phase evolution by the modified gnamma morphological analysis (GMA) method, and shed new light on the possible genesis and the influencing factors. Following the modified GMA method, weathering pits in Qing Mountain have been divided into six groups and compared with analogous sites to deduce their approximate age, which might be no older than 30 ka B.P., and explore the possibility that the multi-phase evolution of weathering pits may arise from responses to climate change. In consequence, we suggest that the combination of weathering, especially salt weathering, and wind erosion, both of which are closely related to climatic variation, take the main responsibility for the formation and development of weathering pits in Qing Mountain.