Vertical changes of POC flux and indicators of early degradation of organic matter in the South China Sea

Tie-series sediment trap materials at different water depths and surface sediments in northern and central South China Sea (SCS) were analyzed for organic carbon, amino acids, amino sugars and carbohydrates. Results show that particulate organic carbon (POC) is mainly derived from marine plankton, only 1.4%–1.6% of primary production sinks into deep SCS water column and less than 0.22 % of primary production ultimately reaches the sediments. The ranineralization and dissolution of organic matter as well as the compositional alterations of organic matter mixtures may mainly take place in the upper few hundred meters of water column, deep carbonate (opal) lysocline zones, and interface layers between sediments and water column, rather than in mid-waters. The organic geochemical parameters such as (T ^aa +T ^sug )OC%, AA/AS, Gluam/Galam, Arom. AA/non-prot. AA, ASP/b-ALA, Glu/g-ABA decrease from living marine plankton (or planktonic shells), to settling particulate matter and to sediments suggesting that they appear to be gad early degraded indicators of organic matter. Project supported by the National Natural Science Foundation of China (Grant No. 49776297). Cruises financially supported by State Oceanic Administration and German Federal Ministry of Research and Technology.     

Conduit system and formation mechanism of heat fluids in diapiric belt of Yinggehai basin, China

The conduit system of heat fluids in diapiric belt of Yinggehai basin is dominantly vertical faults and fractures. Detailed research on the formation mechanism and their occurrence features shows that the faults and fractures can be classified into three types: intrastratal dispersive hydrofracture, puncturing fault and upwarping-extensional fault. The development of the fault and fracture system not only resulted in the changes of the temperature and pressure fields in the basin, but also affected the hydrocarbon migration in the overpressured system. These faults and fractures constituted the main pathways for vertical hydrocarbon migration, and opening and closing intermittently led to episodic expulsion of overpressured fluid compartment. Thus there formed the pool-forming model of multi-source mixing and ploy-stage migration and accumulation for hydrocarbons in the Yinggehai basin. Project jointly supported by the Ministry of Science and Technology of China (Grant No.95-Pre-39) and the National Natural Science Foundation of China (Grant No. 49732005), and A Hundred Excellent Researchers Foundation from the Ministry of Land and Resources.     

Selective chemical degradation of kerogen from Nenjiang Formation of the southern Songliao Basin

A sequential selective chemical degradation has been performed on the kerogen from the Nenjiang Formation of the southern Songliao Basin by using a series of mild chemical degradations (alkaline hydrolysis, cleavage of ether-bonds and sulfur-bonds, and ruthenium tetroxide (RuO4) oxidation). Subsequently, the GC-MS analyses are carried out on different degradation products. The results show that chemical degradations can release a great number of GC/MS-determinable biomarkers from insoluble kerogen, such as, alkaline hydrolysis products mainly comprise n-alkanes, fatty acids and alkanols; thiophene compounds are predominantly ether-bound to kerogen matrix; the products from the cleavage of sulfur-sulfur and sulfur-carbon bonds in the kerogen include fatty acids, alkanols and some n-alkanes with high carbon numbers; RuO4 oxidation products are predominantly monocarboxylic acids and α,ω-dicarboxylic acids. The distributions of main degradation products indicate that organic matter in this kerogen is predominantly derived from algae and bacteria, and that small amounts of high plant-derived organic matter are possibly combined into kerogen matrix at the late stage by sulfur bonds and other means. This study will provide an important approach for further discussing sources of organic matter in source rocks and their depositional paleoenvironments.     

N2-Ar-He systematics and source of ore-forming fluid in Changkeng Au-Ag deposit, central Guangdong, China*

Changkeng Au-Ag deposit is a newly-discovered new type precious metal deposit. N₂-Ar-He systematics studies and³He/⁴He and δD- δ¹⁸O composition analyses show that the ore-forming fluid of the deposit is composed mainly of formation water (sedimentary brine) but not of meteoric water, which was thought to be source of the ore-forming fluid by most previous researchers. The content of mantle-derived magmatic water in the ore-forming fluid is quite low, usually lower than 10%. According to the source of the ore-forming fluid, the Changkeng Au-Ag deposit should belong to sedimentary brine transformed deposits. From the Late Jurassic to the Early Cretaceous Period, with deposition and accumulation of thick sediments in Sanzhou Basin, the formation water in the sedimentary layers was expelled from the basin because of overburden pressure and increasing temperature. The expelled fluid moved laterally along sedimentary layers to the margin of the basin, and finally moved upward along a gently-dipping interlayer fault. Because of a decline in pressure and temperature, ore minerals were deposited in the fault. Project supported by the National Natural Science Foundation of China (Grant No. 495020291, the Natural Science Foundation of Zhongshan University, the Research Foundation of National Key Laboratory of Metallogenesis in Nanjing University (Grant No. 039704) and the Lingnan Foundation.     

Crude oil as carrier of gold: petrological and geochemical evidence from Lannigou gold deposit in southwestern Guizhou, China

Organic matter is related closely to mineralization of Lannigou gold deposit in southwestern Guizhou, China. Regionally, the distribution of organic carbon agrees well with that of faults within which gold deposits are hosted. Studies on organic petrology show that pyrobitumen, which is related most closely to mineralization, adheres to quartz vein or fills quartz veinlet. Proton-induced X-ray emission (PIXE) analysis shows an evident abundance of Au in pyrobitumen. Pyrobitumen paragenetically associates with pyrite and arsenopyrite which are the main carrier minerals of Au. The thermal simulation experiment indicates that about 99% of Au will be concentrated in oil phase in the coexisting system of oil and brine and rock. The role of crude oil in ore-forming process is: as carrier of Au, crude oil moves upwards, and undergoes thermal decomposition and thermochemical reduction when it encounters the oxidizing fluid within the Trassic turbidity; Au is thus released from crude oil, reduced and precipitated. Project supported by the Climbing Project (No. PA30) and the National Natural Science Foundation of China (Grant No. 49673190).     

Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform, China

Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carhon group of isotopes with the δ¹³C values from - 27% to - 35 %, which are lower than those of the contempomneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristies of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks. Project supported by the National Natural Science Foundation of China (Grant No. 49472114) and the Open Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.     

The discovery of annually laminated sediments (varves) from shallow Sugan Lake in inland arid China and their paleoclimatic significance

Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments re-ported in arid western China.     

Soil organic carbon storage and soil CO<Subscript>2</Subscript> flux in the alpine meadow ecosystem

High-resolution sampling, measurements of organic carbon contents and ¹⁴C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of ¹⁴C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO₂ flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×10⁴ kg C hm⁻² to 30.75×10⁴ kg C hm⁻² in the alpine meadow ecosystems, with an average of 26.86×10⁴ kg C hm⁻². Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO₂ flux ranges from 103.24 g C m⁻² a⁻¹ to 254.93 gC m⁻² a⁻¹, with an average of 191.23 g C m⁻² a⁻¹. The CO₂ efflux produced from microbial decomposition of organic matter varies from 73.3 g C m⁻² a⁻¹ to 181 g C m⁻² a⁻¹. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO₂ emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research. Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong Provincial Natural Science Foundation of China (Grant No. 06300102)     

Organic and inorganic occurrence of selenium in Laerma Se-Au deposit

Se and other trace elements in kerogen are determined. Based on biochemical evidence, theoretical calculations and infrared spectra, it is indicated that Se may occur as organic minerals by combining with organic legends. The inorganic occurrence of selenium is also discussed. Project supported by the National Natural Science Foundation of China (Grant No. 60633110).     

Vertical transferring process of rare elements in coral reef lagoons of Nansha Islands, South China Sea

The vertical fluxes and vertical transferring forms of 18 rare elements were studied for the first time in the coral reef ecosystem of Nansha Islands, South China Sea, by deploying sediment traps. The results showed that the vertical transferring flux of most of the measured rare elements in Yongshu lagoon were higher than that in Zhubi lagoon. The vertical transferring forms of rare elements were mainly in the carbonate form, but Ta, As, Th mainly in the ion-exchange form, Ag in iron-manganese oxide form and Sb in the organic matter+sulphide form. None of the 18 rare elements was transferred mainly in the form of detritus silicate to sea floor. This proved that rare elements originating from the earth’s crust were redistributed in sinking particulates after they were brought into ocean. The relation between the fluxes and surface seawater temperature (STT) was also studied. The sensitivity of rare elements to SST was in order:Rb>V>As>Ti>U>Zn>Sb>Hf>Ag>Cs. Project supported by the National Natural Science Foundation of China (Grant No. 49576291).     

Carbon isotopic composition and its implications on paleoclimate of the underground ancient forest ecosystem in Sihui,Guangdong

We present the carbon isotopic composition of the total organic carbon (TOC) and fine roots in the sedimentary profile from the underground ancient forest in Sihui to study the climatic and environmental changes from 4.5 ka BP to 0.6 ka BP. Results show that C₃ plant was the main vegetation from 4.5 ka BP to 0.6 ka BP in this region. The ancient forest began to develop in the wetland at around 4 ka BP and disappeared together with the wetland at about 3.0 ka BP, implying that the climate had changed greatly at around 3.0 ka BP. As indicated by the simulation results, the content of atmospheric CO₂ increased slightly during 3.5 ka BP to 3.0 ka BP, implying climate warming during that period. The interval of radiocarbon age between 3.0 ka BP to 1.2 ka BP was possibly caused by the strong erosion when the block was lifted in the neotectonic movement. From 1.2 ka BP to 0.6 ka BP, the region remained in terrestrial sedimentary environment, and the surface plant biomass declined gradually. Drought caused by the climate change was the likely cause for the disappearance of the ancient forest. South transition of Intertropical Convergence Zone (ITCZ) was probably the main mechanism for the climate change. Supported by National Natural Science Foundation of China (Grant Nos. 40231015 and 40473002), National Basic Research Program of China (Grant No. 2005CB422004), the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KSCX2-SW-133) and Open Funds of State Key Laboratory of Organic Geochemistry (Grant No. OGL-200607)     

Quantitative assessment of gas washing of oils in the Tazhong area of the Tarim Basin,Northwest China

Gas washing has been known in the Tazhong area of the Tarim Basin, but its quantitative assessment has not yet been reported. Here the influence of gas washing fractionation in the area was discussed based on the gas chromatogram data of 68 oils and the results of the mixing experiments of a black oil and a condensate. The results show that the intensity of gas washing fractionation decreased generally from northern to southern part and vertically from deep reservoirs to shallow reservoirs. The gas washing fractionation was mainly controlled by fault systems in this area, with the increase of n-alkane mass depletion positively correlated to the number and scale of faults. Gas washing fractionation appears to have affected the hydrocarbon property, and as a result the diversity of the crude oils is markedly controlled by gas washing. In addition, the occurrence of waxy oil in this area may be resulted from multiple factors including gas washing, mixed filling and migration fractionation. Supported by National Basic Research Program of China (Grant No. 2006CB202303) and the National Natural Science Foundation of China (Grant No. 40672091)     

Three-dimensional thermal structure of the Chinese continental crust and upper mantle

We invert S-wave velocities for the 3D upper-mantle temperatures, in which the position with a temperature crossing the 1300℃ adiabat is corresponding to the top of the seismic low velocity zone. The temperatures down to the depth of 80 km are then calculated by solving steady-state thermal conduction equation with the constraints of the inverted upper-mantle temperatures and the surface temperatures, and then surface heat flows are calculated from the crustal temperatures. The misfit between the calculated and observed surface heat flow is smaller than 20% for most regions. The result shows that, at a depth of 25 km, the crustal temperature of eastern China (500―600℃) is higher than that of western China (<500℃). At a depth of 100 km, temperatures beneath eastern and southeastern China are higher than the adiabatic temperature of 1300℃, while that beneath west China is lower. The Tarim craton and the Sichuan basin show generally low temperature. At a depth of 150 km, temperatures beneath south China, eastern Yangtze craton, North China craton and around the Qiangtang terrane are higher than the adiabatic temperature of 1300℃, but is the lowest beneath the Sichuan basin and the regions near the Indian-Eurasian collision zone. At a depth of 200 km, very low temperature occurs beneath the Qinghai-Tibet Plateau and the south to the Tarim craton.     

Deep electrical structure of the Sulu orogen and neighboring areas

Because of the discovery of ultrahigh pressure metamorphic (UHPM) belt beneath the Sulu (Jiangsu Province-Shandong Province) orogen, this area has become a focused subject of current geoscience, as it has a close relationship with the evolution of the orogen and the neighboring North China craton. Probing the deep structure beneath this area would be of great significance for the geological interpretation of this issue. In this study, we make an analysis of magnetotelluric (MT) data along a profile across the Sulu orogen to provide evidence of deep structure below this region. The profile begins in west from the North China block, extending in S129°E, across the Tan-Lu fault, Sulu UHPM zone, and Sulu high pressure metamorphic (HPM) zone, and terminates in the Yangtze block in east. We use the nonlinear conjugate gradient method and TE-TM combined mode to perform inversion and interpretation of the MT data, and obtain an electrical structure image above depth of 150 km along the profile. It shows that the structure can be divided into seven sections in lateral direction, between which the electric boundaries coincide well with the major faults, such as the Tan-Lu, Haizhou-Siyang, and Jiashan-Xiangshui faults. In vertical direction the electrical structure can be subdivided into six layers of different resistivities. It is noted that there exist high-conductivity areas in crust below the North China block and Yangtze block, while such a feature is not present beneath the Sulu orogen, which is very different from the Dabie orogen. It is also observed that a fairly continuous zone of relatively low-resistivity exists at depths of 50–90 km of the electrical structure image, which is presumably a weak zone in the uppermost mantle. Just below this low-resistivity zone are the relatively high- resistivity layer of the North China block, relatively low-resistivity layer of the Sulu orogen, and relatively high-resistivity layer of the Yangtze block, all in the shallow upper mantle, respectively. From the whole 2D electrical structure image, there is no abnormally low-resistivity layer in the shallow upper mantle beneath the Sulu orogen and neighboring areas, indicating that no hot asthenoshperic material associated with lithospheric thinning exists at present. Supported by National Natural Science Foundation of China (Grant No. 40534023) and Director Foundation of Institute of Geology, China Earthquake Administration (Grant No. DF-IGCEA-0608-2-16)     

Seismic response analysis of arch dam-water-rock foundation systems

The effect of water compressibility on the seismic responses of arch dams is not well understood. In this paper, a numerical model is developed with rigorous representation of the dynamic interaction between arch dam-water-rock foundation. The model is applied to the seismic response a nalysis of an arch dam with a height of 292m designed to aseismic intensity of IX. It is shown that consideration of the water compressibility clearly decreases the stress responses at key positions of the dam, while the added mass model gives a conservative estimate.     

Conductivity of NaCl solution at 0.4–5.0 GPa and 25–500 °C

NaCI-H₂O is the most fundamental ternary system in geology. Until now, the measurements of electrical conductivity of NaCl solutions are still little at high pressures (> O.5 GPa) We measured the conductivity of 0.01 m NaCl solution at 0.4–5.0 GPa and 25-500°C. The results are consistent with that of Quist and Marshall (1968) at 0.4 GPa. The conductivity of NaCl solution increases with increasing temperature. The results also show that the conductivity of NaCl solution changes little with increasing pressure below 1.5 GPa and changes rapidly with increasing pressure above 1.5 GPa. The rapid increase of the conductivity of NaCl solution may play an important role in many geological processes (such as the genesis of ore deposits under hydrothermal condition) and other fields. Project supported by the National Natural Science Foundation of China.     

Experimental observation of the nano-scale particles in geogas matters and its geological significance

The geogas collectors showing a geogas anomaly in field geogas prospecting and in simulation tests were selected for the observation under high resolution microscopy. The result demonstrates that the geogas matter is transported in the form of nano-scale particles with a size of aboutN nm to N-10 nm, and accumulated into aggregations of 1-2 μm to N.10 μm, with globular and film shape, and the component of Cu, Zn, Cr, Au, Al, V, Si, Br, C1, S, Ca, etc. Based on the knowledge of nano science and technique, the mechanism of the geogas prospecting and its significance in geology and mineral prospecting are discussed. Project supported by the National Natural Science Foundation of China (Grant No. 49673202) and the Department of Science and Technology of MGMR, PRC (Grant No. 9505201-1)     

Temporal and spatial features of the soil moisture in boreal spring in eastern China

Soil moisture data of 45 years from European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the in situ observational data are used to study the temporal and spatial characteristics of the soil moisture in boreal spring in the area to the east of 100°E in China. Results show that ERA-40 soil moisture well reproduces the temporal and spatial features of observations. ERA-40 data capture the spatial pattern that the soils in Northeast China and Southwest China are wetter than those...     

Grey characteristics of microbanding of stalagmite in Shihua Cave, Beijing and its climatic signification(I)

Grey microstructure of microbanding in thin sections of stalagmite T9501 from Shihua Cave, Beijing was studied. The types of grey and the morphologic features of organic material were classified. The signification of microbanding and annual layer was discussed. The standard distinguishing the false annual layer and the multi-year layer is set up, which provides the theoretic fundaments for paleoclimatic study. Project supported by the National Natural Science Foundation of China (Grant No. 49672134).     

Proposed GSSP for the base of Cambrian Stage 9, coinciding with the first appearance of <Emphasis Type="Italic">Agnostotes orientalis</Emphasis>, at Duibian,Zhejiang, China

Exposed in natural outcrops near the Duibian Village, Jiangshan County, Zhejiang Province, China, the Duibian B section is proposed as the boundary stratotype for the base of an unnamed stage termed provisionally Cambrian Stage 9. The proposed position of the GSSP is 108.12 m above the base of the Huayansi Formation, at a horizon coinciding with the first appearance of the cosmopolitan agnostoid trilobite Agnostotes orientalis. This horizon coincides also with the first appearance of the cosmopolitan polymerid trilobite Irvingella angustilimbata. The section fulfills all the requirements for a GSSP, and the horizon can be constrained not only by the primary stratigraphic marker (A. orientalis) but also with secondary biostratigraphic, chemostratigraphic, and sequence-stratigraphic correlation tools. The first appearance of A. orientalis is one of the most readily recognizable levels in Cambrian, and can be correlated with precision to all paleocontinents. Supported by Chinese Academy of Sciences (Grant No. KZCX2-YW-122), the Ministry of Science and Technology of China (Grant Nos. 2006FY120300, 2006CB806400), National Natural Science Foundation of China (Grant Nos. 40072003, 40023002, 40332018, 40672023, 40602002), and the U.S. National Science Foundation (Grant No. EAR-0106883)