Sedimentary environment and organic matter accumulation of Wufeng-Longmaxi shales,southwest Yangtze Plate,China:Insights from geochemical and petrological evidence

Upper Ordovician-Lower Silurian Wufeng-Longmaxi Formation is the most developed strata of shale gas in southern China.Due to the complex sedimentary environment adjacent to the Kangdian Uplift,the favorable area for organic-rich shale development is still undetermined.The authors,therefore,focus on the mechanism of accumulation of organic matter and the characterization of the sedimentary environment of the Wufeng-Longmaxi Shales to have a more complete understanding and new discovering of organic matter enrichment and favorable area in the marginal region around Sichuan Basin.Multiple methods were applied in this study,including thin section identification,scanning electron microscopy(SEM)observations and X-ray diffraction(XRD),and elemental analysis on outcrop samples.Five lithofacies have been defined according to the mineralogical and petrological analyses,including mudstone,bioclastic limestone,silty shale,dolomitic shale,and carbonaceous siliceous shale.The paleo-environments have been reconstructed and the organic enrichment mechanism has been identified as a reduced environment and high productivity.The Wufeng period is generally a suboxic environment and the early Longmaxi period is a reducing environment based on geochemical characterization.High dolomite content in the study area is accompanied by high TOC,which may potentially indicate the restricted anoxic environment formed by biological flourishing in shallower water.And for the area close to the Kangdian Uplift,the shale gas generation capability is comparatively favorable.The geochemical parameters implied that new favorable areas for shale gas exploration could be targeted,and more shale gas resources in the mountain-basin transitional zone might be identified in the future.

Quantitative geochemical reconstruction of Eocene paleoenvironment in Fushun Basin,northeast China

The quantitative estimation of key parameters of paleotemperature and paleoprecipitation is crucial for paleoclimate reconstruction.Geochemical data from mod-ern sediments are highly consistent with climate data,and their relationship can provide an important reference for the quantitative reconstruction of the paleoclimate.In this study,detailed inorganic geochemical analysis was carried out using high-precision sampling of the Paleogene(LFD-1 well)Guchengzi,Jijuntun and Xiloutian Formations in the Fushun Basin located in the mid-latitudes of the Northern Hemisphere.The Eocene Guchengzi Formation(54.51–47.8 Ma)and Jijuntun Formation(47.8–41.2 Ma)in the Fushun Basin were found to have been deposited under a humid climate.The lower(41.2–40.1 Ma)and upper(40.1–37.8 Ma)parts of the Xiloutian Formation were character-ized by semiarid and semihumid–semiarid climates,respec-tively,which is very similar to the paleoclimatic information reflected by organic carbon isotopes.The Eocene Thermal Maximum 2(ETM2,~53.7 Ma),Early Eocene Climatic Optimum(EECO,~53.1–46.5 Ma),Eocene Thermal Maxi-mum 3(ETM 3,~52.8 Ma),and Middle Eocene Climatic Optimum(MECO,~40.7–40.1 Ma)events significantly enhanced chemical weathering during these periods.The rapid increase in pCO_(2)concentration leads to an increase in temperature,precipitation,and surface runoff,exhibiting strong chemical weathering.The mean annual temperature(MATa)and mean annual precipitation(MAPa,MAPb,and MAPc)were estimated using parameters,such as the corrosion index without potassium(CIA-K),CaO/Al_(2)O_(3),and(Na_(2)O+K_(2)O)/Al_(2)O_(3).Comparing MAPa,MAPb,and MAPc with the MAP estimated using pollen data,MAPa and MAPb were found to be more sensitive to the climate during high precipitation periods(precipitation>1000 mm,Guchengzi Formation),and the recovered average precipi-tation was similar to MAP.In contrast,MAPc was more sensitive to the climate during low precipitation periods(precipitation<1000 mm,Jijuntun,and Xiloutian Forma-tions),with higher accuracy.To fully consider the influence of soluble inorganic salts Ca^(2+)and Na^(+),multivariate linear equations of CIA-K and CaO/Al_(2)O_(3)with CIA,and CIA-K and CaO/Al_(2)O_(3)with MAP were constructed,namely MAPd and MAPe.The results show that MAPe has the highest per-formance and can be effectively used to estimate the change of paleoprecipitation in Northeast Asia.

Distribution and geochemical significance of alkylbenzenes for crude oil with different depositional environments and thermal maturities

A total of 45 alkylbenzenes were detected and identified in crude oils with different depositional environments and thermal maturities from the Tarim Basin,Beibuwan Basin,and Songliao Basin using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry(GC×GCTOFMS).By analyzing the distribution characteristics of C0-C5alkylbenzenes,it is found that the content of some alkylbenzenes varies greatly in crude oils.Based on the distribution characteristics of 1,2,4,5-tetramethylbenzene(Te MB)and 1,2,3,4-Te MB,the ratio of 1,2,4,5-Te MB to 1,2,3,4-Te MB is proposed to indicate the organic matter origin and depositional environment of ancient sediments.Oil samples originated mainly from lower hydrobiont,algae,bacteria and source rocks deposited under reducing/anoxic conditions have low 1,2,4,5-/1,2,3,4-Te MB values(less than 0.6),while oil samples originated mainly from terrestrial higher plants and source rocks deposited under oxic/sub-oxic conditions have higher 1,2,4,5-/1,2,3,4-Te MB values(greater than 1.0).The significant difference of 1,2,4,5-/1,2,3,4-Te MB values is controlled by 1,2,4,5-Te MB content.1,2,4,5-Te MB content in oils derived from source rocks deposited in oxidized sedimentary environment(greater than 1.0 mg/g whole oil)is higher than that in oils from source rocks deposited in reduced sedimentary environment(less than 1.0 mg/g whole oil).1,2,4,5-/1,2,3,4-Te MB ratio might not or slightly be affected by evaporative fractionation,biodegradation and thermal maturity.1,2,4,5-/1,2,3,4-Te MB ratio and 1,2,4,5-Te MB content can be used as supplementary parameter for the identification of sedimentary environment and organic matter input.It should be noted that compared to the identification of organic matter sources,the 1,2,4,5-/1,2,3,4-Te MB parameter is more effective in identifying sedimentary environments.

Geochemical records of phosphorus in Jiaozhou Bay sediments—Impli-cations for environmental changes in recent hundred years

Phosphorus is a key element and plays an important role in global biogeochemical cycles. The evolution of sedimentary environment is also influenced by phosphorus concentrations and fractions as well as phosphate sorption characteristics of the marine sediments. The geochemical characteristics of phosphorus and their environmental records were presented in Jiaozhou Bay sediments. Profiles of different forms of phosphorus were measured as well as the roles and vertical distributions of phosphorus forms in response to sedimentary environment changes were investigated. The results showed that inorganic phosphorus （IP） was the major fraction of total phosphorus （TP）; phosphorus which is bound to calcium, iron and occluded phosphorus, as well as the exchangeable phosphorus were the main forms of IP, especially calcium - phosphorus, including detrital carbonate-bound phosphorus （Det- P） and authigenic apatite-bound phosphorus （ACa- P）, are the uppermost constituent of IP in Jiaozhou Bay sediments. Moreover, the lead-210 chronology technology was employed to estimate how much phosphorus was buried ultimately in sediments. And the research showed that the impacts of human activities have increased remarkably in recent years especially between the 1980s and 2000. According to research, the development of Jiaozhou Bay environment in the past hundred years can be divided into three stages ： （ 1 ） before the 1980s characterized by the relatively low sedimentation rate, weak land-derived phosphorus inputs and low anthropogenic impacts; （2） from the 1980s to around 2000, accelerating in the 1990s, during which high sedimentation rates, high phosphorus abundance and burial fluxes due to the severe human activities impacted on the whole environmental system ; （ 3 ） after 2000, the period of the improvement of environment, the whole system has been improved including the decreasing sedimentation rates, concentration and the burial fluxes of phosphorus.

Geochemical Characteristics of the Upper Permian Longtan Formation from Northeastern Sichuan Basin:Implications for the Depositional Environment and Organic Matter Enrichment

A set of organic-rich shales of the upper Permian Longtan Formation,which is widely developed in the northeastern part of the Sichuan Basin,is a key formation for the next step of exploration and development.At present,most studies on this set of formations have focused on the reservoir characteristics and reservoir formation mechanism of the shales,and basic studies on the palaeoenvironment and organic matter(OM)enrichment mechanism have not been fully carried out.In this paper,we recovered the sedimentary palaeoenvironment by mineralogical,elemental geochemical and organic geochemical analyses,and explored the enrichment mechanism of OM under the constraints of palaeoenvironmental evolution.The shales can be divided into two stages of sedimentary evolution:compared with the shales of the Lower Longtan Formation,the shales of the Upper Longtan Formation are relatively rich in quartz,poor in clay and carbonate minerals,and the OM type changes from typeⅢto typeⅡ_(2).The depositional environment has undergone a change from sea level rise,from warm and wet climate to dry and cold climate,and from oxygen-poor condition restricted to open reduction environment;the land source input has decreased,the siliceous mineral content has increased,the biological productivity has improved,and the deposition rate has changed from high to low.A depositional model was established for the shales of the Longtan Formation,reflecting the differential reservoir formation pattern of organic matter.For the Lower Longtan Formation shales,the most important factors controlling OM content are terrestrial source input and deposition rate,followed by paleoclimate and paleooxygen conditions.For the Upper Longtan Formation shales,the most important controlling factor is paleo-productivity,followed by sedimentation rate.The depositional model constructed for the Upper and Lower Longtan Formation shales can reproduce the enrichment of organic matter and provide a basis for later exploration and development.

Geochemical and Environmental Evaluation of Um Shashoba Gold Mine Area,Southeastern Desert,Egypt

A suite of elements（Ag,Au,Ba,Bi,Cd,Co,Cr,Cu,Ga,Hf,Hg,Mn,Mo,Ni,Pb,Rb,Sb,Se, Sr,Te and Zn）,total organic carbon（TOC）and pH were analyzed in stream sediment and tailing samples from Um Shashoba area,in order to evaluate Au placer and the sediments being impacted by old mining activities.Analytical results were examined using statistical,graphical and mapping methods.In spite of the results revealing that Au and most of the elements in sediments were in general significantly lower than those in tailing,Au was concentrated in the NE and SW parts forming Au placer.It is remarkably a close association of Au with Hg and Sb;both are useful as pathfinder elements for Au placers.Values of pH could not control a fate of analyzed elements,whereas TOC and Mn oxides and hydroxides could uptake some elements Au,Ba,Co,Cr,Hg,Ni,and Sr.The results also indicated that the sediments were contaminated by anthropogenic factors causing moderate,strong to very strong pollution with respect to Bi,Se and Te,respectively.Additionally,geogenic factors could also contribute elemental enrichment to the drainage system and cause significant toxicity level.

Geochemical characteristics of the Xuanwei Formation in West Guizhou:Significance of sedimentary environment and mineralization

The Upper Permian Xuanwei Formation widely occurs in western Guizhou,unconformably overlying the Emeishan basalts,and mainly consists of black shales.It is～170 m thick at Cuyudong Village,Weining County,West Guizhou,China,where the samples of black shale and sandy shale were collected and analyzed.The shales mainly contain SiO2,18.9%?44.1%,Al2O3,14.8%?52.8%,Fe2O3,1.0%?41.2%,LOI,3.2%?21.1%,TiO2,1.0%-6.7%,and MgO,0.2%?2.5%.The contents of all other major elements are lower than 1.0%.It is shown that the black shales have higher contents of Fe2O3 and LOI than normal shales.The siderites occurred in the black shales with higher contents of Fe2O3,which may be attributed to hydrothermal activities on seafloor.All analyzed shale samples have extremely high Ga,47.8×10-6-109.9×10-6(70.5×10-6 on average),higher than the industrial mining standard of Ga Resource Industry Standard.The total contents of rare-earth elements(REE) of 9 black shale samples vary from 213×10-6 to 1460×10-6,suggesting that these black shales are enriched in REE.The shale-normalized REE patterns display both positive and negative Ce anomalies(Ce/Ce* from 0.5 to 1.7),revealing that the Xuanwei shales were precipitated under oxic and anoxic conditions.The Rb-Sr chronological diagram of 6 shale samples in the Xuanwei Formation shows an age of 255±12 Ma.Strontium isotopic ratios(87Sr/86Sr)t0 range from 0.70635 to 0.70711,suggesting that these Xuanwei black shales might be derived from chemical weathering of the Emeishan basalts.

Geochemical Indication of Sinian Bedded Siliceous Rocks in the Hunan-Guizhou-Guangxi Area and Their Environmental Significance

: In the Hunan-Guizhou-Guangxi area there have developed very thick bedded siliceous rocks of the late Sinian. The rocks have a fairly pure composition, with an average content of siliceous minerals exceeding 95%. They are relatively rich in Fe and Mn, and poor in Al, Ti and Mg. The Fe/Ti, (Fe+Mn)/Ti, Al/(Al+Fe+Mn) and U/Th ratios and the Al-Fe-Mn and Fe-Mn-(Ni+Co+Cu)×10 triangle diagrams all show that they are hydrothermal sedimentary siliceous rocks. In the rocks the total amount of REEs is low, the δCe shows an obvious negative anomaly and the δEu a weak anomaly, and LREE>HREE, all indicating that they are products of hydrothermal processes. The δ30Si and δ18O values, as well as the formation temperature of the rocks all clearly show that the silica forming the rocks comes from hot water. Besides, analyses of the depositional environment of the rocks using the MnO/TiO2 ratio and the δCe and δ30Si values yield the same conclusion that they are formed in environments from continental marginal slopes of a bathyal environment to oceanic basins of a deep-sea environment.

Amelioration of the biogeochemical environment with iodine in kelp

An artificial way to prevent and cure the iodine deficiency disorder(IDD) through ameliorating the biogeochemical environment of the regions where iodine is deficient was put forward. In this paper, the concrete method to achieve this way was given and its feasibility is confirmed by test.

Geochemical characteristics of the Permian marine mudstone and constraints on its provenance and paleoenvironment in the Fenghai area,Fujian Province, southeastern China

Permian marine strata have gradually become a research focus in the world.The marine strata of the Late Permian Dalong Formation(P3d)in the Fenghai area,Fujian Province,have become more and more important as their geochemical characteristics record important geological information and are a good indicator for recovering and reconstructing the paleosedimentary environments and tectonic attributes.The major elements,trace elements and rare earth elements were analyzed by XRF and ICP-MS,respectively.Based on the results of detailed field geological surveys,profile measurements as well as typical sample collection,the tectonic setting and provenance of Permian marine mudstone were comprehensively discussed.The results showed that the Dalong Formation(P3d)was deposited in an active continental margin tectonic environment as revealed by the relation between Fe2O3 + MgO and TiO2 and Al2O3/SiO2.The fingerprint characteristics of Mn,Fe,Co,Ni and REE and the ratio of U/Th,V/Cr,Sr/Ba,(La/Yb)N and V/(V +Ni)indicated that the sedimentary provenance was mainly derived from potassium feldspar,followed by muscovite.Sedimentary water bodies showed a gradually decreasing depositional rate trend,water depth gradually shallowing and paleo-salinity and productivity gradually increasing.Moreover,since transient delamination occurred during sedimentary processes,sedimentary water bodies showed obvious neritic characteristics.It was consistent with the results revealed by lithological and geochemical characteristics.Calcareous mudstone and siltstone transitioned into fine sandstone from bottom to top,indicating paleo-water bodies became shallow.The research results provided good reference and guidance for understanding Permian paleo-sedimentary environments and tectonic attributes of the Yong’an area,Fujian Province,southeastern China.

Environmental geochemical features of arsenic in soil in China

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GEOCHEMICAL CHARACTERISTICS OF SEDIMENTS AND ANALYSIS OF THE CHANGJIANG ESTUARY ENVIRONMENT

Analysis of material from three 55- cm long cores collected with box corer m summer of 1988 in the Changjiang Estuary region yielded data on the sedimentation rate, granulometric composition and contents of carbonates, organic matter, Al, Fe, Mn, Zn, Cu and Pb there. Subsequent study of the data led to the conclusion that there is no obvious pollution in the region based on the absolute value of the content of heavy metals, but the region is in potential danger of being polluted as seen by the obvious increase of sedimentation flux of heavy metals to and the enrichment of them on the surface sediment during the last several years, e.g. Pb increased by 10-20μg/g, Zn by about 30μg/g, Cu by 5-10μg/g and Mn by 150μg/g.A ferromanganese redox interface was found at about 40 cm depth of sediments where Fe and Mn and associated trace metals are enriched. The trace metals such as Zn, Cu have (but Pb does not) the same source, forms, displacement mechanism and geochemical behaviours as those of Fe and Mn in

GEOCHEMICAL CHARACTERISTICS OF GRANITES AND ITS STRUCTURAL GENETIC ENVIRONMENT IN THE NANDAN-HECHI METALLOGENETIC BELT, NORTHWEST GUANGXI

The Nandan-Hechi metallogenetic belt is the most important tin-polymetallic producing district in China, and is the location of the Dachang super-large tin deposit. Based on the detailed field investigation and isotopic data, the stages of magmatic activity in the Nandan-Hechi metallogenetic belt have been lined out in this paper. Through the study about the geochemical characteristics of different granites, and by using ω(Al2O3)-ω(SiO2), ω(TFeO)/[ω(TFeO)+ω(MgO)]-ω(SiO2), AFM, ACF and Rb-Yb+Ta, Rb-Y+Nb, Ta-Yb, Nb-Y discrimination diagrams in combination with regional geological setting analysis, the authors carried out analyses about the structural environment for the formation of the granites, and discussed the structural environment and dynamic setting for the large scale mineralization in this area. Our study indicates that the majority of the granites in Nandan-Hechi metallogenetic belt belong to the POG type, while the later stage alaskite belongs to the RRG+CEUG type. The granites were formed at the stage of structural transformation from postorogenic phase to intraplate setting. But the major structural environment is characterized by steady regional extension. The formation age for the granites coincides with the time for this transformation, and this translation environment is favored for large-scale metallogenesis.

Depositional Environments of Bedded Chens in Western Yunnan Segment of Paleo－Tethys， China： a Geochemical Approach

Differences in rare earth elements and other trace elements in bedded chens reflect the deposihonal settings of the sediments. Based on cerium anomaly (Ce/Ce ), total REE (ΣREE) and other trace element abundance variahons preserved in the bedded cherts in the Paleo-Tethys, Western Yunnan, three deposihonal regimes can be recotwzed: spreading ridge proximal, ocean-basin floor and conhnental margin. This geochemical method of discriminating deposihonal environments for thine marine sedimentary rocks which are physically indistinct provides a powerful new tool for paleotectonic and paleogeographic recondruchons.

Comprehensive geochemical identification of highly evolved marine hydrocarbon source rocks: Organic matter, paleoenvironment and development of effective hydrocarbon source rocks

This study analyzed the developing environments of hydrocarbon source rocks in the Ordos Basin and evaluated carbonate rocks as hydrocarbon source rocks and their distributions on account of the fact that China’s marine carbonate rocks as hydrocarbon source rocks are characterized by the intensive thermal evolution and relatively low abundance of organic matter, by taking the Lower Paleozoic of the Ordos Basin for example and in light of the calculated enrichment coefficients of trace elements, the profile analysis of trace element contents, ratios of relevant elements, and stable isotopic compositions and their three-dimensional diagrammatization in combination with the necessary organic parameters. As for the Ordos Basin, TOC=0.2% is an important boundary value. Studies have shown that in the strata TOC>0.2%, V/(V+Ni)>0.50, Zr/Rb<2, Rb/K(×104)>30, Z>122, Th/U>0.80, Zn and Mo are enriched with a positive δ13Ccarb excursion. All these indicated a stagnant and stratified sedimentary environment that has low energy, anoxia and high salinity in bottom water. In these strata the geological conditions are good for the preservation of organic matter, hence favoring the development of hydrocarbon source rocks. These strata have δ13Corg<-28‰ (Ⅰ- Ⅱ type) and high hydrocarbon-generated potential. The Klimory and Wulalik formations show certain regularities in those aspects, therefore, they can be regarded as the potential effective hydrocarbon source rocks. In the strata TOC≤0.2%, Zr/Rb>1, V/(V+Ni)<0.50, Rb/K<30, Th/U<0.80, Cu, Zn, etc are depleted, and δ13Corg values range from -24‰ to -28‰. All these facts showed that most of the carbonate rocks or mudstones were formed in high-energy oxidizing environments, thus unfavorable to the development of hydrocarbon source rocks. It is feasible to make use of the geochemical method to comprehensively assess the highly evolved marine carbonates rocks as potential hydrocarbon source rocks and their distributions.

PEAT GEOCHEMICAL MONITORING FORENVIRONMENTAL CHANGES

High peat is a good message carrier of atmospheric geochemical environment .The distribution of heavy metals monitored in vertical vertion of high peat is the reflection of sequence atmospheric chemical composition. It can record and remain thenatural geochemical background of the atmosphere. The changes of heavy metal contets in sections of the Da Hinggan Mountainsmanifest that the influence of human human on atmosphere is continuously becoming heavier. Compared with other areas inEurasia, the atmospheric geochemical anomaly of this area is not obvious. By monitoring high peats in different geographic areas,the character of anthropologic geochemical anomaly in atmosphere could be ascertained.

Geochemical characteristics and sedimentary environment of the Middle Devonian organic-rich shales in the Northwest of Guizhong Depression, Southwest China

In order to figure out the redox conditions and paleo-sedimentary environment of the Middle Devonian shales in the northwest of Guizhong Depression,the trace element analysis was conducted on the Middle Devonian cores(320.35–938.50 m)of the typical shale gas investigation well(GY-1)at a 1.50 m sampling interval through X-ray fluorescence spectroscopy(XRF)and inductively coupled plasma mass spectrometry(ICP-MS).According to the test result,the average values of V/(V+Ni),V/Cr and Ni/Co in Nabiao formation(Fm.)are larger than 0.67,4.65 and 7.71 respectively,and Nabiao Fm.is rich in biological assemblages such as tabasheer,ammonite,etc.These evidences indicate the rising sea level rose relatively in the sedimentation period of Nabiao Fm.and a deepwater shelf environment,which was favorable for the preservation of organic matters.The V/(V+Ni),V/Cr and Ni/Co in Luofu Fm.and Tangting Fm.are 0.38–0.65,0.73–4.10 and 3.70–6.72 respectively,indicating that the sea level dropped relatively in their sedimentation period,during which the water bodies became shallow,and the sedimentary environment was a weak oxidizing shallow water shelf environment.In addition,the variation of TOC has a high correlation with the enrichment degree of Ba element,indicating the favorable conditions for the enrichment and preservation of organic matters under an oxygen-deficient environment.Moreover,according to the identification of trace element indexes,the northwest of Guizhong Depression experienced the sedimentary cycle of relative rise to relative fall of sea level from bottom to top in the Middle Devonian sedimentation period.The relative sea level rose to the highest in the sedimentation period of Nabiao Fm.,in which the organic-rich shales with stable thickness and high organic content were deposited.Hence,the Nabiao Fm.could be regarded as the favorable exploration target interval in this area.

Geochemical characteristics of illite clay rocks from the Shihezi Formation in the Hanxing mining area and its sedimentary environment

We studied the geochemical characteristics of illite clay rocks and their importance from the 5hihezi Formation of Late Permian in the Hanxing mining area by means of ICP-M5 and sequential X-ray fluorescence spectrometry. The results show that the amount of SiO2 is between 53.37% and 61.58% （by weight） and that of Al2O3 22.40% and 31.31% （by weight）. The ratio of SiO2/Al2O3 lies between 1.71 and 2.75. The amount of K2O ranges from 1.11% to 2.56% （by weight）. The amounts of Fe and Ti are higher than the theoretical values in illite clay rock would indicate. The amounts of some trace elements, such as Ga, As, Ba, Cu, Th and U are higher than their Clark values, while that of another 23 trace elements are found to be dose to their Clark values. The amounts of REE range from 22.59 to 570.54 μg/g, with an average of 163.23μg/g. The ratios of LREE/HREE range from 5.41 to 21.82, with an average of 8.87. These characteristics show that LREE are much richer in content than HREE. The REE distribution patterns of our samples were characterized by clearly negative Ce and Eu anomalies. We analyzed the sedimentary environment of the Hanxing mining area in Late Permian by the characteristic element ratio method. The ratios of Mn/Fe range from 0 to 0.0168, which are lower than those in a marine sedimentary environment. The ratios of Sr/Ba （0.20-0.41） are less than 1. These are all indications that the sediments of the Hanxing mining area in Late Permian form largely a continental sedimentary environment. The sedimentary water is freshwater, a conclusion reached on the basis of the ratios of Th/U （2.66-6.62） and of Ca/（Ca ＋ Fe） （0.01-0.059）; the average ratio of Fe2＋/Fe3＋ is 4.8. The sedimentary water condition is weakly acidic and weakly oxidative-weakly reductive, a conclusion reached on the basis of ratios of Fe2＋/Fe3＋ （4.8） and of Ceanom （-0.08）.

Geochemical migration of arsenic and its environmental efect

This paper presents the results of a field study regarding the transport and environmental fate of arsenic. Concentrations of arsenic and various forms of its compounds in rock, soil, river water, and river bottom deposits in an area near Hangzhou, China, were measured and analyzed. On the basis of these field data, the source and interface transfer of arsenic were discussed. A few very interesting findings were reported. This paper indicates that there was relatively low arsenic concentration in Jing Hang Canal, whereas, rather high arsenic concentration in the river bottom mud was found. The paper attributed this phenomenon to mechanism of arsenic deposition and absorption in the water column, the canal has a rather high self purification ability relative to the arsenic input.

The Mineral Geochemical Discrimination of the Calcite Crystals in the Pores of Upper Ordovician Limestone and Its Environmental Significance: Take Tazhong Oilfield of Tarim Basin for Example

Based on the analysis of the morphology, order, cathodoluminescence and microelement of the calcite crystals in the pores of Upper Ordovician limestone in Tazhong oilfield of Tarim Basin, this paper suggest that the calcite crystals can divided 11 kinds of cements into three stages, and confirms their cementation sequence characteristics and formation environment. First stage of the cementation occurred on the bottom of the diagenetic environment, the product of which mainly are microcrystalline, fine shape, radiation fibrous, fasciculation, radiation axis shape calcites and a ball-like aragonite, whose filling pore is 0%–30%; the second one occurred in the atmospheric fresh water environment, with main cement types of crescent or pendulous shape, vadose silt, hyperplasia of coaxial, the filling pore of which is 5%–100%; the third one occurred in a burial environment, the crystals of which are bright and thick, mainly coarse sparry and poikilitic calcite, with filling pore of 5%–5%. In this paper, influence from each stage of cementation on porosity is analyzed, and pore evolution is established.