Organic Matter Accumulation in the Upper Permian Dalong Formation from the Lower Yangtze Region,South China

The Late Permian was marked by a series of important geological events and widespread organic-rich black shale depositions,acting as important unconventional hydrocarbon source rocks.However,the mechanism of organic matter(OM)enrichment throughout this period is still controversial.Based on geochemical data,the marine redox conditions,paleogeographic and hydrographic environment,primary productivity,volcanism,and terrigenous input during the Late Permian in the Lower Yangtze region have been studied from the Putaoling section,Chaohu,to provide new insights into OM accumulation.Five Phases are distinguished based on the TOC and environmental variations.In Phase I,anoxic conditions driven by water restriction enhanced OM preservation.In Phase II,euxinic and cycling hydrological environments were the two most substantial controlling factors for the massive OM deposition.During Phase III,intensified terrestrial input potentially diluted the OM in sediment and the presence of oxygen in bottom water weakened the preservation condition.Phase IV was characterized by a relatively higher abundance of mercury(Hg)and TOC(peak at 16.98 wt%),indicating that enhanced volcanism potentially stimulated higher productivity and a euxinic environment.In Phase V,extremely lean OM was preserved as a result of terrestrial dilutions and decreasing primary productivity.Phases I,II and IV are characterized as the most prominent OM-rich zones due to the effective interactions of the controlling factors,namely paleogeographic,hydrographic environment,volcanism,and redox conditions.

A novel redox indicator based on relative abundances of C_(31) and C_(32) homohopanes in the Eocene lacustrine Dongying Depression, East China

A suite of oils and bitumens from the Eocene Shahejie Formation(Es) in Dongying Depression was geochemically characterized to illustrate impact of source input and redox conditions on distributions of pentacyclic terpanes. The Es_(4) developed under highly reducing, sulfidic hypersaline conditions, while Es_(3) formed under dysoxic, brackish to freshwater conditions. Oils derived from Es_(4) are enriched in C_(32) homohopanes(C_(32) H), while those from Es_(3) are prominently enriched in C_(31) homohopanes(C_(31) H). The C_(32) H/C_(31) H ratio shows positive correlation with homohopane index(HHI), gammacerane index, and negative correlation with pristane/phytane ratio, and can be used to evaluate oxic/anoxic conditions during deposition. High C32 H/C_(31) H ratio(> 0.8) is an important characteristic of oils derived from anoxic environments, while low values(< 0.8) indicate dysoxic conditions and extremely low values(< 0.4)indicate strong oxic conditions. The C_(32) H/C_(31) H ratio can be applied for deposition condition diagnosis because carboxyl group of C_(32) hopanoic acids might be reduced to C_(32) homohopanes under anoxic conditions, and oxidized to C_(31) homohopane under oxic conditions. Advantages to use C_(32) H/C_(31) H ratio as redox condition proxy compared to the HHI and gammacerane indexes are wider valid maturity range,less sensitive to biodegradation influence and better differentiating reducing from oxic environments.

The main controlling factors and developmental models of Oligocene source rocks in the Qiongdongnan Basin,northern South China Sea

Coals developed in the Oligocene Yacheng and Lingshui formations in the Qiongdongnan Basin have high organic matter abundance, and the dark mudstones in the two formations have reached a good source rock standard but with strong heterogeneity. Through the analysis of trace elements, organic macerals and biomarkers, it is indicated that plankton has made little contribution to Oligocene source rocks compared with the terrestrial higher plants. The organic matter preservation depends on hydrodynamics and the redox environment, and the former is the major factor in the study area. During the sedimentary period of the Yacheng Formation, tidal flats were developed in the central uplift zone, where the hydrodynamic conditions were weak and the input of terrestrial organic matter was abundant. So the Yacheng Salient of the central uplift zone is the most favorable area for the development of source rocks, followed by the central depression zone. During the sedimentary period of the Lingshui Formation, the organic matter input was sufficient in the central depression zone due to multiple sources of sediments. The semi-enclosed environment was favorable for organic matter accumulation, so high quality source rocks could be easily formed in this area, followed by the Yacheng salient of central uplift zone. Source rocks were less developed in the northern depression zone owing to poor preservation conditions,

用林帮的副反应思想处理氧化还原滴定分析

用林帮的副反应思想处理氧化还原滴定分析,得到了和络合滴定相似的滴定曲线方程和终点误差公式,在理论上和络合滴定达到了统一,使氧化还原滴定理论完善,内容精练,体系科学.

Geochemical assessment of upper Cretaceous crude oils from the Iranian part of the Persian Gulf Basin:Implications for thermal maturity,potential source rocks,and depositional setting

The Upper Cretaceous carbonate successions of the Sarvak Formation host giant oil reservoirs in the Persian Gulf.In this research,a total of 28 oil samples from nine oilfields located in the western,central and eastern parts of the Persian Gulf region were studied to determine the genetic relationships of oils,depositional setting of possible source rocks,thermal maturity,and source-rock ages in the Persian Gulf basin.According to the measured geochemical data,the source rocks facies vary from marine carbonates and marl/carbonates in the central and eastern oilfields to shale/carbonates in the western oilfields.The Pr/Ph ratio,steranes and terpanes suggest anoxic to dysoxic conditions of the depositional environments.The depositional environments experienced both low water stratification/low salinity and normal salinity/unstratified conditions.Evaluation of the saturated and aromatic biomarkers shows that all oil samples are mature and most of the source rocks lie within the beginning of the oil-generation window.The thermal maturity of the central oilfields is higher than that of the other samples,and has gone beyond the oil-generation stage.The C2s/C2g steranes ratio suggest that the central oilfelds of the Persian Gulf have Paleozoic and Jurassic source rocks,whereas the Sarvak reservoir in other parts of this region is sourced from Cretaceous carbonate rocks.

Exogenous-organic-matter-driven mobilization of groundwater arsenic

The potential release capacity of arsenic(As)from sediment was evaluated under a high level of exogenous organic matter(EOM)with both bioreactive and chemically reactive organic matters(OMs).The OMs were characterized by FI,HIX,BIX,and SUVA254 fluorescence indices showing the biological activities were kept at a high level during the experimental period.At the genus level,Fe/Mn/As-reducing bacteria(Geobacter,Pseudomonas,Bacillus,and Clostridium)and bacteria(Paenibacillus,Acidovorax,Delftia,and Sphingomonas)that can participate in metabolic transformation using EOM were identified.The reducing condition occurs which promoted As,Fe,and Mn releases at very high concentrations of OM.However,As release increased during the first 15-20 days,followed by a decline contributed by secondary iron precipitation.The degree of As release may be limited by the reactivity of Fe(hydro)oxides.The EOM infiltration enhances As and Mn releases in aqueous conditions causing the risk of groundwater pollution,which could occur in specific sites such as landfills,petrochemical sites,and managed aquifer recharge projects.

Origin and geochemical characterization of the glauconites in the Upper Cretaceous Lameta Formation, Narmada Basin, central India

This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.

Variation of iron species in sliding mud

Results of Mossbauer spectroscopy and ICP-AES measurement revealed a special distribution pattern of iron species in four crossing profiles of the Tertiary Formation Type of Landslides in Japan. In comparison with host rocks, the sliding mud in the landslide slip zone contains the higher ferrous iron content and/or trace pyrite, which indicates that the forming environment was relatively reducing. The total iron content also increased with an increase in ferric iron and pyrite, in contrast, decreased with an increase in ferrous iron content. The deep-gray and black mud layers formed and accumulated in various volumes within landslide slip zones are treated as the basic criteria for the slipping activity, because the soft mud saturated with groundwater is easy to create a plastic deformation.

Paleo-Environment Reconstruction of the Middle Permian Lucaogou Formation,Southeastern Junggar Basin,NW China:Implications for the Mechanism of Organic Matter Enrichment in Ancient Lake

The Middle Permian Lucaogou Formation is the source rock and the main oil shale producing formation in the southeastern Junggar Basin.This study focused on the Lucaogou Formation exposed in two outcrop sections on the northern flank of the Bogda Mountain,namely the Jingjingzigou and Dalongkou sections.Here,we present integrated analysis of the sedimentology,major and trace elements,mineral components and total organic carbon contents.The paleo-environment was reconstructed including provenance,redox conditions,paleo-salinity,chemical weathering intensity and primary organic matter productivity.The results showed that the upper and lower units were deposited in distinct depositional environments with different organic matter accumulation mechanisms.The lower unit was characterized by low lake level,dry climate,fresh-brackish and well-oxygenated water.While during the deposition of the upper unit the lake level rose,climate turned wetter and the bottom water became less oxidized and much saltier.The mechanism of the organic matter accumulation is different for these two units.The preserved organic matters were mainly controlled by the primary productivity in the lower unit and by the redox conditions in the upper unit.

Lithofacies distribution characteristics and its controlling factors of shale in Wufeng Formation-Member 1 of Longmaxi Formation in the Jiaoshiba area

It is essential to investigate shale lithofacies distribution and controlling factor of the shale for geological evaluation of shale gas exploration and development.Through comprehensive analysis of cores,thin sections,cathode luminescence,whole-rock X-ray diffraction,element capture spectroscopy,major/trace element and other data,three major types and eight sub-type shale lithofacies in the shale of Wufeng Formation-Member 1 of Longmaxi Formation in Jiaoshiba area are identified by the three-end-member method and shale lithological classification nomenclature,and the spatiotemporal distribution law and main development controlling factors of shale lithofacies are well studied.In the Jiaoshiba area,vertically,the marine shale develops siliceous shale,mixed shale and argillaceous shale from bottom to top.Besides,lateral distribution of the shale is different from north to south;the shale lithofacies in the north area changes rapidly,the mixed shale in the north area is much thicker than that in the south area,while the siliceous shale in the south area is relatively thicker.Difference in the shale lithofacies is controlled by special sedimentary geologic events;development of the siliceous shale is controlled by the Ordovician-Silurian global volcanic event to some extent,while the mixed shale is significantly influenced by effect of bottom current,and the argillaceous shale is mainly affected by supply of terrestrial clastic material.

Depositional environment of shale in Wufeng and Longmaxi Formations, Sichuan Basin

Formation of organic-rich shale was controlled by depositional processes and environment condition.According to petrology,mineralogy,fossil composition and sedimentary structure,seven lithofacies of shale were identified in the Wufeng Formation to Longmaxi Formation,e.g.,siliceous shale,silty shale,argillaceous shale,calcareous shale,shell-bearing argillaceous limestone/calcareous mudstone,siltstonefine sandstone and bentonite.For shale in the Wufeng and Longmaxi Formations,the depositional mode was not only the suspension deposition under the low-energy hydrodynamic condition,but also the biogenic deposition,the storm deposition and the bottom current deposition indicated by large amount of siliceous biological fossils,biological detritus with size graded structure,silt laminations,lenticular bedding,ripple cross-bedding and other sedimentary structures.Trace element analysis suggested that the siliceous shale in theWufeng Formation and the lower part of Longmaxi Formation was developed in the oxygen-dysoxic/anoxic depositional environment,which was rich in organic matters;then due to influence of the sea level gradually decline and bottom current,the silty and argillaceous shales were formed,and the oxygen-dysoxic/anoxic depositional environment was destroyed,gradually leading to the worse preservation condition of organic matter.

Effects of sulfate-reducing bacteria on methylmercury at the sediment–water interface

Sediment cores（containing sediment and overlying water） from Baihua Reservoir（SW China）were cultured under different redox conditions with different microbial activities, to understand the effects of sulfate-reducing bacteria（SRB） on mercury（Hg） methylation at sediment–water interfaces. Concentrations of dissolved methyl mercury（DMe Hg） in the overlying water of the control cores with bioactivity maintained（BAC） and cores with only sulfate-reducing bacteria inhibited（SRBI） and bacteria fully inhibited（BACI） were measured at the anaerobic stage followed by the aerobic stage. For the BAC and SRBI cores, DMe Hg concentrations in waters were much higher at the anaerobic stage than those at the aerobic stage, and they were negatively correlated to the dissolved oxygen concentrations（r =- 0.5311 and r =- 0.4977 for BAC and SRBI, respectively）. The water DMe Hg concentrations of the SRBI cores were 50% lower than those of the BAC cores, indicating that the SRB is of great importance in Hg methylation in sediment–water systems, but there should be other microbes such as iron-reducing bacteria and those containing specific gene cluster（hgc AB）, besides SRB,causing Hg methylation in the sediment–water system.

Microfossil Assemblages and Indication of the Source and Preservation Pattern of Organic Matter from the Early Cambrian in South China

The beginning of the Phanerozoic was marked by abundant phytoplankton,the occurrence of animals and a newly established ecosystem structure,which in turn,resulted in different modes of organic matter(OM)cycling and preservation.In this study,we present an integrated paleontological and geochemical study of the Lower Cambrian Yanjiahe and Shuijingtuo formations in the Three Gorges area,South China.Rock samples were analyzed for major and trace elements,in order to evaluate the marine productivity.Fossil samples were recovered using palynological methods,destructive analytical techniques,SEM analysis and thin section microscopy.The organic-walled microfossils in the investigated sections include marine microphytoplankton,linings of sponge spicules,small shelly fossils and some unnamed sheet-like and net-like microfossils(animal parts).Additionally,fecal structures and coprolites fossils were found.Three intervals in the Luojiacun Section were proposed to discuss the links among microfossil assemblages and their influence on OM cycling and preservation.We found that the marine microphytoplankton was the main source of OM in the investigated sections.The appearance of fecal structures groups and massive appearance of animals in the pelagic zone indicate a higher transfer efficiency of OM aggregates through the water column.Oxygenated conditions in the water-column would have led to a moderate to low preservation of OM,an effect which would have been further enhanced by the potential presence of bioturbators.Overall,our study reveals the contribution of various organisms to the sedimentary OM and highlights the links and feedbacks among microfossil assemblages,OM recycling efficiency and OM preservation in the tipping point of the Phanerozoic“new world”.

Flooding impact on the distribution of microbial tetraether lipids in paddy rice soil in China

Isoprenoid and branched glycerol dialkyl glycerol tetraethers （GDGTs） lipids were studied in flooded and non-flooded paddy soil in Wuhan, central China, to examine the response of the GDGTs distribution to the soil flooding. Samples were collected before and after the soil flooding in four specific months. Both core （CL） and intact polar （IPL） GDGTs were quantified. Increase in the abundance of archaeol and caldarchaeol may be indicative of the occurrence of methanogens in the flooded soil. A negative correlation was observed between the ratio of IPL branched GDGT-IIa to GDGT-Ia and the soil pH. The rise of the soil pH in the acid soil is known to be controlled by the redox conditions resulting from flooding. Thus, the branched GDGTs distribution may be controlled by the water content in the paddy soil. In addition, we suggest that the anoxic conditions resulting from flooding may also control the abundance of branched GDGTs relative to crenarchaeol, which in turn results in the increase of branched and isoprenoidal tetraethers （BIT） values, the index for the terrestrial input to the marine sediments.