Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge:evidence from sulfide chronology

The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.

New discovery of seafloor hydrothermal activity on the Indian Ocean Carlsberg Ridge and Southern North Atlantic Ridge-progress during the 26th Chinese COMRA cruise

The 26th Chinese COMRA （China Ocean Mineral Resources Research ＆ Development Association） cruise was an important cruise. The Carlsberg Ridge （CR） of the Northwest Indian Ocean and the North Atlantic Ridge （NAR）, in which less investigation has been carried out for hydrothermal activities, were investigated and studied during the first two legs of the 26th COMRA cruise. During the first leg, we found one hydrother- mal activity field located in the CR at 3.5^-3.8~ N on the Northwest Indian Ocean Ridge （NWIR）, and sampled seafloor polymetallic sulfide deposits where only abnormalities were found before. During the second leg, we found a new hydrothermal anomaly field located in the NAR at 4^-7~N. The discovery of two hydrother- real and anomaly fields filled in the gap of hydrothermal investigation and study in the corresponding re- ~ions for China.

Heat and mass flux estimation of modern seafloor hydrothermal activity

Research on heat and mass flux yielded by modern seafloor hydrothermal activity is very important, because it is involved not only in the base of ocean environment research, but also in the historical evolution of seawater properties. Currently, estimating heat flux is based on the observation data of hydrothermal smokers, low-temperature diffusive flow and mid-ocean ridge mainly. But there are some faults, for example, there is lack of a concurrent conductive item in estimating the heat flux by smokers and the error between the half-space cooling model and the observation data is too large. So, three kinds of methods are applied to re-estimating the heat flux of hydrothermal activity resepectively, corresponding estimation is 97. 359 GW by hydrothermal smoker and diffusive flow, 84.895 GW by hydrothermal plume, and 4. 11 TW by exponential attenuation method put forward by this paper. Research on mass flux estimation is relatively rare, the main reason for this is insufficient field observation data. Mass fluxes of different elements are calculated using hydrothermal vent fluid data from the TAG hydrothermal area on the Mid-Atlantic Ridge for the first time. Difference of estimations by different methods reflects the researching extent of hydrothermal activity, and systematically in - situ observation will help to estimate the contribution of hydrothermal activity to ocean chemical environment, ocean circulation and global climate precisely.

Quantifying the influence of magmatism and tectonism on ultraslow-spreading-ridge hydrothermal activity:Evidence from the Southwest Indian Ridge

Hydrothermal activity in mid-ocean ridges(MORs)is an important intermediary for the mass and heat exchange between the ocean and lithosphere.The development of hydrothermal activity on MORs is primarily controlled by coupled magmatic and tectonic activities.In ultraslow-spreading ridges,deepdipping low-angle normal faults with large offsets,typically detachment faults in the inside corners of ridge offsets,favor the formation of tectonic-related hydrothermal activities,whereas volcanic-related hydrothermal fields are typically developed in neovolcanic zones in this category of the ridge system.However,whether tectonic or magmatic activity is dominant and to what extent they control the formation of hydrothermal activities on ultraslow-spreading ridges remain unclear.Segments in the west and east of the Gallieni transform fault(TF)located in the ultraslow-spreading Southwest Indian Ridge(SWIR),namely,western area(WA)and eastern area(EA),exhibit distinct magma-supply conditions that provide favorable conditions for examining the influence of magmatic and tectonic activities.We generated prediction models for these areas using the spatial analysis of the water depth,minor faults,large faults,ridge axis,nontransform discontinuity(NTD)inside corners,TF inside corners,Bouguer gravity anomaly,magnetic anomalies,and seismic activities.By employing the weights of evidence method,we reported that the formation of seafloor hydrothermal systems in SWIR was primarily correlated to the NTD inside corner,ridge axis,and minor fault(i.e.,contrast values(C)of 4.186,3.727,and 3.482 in WA and 4.278,3.769,and 3.135 in EA).Furthermore,EA was significantly affected by the TF inside corner(C=3.501),whereas WA was influenced by large faults(C=4.062).Our results demonstrated that tectonism was the primary controlling factor in the development of hydrothermal activities in the study area,and the contribution of magmatism was secondary,even in WA,which has a relatively robust magma supply.We delimited prominent prospecting areas at each side based on posterior probability.Our results provided insights into the formation mechanisms of hydrothermal activities and support prospecting in MORs.

Sonocatalytic activity of LuFeO_3 crystallites synthesized via a hydrothermal route

LuFeO3 crystallites of different sizes and morphologies were synthesized via a hydrothermal route. The sonocatalytic properties of the as-synthesized samples were investigated by degrading various organic dyes, including acid orange 7 （AOT）, rhodamine B （RhB）, methyl orange （MO）, and methylene blue （MB）, under ultrasonic irradiation, revealing that they exhibit excellent sonocatalytic activity toward the degradation of these dyes. Particularly, the synthesized bar-like particles with lengths of-3 μm and widths of-1μm have the highest sonocatalytic activity, and the degradation percentage of AO7 reaches 89% after 30 min of sonocatalysis. The effects of inorganic anions such as CI-, NO3-, SO42-, PO43-, and HCO3- on the sonocatalysis efficiency were investigated. Hydroxyl radicals （·OH） detected by fiuorimetry using terephthalic acid as a probe molecule were found to be produced over the ultrasonic-irradiated LuFeO3 particles. The addition of ethanol, which acts as a· OH scavenger, leads to quenching of ＂OH radicals and a simultaneous decrease in the dye degrada- tion. This suggests that ＂OH is the dominant active species responsible for the dye degradation.

Sedimentary paleoenvironment and its control on organic matter enrichment in the Mesoproterozoic hydrocarbon source rocks in the Ordos Basin,southern margin of the North China Craton

The black shale of the Mesoproterozoic Cuizhuang Formation in the Changcheng System in Yongji city,North China Craton,is a potential source rock.Understanding the organic matter enrichment mechanism is crucial for evaluating source rock resources and understanding oil and gas accumulation mechanisms.In this study,we evaluated the sedimentary paleoenvironment and organic matter enrichment mechanisms of shale using thin section observations,mineral composition analysis,organic geochemistry,and elemental geochemistry.We found significant differences in the sedimentary paleoenvironment and organic matter enrichment mechanisms between the lower Cuizhuang Formation and the Beidajian Formation shale.The Cuizhuang Formation was deposited in a late-stage,restricted basin environment during the rift phase,and elemental and geochemical indicators showed that the Cuizhuang Formation was in a suboxic-anoxic water environment,that was influenced by a warm and humid paleoclimate and submarine hydrothermal activities,which promoted the accumulation of organic matter.However,the enrichment of organic matter in the Cuizhuang Formation was mainly controlled by redox conditions.The formation of suboxic-anoxic water environments may be closely related to the warm and humid paleoclimate and submarine hydrothermal activities.Warm conditions promote continental weathering and increase marine productivity,thereby consuming oxygen in the bottom water.Moreover,acidic hydrothermal activity also helps to establish an anoxic environment.Our results reveal the effects controlling various coupled mechanisms dominated by redox conditions,which may explain the development of source rocks in the Cuizhuang Formation.

Elemental geochemical records of seafloor hydrothermal activities in the sediments from the Okinawa Trough

The major and minor element contents in the sediment core H9 from the hydrothermal fields of the Okinawa Trough show a sharp change at the depth of 80 cm. The elements enriched in the upper 80 cm core are those enriched in the hydrothermal deposits and in the surface sediments recovered from the hydrothermal fields in the trough, which indicates the input of hydrothermal materials. Comparing with other hydrothermal sediments from Mid-ocean Ridges or the Lau Basin, the degree of the enrichment of elements iron, copper,cobah, and nickel is relatively low. However, the enrichment of elements manganese, lead, arsenic, antimony and mercury is remarkable. The average contents of these elements in the upper 80 cm core sediments are three to six times those in the lower section, and 3 - 12 times those in the surface sediments which are not influenced by hydrothermal activities. Hydrothermal activities have contributed significant manganese, lead, arsenic, antimony and mercury to the sediments, and these elements are distinct indicators for the hydrothermal activity in the Okinawa Trough. The significant enrichment of these elements in Core H9 upward from the depth 80 cm indicates the start or the significant enhancing of the hydrothermal activity in this area at about 5 740 aB. P. The average accumulation rate of manganese during this period is about 40 461μg/（ cm^2·ka） , which is similar to the hydrothermal sediments in the Lau Basin or the East Pacific Rise.

TEM investigations of South Atlantic Ridge 13.2°S hydrothermal area

According to the exploration contract about polymetallic sulfides in the SWIR （Southwest Indian Ridge） signed by China with the International Seabed Authority, to delineate sulfide minerals and estimate resource quantity are urgent tasks. We independently developed our first coincident loop Transient Electromagnetic Method （TEM） device in 2010, and gained the TEM data for seafloor sulfide at South Atlantic Ridge 13.2°S in June 2011. In contrast with the widely applied CSEM （Marine controlled-source electromagnetic） method, whose goal is to explore hydrocarbons （oil/gas） of higher resistivity than seawater from 102 to 103 m below the sea floor, the TEM is for low resistivity minerals, and the target depth is from 0 to 100 m below the sea floor. Based on the development of complex sulfide geoelectrial models, this paper analyzed the TEM data obtained, proposing a new method for seafloor sulfide detection. We present the preliminary trial results, in the form of apparent resistivity sections for both half-space and full-space conditions. The results cor- respond well with the observations of the actual hydrothermal vent area, and the detection depth reached 50-100m below the bed, which verified the capability of the equipment.

Distal axis sulfide mineralization on the ultraslow-spreading Southwest Indian Ridge:an LA-ICP-MS study of pyrite from the East Longjing-2 hydrothermal field

The newly discovered East Longjing-2 hydrothermal field(ELHF-2)is located on the Dragon Horn oceanic core complex of the ultraslow-spreading Southwest Indian Ridge,approximately 12 km from the ridge axis.This study measured the chemical compositions of pyrite from ELHF-2 using a laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)to investigate the genesis of the field.Three generations of pyrite were classified,and found that:Py1 and Py2,rich in V,Mn,U,and Se,occur in altered basalt debris and the silica alteration matrix,respectively.Py3 was mainly intergrown with chalcopyrite in quartz veins and had higher Cu,In,Ag,Sb,and Au contents than Py1 and Py2.Some elements,such as Au,Se,and Pb,are likely presented as direct substitution with Fe^(2+)in pyrite,while Cu,Zn,Co,Ni,and Ag probably occur both as direct substitution with Fe and as distributed micro-to nanoparticle-sized sulfides.Meanwhile,the occurrence of V,Mn,and U is likely presented as oxide inclusions.Trace element geochemistry suggested that the pyrite was formed under hightemperature conditions,and the ore forming elements were likely derived from ultramafic rocks.In addition,Py1and Py2 were formed under higher water/rock ratio and higher temperature conditions,with more seawater involvement compared with Py3.The formation of ELHF-2 was probably driven by exothermic serpentinization reactions with an additional magmatic heat.This study shows that high-temperature hydrothermal circulation driven by magmatic activity can be developed on distal rift flank areas of magma-starved ultraslow-spreading ridges.

Use of portable X-ray fluorescence in the analysis of surficial sediments in the exploration of hydrothermal vents on the Southwest Indian Ridge

Hydrothermal plumes released from the eruption of sea floor hydrothermal fluids contain large amounts of oreforming materials. They precipitate within certain distances from the hydrothermal vent. Six surficial sediment samples from the Southwest Indian Ridge（SWIR） were analyzed by a portable X-ray fluorescence（PXRF） analyzer on board to find a favorable method fast and efficient enough for sea floor sulfide sediment geochemical exploration. These sediments were sampled near, at a moderate distance from, or far away from hydrothermal vents. The results demonstrate that the PXRF is effective in determining the enrichment characteristics of the oreforming elements in the calcareous sediments from the mid-ocean ridge. Sediment samples（〉40 mesh） have high levels of elemental copper, zinc, iron, and manganese, and levels of these elements in sediments finer than 40 mesh are lower and relatively stable. This may be due to relatively high levels of basalt debris/glass in the coarse sediments, which are consistent with the results obtained by microscopic observation. The results also show clear zoning of elements copper, zinc, arsenic, iron, and manganese in the surficial sediments around the hydrothermal vent. Sediments near the vent show relatively high content of the ore-forming elements and either high ratios of copper to iron content and zinc to iron content or high ratios of copper to manganese content and zinc to manganese content. These findings show that the content of the ore-forming elements in the sediments around hydrothermal vents are mainly influenced by the distance of sediments to the vent, rather than grain size. In this way, the PXRF analysis of surface sediment geochemistry is found to satisfy the requirements of recognition geochemical anomaly in mid-ocean ridge sediments. Sediments with diameters finer than 40 mesh should be used as analytical samples in the geochemical exploration for hydrothermal vents on mid-oceanic ridges. The results concerning copper, zinc, arsenic, iron, and manganese and their ratio features can be used as indicators in sediment geochemical exploration of seafloor sulfides.

Geological characteristics of the Qiaoyue Seamount and associated ultramafic-hosted seafloor hydrothermal system(~52.1°E,Southwest Indian Ridge)

Hydrothermal vent incidence was once thought to be proportional to the spreading rate of the mid-ocean ridges(MORs).However,more and more studies have shown that the ultraslow-spreading ridges(e.g.,Southwest Indian Ridge(SWIR))have a relatively higher incidence of hydrothermal venting fields.The Qiaoyue Seamount(52.1°E)is located at the southern side of segment#25 of the SWIR,to the west of the Gallieni transform fault.The Chinese Dayang cruises conducted eight preliminary deep-towed surveys of hydrothermal activity in the area during 2009 and 2018.Here,through comprehensive analyses of the video and photos obtained by the deep-towed platforms,rock samples,and water column turbidity anomalies,a high-temperature,ultramafic-hosted hydrothermal system is predicted on the northern flank of the Qiaoyue Seamount.We propose that this hydrothermal system is most likely to be driven by gabboric intrusions.Efficient hydrothermal circulation channels appear against a backdrop of high rock permeability related to the detachment fault.

Influence on lacustrine source rock by hydrothermal fluid： a case study of the Chang 7 oil shale, southern Ordos Basin

Hydrothermal fluid activity during sedimenta- tion of the Triassic Yanchang Formation in the Ordos Basin and the impact of said activity on formation and preservation conditions of source rocks have received little attention. Oil yield, major element, trace element, rare earth element, and total sulfur （TS） data from the oil shale within the Yanchang are here presented and discussed in the context of hydrothermal influence. Oil shale samples returned relatively high total organic carbon （TOC）, in the range of 4.69%-25.48%. A high correlation between TS and TOC suggests TS in the oil shale is dominated by organic sulfur and affected by organic matter. The low Al/ Si ratio of oil shale samples implies quartz is a major mineralogical component. Si/（Si ＋ Al ＋ Fe） values suggest close proximity of the oil shale to a terrigenous source. δEu; Fe versus Mn versus （Cu ＋ Co ＋ Ni）× 10; and SiO2/（K2O ＋ Na2O） versus MnO/TiO2, Fe/Ti, and （Fe ＋ Mn）/Ti are evidence of hydrothermal fluid activity during oil shale sedimentation, and δU and U/Th of the oil shale indicate reducing conditions. The Sr/Ba of oil shale samples suggests fresh-water deposition. The high correlations of Fe/Ti and （Fe ＋ Mn）/Ti with δU, U/Th, and TS demonstrate that hydrothermal fluid activity promotes reducing conditions. Sr/Ba ratios had low correlation with Fe/Ti and （Fe ＋ Mn）/Ti, implying that hydrothermal fluid activity had little impact （Fe ＋ Mn）/Ti, δU, U/Th, and on paleosalinity. Fe/Ti, Cu ＋ Pb ＋ Zn all exhibited high positive correlation coefficients with TOC in oil shale samples, suggesting that more intense hydrothermal fluid activity improves conditions in favor of formation and preservation of organic matter.

Hydrothermal Synthesis and Visible-light Photocatalytic Activities of SnS_2 Nanoflakes

SnS2 nanoflakes were successfully synthesized via a simple hydrothermal process. The as-prepared SnS2 samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, nitrogen adsorption-desorption isotherms, and UV-vis diffuse reflectance spectroscopy（DRS）. The photocatalytic activities of the as-prepared SnS2 nanoflakes under visible light irradiation（λ〉420 nm） were evaluated by the degradation of rhodamine B（Rh B）. The effect of hydrothermal temperatures on the photocatalytic efficiency of as-prepared SnS2 nanoflakes was investigated. The experimental result showed that SnS2 nanoflakes synthesized at the temprature of 160 o had higher photocatalytic efficiency and good photocatalytic stability.

Geological context and vents morphology in the ultramafic-hosted Tianxiu field, Carlsberg Ridge

The Tianxiu hydrothermal field(TXHF) located on Carlsberg Ridge is one of the few active ultramafic-hosted venting systems known in the Indian Ocean. Despite numerous investigations, there is limited understanding of its sulfide structure morphology, and the factors controlling the formation of TXHF are poorly understood. In this study, we conducted detailed seafloor mapping using visual data obtained by dives using the human-occupied vehicle(HOV) Jiaolong. The TXHF is found to be an active, off-axis, ultramafic-hosted, high-temperature hydrothermal area in which serpentine peridotite is exposed. Two main hydrothermal sites were identified, i.e., P and Y, both of which feature a complex of chimneys and beehive diffusers constituting a “chimney jungle” and isolated large steep-sided structures developed on flat-lying sulfide mounds. In addition, some sporadic inactive chimneys and outcrops of hydrothermal deposits were noted. The chimneys are rich in Fe and Zn sulfide, and lack the central fluid channel formed by focused high-temperature fluid flow. Hydrothermal venting at TXHF is likely related to low-angle detachment faults that focus and transport hydrothermal fluids away from a heat source along the valley wall. Our results complement and expand upon previous works concerning sulfide chimney morphology and their corresponding mineral paragenesis in ultramafic-hosted hydrothermal systems in the Indian Ocean and further our understanding of modern seafloor hydrothermal systems.

Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian,Weng'an,Guizhou Province

The black shales of the Lower Cambrian Niutitang Formation in Weng＇an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements （PGE） has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum （Mo）, nickel （Ni）, vanadium （V）, lead （Pb）, strontium （Sr）, barium （Ba）, uranium （U）, arsenic （As）, and rare earth elements （REE） in abundance. High uranium/ thorium （U/Th） ratios （U/Th〉I） indicated that mineralization was mainly influenced by the hydrothermal process. The 8U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements （LREE） （heavy rare earth elements （HREE） （LREE/HREE=5-17）, slightly negative europium （Eu） and cerium （Ce） anomalies （δEu=0.81- 0.93）, and positive Ce anomalies （δCe=0.76-1.12）. PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum （Pt）, palladium （Pd）, ruthenium （Ru） and osmium （Os）. The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.

Multiple Dolomitization and Fluid Flow Events in the Precambrian Dengying Formation of Sichuan Basin, Southwestern China

The Precambrian Dengying Formation is a set of large-scale, extensively dolomitized, carbonate reservoirs occurring within the Sichuan Basin. Petrographic and geochemical studies reveal dolomitization was a direct result of precipitation by chemically distinct fluids occurring at different times and at different intensities. Based on this evidence, dolomitization and multiple fluid flow events are analyzed, and three types of fluid evolution models are proposed. Results of analysis show that Precambrian Dengying Formation carbonates were deposited in a restricted peritidal environment （630- 542 Ma）. A high temperature and high Mg2＋ concentration seawater was a direct result of dolomitization for the micrite matrix, and for fibrous aragonite in primary pores. Geochemical evidence shows low δ18O values of micritic dolomite varying from -1.29%o to -4.52%o PDB, abundant light rare earth elements （REEs）, and low dolomite order degrees. Microbes and meteoric water significantly altered dolomite original chemical signatures, resulting in algal micritic dolomite and the fine-grained, granular, dolosparite dolomite having very negative δ18O values. Finely crystalline cement dolomite （536.3-280 Ma） and coarsely crystalline cement dolomite have a higher crystallization degree and higher order degree. The diagenetic sequence and fluid inclusion evidence imply a linear correlation between their burial depth and homogenization temperatures, which closely resemble the temperature of generated hydrocarbon. Compared with finely crystalline dolomite, precipitation of coarsely crystalline dolomite was more affected by restricted basinal fluids. In addition, there is a trend toward a more negative δ18O value, higher salinity, higher Fe and Mn concentrations, REE-rich. Two periods of hydrothermal fluids are identified, as the exceptionally high temperatures as opposed to the temperatures of burial history, in addition to the presence of high salinity fluid inclusions. The early hydrothermal fluid flow event was characterized by hot magnesium- and silicon-rich fluids, as demonstrated by the recrystallized matrix dolomite that is intimately associated with flint, opal, and microcrystalline quartz in intergranular or intercrystalline pores. This event was likely the result of a seafloor hydrothermal chimney eruption during Episode I of the Tongwan Movement （536.3-5.5 Ma）. In contrast, later hydrothermal fluids, which caused precipitation of saddle dolomite, were characterized by high salinity （15-16.05wt% NaCI equivalent） and homogenization temperatures （250 to 265℃）, δ18O values that were more enriched, and REE signatures. Geochemical data and the paragenetic sequence indicate that this hydrothermal fluid was related to extensive Permian large igneous province activity （360-280 Ma）. This study demonstrates the presence of complicated dolomitization processes occurring during various paleoclimates, tectonic cycles, and basinal fluids flow; results are a useful reference for these dolomitized Precambrian carbonates reservoirs.

Abundance and Distribution of Fatty Acids in Sediments of the South Mid-Atlantic Ridge

Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer （GC-MS） for the abundance and distributions of total fatty acids （TFAs）. Approximately 34 fatty acids were identified, with the chain-lengths ranging from C12 to C30. The total concentrations of TFAs （∑TFA） ranged from 7.15 to 30.09 μgg-l dry sediment, and ∑TFA was weakly correlated with bitumen content （R2=0.69）. The ∑TFA of samples around hydrothermal areas were significantly higher than that of samples away from hydrothermal areas, indicating intense primary production and large biomass in the hydro- thermal areas, and suggesting a close relationship between hydrothermal activity and ∑TFA of samples. The characteristics of the TFA composition in the present study are rich in monounsaturated fatty acids and lacking in polyunsaturated fatty acids, and the ra- tios between the concentrations of monounsaturated fatty acids and ∑TFAs in samples close to the hydrothermal areas, are about 0.8, but for samples far from the hydrothermal areas, they are only about 0.5. Several fatty acids （e.g., a/iC15：0 and C16：1co7）, which are signature biomarkers for sulfur-metabolizing bacteria, show the same distribution trend as ∑TFA of samples, further highlighting the close relationship between fatty acid content and hydrothermal activity and/or hydrothermal communities. The metabolic activities of hydrothermal communities, especially those of microorganisms, are likely the main source of fatty acids in samples.

Paleoenvironment and organic matter enrichment of the Carboniferous volcanic-related source rocks in the Malang Sag,Santanghu Basin,NW China

Volcanic activity was quite frequent during the deposition of the Late Carboniferous Ha’erjiawu Formation in the Santanghu Basin.The petrology and organic and inorganic geochemical indicators were used to investigate hydrocarbon potential,paleoenvironmental conditions and organic matter enrichment of the mudstones.The results show that the oil generation capacity of the Ha’erjiawu Formation mudstones,which has abundant oil-prone organic matter(TypeⅡkerogen with hydrogen index values mainly ranging from 250 to 550 mg HC/g TOC)in mature stage(Tmax values mainly ranging from 435 to 450℃),is considerable.The Ha’erjiawu Formation was deposited in a dysoxic,freshwater-mildly brackish,and warm-humid environment.During its deposition,the Ha’erjiawu Formation received hydrothermal inputs.The volcanic hydrothermal activities played an important role in the organic matter enrichment.In addition,the total organic carbon(TOC)is significantly positively correlated with the felsic mineral content,but it is negatively correlated with the carbonate mineral content and C27/C29 ratios,indicating that terrigenous organic matter input also contributed to the primary productivity in the surface water.Therefore,the formation of the high-quality source rocks in the Ha’erjiawu Formation was jointly affected by the hydrothermal activity and the terrigenous organic matter input.

Component characteristics of polycyclic aromatic compounds in sediments of the South Mid-Atlantic Ridge

10 samples of sediments obtained from the South Mid-Atlantic Ridge were measured for the abundances and distributions of polycyclic aromatic compounds（PAHs）. The total concentrations of PAHs（∑PAHs） ranged from 2.768 to 9.826 μg/g dry sediment. The ∑PAHs was higher in sample 22V-TVG10 and sample 26V-TVG05 which were close to hydrothermal fields, with the lowest value in sample 22V-TVG14 which was farthest from hydrothermal fields, suggesting a probable hydrothermal origin of ∑PAHs of samples. Approximately nine kinds of PAHs were identified, and low molecular mass tricyclic and tetracyclic aromatic compounds were predominant in the samples. The concentrations of fluoranthene which were typical as hydrothermal alteration compounds were the highest among PAHs with dry weight between 0.913–3.157 μg/g. The phenanthrene homologue was most abundant in the samples, and the ratios between parent phenanthrene and methylphenanthrene which probably reflected the degree of hydrothermal alteration ranged from 0.097 to 1.602. The sample 22V-TVG10 possessing a maximum ratio value showed the intense influence of the hydrothermal alteration on this sample, which might further imply that PAHs in sediments were mainly derived from the hydrothermal alteration.

Sedimentary facies characteristics and organic matter enrichment mechanism of lower Cambrian Niutitang Formation in South China

The purpose of this study was to examine the sedimentary facies characteristics of lower Cambrian Niutitang Formation(∈1n)in South China,to reveal the mechanism of organic matter enrichment,and to guide exploration of shale gas.Macro investigation and experimental analyses were used to assess the lithology in detail,total organic matter mass fraction w(TOC),mineral composition,and trace element characteristics of∈1n.The influencing factors of organic matter enrichment were discussed extensively,and a sedimentary facies mode was suggested.In the early stage of∈1n,the locations of Well E’yangye 1,Well Ciye 1,Well Changye 1,and Well Anye 1 respectively develop,platform inner sag,outer shelf,Jiangnan slope belt,and South China detention basin.In the late stage of∈1n,the sedimentary facies evolve with decreasing sea level.The study area presents a complete three-step basin in the Early Cambrian.In the early stage of∈1n,the first step is the Yangtze carbonate platform,the second step is the outer shelf and slope,and the third step is the deep-water basin.From the Yangtze carbonate platform to the deep-water basin,w(TOC)and the mass fraction of quartz gradually increase,the mass fraction of carbonate mineral decreases,and the mass fraction of clay mineral is higher in the second step.The sea level fluctuation results in a higher w(TOC)vertically in the lower∈1n shale,and the paleogeographic(provenance)conditions lead to better horizontal development of organic matter in the outer shelf,slope and detention basin.Trace elements are abundant in the lower∈1n,and w(TOC)is correlated positively with many trace elements.In the outer shelf,slope,and adjacent areas,hydrothermal activity and upwelling current bring nutrient-rich material and promote organic matter enrichment under a strong reducing condition.Deep-shelf,slope and deep-water basin are the best facies for the formation and preservation of organic matter,especially deep-water basin facies.It remains necessary to strengthen the exploration of shale gas in the deep-water basin of∈1n in central Hunan,China.