2014 Vol. 25, No. 2
In this paper, the relationship between rare earth elements (REEs) geochemical behavior and their ionic radii was studied. According to the basic law called the effect on geochemistry of lanthanides, five types and some of subtypes of REEs occurrence, both in magmatic rocks and their minerals, were found, which may correspond to the evolutionary way of magmatic rocks. Analysis of REEs data for an amazonite-topaz granite pluton in East Xinjiang, one of the administrative regions of West China, and Cenozoic alkaline volcanic-intrusive rocks in the Xialiaohe depression of Bohai Bay Basin, China show that types II1, III and IV of effect on geochemistry of lanthanides not only reflect fluid complexation and fractional crystallization existed in magmatic evolution directly, but also can determine semi-quantitatively the strength of fluid complexation and fractional crystallization. Therefore, the effect on geochemistry of lanthanides, a new way to study semi-quantitatively evolution of magmatic rocks, is probably practicable. Moreover, the mafic lavas of different sources from the margin of Gonghe Basin, Qinghai Province, China, can be effectively distinguished in the diagram which can be drawn with some parameters of linear equation of LREEs and its ion radius.
In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deepwater area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of structural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic patterns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sandstone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.
Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed atthe diachronous problem generally existed in volcanic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edificesand bodies were identified and traced. The results indicated that aimed strata in study areas could becarved up to six layers of YC1I1, YC1I2, YC1I-II, YC1II1, YC1II2 and YC1III from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable consistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanicreservoir and it had very important significance to effective development of volcanic reservoir in practice.
To investigate climate evolution during the Miocene, especially during the Middle Miocene climate transition on the northeastern Tibetan Plateau, stable oxygen and carbon isotopes of carbonates from a 288-m-thick lacustrine-fluvial sediment sequence covering the period from 17.1 to 6.1 Ma from Tianshui Basin, China, were analyzed. The relatively low stable oxygen isotope values indicate the prevalence of wet climate conditions during the period of 17.1–13.6 Ma, an interval corresponding to the well-known Middle Miocene Climate Optimum. The interval between 13.6 and 11.0 Ma (i.e., the late Middle Miocene) is marked by a progressive increase in the δ18O values, indicative of a decrease in precipitation, probably linked to the expansion of the East Antarctic Ice Sheet and global cooling since about 14 Ma. The climate in the study area continued to get drier as shown by the enrichment of the heavy oxygen isotope from 11 Ma. Weattribute these stepwise climatic changes as revealed by our carbonate δ18O record from the northeastern Tibetan Plateau to the sustained global cooling that may have reduced moist transport to Central Asia, which in turn led to a permanent aridification.
Al-rich metapelites from the Mashan khondalite series are characterized by the assemblage Spl+Grt+Sil+Crd+Bt+Pl (An72)+Kfs+Quartz+graphite. Large amounts of spinel+quartz assemblages occur as inclusions in garnet and prismatic sillimanite in the Al-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich (XZn=0.33–0.40. XZn=Zn/Zn+Mg+Fe*) (Fe*=Fe2++Fe3+) and Fe3+ rich (up to 0.31 p.f.u.). The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path.
In order to investigate the evolution of Shiquanhe-Yongzhu-Jiali ophiolitic mélange belt, the gabbros from new discovered Zhongcang ophiolitic mélange are studied through petrology, whole-rock geochemistry, zircon U-Pb dating and Lu-Hf isotope. The gabbros investigated in this paper contain cumulate gabbro and gabbro dike, and they have undergone greenschist-amphibolite facies metamorphism. The chondrite normalized rare earth element (REE) patterns of most of these rocks show flat types with slightly light REE (LREE) depletion and the N-MORB normalized incompatible elements diagrams indicate depletion in high field strength elements (HFSE) (Nb, Ta) and enrichment in large ion lithophile elements (LILE). These gabbros have island arc and mid-ocean ridge basalt af-finities, suggesting that they were originated in an oceanic back arc basin. Whole rock geochemistry and high positive εNd(t) values show that these gabbros were derived from ~30% partial melting of a spinel lherzolite mantle, which was enriched by interaction with slab-derived fluids and melts from sediment. U-Pb analyses of zircons from cumulate gabbro yield a weighted mean age of 114.3±1.4 Ma. Based on our data and previous studies, we propose that an intra-oceanic subduction system and back arc basin operated in the Neo-Tethy Ocean of central Tibet during Middle Jurassic and Early Creta-ceous, resembling modern active intra-oceanic subduction systems in the western Pacific.
A sequence of terrigenous siliciclastic rocks crop out at Baxiandun, Qingdao, near the Mesozoic collisional boundary between North China block (NCB) and South China block (SCB). These low-grade metamorphosed siliciclastic rocks are dominated by greywacke with shale, manganiferous fine-grained sandstone, arkose and conglomerate layers. There are two basic interpretations about the formation of these rocks. One considered that this sequence was formed within NCB, and is part of the Cretaceous Laiyang Group and Qingshan Group fluvial facies and volcanic debris facies, as shown on the Shandong Regional Geological Map. Another opinion suggested that these rocks represent turbidity depositional systems in the slope and the basin facies was mainly deposited in Ordovician. Based on field observation, petrological analysis, and most importantly, geochemical results in this study, the sedimentary strata at Baxiandun Section mainly consist of siltstone, sand-stone and mudstone lithologies. They are dominated by deepwater debris and turbidity deposits in the slope and base of a lake. The U-Pb detrital zircon dating of the rocks at the Baxiandun Section indicates that the source rocks are very complex and their ages are varied from Archean to Early Cretaceous. The youngest age of the terrigenous detritus could represent the age of the sedimentary strata. Therefore, we infer that the sedimentary rocks belong to Early Cretaceous deepwater lacus-trine sedimentary sequences and have multiple sources origined from the erosion of the Sulu UHP orogen and South China block margin.
In this study, 465 m of Tarbur Formation in Tang-e Kushk and east of Sarvestan area stratigraphic sections are studied and 185 thin sections are provided and analyzed. Based on lithostratigraphic studies, Tarbur Formation in these two stratigraphic sections is divided into upper and lower parts. Lower part includes medium-bedded rudist limestones which is consist of iron nodules with Gastropoda. Upper part is made of light grey massive organodetrital limestone. Identified foraminifers of both studied sections are comprised of: Orbitoides media, Orbitoides triangularis, Orbi-toides tissoti, Orbitoides orientalis, Orbitoides apiculata, Antalyna korayi, Rotalia skourensis, Dicyclina schlumbergeri, Nezzazatinella sp., Omphalocyclus macroporus, Trochospira sp., Siderolites calcitrapoides, Broeckinella sp., Lepidorbitoides socialis, Gavelinella pertusa, are detected, and also it has Dasycladacea of Salpingoporella dinarica, Salpingoporella turgida, Salpingoporella sp.. According to diagnosed fo-raminifera, the age determination of Tarbur Formation is assigned to Upper Maastrichtian
Morphology and structure of a faulted zone not only express the present status but also preserve the evidences of early seismo-tectonic occurrences. The present paper aims to assess the morphological as well as subsurface evidences of early seismo-tectonic occurrences in an earthquake prone zone of Baromura Hill, Tripura. Tectonically this is a part of Tripura-Mizoram fold belt and fall within Zone V of BIS seismic map. In the present research the tectonic lineaments of Baromura Hill was identified by using satellite data. For that purpose, Landsat TM shortwave infrared, midwave infrared and near infrared was selected for preparing suitable band combination. A classified thermal infrared was used for final operation. From the remote sensing operation five clear tectonic lineaments were found. During the field work rock samples were collected for laboratory testing. Thin sections of the rocks show that complex stress pattern was developed during the geological past which caused strong seismo-tectonic occurrences. From the study it can be assessed that though the nature of the paleo-seismic occurrences were almost same but the level of impact varied through spatial and temporal scales due different physical properties and arrangements. It is also clear from the study that the geological evolution of this place is more complex as it seems to be. Tectonic and geomorphic processes worked together through the Tertiary and Quaternary periods and played equally important role for landform evolution
Statics are big challenges for the processing of deep reflection seismic data. In this paper several different statics solutions have been implemented in the processing of deep reflection seismic data in South China and their corresponding results have been compared in order to find proper statics solutions. Either statics solutions based on tomographic principle or combining the low-frequency components of field statics with the high-frequency ones of refraction statics can provide reasonable statics solutions for deep reflection seismic data in South China with very rugged surface topography, and the two statics solutions can correct the statics anomalies of both long spatial wavelengths and short ones. The surface-consistent residual static corrections can serve as the good compensations to the several kinds of the first statics solutions. Proper statics solutions can improve both qualities and reso-lutions of seismic sections, especially for the reflections of Moho in the upmost mantle
Heshan, a city in Southwest China, has been built over an old coal mining area. Due to low level of reclamation, coal gangue had been stacked in large heaps and caused geological environmental problems. To facilitate designing management project of coal gangue, we made an investigation of the largest coal gangue heap in Dongkuang Mine of Heshan. Firstly, the grain composition of coal gangue was estimated through the sieving method, then the representative grading curve was drawn through the statistics method of coarse grain content, and lastly the relationship between the repose angle and grain grading was studied by piling up coal gangue with different mix proportion. The result indicates that there is a wider range of grain size in the upper part of coal gangue heap, and the representative grain grading is well graded and easy to be compacted as filling materials. Besides, the wavy relationship curve of repose angle and coarse grain content shows that the content of 70% is the inflec-tion point of ascent stage and 85% the inflection point of descent stage of the repose angle. What’s more, the repose angle corresponding to the representative grading of coal gangue is approximately 38.4° and this has guiding significance for management project of coal gangue
The Tarim Basin was a craton block during the Carboniferous period. Except for its open southwestern (SWW) deepening basin margin, the central part of the basin was surrounded by northern, eastern, and southern uplifts. In most parts of the basin, there are three layers of carbonate rocks called Biocalcarenite member, standard limestone member and Xiaohaizi Formation. The present-day Maigeti slope, located in the southwestern area of the basin, was ever a paleogeographic carbonate platform margin to clinoform. Boreholes in the area reveal over ten meters of high-energy bio-spararenite of beach deposition in Xiaohaizi Formation. This feature is quite different from the low-energy micritic limestone of equivalent horizon in the middle and northern basins. Such typical carbonate beach and platform margin backgrounds indicate an environment conducive for reef growth. According to an interpretation of 3-D seismic data on a 600 km2 Xinbaza survey, a 25 km-long barrier reef orientated in an east-westward direction is delineated with a hummocky geometry, a 1–2 km wide south-dip reef front, and a 3–6 km wide north-dip backreef. The reef buttress and outlines are also shown on an isopach map of the Xiaohaizi Formation as well as horizon slices of coherency, amplitude, and frequency attributes. The reef extends beyond the range of the rectangular 3-D seismic survey. The thickness of the Xiaohaizi Formation is over 60 m at the central reef, and 12 m larger than the outside of the reef. The barrier reef consists of segments separated by narrow tidal inlets. The neighborhood of the reef is mainly beach deposition of bioclasticgrainstones. Due to Late Permier and Late Tertial tectonic movements, the barrier reef was tilted to dip in a SWW direction. Its updip part was broken and misplaced by a set of reverse faults. Nevertheless, potential stratigraphic pools of a large amount of hydrocarbon reserves related to the reef are expected to be found in the future based on the substantial reef scale and the recent borehole indications beside it.
Tanlu fault (Liaozhong segment) goes straight through Liaodong Bay along NNE direction and it is divided into three segments, i.e., the northern segment, the middle segment and the southern segment, according to the differences in structural features. There are obvious changes in deposit thickness, sag structure, tectonic nature and other aspects of the layers. Tanlu fault is a special controlling factor concerning the reservoir formation in Liaozhong sag. First, its activities affect paleogeomorphology and paleogeographic framework and control the distribution of the sedimentary facies and then they proceed to control the distribution of the source rock and reservoir sand bodies. Second, its activities affect the formation and deformation of the structure, control the formation of abundant traps and cause the destruction of some traps. Third, its activities also affect the juxtaposition relation among the fault, the sand bodies and unconformity surfaces and control the function and efficacy of the three as the main hydrocarbon translocation system. In this paper the hydrocarbon reservoir formation process of JZ21-1, JX1-1 and LD27-2 oil and gas fields, the representatives of Tanlu strike slip fault zone are mainly analyzed. The modes of hydrocarbon reservoir formation can be generalized as follows—hydrocarbon source acts as “soil” and oil and gas as “nutrient”; hydrocarbon expulsion relies on “roots”; hydrocarbon migration relies on “trunks”; reservoir forms in “brunches” and the whole process follows the pattern that “hydrocarbon accumulates in strike slips and oil and gas reservoir forms like the growth of trees”
Taking member one of Yingcheng Formation of Cretaceous in Xudong area, Xushen Gas Field of Songliao Basin for an example and aimed at the diachronous problem generally existed in volcanic reservoir division, firstly advanced the method of two steps and two unites in the researches of volcanic reservoir finely division that guided by the method that sources controlled and founded the stratigraphic trellis. In this process, volcanic edifices and bodies were identified and traced. The results indicated that aimed strata in study areas could be carved up to six layers of YC1I1, YC1I2, YC1I-II, YC1II1, YC1II2 and YC1III from the top to the bottom. Analyzing causes and firmly united of well data and seismic data could achieve fine stratigraphic division of volcanic reservoir. Surfaces of layers and volcanic bodies were basically unanimous in side direction. Stratum inclination gradually reduced with the distances increased from craters. The results of volcanic reservoir division had preferable consistency with lithologies and volcanic lithofacies and dynamic development data. The researches offered a useful method to stratigraphic division of volcanic reservoir and it had very important significance to effective development of volcanic reservoir in practice.
Economic development, industrialization and dense population in Trabzon City have caused residential construction to increase by 300% in the last decade. The settlement area is mountainous and covered with heavy vegetation. Thus, the steep-sided topography and heavy precipitation means floods and landslides are common and in areas with little flat land. Since the mass movements in some parts of city create an enormous danger for buildings, site selection for residential areas becomes increasingly important. This paper describes geotechnical and seismic properties of Tertiary volcanic rock and establishes the link between these units and construction. In this study, refraction tomography and multichannel analysis surface wave methods were applied in order to seek the best construction site in the residential area. The results of the geophysical study were com-pared with the borehole applications. A series of geomechnical tests were carried out on the core samples. Following that, statistical correlations were conducted by regression analysis to evaluate re-lationships between measured parameters. Rock Quality Designation and weathering degree were also determined. The methodology defined in this investigation proves to be an appropriate ap-proach to determine geotechnical properties of the foundation rocks and soils and a proper guide on future geotechnical studies for other cities
Understanding the past and present changes is critical for evaluating the future climatic changes. In order to understand the paleoproductivity and depositional environments of Northern Indian Ocean, two sediment cores were collected, one each from the Arabian Sea (lat. 16°51.40′N and long. 71°54.37′E, water depth 803 m) and the Bay of Bengal (lat. 13°05.35′N and long. 91°28.21′E, water depth 3 054 m). The surface seawater samples indicate higher pCO2 values in Arabian Sea as com-pared to the Bay of Bengal. The sediment organic carbon variations along with sedimentological and other geochemical parameters were studied. Sediment organic carbon varied from 0.5%–4.7% and 0.3%–1.22% in Arabian Sea and the Bay of Bengal, respectively. In Arabian Sea, low productivity, oxic conditions and less intense southwest monsoon prevailed during the deglacial period, whereas productivity has increased from last 16 kyr to the modern age. In the Bay of Bengal, organic carbon decreased from the Last Glacial Maxima (LGM) to the modern age, indicating higher productivity in the past as compared to modern age. Fe was associated with organic carbon in the Bay of Bengal and increased during LGM, showing similar trend to that of organic carbon, indicating that Fe may be the limiting factor for the growth of phytoplankton in the Bay of Bengal in the modern age. In the Bay of Bengal, Mn is enriched during modern age and is depleted during LGM, whereas chromium showed the opposite trend indicating anoxic conditions during the LGM, whereas in Arabian Sea the trends are opposite to the Bay of Bengal.
The determination of total glacial volume is important for the observation of climatic change and its consequences such as global sea-level rise. The tongue area of Glacier No. 4 of Sigong River over Mt. Bogda, eastern Tianshan was surveyed by ground-penetrating radar (GPR) and real time kinematic (RTK)-global positioning system (GPS) during the summer campaign 2009. In order to calculate the glacier volume, both co-kriging algorithm and estimation based on the theory of perfectly plastic material were employed. Results indicated that the ice-thickness distribution of the investigated glacier ranges from 0 to 105.0 m, with the mean thickness of 27.6 m in 2009. The corresponding ice volume was ~0.076 km3 (~0.068 km3 water equivalent). The bedrock topography shows more undulating than the glacier surface. The difference of the calculated ice volume in this study and the estimated value from the empirical formula is large. Therefore, it is urgent to validate the applicability of the existing empirical formula.
In June 2006, samples were collected from a 90 cm snow-pit at an elevation of 5 040 m a.s.l. in the northern branch firn basin of the Glacier No. 12, Laohugou Valley, in the western part of Qilian Mountain, China. Oxygen isotopes (δ18O) and major soluble ions were measured. Results showed that Ca2+ is the dominant cation, and SO42- is the dominant anion. All major ions have close positive correlations with eachother except NO3- and NH4+. δ18O show positive correlation with air temperature. The method of correlation analysis, sea-salt ion tracer and trend analysis were used to determine the source of the chemical components. The correlation analysis and HYSPLIT backward trajectory analysis suggest that atmospheric soluble dust species dominate the chemical signature.
Although arsenic-contaminated groundwater in the Datong Basin has been studied for more than 10 years, little has been known about the complex patterns of solute transport in the aquifer systems. Field monitoring and transient 3D unsaturated groundwater flow modeling studies were carried out on the riparian zone of the Sanggan River at the Datong Basin, northern China, to better understand the effects of groundwater flow on As mobilization and transport. The results indicate that irrigation is the primary factor in determining the groundwater flow paths. Irrigation can not only increase groundwater level and reduce horizontal groundwater velocity and thereby accelerate vertical and horizontal groundwater exchange among sand, silt and clay formations, but also change the HS- concentration, redox conditions of the shallow groundwater. Results of net groundwater flux estimation suggest that vertical infiltration is likely the primary control of As transport in the vadose zone, while horizontal water exchange is dominant in controlling As migration within the sand aquifers. Recharge water, including irrigation return water and flushed saltwater, travels downward from the ground surface to the aquifer and then nearly horizontally across the sand aquifer. The maximum value of As enriched in the riparian zone is roughly estimated to be 1 706.2 mg?d-1 for a horizontal water exchange of 8.98 m3?d-1 close to the river and an As concentration of 190 μg?L-1.
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data covering the Jiafushaersu area in Xinjiang were used for mapping lithology and hydrothermal alteration. The study area situates at a potential mineralization zone in relation to small hypabyssal granodiorite or quartz monzonite intrusions along the margin of granitoid batholiths of Darbut foot wall. The false colour composition of bands 521 and the first three principal component analyses (PCA1, PCA2, PCA3) in RGB identify the lithological units and discriminate the small intrusions very well from the adjacent granitoid batholiths. PCA and spectral angle mapper (SAM) algorithm were employed to discriminate alteration minerals. The results indicate that the hydroxyl-bearing or ferric and less commonly carbonate types show good correlation with the quartz monzonite porphyry and aplite. Field verification led to finding of the Jiafushaersu molybdenum mineralization. The lithological and geochemical features imply that the molybdenum mineralization is close to the porphyry type. This study further verified that the foot wall of the Darbut suture could have served as a more important metallogenic district for the porphyry copper and molybdenum deposits. It is concluded that the ASTER data-based methods can be used as a powerful tool for small intrusion-type mineral resources targeting.
Ontologies are increasingly deployed as a computer-accessible representation of key semantics in various parts of a data life cycle and, thus, ontology dynamics may pose challenges to data management and re-use. By using examples in the field of geosciences, we analyze challenges raised by ontology dynamics, such as heavy reworking of data, semantic heterogeneity among data providers and users, and error propagation in cross-discipline data discovery and re-use. We also make recommendations to address these challenges: (1) communities of practice on ontologies to re-duce inconsistency and duplicated efforts; (2) use ontologies in the procedure of data collection and make them accessible to data users; and (3) seek methods to speed up the reworking of data in a Semantic Web context.