A comprehensive examination of detrital sandstone modes from the Sylhet Trough reveals a diverse range of sub-lithic to sub-feldspathic quartz arenites.Soil samples were gathered from Dupi Gaon(Jaintiapur)in Banglades...A comprehensive examination of detrital sandstone modes from the Sylhet Trough reveals a diverse range of sub-lithic to sub-feldspathic quartz arenites.Soil samples were gathered from Dupi Gaon(Jaintiapur)in Bangladesh,followed by a thorough analysis using field examination,X-ray diffraction(XRD),X-ray fluorescence(XRF),petrography,and heavy mineral concentration analyses.Field observations revealed the soil sample varying from white to yellowish to variegated,with thicknesses ranging from 15 cm to about 4 m,and exhibiting moderate softness.XRF analysis revealed significant SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3)levels in the samples,with zirconium(Zr)and copper(Cu)showing consistently high concentrations.XRD analysis identified quartz as predominant,along with muscovite,biotite,and accessory minerals like rutile and magnetite.Petrographic analysis highlighted quartz as dominant,with fractures suggesting tectonic influences,while heavy mineral separation techniques identified zircon,garnet,goethite,rutile,and magnetite.These findings provide insights into sediment provenance,depositional processes,and environ-mental conditions during the formation of the Dupi Tila Formation.The comprehensive geochemical data of the entire rock indicates that most of the sediments originated from felsic igneous sources,and also suggests a moderate to high level of weathering in the source region.Overall,the analyses suggested an in situ origin of the Dupi Tila Formation,with parent materials being predominantly detrital rather than authigenic,supported by the presence of detrital quartz and an assessment of the depositional environment,providing insights into the geological conditions of the era and potential modes of sediment transportation.展开更多
Geochemical analysis reveals that Middle Triassic radiolarian cherts from northern Thailand,including Chiang Dao,Lamphun and Den Chai,are of biogenic origin.These cherts present slightly high SiO2 content which was po...Geochemical analysis reveals that Middle Triassic radiolarian cherts from northern Thailand,including Chiang Dao,Lamphun and Den Chai,are of biogenic origin.These cherts present slightly high SiO2 content which was possibly modified by diagenetic alteration and migration processes as indicated by negative correlation between SiO2 and most of the other major elements.The relatively high content of Cr,Zr,Hf,Rb and Th and high positive correlation of these elements with Al and Ti from the majority of cherts suggest a close relation to terrigenous component.The Ce anomaly（Ce/Ce＊） with geometric means ranging from 0.85 to 0.93 is compatible with that of continental margin composi-tion（0.67-1.52） from Murray et al.（1990） which is also consistent with low Eu anomalies（Eu/Eu＊,0.91-0.94）.Moreover,the slightly low ratios of La and Ce NASC normalized（Lan/Cen,0.91-0.94） and the low LREE and HREE ratios in most of our samples（Lan/Ybn,0.62-0.85） are in agreement with the continental margin.The result from Lan/Cen vs.Al2O3/（Al2O3＋Fe2O3） discrimination diagrams also supports the continental margin（residual basin,s.str.） interpretation.These geochemical results are compatible with geological evidence,which suggest that during the Middle Triassic,radio-larian cherts were deposited within a deeper part of a residual basin in which an accommoda-tion space was possibly controlled by faults un-der extensional regime subsequent to Late Variscan（Permian） orogeny.Paleogeographi-cally,the main Paleotethys which closed during Late Triassic should be located further to the west of these study localities.This scenario is in agreement with the current view of the Tethys in this part of the world.展开更多
In the southwestern Tianshan,the geologic ages of many strata and their depositional environments are still poorly constrained because of complex structures.The Mada＇er area is located in the Kuokesaleling belt,South...In the southwestern Tianshan,the geologic ages of many strata and their depositional environments are still poorly constrained because of complex structures.The Mada＇er area is located in the Kuokesaleling belt,Southwestern Tianshan.The cherts from the former Wupata＇erkan Group contain abundant radiolarian fossils,including 10 species which are identified as late Devonian to early Carboniferous in age.Eleven chert samples have SiO_2 contents ranging from 88.80 wt%to 93.28 wt%, and 2.02 wt%to 3.72 wt%for Al_2O_3.The SiO_2/Al_2O_3 ratios of all samples vary from 23.84 to 46.11, much lower than those of the pure cherts（80-1400）.These values suggest that the cherts contain high ratios of terrigenous materials.The Al_2O_3/（Al_2O_3＋Fe_2O_3）ratios vary between 0.64 and 0.77,whereas V and Cu concentrations range from 10.92 ppm to 26.7 ppm and from 2.15 ppm to 34.1 ppm respectively. The Ti/V ratios vary from 25.53 to 44.93.The total REE concentrations of the cherts are between 30.78 ppm and 59.26 ppm,averaging 45.46 ppm.The（La/Ce）_N ratios range from 0.81 to 1.12,and 0.88-1.33 for（La/Yb）_N,averaging 1.09,which suggests a continental margin environment.Consequently,it is inferred that the cherts formed in a residual sea environment during the late Devonian to early Carboniferous time,which suggests that the collision between the Karakum-Tarim and Kazakhstan-Junggar plates did not occur at the time.In addition,the regional geological information indicates that the study area experienced a post-collision stage during the early Permian,and thus it is likely that the collision between the two plates took place in the late Carboniferous.展开更多
The first data of geochemical study of the Benevka Section cherty rocks belonging to the Taukha terrane of the Sikhote-Alin Late Jurassic-Early Cretaceous accretionary prism, Russia Far East are presented. These data ...The first data of geochemical study of the Benevka Section cherty rocks belonging to the Taukha terrane of the Sikhote-Alin Late Jurassic-Early Cretaceous accretionary prism, Russia Far East are presented. These data demonstrate essential distinctions of major, trace and rare earth element concentrations in different parts of the measured stratigraphic section. The lower chert horizons exhibit high Fe2O3 and MnO contents, low concentrations of Al2O3 and TiO2, relatively high V/Y ratio, and extremely low value of negative Ce anomaly. In contrast the upper horizons composed of clayey cherts and siliceous mudstones are characterized by high Al2O3, TiO2 and K2O contents, low Fe2O3 and MnO values, low V/Y ratio, and slightly negative Ce anomaly. In the middle part of the Benevka Section, in which cherts gradually changed to clayey cherts, intermediate geochemical characteristics are present. Based on these data obtained the depositional environments correspond to proximal to the spreding ridge, open-ocean and near continental margin regimes were successfully reconstructed from bottom to top of the Benevka Section, that indicate that significant horizontal movement took place of the sea-floor, on which the cherts were deposited.展开更多
By means of techniques such as inductively coupled plasma-mass spectrometry （ICP-MS） and X-ray fluorescence spectrometry （XRF）,REE geochemical characteristics and depositional environment of the black shales in Ba...By means of techniques such as inductively coupled plasma-mass spectrometry （ICP-MS） and X-ray fluorescence spectrometry （XRF）,REE geochemical characteristics and depositional environment of the black shales in Baiguoyuan Ag-V deposit,Xingshan,Hubei Province,were studied in this work. The black shales in a typical TC5 profile of Doushantuo Formation of upper Sinian period were obviously enriched in REE,especially in LREE. The REE patterns of the investigated samples normalized by Post Archean Australian Shale （PAAS） showed a flat or slight rightward inclination. The characteristic elements,their ratio and correlation diagrams showed that it should be hot-water deposit and the black shale in the study area was of a sedimentary origin. Redox sensitive metal elements pattern,trace elements index measurement in anoxic environment,Ce anomaly and δEu negative anomaly showed that the deposit environment of the black shales was a reducing and anoxic one and a slight change of the sea level could be identified. The samples relatively focused on the superimposed area of sedimentary rock and basalt in the diagram of La/Yb-ΣREE and La/Yb-Ce/La. So there might be accession of hot-water sedimentation during the period of the formation of the black rock series,mostly in normal terrigenous sedimentation with the participation of deep hot-water deposit.展开更多
Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）...Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.展开更多
The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin,the East Sea（Sea of Japan）.The data include sediment color（L^＊）,X-ray radiographs,grain size ...The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin,the East Sea（Sea of Japan）.The data include sediment color（L^＊）,X-ray radiographs,grain size distribution and AMS^14C date.Four kinds of sediments（homogeneous,laminated,crudely laminated and hybrid sediments） are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation.Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon（EAM）.The relative contributions of the East China Sea Coastal Water（ECSCW） and the Tsushima Warm Current（TWC） were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP.During the interstadial,the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia,and then more strongly low-salinity,nutrient-enriched water was introduced into the East Sea.The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition.During the lowest stand of sea level in the last glacial maximum（LGM）,the isolated East Sea dominated by stratified water masses and the euxinic depositional environment formed.The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high.During the late Younger Dryas（YD） period,the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM.The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.展开更多
Objective The Yubei area is located in the mid-east Maigaiti slope of southwestern Tarim Basin, China, with an exploration history of several years. Recent exploration has preliminarily indicated that the Ordovician ...Objective The Yubei area is located in the mid-east Maigaiti slope of southwestern Tarim Basin, China, with an exploration history of several years. Recent exploration has preliminarily indicated that the Ordovician carbonate formations in this area have some oil and gas potential. Carbonate microfacies provides material basis for reservoir development, seal formation and hydrocarbon generation. Therefore, this work utilized the standard microfacies （SMF） types to study the microfacies of the Ordovician formations in the Yubei area in order to provide theoretical basis for the next exploration.展开更多
The Luconia Province-offshore Sarawak-is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Nevertheless, little effort has been made to address the palaeoenvironmental char...The Luconia Province-offshore Sarawak-is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Nevertheless, little effort has been made to address the palaeoenvironmental characteristics of the Tertiary carbonates in the key sector of Central Luconia.We study the sedimentology and petrography of core samples from a well in Central Luconia, for which thirteen microfacies have been identified reflecting different depositional settings. This is the first microfacies scheme elaborated for Luconian carbonates. Lithofacies and microfacies distribution are compatible with deposition in a reef complex, originating around a framework reef, within the euphotic zone. Sediments were deposited in environments of backreef, reef crest, and forereef. The fair weather wave base is marked by the presence of coralline red algae, foraminifera, decreasing degree of bioclast fragmentation and other microfacies features. As a result, a depositional-environmental model is constructed, depicting a reef complex built around a framework reef developed on the margin of an isolated platform. In addition, an innovative, preliminary time series analysis of facies, microfacies and depositional environment data reveal the existence of seasonal cycles in the stacking patterns of facies and microfacies.展开更多
The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,a...The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,and oil shale from the Beibu Gulf Basin were analyzed to investigate their organic geochemistry,palynofacies,and trace elements.Hydrocarbon potential was higher in the oil shale(29.79 mg/g)than in the general-quality source rock(3.82 mg/g),and its kerogen type wasⅠ-Ⅱ2.Hydrogen-rich liptinite(cutinite and sporinite)components derived from terrigenous higher plants provided most of the hydrocarbon potential of excellent-quality source rock and oil shale.Under the influence of depressioncontrolling fault activity,a deeper subsidence center promotes the deposition of excellent-quality source rock and oil shale in brackish-hypoxic bottom water.A shallower subsidence center,due to subsag-controlling fault activity,promotes the formation of excellent-quality source rock under freshbrackish and weak oxidation-weak reducing conditions.The local uplift and shallow-slope led to the formation of general-quality source rock,under freshwater weak-oxidation conditions.A model was established for organic matter(OM)accumulation in organic-rich shales,accounting for fault activity,terrigenous hydrogen-rich OM,and the preservation conditions,to predict the development of excellent-quality source rock from areas with low levels of exploration.展开更多
The depositional environment of the Upper Permian quartzose sandstone （Kuishan sandstone in Shihezi Formation of Upper Permian） in the North China epicontinental basin is controversial. In order to test the previous...The depositional environment of the Upper Permian quartzose sandstone （Kuishan sandstone in Shihezi Formation of Upper Permian） in the North China epicontinental basin is controversial. In order to test the previous hypotheses, we analyzed sedimentological characteristics of the Kuishan sandstones in outcrops and boreholes, and carried out trace element geochemical analysis by electron probe microanalyzer. Three lithofacies were recognized, including normal-graded conglomerate （Cng）, trough and planar cross-bedded coarse sandstone （CStpc）, and planar cross-bedded medium sandstone （MSpc）. Normal-graded conglomerate （Cng） formed in the meandering river or deltaic distributary channels. Trough and planar cross-bedded coarse sandstone （CStpc） formed in meandering river or distributary channels of near-source deltaic plain. Planar cross-bedded medium sandstone （MSpc） formed in the siliciclastic beach with highto moderate-energy conditions. By the petrology and trace elements analysis, three relatively large-scale transgressions were revealed. Each transgression was reflected by the lower content of Ba and ratios of Fe/Mn, and the high content of B and ratios of B/Ga. The ratios of Ni/Co of all samples are all lower than 2, suggesting oxygen-enriched shallower water en- vironment during deposition of the Kuishan sandstones.展开更多
The effect of various depositional parameters including paleoclimate,paleosalinity and provenance,on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment.The ...The effect of various depositional parameters including paleoclimate,paleosalinity and provenance,on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment.The classification of shale lithofacies and the interpretation of shale depositional environment are key features used in shale oil and gas exploration and development activity.The lower 3rd member of the Eocene Shahejie Formation(Es_(3)^(x)shale)was selected for this study,as one of the main prospective intervals for shale oil exploration and development in the intracratonic Bohai Bay Basin.Mineralogically,it is composed of quartz(avg.9.6%),calcite(avg.58.5%),dolomite(avg.7%),pyrite(avg.3.3%)and clay minerals(avg.20%).An advanced methodology(thin-section petrography,total organic carbon and total organic sulfur contents analysis,X-ray diffraction(XRD),X-ray fluorescence(XRF),field-emission scanning electron microscopy(FE-SEM))was adopted to establish shale lithofacies and to interpret the depositional environment in the lacustrine basin.Six different types of lithofacies were recognized,based on mineral composition,total organic carbon(TOC)content and sedimentary structures.Various inorganic geochemical proxies(Rb/Sr,Ca/(Ca+Fe),Ti/Al,Al/Ca,Al/Ti,Zr/Rb)have been used to interpret and screen variations in depositional environmental parameters during the deposition of the Es_(3)^(x)shale.The experimental results indicate that the environment during the deposition of the Es_(3)^(x)shale was warm and humid with heightened salinities,moderate to limited detrital input,higher paleohydrodynamic settings and strong oxygen deficient(reducing)conditions.A comprehensive depositional model of the lacustrine shale was developed.The interpretations deduced from this research work are expected to not only expand the knowledge of shale lithofacies classification for lacustrine fine-grained rocks,but can also offer a theoretical foundation for lacustrine shale oil exploration and development.展开更多
Molecular biomarker and whole oil carbon isotope(δ^(13)C_(oil)) analyses were conducted on eleven typical crude oils from the Qiongdongnan Basin to investigate their biological sources and depositional environments. ...Molecular biomarker and whole oil carbon isotope(δ^(13)C_(oil)) analyses were conducted on eleven typical crude oils from the Qiongdongnan Basin to investigate their biological sources and depositional environments. Saturated hydrocarbon biomarkers in most samples are characterized by angiosperm-derived compounds, with aromatic compounds dominated by the naphthalene, phenanthrene, biphenyl, and fluorene series. The related source rocks of these oils were mainly deposited under oxic condition, but a subanoxic-suboxic and enclosed water column condition in the Central Depression during Oligocene.The identification of simonellite and related compounds in the aromatic fractions provides reliable evidence for the input of coniferous gymnosperms. Cadalene may also have a potential association with gymnosperms since it shows a strong positive correlation with simonellite. Evidence from density, nalkanes, short-chain alkylbenzenes and secondary brine inclusions indicates that the unique crude oil B13-1 may have suffered from thermal alteration. These crude oils(excluding B13-1) can be classified into four types based on the δ^(13)C_(oil)values and molecular biomarkers. Type A oil(solely S34-3) is characterized by non-angiosperm plants, with minor dinoflagellates and increasing contribution from conifer gymnosperms than others. Type B oils(L17-2, L18-1, L25-1, and L25-1W) show heavy δ^(13)C_(oil)(-24 ‰to-25 ‰) and mixed contributions from both angiosperms and marine algae, with the marine algae contribution increasing. Type C oils(L13-2 and B21-1) share similar biological sources with Type B, but the moderately δ^(13)C_(oil)(-25‰ to-26‰) and high level of terrestrial biomarkers suggesting a predominant contribution of angiosperms. Type D oils(Y13-1a, Y13-1b, and Y13-4) possess the lightestδ^(13)C_(oil)(mainly below-26‰) and are primarily derived from angiosperms, with mangrove vegetation playing an important role. Spearman correlation analysis among 14 source biomarker parameters withδ^(13)C_(oil)and geological setting of related source rocks implied that the marine algae should be responsible for the heavy δ^(13)C_(oil)in the Type B. The contribution of marine algae in the Central Depression may have been neglected in the past, as it is usually covered by remarkable angiosperm biomarkers.展开更多
Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizonta...Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.展开更多
Shuidonggou site has abundant Paleolithic remains of Late Pleistocene deposition. Studying the evolution of depositional environments is essential to the comprehensive understanding of the living conditions of ancient...Shuidonggou site has abundant Paleolithic remains of Late Pleistocene deposition. Studying the evolution of depositional environments is essential to the comprehensive understanding of the living conditions of ancient populations. To reconstruct the depositional environment at Shuidonggou, we carried out archaeological excavations and collected systematic deposition samples at the key position of Shuidonggou Locality 2 for grain size analysis and sporopollen statistics. The environmental evolution around the Shuidonggou site generally underwent four stages at ~72-18 kaBP. During the first stage （~72-41 kaBP）, the river developed with gravel and sand stratums. During the second stage （41-34 kaBP）, a swamp with numerous aquatic plants formed. In the third stage （34-29 kaBP）, site formation was characterized by shallow lake depositional conditions; the climate was relatively warm and humid. The marginal bank depositional conditions deteriorated during the fourth stage （29-18 kaBP）, and the site underwent several dry events; the climate also became drier and colder.展开更多
Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin,Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatograph...Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin,Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry.The bulk carbon isotopic values of the whole rock extracts,saturate and aromatic fractions range from–28.7‰to–26.8‰,–29.2‰to–27.2‰and–28.5‰to–26.7‰,respectively while the bulk carbon isotopic values of the whole oils,saturate and aromatic fractions range from–25.4‰to–27.8‰,–25.9‰to–28.4‰and–23.5‰to–26.9‰,respectively.The average carbon isotopic compositions of individual alkanes(nC12-nC33)in the rock samples range from–34.9‰to–28.2‰whereas the average isotopic values of individual n-alkanes in the oils range from–31.1‰to–23.8‰.Theδ13C isotope ratios of pristane and phytane in the rock samples range from–29.2‰to–28.2‰and–30.2‰to–27.4‰respectively while the pristane and phytane isotopic values range from–32.1‰to–21.9‰and–30.5‰to–26.9‰,respectively.The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments.The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.展开更多
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 var...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.展开更多
The Sarvak Formation is the second major oil-bearing reservoir in the south and south west of Iran. The Middle Cretaceous Sarvak formation in the Zagros Mountains (Zagros Basin) is mainly composed of carbonate sequenc...The Sarvak Formation is the second major oil-bearing reservoir in the south and south west of Iran. The Middle Cretaceous Sarvak formation in the Zagros Mountains (Zagros Basin) is mainly composed of carbonate sequences. Based on facies studied, thirteen microfacies were recognized in the studied area, which were categorized in the three facies groups: including inner ramp, mid ramp and outer ramp. Evidences such as the gradual changes in the facies (basin slope), the absence of extensive uninterrupted barrier reef, the lack of calciturbidite and gravity sediments as well as the high proportion of grain-supported indicated that the Sarvak Formation was deposited in the ramp like depositional system, particularly on an inner ramp setting. Inner ramp facies group is the principal setting and subdivided to tidal flat, restricted and unrestricted lagoon as well as shoal sub-environments.展开更多
In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section include...In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section includes about 380 meters of conglomerate at the base, chalk, limestone, marl, and shale. Petrographic studies with facies analysis have led to the identification of 12 microfacies, these microfacies have been deposited in four facies groups including tidal flat, lagoon, barrier and open marine. Study of horizontal and vertical facies changes and their comparison with recent and ancient environments reveals that Qom Formation in this section relates to shallow marine environment and its facies were deposited in a shelf carbonate platform and are comparable with contemporary shelf platforms such as Florida and old shelf platforms such as Mozduran. The most important diagenetic processes affecting the studied section include micritization, bioturbation, cementation, dissolution, neomorphism, fracturing, mechanical and chemical compaction, hematitization and dolomitization. These processes have formed in marine, meteoric and burial diagenetic environments.展开更多
The Endengue Banded Iron Formation (BIF) is located in the northwestern edge of the Congo craton in Cameroon. Here<span style="font-family:Verdana;">,</span><span style="font-family:Verda...The Endengue Banded Iron Formation (BIF) is located in the northwestern edge of the Congo craton in Cameroon. Here<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> we report geochemical data of trace and rare earth elements (REE) of the Endengue BIF samples from the Archean Ntem complex and investigate their environmental setting. Two types of BIF occur at Endengue area, both containing minimal contamination from terrestrial material. Total REE (</span><span style="line-height:99%;font-family:Verdana;">Σ</span><span style="font-family:Verdana;">REE) contents in the Type 1 BIF are extremely low, ranging from 0.34 to 1.83 ppm, similarly to pure chemical sediments while Type 2 BIF displays</span><span style="font-family:;" "=""> </span><span style="line-height:99%;font-family:Verdana;">Σ</span><span style="font-family:Verdana;">REE contents ranging from 2.98 to 24.26 ppm. The PAAS-normalized REE</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">+</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">Y patterns of the two BIF types display LREE enrichment relative to HREE and weak positive Eu anomaly, most likely suggesting that the source of iron and siliceous of the Endengue BIFs is mainly from the contribution of low-temperature hydrothermal alteration of the crust. Type 1 BIF shows very low Nd content (<1 ppm) with positive correlation between Nd and Ce/Ce</span><span style="font-family:Verdana;">*</span><span style="font-family:Verdana;"> and positive Ce anomalies which suggests suboxic or anoxic seawater similar to the depositional environment of Elom BIF in Archean Ntem complex. In contrast, Type 2 BIF displays low to moderate Nd contents (1 and 100 ppm with the exception of sample LBR65) with negative correlation between Nd and Ce/Ce</span><span style="font-family:Verdana;">*</span><span style="font-family:Verdana;"> and negative Ce anomalies. These features indicate precipatation of Type 2 BIF from oxic iron-rich solution that changed to oxidized surface by rapid precipitation of the hydrothermal Fe. The Endengue BIFs were deposited in the continental margin ocean in presence of low-temperature hydrothermal fluids mixed with seawater, similar to Paleoproterozoic Kpwa</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">Atog Boga BIFs within the Nyong group and other Paleoproterozoic Superior</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">type BIFs worldwide.</span>展开更多
文摘A comprehensive examination of detrital sandstone modes from the Sylhet Trough reveals a diverse range of sub-lithic to sub-feldspathic quartz arenites.Soil samples were gathered from Dupi Gaon(Jaintiapur)in Bangladesh,followed by a thorough analysis using field examination,X-ray diffraction(XRD),X-ray fluorescence(XRF),petrography,and heavy mineral concentration analyses.Field observations revealed the soil sample varying from white to yellowish to variegated,with thicknesses ranging from 15 cm to about 4 m,and exhibiting moderate softness.XRF analysis revealed significant SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3)levels in the samples,with zirconium(Zr)and copper(Cu)showing consistently high concentrations.XRD analysis identified quartz as predominant,along with muscovite,biotite,and accessory minerals like rutile and magnetite.Petrographic analysis highlighted quartz as dominant,with fractures suggesting tectonic influences,while heavy mineral separation techniques identified zircon,garnet,goethite,rutile,and magnetite.These findings provide insights into sediment provenance,depositional processes,and environ-mental conditions during the formation of the Dupi Tila Formation.The comprehensive geochemical data of the entire rock indicates that most of the sediments originated from felsic igneous sources,and also suggests a moderate to high level of weathering in the source region.Overall,the analyses suggested an in situ origin of the Dupi Tila Formation,with parent materials being predominantly detrital rather than authigenic,supported by the presence of detrital quartz and an assessment of the depositional environment,providing insights into the geological conditions of the era and potential modes of sediment transportation.
基金supported mainly by the National Natural Science Foundation of China (No. 40772143)the Special Fund of the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciencesthe Faculty of Science,Mahasarakham University
文摘Geochemical analysis reveals that Middle Triassic radiolarian cherts from northern Thailand,including Chiang Dao,Lamphun and Den Chai,are of biogenic origin.These cherts present slightly high SiO2 content which was possibly modified by diagenetic alteration and migration processes as indicated by negative correlation between SiO2 and most of the other major elements.The relatively high content of Cr,Zr,Hf,Rb and Th and high positive correlation of these elements with Al and Ti from the majority of cherts suggest a close relation to terrigenous component.The Ce anomaly（Ce/Ce＊） with geometric means ranging from 0.85 to 0.93 is compatible with that of continental margin composi-tion（0.67-1.52） from Murray et al.（1990） which is also consistent with low Eu anomalies（Eu/Eu＊,0.91-0.94）.Moreover,the slightly low ratios of La and Ce NASC normalized（Lan/Cen,0.91-0.94） and the low LREE and HREE ratios in most of our samples（Lan/Ybn,0.62-0.85） are in agreement with the continental margin.The result from Lan/Cen vs.Al2O3/（Al2O3＋Fe2O3） discrimination diagrams also supports the continental margin（residual basin,s.str.） interpretation.These geochemical results are compatible with geological evidence,which suggest that during the Middle Triassic,radio-larian cherts were deposited within a deeper part of a residual basin in which an accommoda-tion space was possibly controlled by faults un-der extensional regime subsequent to Late Variscan（Permian） orogeny.Paleogeographi-cally,the main Paleotethys which closed during Late Triassic should be located further to the west of these study localities.This scenario is in agreement with the current view of the Tethys in this part of the world.
基金supported by National 305 Project(2007BAB25B05,2011BAB06B02- 04)NSFC grant(40925006,40772045,40572047)111 Project(B07011)
文摘In the southwestern Tianshan,the geologic ages of many strata and their depositional environments are still poorly constrained because of complex structures.The Mada＇er area is located in the Kuokesaleling belt,Southwestern Tianshan.The cherts from the former Wupata＇erkan Group contain abundant radiolarian fossils,including 10 species which are identified as late Devonian to early Carboniferous in age.Eleven chert samples have SiO_2 contents ranging from 88.80 wt%to 93.28 wt%, and 2.02 wt%to 3.72 wt%for Al_2O_3.The SiO_2/Al_2O_3 ratios of all samples vary from 23.84 to 46.11, much lower than those of the pure cherts（80-1400）.These values suggest that the cherts contain high ratios of terrigenous materials.The Al_2O_3/（Al_2O_3＋Fe_2O_3）ratios vary between 0.64 and 0.77,whereas V and Cu concentrations range from 10.92 ppm to 26.7 ppm and from 2.15 ppm to 34.1 ppm respectively. The Ti/V ratios vary from 25.53 to 44.93.The total REE concentrations of the cherts are between 30.78 ppm and 59.26 ppm,averaging 45.46 ppm.The（La/Ce）_N ratios range from 0.81 to 1.12,and 0.88-1.33 for（La/Yb）_N,averaging 1.09,which suggests a continental margin environment.Consequently,it is inferred that the cherts formed in a residual sea environment during the late Devonian to early Carboniferous time,which suggests that the collision between the Karakum-Tarim and Kazakhstan-Junggar plates did not occur at the time.In addition,the regional geological information indicates that the study area experienced a post-collision stage during the early Permian,and thus it is likely that the collision between the two plates took place in the late Carboniferous.
基金financially supported by the President of the Russian Federation (No. 1159.2014.5)the Far Eastern Branch of the Russian Academy of Sciences (No. 15-1-2-013-2)
文摘The first data of geochemical study of the Benevka Section cherty rocks belonging to the Taukha terrane of the Sikhote-Alin Late Jurassic-Early Cretaceous accretionary prism, Russia Far East are presented. These data demonstrate essential distinctions of major, trace and rare earth element concentrations in different parts of the measured stratigraphic section. The lower chert horizons exhibit high Fe2O3 and MnO contents, low concentrations of Al2O3 and TiO2, relatively high V/Y ratio, and extremely low value of negative Ce anomaly. In contrast the upper horizons composed of clayey cherts and siliceous mudstones are characterized by high Al2O3, TiO2 and K2O contents, low Fe2O3 and MnO values, low V/Y ratio, and slightly negative Ce anomaly. In the middle part of the Benevka Section, in which cherts gradually changed to clayey cherts, intermediate geochemical characteristics are present. Based on these data obtained the depositional environments correspond to proximal to the spreding ridge, open-ocean and near continental margin regimes were successfully reconstructed from bottom to top of the Benevka Section, that indicate that significant horizontal movement took place of the sea-floor, on which the cherts were deposited.
基金Project supported by the Key Scientific and Technological Project of Hubei Province, China (2007AA301C51)
文摘By means of techniques such as inductively coupled plasma-mass spectrometry （ICP-MS） and X-ray fluorescence spectrometry （XRF）,REE geochemical characteristics and depositional environment of the black shales in Baiguoyuan Ag-V deposit,Xingshan,Hubei Province,were studied in this work. The black shales in a typical TC5 profile of Doushantuo Formation of upper Sinian period were obviously enriched in REE,especially in LREE. The REE patterns of the investigated samples normalized by Post Archean Australian Shale （PAAS） showed a flat or slight rightward inclination. The characteristic elements,their ratio and correlation diagrams showed that it should be hot-water deposit and the black shale in the study area was of a sedimentary origin. Redox sensitive metal elements pattern,trace elements index measurement in anoxic environment,Ce anomaly and δEu negative anomaly showed that the deposit environment of the black shales was a reducing and anoxic one and a slight change of the sea level could be identified. The samples relatively focused on the superimposed area of sedimentary rock and basalt in the diagram of La/Yb-ΣREE and La/Yb-Ce/La. So there might be accession of hot-water sedimentation during the period of the formation of the black rock series,mostly in normal terrigenous sedimentation with the participation of deep hot-water deposit.
基金Financial support was provided by the National Science and Technology Major Project of China (No.2011ZX05023-002-003)
文摘Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.
基金The National Natural Science Foundation of China under contract Nos 40431002,40606016 and 40710069004the China-Korea joint research programme and the Primary Science Foundation of First Institute of Oceanography under contract No. 2007T09
文摘The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin,the East Sea（Sea of Japan）.The data include sediment color（L^＊）,X-ray radiographs,grain size distribution and AMS^14C date.Four kinds of sediments（homogeneous,laminated,crudely laminated and hybrid sediments） are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation.Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon（EAM）.The relative contributions of the East China Sea Coastal Water（ECSCW） and the Tsushima Warm Current（TWC） were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP.During the interstadial,the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia,and then more strongly low-salinity,nutrient-enriched water was introduced into the East Sea.The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition.During the lowest stand of sea level in the last glacial maximum（LGM）,the isolated East Sea dominated by stratified water masses and the euxinic depositional environment formed.The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high.During the late Younger Dryas（YD） period,the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM.The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.
基金funded by the National Natural Science Foundation of China(grant No.41572117)Technological&Developmental Department of China Petroleum&Chemical Corporation(grants No.P13040 and P14128)China Geological Survey(grant No.DD20160175-1-1)
文摘Objective The Yubei area is located in the mid-east Maigaiti slope of southwestern Tarim Basin, China, with an exploration history of several years. Recent exploration has preliminarily indicated that the Ordovician carbonate formations in this area have some oil and gas potential. Carbonate microfacies provides material basis for reservoir development, seal formation and hydrocarbon generation. Therefore, this work utilized the standard microfacies （SMF） types to study the microfacies of the Ordovician formations in the Yubei area in order to provide theoretical basis for the next exploration.
基金financial assistance throughout the research under the grant YUTP 0153AAA14financial support from UTP through the grant URIF 2014-00735
文摘The Luconia Province-offshore Sarawak-is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Nevertheless, little effort has been made to address the palaeoenvironmental characteristics of the Tertiary carbonates in the key sector of Central Luconia.We study the sedimentology and petrography of core samples from a well in Central Luconia, for which thirteen microfacies have been identified reflecting different depositional settings. This is the first microfacies scheme elaborated for Luconian carbonates. Lithofacies and microfacies distribution are compatible with deposition in a reef complex, originating around a framework reef, within the euphotic zone. Sediments were deposited in environments of backreef, reef crest, and forereef. The fair weather wave base is marked by the presence of coralline red algae, foraminifera, decreasing degree of bioclast fragmentation and other microfacies features. As a result, a depositional-environmental model is constructed, depicting a reef complex built around a framework reef developed on the margin of an isolated platform. In addition, an innovative, preliminary time series analysis of facies, microfacies and depositional environment data reveal the existence of seasonal cycles in the stacking patterns of facies and microfacies.
基金supported by the Certificate of National Science and Technology Major Project of the Ministry of Science and Technology of China(2016ZX05006-007-004)National Natural Science Foundation of China(41702139,41772138,41602142,42072130)the Fundamental Research Funds for the Central Universities(18CX02008A)。
文摘The mechanisms of lacustrine organic-rich shale formation have attracted attention due to its association with global shale oil and shale gas exploration.Samples of general-quality and excellent-quality source rocks,and oil shale from the Beibu Gulf Basin were analyzed to investigate their organic geochemistry,palynofacies,and trace elements.Hydrocarbon potential was higher in the oil shale(29.79 mg/g)than in the general-quality source rock(3.82 mg/g),and its kerogen type wasⅠ-Ⅱ2.Hydrogen-rich liptinite(cutinite and sporinite)components derived from terrigenous higher plants provided most of the hydrocarbon potential of excellent-quality source rock and oil shale.Under the influence of depressioncontrolling fault activity,a deeper subsidence center promotes the deposition of excellent-quality source rock and oil shale in brackish-hypoxic bottom water.A shallower subsidence center,due to subsag-controlling fault activity,promotes the formation of excellent-quality source rock under freshbrackish and weak oxidation-weak reducing conditions.The local uplift and shallow-slope led to the formation of general-quality source rock,under freshwater weak-oxidation conditions.A model was established for organic matter(OM)accumulation in organic-rich shales,accounting for fault activity,terrigenous hydrogen-rich OM,and the preservation conditions,to predict the development of excellent-quality source rock from areas with low levels of exploration.
基金financially supported by the National Natural Science Foundation of China (No. 41202070)Shandong Outstanding Young and Middle-Aged Scientists’ Research Award Fund (No. 2011BSB01335)SDUST Research Fund (No. 2012KYTD101)
文摘The depositional environment of the Upper Permian quartzose sandstone （Kuishan sandstone in Shihezi Formation of Upper Permian） in the North China epicontinental basin is controversial. In order to test the previous hypotheses, we analyzed sedimentological characteristics of the Kuishan sandstones in outcrops and boreholes, and carried out trace element geochemical analysis by electron probe microanalyzer. Three lithofacies were recognized, including normal-graded conglomerate （Cng）, trough and planar cross-bedded coarse sandstone （CStpc）, and planar cross-bedded medium sandstone （MSpc）. Normal-graded conglomerate （Cng） formed in the meandering river or deltaic distributary channels. Trough and planar cross-bedded coarse sandstone （CStpc） formed in meandering river or distributary channels of near-source deltaic plain. Planar cross-bedded medium sandstone （MSpc） formed in the siliciclastic beach with highto moderate-energy conditions. By the petrology and trace elements analysis, three relatively large-scale transgressions were revealed. Each transgression was reflected by the lower content of Ba and ratios of Fe/Mn, and the high content of B and ratios of B/Ga. The ratios of Ni/Co of all samples are all lower than 2, suggesting oxygen-enriched shallower water en- vironment during deposition of the Kuishan sandstones.
基金supported by the National Science and Technology Major Project of China(Grant No.2017ZX05009-002)the National Natural Science Foundation of China(Nos.U1762217,41702139,42072164 and 41821002)+2 种基金Taishan Scholars Program(No.TSQN201812030)the Fundamental Research Funds for the Central Universities(19CX07003A)the School of Geosciences,China University of Petroleum,East China,for analytical support and financial support。
文摘The effect of various depositional parameters including paleoclimate,paleosalinity and provenance,on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment.The classification of shale lithofacies and the interpretation of shale depositional environment are key features used in shale oil and gas exploration and development activity.The lower 3rd member of the Eocene Shahejie Formation(Es_(3)^(x)shale)was selected for this study,as one of the main prospective intervals for shale oil exploration and development in the intracratonic Bohai Bay Basin.Mineralogically,it is composed of quartz(avg.9.6%),calcite(avg.58.5%),dolomite(avg.7%),pyrite(avg.3.3%)and clay minerals(avg.20%).An advanced methodology(thin-section petrography,total organic carbon and total organic sulfur contents analysis,X-ray diffraction(XRD),X-ray fluorescence(XRF),field-emission scanning electron microscopy(FE-SEM))was adopted to establish shale lithofacies and to interpret the depositional environment in the lacustrine basin.Six different types of lithofacies were recognized,based on mineral composition,total organic carbon(TOC)content and sedimentary structures.Various inorganic geochemical proxies(Rb/Sr,Ca/(Ca+Fe),Ti/Al,Al/Ca,Al/Ti,Zr/Rb)have been used to interpret and screen variations in depositional environmental parameters during the deposition of the Es_(3)^(x)shale.The experimental results indicate that the environment during the deposition of the Es_(3)^(x)shale was warm and humid with heightened salinities,moderate to limited detrital input,higher paleohydrodynamic settings and strong oxygen deficient(reducing)conditions.A comprehensive depositional model of the lacustrine shale was developed.The interpretations deduced from this research work are expected to not only expand the knowledge of shale lithofacies classification for lacustrine fine-grained rocks,but can also offer a theoretical foundation for lacustrine shale oil exploration and development.
基金supported by the National Natural Science Foundation of China (Grant No. 42302189)。
文摘Molecular biomarker and whole oil carbon isotope(δ^(13)C_(oil)) analyses were conducted on eleven typical crude oils from the Qiongdongnan Basin to investigate their biological sources and depositional environments. Saturated hydrocarbon biomarkers in most samples are characterized by angiosperm-derived compounds, with aromatic compounds dominated by the naphthalene, phenanthrene, biphenyl, and fluorene series. The related source rocks of these oils were mainly deposited under oxic condition, but a subanoxic-suboxic and enclosed water column condition in the Central Depression during Oligocene.The identification of simonellite and related compounds in the aromatic fractions provides reliable evidence for the input of coniferous gymnosperms. Cadalene may also have a potential association with gymnosperms since it shows a strong positive correlation with simonellite. Evidence from density, nalkanes, short-chain alkylbenzenes and secondary brine inclusions indicates that the unique crude oil B13-1 may have suffered from thermal alteration. These crude oils(excluding B13-1) can be classified into four types based on the δ^(13)C_(oil)values and molecular biomarkers. Type A oil(solely S34-3) is characterized by non-angiosperm plants, with minor dinoflagellates and increasing contribution from conifer gymnosperms than others. Type B oils(L17-2, L18-1, L25-1, and L25-1W) show heavy δ^(13)C_(oil)(-24 ‰to-25 ‰) and mixed contributions from both angiosperms and marine algae, with the marine algae contribution increasing. Type C oils(L13-2 and B21-1) share similar biological sources with Type B, but the moderately δ^(13)C_(oil)(-25‰ to-26‰) and high level of terrestrial biomarkers suggesting a predominant contribution of angiosperms. Type D oils(Y13-1a, Y13-1b, and Y13-4) possess the lightestδ^(13)C_(oil)(mainly below-26‰) and are primarily derived from angiosperms, with mangrove vegetation playing an important role. Spearman correlation analysis among 14 source biomarker parameters withδ^(13)C_(oil)and geological setting of related source rocks implied that the marine algae should be responsible for the heavy δ^(13)C_(oil)in the Type B. The contribution of marine algae in the Central Depression may have been neglected in the past, as it is usually covered by remarkable angiosperm biomarkers.
基金supported by the National Natural Science Foundation of China (No. 41072003)the Fostering Foundation of Henan Polytechnic University for the Excellent Ph. D Dissertation (No. 2011011001)
文摘Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.
基金supported by the National Natural Science Foundation of China (Grant No. 40902013)"Strategic Priority Research Program - Climate Change:Carbon Budget and Relevant Issues" of the ChineseAcademy of Sciences (Grant No.XDA05130202)
文摘Shuidonggou site has abundant Paleolithic remains of Late Pleistocene deposition. Studying the evolution of depositional environments is essential to the comprehensive understanding of the living conditions of ancient populations. To reconstruct the depositional environment at Shuidonggou, we carried out archaeological excavations and collected systematic deposition samples at the key position of Shuidonggou Locality 2 for grain size analysis and sporopollen statistics. The environmental evolution around the Shuidonggou site generally underwent four stages at ~72-18 kaBP. During the first stage （~72-41 kaBP）, the river developed with gravel and sand stratums. During the second stage （41-34 kaBP）, a swamp with numerous aquatic plants formed. In the third stage （34-29 kaBP）, site formation was characterized by shallow lake depositional conditions; the climate was relatively warm and humid. The marginal bank depositional conditions deteriorated during the fourth stage （29-18 kaBP）, and the site underwent several dry events; the climate also became drier and colder.
文摘Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin,Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry.The bulk carbon isotopic values of the whole rock extracts,saturate and aromatic fractions range from–28.7‰to–26.8‰,–29.2‰to–27.2‰and–28.5‰to–26.7‰,respectively while the bulk carbon isotopic values of the whole oils,saturate and aromatic fractions range from–25.4‰to–27.8‰,–25.9‰to–28.4‰and–23.5‰to–26.9‰,respectively.The average carbon isotopic compositions of individual alkanes(nC12-nC33)in the rock samples range from–34.9‰to–28.2‰whereas the average isotopic values of individual n-alkanes in the oils range from–31.1‰to–23.8‰.Theδ13C isotope ratios of pristane and phytane in the rock samples range from–29.2‰to–28.2‰and–30.2‰to–27.4‰respectively while the pristane and phytane isotopic values range from–32.1‰to–21.9‰and–30.5‰to–26.9‰,respectively.The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments.The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.
文摘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.
文摘The Sarvak Formation is the second major oil-bearing reservoir in the south and south west of Iran. The Middle Cretaceous Sarvak formation in the Zagros Mountains (Zagros Basin) is mainly composed of carbonate sequences. Based on facies studied, thirteen microfacies were recognized in the studied area, which were categorized in the three facies groups: including inner ramp, mid ramp and outer ramp. Evidences such as the gradual changes in the facies (basin slope), the absence of extensive uninterrupted barrier reef, the lack of calciturbidite and gravity sediments as well as the high proportion of grain-supported indicated that the Sarvak Formation was deposited in the ramp like depositional system, particularly on an inner ramp setting. Inner ramp facies group is the principal setting and subdivided to tidal flat, restricted and unrestricted lagoon as well as shoal sub-environments.
文摘In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section includes about 380 meters of conglomerate at the base, chalk, limestone, marl, and shale. Petrographic studies with facies analysis have led to the identification of 12 microfacies, these microfacies have been deposited in four facies groups including tidal flat, lagoon, barrier and open marine. Study of horizontal and vertical facies changes and their comparison with recent and ancient environments reveals that Qom Formation in this section relates to shallow marine environment and its facies were deposited in a shelf carbonate platform and are comparable with contemporary shelf platforms such as Florida and old shelf platforms such as Mozduran. The most important diagenetic processes affecting the studied section include micritization, bioturbation, cementation, dissolution, neomorphism, fracturing, mechanical and chemical compaction, hematitization and dolomitization. These processes have formed in marine, meteoric and burial diagenetic environments.
文摘The Endengue Banded Iron Formation (BIF) is located in the northwestern edge of the Congo craton in Cameroon. Here<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> we report geochemical data of trace and rare earth elements (REE) of the Endengue BIF samples from the Archean Ntem complex and investigate their environmental setting. Two types of BIF occur at Endengue area, both containing minimal contamination from terrestrial material. Total REE (</span><span style="line-height:99%;font-family:Verdana;">Σ</span><span style="font-family:Verdana;">REE) contents in the Type 1 BIF are extremely low, ranging from 0.34 to 1.83 ppm, similarly to pure chemical sediments while Type 2 BIF displays</span><span style="font-family:;" "=""> </span><span style="line-height:99%;font-family:Verdana;">Σ</span><span style="font-family:Verdana;">REE contents ranging from 2.98 to 24.26 ppm. The PAAS-normalized REE</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">+</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">Y patterns of the two BIF types display LREE enrichment relative to HREE and weak positive Eu anomaly, most likely suggesting that the source of iron and siliceous of the Endengue BIFs is mainly from the contribution of low-temperature hydrothermal alteration of the crust. Type 1 BIF shows very low Nd content (<1 ppm) with positive correlation between Nd and Ce/Ce</span><span style="font-family:Verdana;">*</span><span style="font-family:Verdana;"> and positive Ce anomalies which suggests suboxic or anoxic seawater similar to the depositional environment of Elom BIF in Archean Ntem complex. In contrast, Type 2 BIF displays low to moderate Nd contents (1 and 100 ppm with the exception of sample LBR65) with negative correlation between Nd and Ce/Ce</span><span style="font-family:Verdana;">*</span><span style="font-family:Verdana;"> and negative Ce anomalies. These features indicate precipatation of Type 2 BIF from oxic iron-rich solution that changed to oxidized surface by rapid precipitation of the hydrothermal Fe. The Endengue BIFs were deposited in the continental margin ocean in presence of low-temperature hydrothermal fluids mixed with seawater, similar to Paleoproterozoic Kpwa</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">Atog Boga BIFs within the Nyong group and other Paleoproterozoic Superior</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">type BIFs worldwide.</span>
