2014 Vol. 25, No. 3
The widespread microbialites deposition that followed the End-Permian mass extinction in the Tethyan realm have been intensively studied because of the evidence they provide on the nature of this crisis and its aftermath. However, the age of the microbialite event remains controversial. New conodont collection across the Permian–Triassic (P–T) transition from Dajiang (Guizhou Province,South China) in this study enable us to discriminate four conodont zones, in ascending order, they are:Hindeodus parvus zone, Isarcicella lobata zone, Isarcicella isarcica zone and Hindeodus sosioensis zone.The age of microbialite in the P–T transition at the Dajiang Section is considered to be within the Hindeodus parvus zone and thus to clearly post-date the main extinction crisis. Reviewing the age of onset of microbialites throughout the Tethyan regions reveals two different ages: a Hindeodus changxingensis zone age is dominant in south-western and westernmost Tethys, whilst most other regions show microbialite deposition began in the Hindeodus parvus zone. Our investigation also indicates that two conodont changes occur at this time: an increase of hindeodid species immediately following a sequence boundary and the mass extinction, and a phase of extinction losses in the earliest Triassic Isarcicella isarcica zone during highstand development.
The boron isotope paleo-pH proxy has been extensively studied due to its potential for understanding past climate change, and further calibrations were considered for accurate applications of the proxy because of significant variability related to biocarbonate microstructure. In this work, we studied the boron isotopic fractionation between modern marine corals and their coexisting seawater collected along shallow area in Sanya Bay, South China Sea. The apparent partition coefficient of boron (KD) ranged from 0.83?10-3 to 1.69?10-3, which are in good agreement with previous studies. As the analyzed coral skeleton (~5 g) spanned the growth time period of 1–2 years, we discussed the boron isotopic fractionation between pristine corals and modern seawater using the annual mean seawater pH of 8.12 in this sea area. Without taking the vital effect into account, (11B/10B)coral values of all living corals spread over the curves of (11B/10B)borate vs. (11B/10B)sw with the ?4-3 values ranging from 0.974 to 0.982. After calibrating the biological effect on the calcifying fluid pH, the field-based calcification on calcifying fluid pH (i.e., Δ(pHbiol-pHsw)) for coral species of Acropora, Pavona, Pocillopora, Faviidae, and others including Proites are 0.42, 0.33, 0.36, 0.19, respectively, and it is necessary to be validated by coral cul-turing experiment in the future. Correlations in B/Ca vs. Sr/Ca and B/Ca vs. pHbiol approve tempera-ture and calcifying fluid pH influence on skeletal B/Ca. Fundamental understanding of the thermody-namic basis of the boron isotopes in marine carbonates and seawater will strengthen the confidence in the use of paleo-pH proxy as a powerful tool to monitor atmospheric CO2 variations in the past.
The granitic rocks around the Utla area (Gadoon), north western, Pakistan are studied in terms of their petrographic features and geochemical characteristics. Although predominantly mega-porphyritic, some of the Utla granites are massive and display fine-grained equi-granular texture.Some of the mega-porphyritic varieties exhibit foliation and seem to be restricted to shear zones.In addition to being distributed largely as phenocrysts, all the essential minerals (plagioclase, perthitic alkali feldspar and quartz) also constitute the groundmass. The studied samples also contain minor to accessory amounts of tourmaline, muscovite and biotite and accessory to trace amounts of apatite,andalusite, garnet, zircon, monazite, epidote and sphene. A detailed geochemical investigation reveals a calc-alkaline and peraluminous character of the Utla granites. The peraluminous character and total lack of hornblende designate their S-type character while a volcanic arc or syn-collisional tectonic setting for their emplacement is indicated by discrimination diagrams. Further examination shows that the melt parental to the Utla granite was derived from a plagioclase-poor, clay-rich rock, i.e., pelite.The petrogenetically significant petrographic and geochemical features of the Utla granite show greater similarity with the Mansehra than the Ambela granites. These include (i) the predominantly megaporphyritic texture, (ii) the presence of andalusite and tourmaline, (iii) the calc-alkaline geochemical signature and (iv) an indication of similar melt source rock character.
We report for the first time the geochemistry of rare earth elements (REE) in the weathered crusts of I-type and calc-alkaline to high-K (shoshonitic) granitic rocks at Mamasa and Palu region, Sulawesi Island, Indonesia. The weathered crusts can be divided into horizon A (lateritic profile)and B (weathered horizon). Quartz, albite, kaolinite, halloysite and montmorrilonite prevail in the weathered crust. Both weathered profiles show that the total REE increased from the parent rocks to the horizon B but significantly decrease toward the upper part (horizon A). LREE are enriched toward the upper part of the profile as shown by La/YbN value. However, HREE concentrations are high in horizon B1 in Palu profile. The total REE content of the weathered crust are relatively elevated compared to the parent rocks, particularly in the lower part of horizon B in Mamasa profile and in horizon B2 in Palu profile. This suggests that REE-bearing accessory minerals may be resistant against weathering and may remain as residual phase in the weathered crusts. The normalized isocon diagram shows that the mass balance of major and REE components between each horizon in Mamasa and Palu weathering profile are different. The positive Ce anomaly in the horizon A of Mamasa profile indicated that Ce is rapidly precipitated during weathering and retain at the upper soil horizon.
The Amdo microcontinent is located within the middle of Bangong-Nujiang suture(BNS) zone in the shape of lens. The basic geological research restricts geologists from understanding the histories of tectonic evolution of BNS and regional geology more deeply. This paper systematically studies the geochronology and geochemistry of granitic gneisses from Amdo basement. These data provide constraints on formation age, source characteristics and tectonic setting of their protolith. The SHRIMP zircon U-Pb dating is operated for granitic gneisses. Samples AGS-2 and AGS-3 (granitic gneiss) yield average zircon U-Pb ages of 485±14 and 487±6 Ma, respectively. These ages should represent the formation age of protolith and indicate that they are formed in the Early Ordovician. Granitic gneisses are characterized by high SiO2, Na2O, K2O and Al2O3, low Fe and Mg,enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), with negative Eu anomaly. The Rittmann index (σ) is 1.77 to 2.60, less than 3.3. The aluminum saturation index(A/CNK) values range from 0.88 to 1.26. These features suggest that protolith of granitic gneisses from Amdo basement show characteristics of calc-alkaline and S-type granite, and they could be derived from partial melting of metamorphic greywackes in the upper crust of low maturity. The tectonic setting is syn-collision. These all suggest that the formation of protolith of granitic gneisses from Amdo are caused by the Early Paleozoic orogeny, which could be related to proto-Tethyan oceanic subduction along Gondwana continental margins, and does not result from the production of Pan-African orogenesis.
The Ordovician carbonate reservoirs in the Tahe Oilfield are highly heterogeneous, which have undergone multiple superimposed transformations by tectonic activities and karst processes,leading to an extremely complex fluid distribution. The geochemical characteristics of geofluids also display great disparities. Results show that the vertical distribution of oil and gas are continuous, however the oil-water interfaces in different blocks of the Tahe Ordovician Oilfield are numerous. Meteoric water infiltration is regarded as the main reason for the high oil-water interface and high water content to the north of Tahe Oilfield, especially in well blocks S78–S73. The isotopic values of deuterium-oxygen in the groundwater and carbon-oxygen from calcite veins confirm that formation water in Ordovician reservoirs of the Tahe Oilfield was a mix of meteoric water and connate water, and the proportion of meteoric water gradually increases from south to north, while connate water decreases. The Tahe Ordovician reservoirs are characterised by multiple hydrocarbon charges, and the general migrating direction is from southeast to northwest and from east to west. High production could be obtained in the northern area of the Tahe Oilfield since the oil layers are thick and oil is highly saturated. The residual water within the reservoirs is low, and heavy oil is dominant in this area. Only a small amount of pore water has been replaced by oil in the southern Tahe Oilfield, leading to low oil saturation and a high content of residual water. Crude oil is herein mainly of medium-light type. During the process of exploration in this region, acid fracturing reformation is usually required for wells to increase their output;however the yield is still low.
The Longmen kaolinite deposit is one of the largest hydrothermal clay deposits of Ganxi volcanic basin (northern Wuyi Mountain area, China). The pristine host rocks are rhyolitic crystal-vitric tuff and minor lapilli tuff from the Late Jurassic Ehuling Formation. The ore consists of kaolin-group minerals (kaolinite, dickite), pyrophyllite with minor quartz, sericite, pyrite, etc.. From the host rocks to the transition zones (altered rocks) then to the vein ores, contents of SiO2 and TFe2O3 decrease, whereas Al2O3 and LOI increase, consistent with the contents increase of kaolin minerals and pyrophyllite in the samples. The total REE abundances of the ores are much lower than that of the host and altered rocks, Rb, Nb, Nd, Zr, Ti and Y are significantly depleted. Apparent zoning features of bulk geochemistry and mineralcomponent reflect that the kaolinite deposit occurred at the expense of the host rock by ascending hydrothermal fluids with distinct removal of SiO2, TFe2O3, Na2O, K2O.According to the mineral assemblage, the formation temperature of this deposit falls within the range of 270–350 ℃. With regard to the industrial applications, the kaolinized ores are suitable for use in ceramics and gemologic materials crafted for seal stones. Moreover, in mineralogical terms, this deposit is also proved to be an excellent example for studying channeled hydrothermal alterations of rhyolitic tuff.
The gravity flow deposit were mainly developed in the lowstand systems tract (LST) of the first member of Upper Miocene Huangliu Formation (Ehl1) in Dongfang area, Yinggehai Basin, has become a valuable target for gas exploration and production. Thegravity flow sedimentary characteristics of lithofacies associations, sedimentary texture, seismic facies and logging facies were described in detail on the basis of integrated analysis of cores, logging and seismic data. The sedimentary microfaciestypes composed of neritic sandbar, continental shelf mud, main channel, bifurcatedor cross-cutting distributary channel, overspill, and natural levee are revealed under the constraint of high resolution sequence stratigraphic framework in the Ehl1.The gravity flow deposit system in the LST is divided into three evolution stages corresponding to periods of three parasequence sets. The gravity flow deposit was induced in the early LST, expanded rapidly in the middle LST and decreased slightly inthe late LST. But its developing scale decreased sharply in the transgression systems tract (TST) and finally vanished in the highstand systems tract (HST). This spatial evolution rule is constrained by the integrated function of sediments supply ofthe Vietnam Blue River in the LST, the development of local gradient change in sea floor (micro-topography, i.e., flexure slope break), and the fall in relative sea level.On the basics of the deep study of the coupling relationship among the three main control factors,the sedimentary model is established as an optimal component of“source-channel-sink” for shallow marine turbidite submarine fan.
Pre-existing models for thermal history modelling have shown deficiency in explicit algorithms to establish the quantitative relationship between maturity indices and thermal gradients in some sedimentary basins that experienced multi-episodic rifting evolution. In this study, a forward and inverse combination model (FICM) is proposed to estimate the vitrinite reflectance (Ro)and thermal gradients. The forward module is used to calculate Ro values. It couples the EASY%Ro model with burial history reconstruction with consideration of thermal gradient variations during basin evolution. The inverse module reconstructs histoical thermal gradients by calibratingcmputed Ro against measured Ro data. The time-temperature series is a necessary input for both forward and inverse modules. Sample density is a profound factor influencing the accuracy of modelling results. In order to obtain satisfying outputs, a sufficient sample density is required. Thermal gradients are assumed to vary linearly between two given samples. Modelling results of case studies indicate that the sensitivity of heating time to Ro evlution is differnt with thermal gradients depending on geolgoical setting. Three difffernt districts, which include the time-sensitive area, the temperature-sensitive area and the non-sensitive area, can be recognized on the the relationship map among Ro variations, heating time and geothermal gradients. This model can be applied to reconstruct the thermal history and maturationevolution in a basin that has undergone complex multi-episodic rifting.
The Beishan area has more than seventy mafic-ultramafic complexes sparsely distributed in the area and is of a big potential in mineral resources related to mafic-ultramafic intrusions. Many mafic-ultramafic intrusions which are mostly in small sizes have been omitted by previous works. This research takes Huitongshan as the studyarea, which is a major district for mafic-ultramafic occurrences in Beishan. Advanced spaceborne thermal emission and reflection radiometer (ASTER) data have been processed and interpreted for mapping the mafic-ultramafic complex. ASTER data were processed by different techniques that were selected based on image reflectance andlaboratory emissivity spectra. The visible near-infrared (VNIR) and short wave infrared (SWIR) data were transformed using band ratios and minimum noise fraction (MNF), while the thermal infrared (TIR) data were processed using mafic index (MI) and principal components analysis (PCA). ASTER band ratios(6/8, 5/4, 2/1) in RGB image and MNF (1, 2, 4) in RGB image were powerful in distinguishing the subtle differences between the various rock units. PCA applied to all five bands of ASTER TIR imagery highlighted marked differences among the mafic rock units and was more effective than the MI indifferentiating mafic-ultramafic rocks. Our results were consistent with information derived from local geological maps. Based on the remote sensing results and fieldinspection, eleven gabbroic intrusions and a pyroxenite occurrence were recognized for the first time. A new geologic map of the Huitongshan area was created by integrating the results of remote sensing, previous geological maps and field inspection.It is concluded that the workflow of ASTER image processing, interpretation and ground inspection has great potential for mafic-ultramafic rocks identifying and relevant mineral targeting in the sparsely vegetated arid region of northwestern China.
A new method of multi-scale modeling and display of geologic data is introduced to provide information with appropriate detail levels for different types of research.The multi-scale display mode employs a model extending existing 2D methods into 3D space. Geologic models with different scales are organized by segmenting data into orthogonal blocks. A flow diagram illustrates an octree method for upscaling between blocks with different scales. Upscaling data from the smallest unit cells takes into account their average size and the Burgers vector when there are mismatches. A geocellular model of the Chengdao Reservoir of the Shengli Oilfield, China is taken as an illustrative case, showing that the methods proposed can construct a multi-scale geologic model correctly and display data from the multi-scale model effectively in 3D.
Aiming at the special demand on SVG_based representation and organization for spatial data in location based services (LBS), the research is made in this article on the conversion method from multiple formats to SVG format, and a harris_corner detector method is proposed and verified to evaluate the conversion result. Based on the above, an optimized compression arithmetic is proposed,which integrated the characteristic of code simplification and GZIP compression. The test shows that the techniques on conversion and compression are feasible, which means that SVG_based representation is suited for spatial data in LBS and the improved compression arithmetic is prior to the former.
In this paper, a coupled numerical groundwater and land subsidence model was developed for the Tianjin Plain. The model was employed to investigate the groundwater resources and their changes over the last decade, and to further predict the changingpatterns of the groundwater level and associated land subsidence in future. First, according to the regional hydrogeology, the simulation area was defined with an area of 10.6×103 km2, which was divided into six aquifer units. A coupled groundwater and land subsidence numerical model was built by using Modflow2005 and the land subsidence simulation module SUB (subsidence and aquifer-system compaction), in which the groundwater flow was modeled as three-dimensional unsteady flow and the land subsidence simulation was based on one-dimensional consolidation theory. The model was then calibrated by using the groundwater level contour lines, hydrographs, and land subsidence hydrographs over the period of 1998–2008. In addition,groundwater balance analysis of the simulation period indicated that under multi-year groundwater withdrawal condition the cross-flow recharge, compression release, and lateral boundary inflow contributed 44.43%, 32.14%, and 21.88% to the deep aquifer recharge, respectively. Finally, themodel was applied to predict the changing patterns of the groundwater levels and the associated variations in land subsidence under the control of groundwater exploitation after implementation of the south-to-north water diversion project. The simulation results demonstrated that the groundwater level may gradually increase year by year with an decrease in the groundwater withdrawal; and the land in dominated land subsidence regions including the urban area, Dagang, Hangu, Jinghai, Wuqing, and Jinnan, may rebound at an average rate of 2–3 mm/a, and the land subsidence rate in the other regions may decrease.
Groundwater is the main water source in the Hebei Plain. Evolution of groundwater chemistry can not only provide scientific data for sustainable usage of groundwaterresources, but also help us in better understanding hydrogeochemical processes in aquifers. Spatial distribution and temporal evolution were analyzed on basis of monitoring data between 1975 and 2005. Results showed that major components in groundwater had increasing trends since 1970s. Major components in shallow groundwater increased more than those in deep one. In shallow groundwater of piedmont alluvial fan-recharge zone, concentrations of Na+, Ca2+, SO42- had great increasing trends, while other major components increased by less than 30%. There were great increasing trends in Na+, Cl-, SO42- concentrations in deep groundwater of central alluvial plain-intermediate zone, while other major components increased by no more than 20%. Deep groundwater from coast plain-discharge zone and piedmont alluvial fan-recharge zone showed no significant variations in major ion concentrations. In shallow groundwater, dissolution, evaporation and human activities played a major role in the increase in major components. However, groundwater mixture resulting from deep groundwater exploitation was believed to be the major factors for the increases in major components in deep groundwater of central alluvial plain-intermediate zone.
A groundwater transient flow model was developed to evaluate the applicability and effectiveness of artificial recharge scenarios in the middle-upper part of the Yongding River alluvial fan in Beijing. These scenarios were designed by taking into account different types of recharge facilities and their infiltration rate with the Middle Route Project for South-to-North Water Transfer (MRP) as the recharge water source. The simulation results suggest that: (1) the maximum amount of artificial recharge water, for scenario I, would be 127.42×106 m3 with surface infiltration facilities; and would be 243.48×106 m3 for scenario II with surface infiltration and recharge wells under the constraint of the upper limit of groundwater; (2) with preferred pattern of recharge facilities, groundwater levels in both optimized recharge scenarios would not exceed the upper limit within the given recharge period; and (3)implementation of the recharge scenarios would efficiently increase the aquifer replenishment and the groundwater budget will change from -54.11×106 to 70.89×104 and 183.36×104 m3, respectively. In addition,under these two scenarios groundwater level would rise up to 30 and 34 m, respectively, without increasing the amount of evaporation. The simulation results indicate that the proposed recharge scenarios are practically feasible, and artificial recharge can also contribute to an efficient recovery of groundwater storage in Beijing.
Understanding the controlling factor of groundwater quality can enhance promoting sustainable development of groundwater resources. To this end, multivariate statistical analysis (MA) and hydrochemical analysis were introduced in this work. The results indicate that the canonical discriminant function with 7 parameters was established using the discriminant analysis (DA) method, which can afford 100% correct assignation according to the 3 different clusters (good water (GW), poor water (PW), and very poor water (VPW)) obtained from cluster analysis (CA). According to factor analysis(FA), 8 factors were extracted from 25 hydrochemical elements and account for 80.897% of the total data variance, suggesting that groundwater with higher concentrations of sodium, calcium, magnesium, chloride, andsulfate in southeastern study area are mainly affected by the natural process; the higher level of arsenic and chromium in groundwater extracted from northwestern part of study area are derived by industrial activities; domestic and agriculture sewage have important contribution to copper, iron, iodine, and phosphate in the northern study area.Therefore, this work can help identify the main controlling factor of groundwater quality in North China plain so as to make better and more informed decisions about how to achieve groundwater resources sustainable development.
The deformation of aquitard is the main contribution to land subsidence in the North China Plain, and the water released from aquitard compaction may be a large portion of the exploited groundwater. In this study, the consolidation test was employedto understand the mechanics on the drainage and deformation of aquitard. The results suggested the strain of aquitard mainly resulted from the difference of hydraulichead between aquifers. And it was decreased with depth of aquitard at the same hydrodynamic pressure. In contrast with the interbed within aquifers, the aquitard was deformable when it was compressed. The weakly bound water was significantly released when the void ratio was about 0.44–0.45, and the EC of water released from the aquitard was decreased with the compacting process. The data from the consolidation test suggested that the pumping of groundwater from aquifer III might be less contribution to the land subsidence with respect to other aquifers in the future.
Environmental tracers are proving to be a unique tool for assessing groundwater sustainability,such as characterization of recharge, identification of pathways and sources of contaminants, and prediction of groundwater change in response to excessive abstraction. This paper helps to better understand the groundwater sustainability in the Quaternary aquifer from the tracer data in the North China Plain. Relatively modern ground waters occur in the piedmont plain with 3H-3He age less than 40 a within a depth 100 m. These ground waters are mainly recharged from the local precipitation and irrigation return. The recharge rate estimated by tracers is in the range of 0.24 to 0.32 m/a. Paleowater which is dated from 10 000 a B.P. to more than 35 000 a B.P. by radiocarbon dating is found in highly-confined portions of Quaternary aquifer systems. This indicates that water recharge took place during the past glacial period. The tracers have suggested a slow natural replenishment rates to the central plain. The aquifer has been overexploited currently. Some strategies that can be implemented to promote a sustainable groundwater supply are needed to implement in future.
The North China Plain (NCP) is one of the water shortage areas of China. Lack of water resources restricted the economic and social development of North China area and resulted in deterioration of ecosystem and natural environment. Influenced by theclimate change and human activities,the water circulation of NCP was largely changed and the crisis of water resources was aggravated.Therefore, it is important to study the features of the extreme climate and the response mechanism of groundwater to climate change. We analyzed the trend of climate change and extreme climate features in the past 60 years based on the monitoring data of meteorological stations. And then the response characteristics of groundwater to climate change were discussed. The average temperature of NCP was in an obviously upward trend. The overall precipitation variation was in a downward trend. The climate change in this area showed a warming-drying trend. The intensity of extreme precipitation displayed a trendof declining and thenincreasing from north to south as well as declining from eastern coastal plain to the piedmont plain. Grey correlation degree analysis indicatedthat groundwater depth had a close relationship with precipitation and human activities in NCP. The response of groundwater level to precipitation differed from the piedmont alluvial-pluvial plain to the coastal plain. The response was more obvious inthe coastal plain than the piedmont alluvial-pluvial plain and the middle plain.Theprecipitation influenced the groundwater depth both directly and indirectly. Under the condition of extreme precipitation, the impact would aggravate, in the forms ofrapid or lag raise of groundwater levels.