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 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
The Benue Trough Basin (BTB) of Nigeria is geologically and geo-morphologically subdivided into upper,middle, and lower segments. The BTB is the subject of geological research due to its rich coal depositsthat have th...The Benue Trough Basin (BTB) of Nigeria is geologically and geo-morphologically subdivided into upper,middle, and lower segments. The BTB is the subject of geological research due to its rich coal depositsthat have the potential for oil and gas. The purpose of the present study is to examine the origins,depositional environments, and thermal history of the selected coals and the processes that influencetheir quality. Coal samples from different open cast coal mines in the middle BTB were examined usingproximate and ultimate, x-ray diffraction (XRD), x-ray fluorescence (XRF), laser ablation induced coupledplasma (LA-ICPMS), and petrographical analyses. The coal samples contained mainly quartz, kaolinite,and organic carbon. The XRD spectra peaks revealed the triclinic and monoclinic structure of kaolin. TheSiO2/Al2O3 ratios confirmed the dominance of quartz and kaolinite. The Ni/Co versus V/Cr, Cu/Zn, and V/Mo values in the studied coals suggest oxic depositional environments, whereas the V/(Ni þ V) and V/(V þ Cr) values indicate oxic to suboxic conditions. The Ce/Ce* values are slightly below 1, which indicates a suboxic depositional environment. Maceral texture is indicative of transformations from subbituminous to high volatile C or B bituminous coal. The maceral components and mineral matter(10%) of the studied coals imply deposition in the planar margin mire, and a river system of planarmargin mire environments, respectively. The high gelification index (GI) and tissue preservation index(TPI) values indicate peat accumulation developed within a wet forest swamp. The ternary diagram ofthe maceral component suggests deposition in a wet moor environment with intermittent moderate tohigh flooding episodes. The studied coals are sub-hydrous vitrinite inferring hydrogen-poor and thermally immature characteristics. The low V and Ni contents, low H/C and high O/C, indicate Type IIIterrestrial organic matter with the potential to generate gaseous hydrocarbons. The investigated coalswere deposited by the river within telmatic, limnic, and limno-telmatic zones in the planar margin mire depositional environments. Overall, the integrated petrologic and geochemical data used in this studyprovides a reliable approach for the assessment of coal depositional environments.展开更多
In the Indian Himalaya,the Cambrian sequences are exposed in the Lesser and Tethyan Himalayan zones(LHZ and THZ).In the LHZ,the Cambrian biozonation is available at four stratigraphic intervals,i.e.,at~542-535 Ma,~524...In the Indian Himalaya,the Cambrian sequences are exposed in the Lesser and Tethyan Himalayan zones(LHZ and THZ).In the LHZ,the Cambrian biozonation is available at four stratigraphic intervals,i.e.,at~542-535 Ma,~524-513 Ma,~516 Ma,and~512 Ma.In the THZ,the Cambrian biozonation exists broadly at two stratigraphic intervals,i.e.,~514-505 Ma(in the Spiti region and partially in the Kashmir region)and~505-498 Ma(in the Zanskar region and partially in the Kashmir region).The Indian Cambrian faunal elements share Gondwanan and peri-gondwanan affinities.The depositional environments of the Cambrian sediments of THZ and LHZ show a wide array of settings.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),and de...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 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
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
A total of 45 alkylbenzenes were detected and identified in crude oils with different depositional environments and thermal maturities from the Tarim Basin,Beibuwan Basin,and Songliao Basin using comprehensive two-dim...A total of 45 alkylbenzenes were detected and identified in crude oils with different depositional environments and thermal maturities from the Tarim Basin,Beibuwan Basin,and Songliao Basin using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry(GC×GCTOFMS).By analyzing the distribution characteristics of C0-C5alkylbenzenes,it is found that the content of some alkylbenzenes varies greatly in crude oils.Based on the distribution characteristics of 1,2,4,5-tetramethylbenzene(Te MB)and 1,2,3,4-Te MB,the ratio of 1,2,4,5-Te MB to 1,2,3,4-Te MB is proposed to indicate the organic matter origin and depositional environment of ancient sediments.Oil samples originated mainly from lower hydrobiont,algae,bacteria and source rocks deposited under reducing/anoxic conditions have low 1,2,4,5-/1,2,3,4-Te MB values(less than 0.6),while oil samples originated mainly from terrestrial higher plants and source rocks deposited under oxic/sub-oxic conditions have higher 1,2,4,5-/1,2,3,4-Te MB values(greater than 1.0).The significant difference of 1,2,4,5-/1,2,3,4-Te MB values is controlled by 1,2,4,5-Te MB content.1,2,4,5-Te MB content in oils derived from source rocks deposited in oxidized sedimentary environment(greater than 1.0 mg/g whole oil)is higher than that in oils from source rocks deposited in reduced sedimentary environment(less than 1.0 mg/g whole oil).1,2,4,5-/1,2,3,4-Te MB ratio might not or slightly be affected by evaporative fractionation,biodegradation and thermal maturity.1,2,4,5-/1,2,3,4-Te MB ratio and 1,2,4,5-Te MB content can be used as supplementary parameter for the identification of sedimentary environment and organic matter input.It should be noted that compared to the identification of organic matter sources,the 1,2,4,5-/1,2,3,4-Te MB parameter is more effective in identifying sedimentary environments.展开更多
Various studies have indicated that microbes were involved in the precipitation of dolostones in the Proterozoic.The identification of ancient microbial dolostones remains challenging due to the rare preservation of m...Various studies have indicated that microbes were involved in the precipitation of dolostones in the Proterozoic.The identification of ancient microbial dolostones remains challenging due to the rare preservation of microbe fossils.In this study,we found ancient microbial dolostones in Paleoproterozoic Chuanlinggou Formation in Beijing,North China,employing thin-section observations,trace and rare earth elements as well as carbon and oxygen isotope analyses to reveal the origin.The paleoenvironment has also been reconstructed.The results indicate that dolostones found in the Chuanlinggou Formation are formed through primary dolomite precipitation induced by cyanobacterial activity.These dolomitized geobodies exhibit various morphologies of mounded,banded and bedded,and all dolostones are microcrystalline textures.The geochemical characteristics of these dolostones show a relatively low δ^(18)O value(average=-7.34‰),Fe(Ⅱ)enrichment,Ce anomaly and comparable patterns of REY.The specific geomorphology(mounded,banded and bedded)and mottled structures of the dolostones indicate that they are formed through in-situ dolomite precipitation induced by cyanobacterial activity.The high Fe(Ⅱ)content suggests a reducing environment,whereas the Ce anomaly indicates anoxic conditions within the water body.The REY patterns provide evidence for the microbial origin of the dolostones.These dolostones were formed in clastic off-shore shelf environments.The seawater was warm,normal in salinity,and the sea floor was slightly agitated to quiet and reducing.The geomorphology of the dolomitized geobodies changes from mounded to banded and bedded in correlation with depth increase and hydrodynamic energy decrease.This study may provide another type of environments for microbial dolostones and the geochemical characteristics of these dolostones may serve as a valuable reference for identifying similar ancient microbial dolostones.展开更多
Jurassic rocks are abundantly developed in the source area of the Yangtze River,South Qinghai,with the greatest thickness of 6311 m,including five stratigraphic units:Qoimaco Formation,Buqu Formation,Xiali Formation,S...Jurassic rocks are abundantly developed in the source area of the Yangtze River,South Qinghai,with the greatest thickness of 6311 m,including five stratigraphic units:Qoimaco Formation,Buqu Formation,Xiali Formation,Suowa Formation,and Xueshan Formation.Based on sufficient fossils of bivalves,ammonites,and brachiopods,the major part of these formations is ascribed to the Middle Jurassic Bathonian to Callovian.No diagnostic fossils have been found from the Lower Qoimaco Formation or Upper Xueshan Formation,which could possibly contain in part Bajocian and Oxfordian taxa respectively.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
Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of th...Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of these targets and associated risks.Assessing shale depositional environments is also challenging due to the fine-grained nature of the sediments and subtle compositional variations.Herein,marine black shales of the Lower Cambrian Shiyantou(SYT)Formation(Fm)and Yu'anshan(YAS)Fm are investigated through a series of experiment,including thin sections,scanning electron microscopy,and major and trace elements analysis.Results show that five lithofacies can be identified in the SYT and YAS shales:(1)calcareous mudstone;(2)wavy-laminated sand,silt,and clay bearing mudstone;(3)laminated and massive mudstone;(4)planar-laminated pyritic mudstone,and(5)thin bedded sand and siltstone.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of SYT Fm are 57.03%,12.74%,4.20%,3.97%,3.93%,3.35%,1.09%,0.68%,0.28%,and 0.05%,respectively.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of Yu'anshan Fm are 54.93%,14.52%,5.26%,6.00%,3.77%,3.88%,0.15%,0.63%,0.19%,and 0.10%,respectively.Samples from SYT Fm are enriched in Li,V,Cr,Co,Zr,Cs,and U relative to Upper Continental Crust(UCC)and most of shale samples from YAS Fm are enriched in Li,V,Co,and U relative to UCC.The marine black shales are deposited in dynamic anoxic to oxic environment in upper Yangtze Plate,which indicated the seabed had already oxidized in the Cambrian Stages 2 and 3.The Chemical Index of Alteration(CIA)values ranged 51.84–79.46 indicate a warm and humid climate in the 2 stages.These findings are consistent with the region's paleogeography and previous studies.They hold significance for sedimentologists,paleontologists,and other researchers involved in petroleum geology.展开更多
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
Although significant progress has been made in micromechanical characterization and upscaling of homogeneous materials,systematic investigations into deposition-controlled micro–macro rheological relationships in het...Although significant progress has been made in micromechanical characterization and upscaling of homogeneous materials,systematic investigations into deposition-controlled micro–macro rheological relationships in heterogeneous sedimentary soft rocks remain limited,particularly concerning timedependent viscous parameter upscaling.This study investigates six typical fluvial and lacustrine microfacies from the Ordos Basin,China,including riverbed lag,natural levee,floodplain lake,point bar,sheet sand,and shallow lake mud.Mineral composition and microstructure are characterized,and nanoindentation creep tests quantify viscoelastic properties.A micro–macro upscaling method that transforms the time-domain Burger model into the frequency domain and utilizes three traditional homogenization schemes:dilute approximation,Mori-Tanaka,and self-consistent methods,for comparative estimation of macroscopic rheological parameters is proposed.Microstructural analysis demonstrates distinct fabric patterns controlled by depositional energy.Floodplain lake and sheet sand microfacies show superior rheological stability due to dense quartz skeletons,whereas riverbed lag and shallow lake mud perform poorly,caused by skeleton relaxation and clay-dominated slip,respectively.The point bar microfacies exhibits a“rigid-soft hybrid”behavior,with high long-term stability but reduced transient stability.Comparatively,the frequency-domain upscaling framework developed in this study,incorporating the Mori-Tanaka scheme,demonstrates satisfactory agreement with experimental data,validating its capability to predict macroscopic viscoelastic properties from microstructural features.展开更多
The study area belongs to the north Afghanistan having complex tectonic setting, because of separation of the Afghanistan plate from Pangea in Early Permian and its subsequent northward journey and collision with Eura...The study area belongs to the north Afghanistan having complex tectonic setting, because of separation of the Afghanistan plate from Pangea in Early Permian and its subsequent northward journey and collision with Eurasian plate. The rock exposed in the area belongs to Paleozoic, Mesozoic to Quaternary with Proterozoic basement. Particularly the Permian succession of Afghanistan is rich in fusulinids (larger foraminifera), is age diagnostic, provides strong biostratigraphic tool for the Permian deposits, and has paleobiogeographic applications. The Bamian zone of north Afghanistan has good exposure to Middle Permian and is designated as Bolula and Khaja Ghar Formation is undertaken in this study. The Bolula Formation overlies the greenschist and basalts, composed mainly of carbonate rocks (Dolostone and limestone), having massive limestone, with some quartz and secondary calcite vein in the succession. The intermittent siliciclastic wedges within the carbonate succession are identified as input within the platform with tectonic pulses in the hinterland. Bolula and Khaja Ghar succession is divided into 8 lithofacies ( Facies A to H) and 6 carbonate Facies viz. Sparry calcites limestone, Micritic limestone, Fossiliferous limestones (Biomicrite), Peloidal limestone (Fecal pellets), Interlaminated micritic and sparite limestone, and sandy limestone (micritic). The Bolula and Khaja Ghar Formation in the Bamian area have deposited in a shallow marine shelf environment because of predominance of carbonate rocks and presence of shallow-water marine fossils including fusulinids, small benthic foraminifera, algae, bivalve, brachiopods fragments, corals and bryozoans, etc. In the Bamian zone the unconformity between Upper Carboniferous and Lower Permian;indicates extensive gap in sedimentation, traceable to many parts of Afghanistan as unconformity or tectonic contact is considered here as sequence boundary.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
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
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
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.
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The Benue Trough Basin (BTB) of Nigeria is geologically and geo-morphologically subdivided into upper,middle, and lower segments. The BTB is the subject of geological research due to its rich coal depositsthat have the potential for oil and gas. The purpose of the present study is to examine the origins,depositional environments, and thermal history of the selected coals and the processes that influencetheir quality. Coal samples from different open cast coal mines in the middle BTB were examined usingproximate and ultimate, x-ray diffraction (XRD), x-ray fluorescence (XRF), laser ablation induced coupledplasma (LA-ICPMS), and petrographical analyses. The coal samples contained mainly quartz, kaolinite,and organic carbon. The XRD spectra peaks revealed the triclinic and monoclinic structure of kaolin. TheSiO2/Al2O3 ratios confirmed the dominance of quartz and kaolinite. The Ni/Co versus V/Cr, Cu/Zn, and V/Mo values in the studied coals suggest oxic depositional environments, whereas the V/(Ni þ V) and V/(V þ Cr) values indicate oxic to suboxic conditions. The Ce/Ce* values are slightly below 1, which indicates a suboxic depositional environment. Maceral texture is indicative of transformations from subbituminous to high volatile C or B bituminous coal. The maceral components and mineral matter(10%) of the studied coals imply deposition in the planar margin mire, and a river system of planarmargin mire environments, respectively. The high gelification index (GI) and tissue preservation index(TPI) values indicate peat accumulation developed within a wet forest swamp. The ternary diagram ofthe maceral component suggests deposition in a wet moor environment with intermittent moderate tohigh flooding episodes. The studied coals are sub-hydrous vitrinite inferring hydrogen-poor and thermally immature characteristics. The low V and Ni contents, low H/C and high O/C, indicate Type IIIterrestrial organic matter with the potential to generate gaseous hydrocarbons. The investigated coalswere deposited by the river within telmatic, limnic, and limno-telmatic zones in the planar margin mire depositional environments. Overall, the integrated petrologic and geochemical data used in this studyprovides a reliable approach for the assessment of coal depositional environments.
基金The IGC-36 funding for preparation of field excursion guide for Renuka-Sector(part of NR008)is gratefully acknowledged.
文摘In the Indian Himalaya,the Cambrian sequences are exposed in the Lesser and Tethyan Himalayan zones(LHZ and THZ).In the LHZ,the Cambrian biozonation is available at four stratigraphic intervals,i.e.,at~542-535 Ma,~524-513 Ma,~516 Ma,and~512 Ma.In the THZ,the Cambrian biozonation exists broadly at two stratigraphic intervals,i.e.,~514-505 Ma(in the Spiti region and partially in the Kashmir region)and~505-498 Ma(in the Zanskar region and partially in the Kashmir region).The Indian Cambrian faunal elements share Gondwanan and peri-gondwanan affinities.The depositional environments of the Cambrian sediments of THZ and LHZ show a wide array of settings.
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.
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.
基金supported by Doctor’s Scientific Research Initiation Project of Yan’an University(YAU202213093)National Natural Science Foundation of China(Grant No.41503029)。
文摘A total of 45 alkylbenzenes were detected and identified in crude oils with different depositional environments and thermal maturities from the Tarim Basin,Beibuwan Basin,and Songliao Basin using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry(GC×GCTOFMS).By analyzing the distribution characteristics of C0-C5alkylbenzenes,it is found that the content of some alkylbenzenes varies greatly in crude oils.Based on the distribution characteristics of 1,2,4,5-tetramethylbenzene(Te MB)and 1,2,3,4-Te MB,the ratio of 1,2,4,5-Te MB to 1,2,3,4-Te MB is proposed to indicate the organic matter origin and depositional environment of ancient sediments.Oil samples originated mainly from lower hydrobiont,algae,bacteria and source rocks deposited under reducing/anoxic conditions have low 1,2,4,5-/1,2,3,4-Te MB values(less than 0.6),while oil samples originated mainly from terrestrial higher plants and source rocks deposited under oxic/sub-oxic conditions have higher 1,2,4,5-/1,2,3,4-Te MB values(greater than 1.0).The significant difference of 1,2,4,5-/1,2,3,4-Te MB values is controlled by 1,2,4,5-Te MB content.1,2,4,5-Te MB content in oils derived from source rocks deposited in oxidized sedimentary environment(greater than 1.0 mg/g whole oil)is higher than that in oils from source rocks deposited in reduced sedimentary environment(less than 1.0 mg/g whole oil).1,2,4,5-/1,2,3,4-Te MB ratio might not or slightly be affected by evaporative fractionation,biodegradation and thermal maturity.1,2,4,5-/1,2,3,4-Te MB ratio and 1,2,4,5-Te MB content can be used as supplementary parameter for the identification of sedimentary environment and organic matter input.It should be noted that compared to the identification of organic matter sources,the 1,2,4,5-/1,2,3,4-Te MB parameter is more effective in identifying sedimentary environments.
基金financially supported by the National Natural Science Foundation of China(Grant No.41872108)。
文摘Various studies have indicated that microbes were involved in the precipitation of dolostones in the Proterozoic.The identification of ancient microbial dolostones remains challenging due to the rare preservation of microbe fossils.In this study,we found ancient microbial dolostones in Paleoproterozoic Chuanlinggou Formation in Beijing,North China,employing thin-section observations,trace and rare earth elements as well as carbon and oxygen isotope analyses to reveal the origin.The paleoenvironment has also been reconstructed.The results indicate that dolostones found in the Chuanlinggou Formation are formed through primary dolomite precipitation induced by cyanobacterial activity.These dolomitized geobodies exhibit various morphologies of mounded,banded and bedded,and all dolostones are microcrystalline textures.The geochemical characteristics of these dolostones show a relatively low δ^(18)O value(average=-7.34‰),Fe(Ⅱ)enrichment,Ce anomaly and comparable patterns of REY.The specific geomorphology(mounded,banded and bedded)and mottled structures of the dolostones indicate that they are formed through in-situ dolomite precipitation induced by cyanobacterial activity.The high Fe(Ⅱ)content suggests a reducing environment,whereas the Ce anomaly indicates anoxic conditions within the water body.The REY patterns provide evidence for the microbial origin of the dolostones.These dolostones were formed in clastic off-shore shelf environments.The seawater was warm,normal in salinity,and the sea floor was slightly agitated to quiet and reducing.The geomorphology of the dolomitized geobodies changes from mounded to banded and bedded in correlation with depth increase and hydrodynamic energy decrease.This study may provide another type of environments for microbial dolostones and the geochemical characteristics of these dolostones may serve as a valuable reference for identifying similar ancient microbial dolostones.
基金supported by National Natural Science Foundation of China(Grant Nos.40772022,40972006)State Key Laboratory of Palaeobiology and Stratigraphy(Nanjing Institute of Geology and Paleontology)Chinese Academy of Sciences(Grant No.10311)
文摘Jurassic rocks are abundantly developed in the source area of the Yangtze River,South Qinghai,with the greatest thickness of 6311 m,including five stratigraphic units:Qoimaco Formation,Buqu Formation,Xiali Formation,Suowa Formation,and Xueshan Formation.Based on sufficient fossils of bivalves,ammonites,and brachiopods,the major part of these formations is ascribed to the Middle Jurassic Bathonian to Callovian.No diagnostic fossils have been found from the Lower Qoimaco Formation or Upper Xueshan Formation,which could possibly contain in part Bajocian and Oxfordian taxa respectively.
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.
基金Supported by the National Natural Science Foundation of China(Nos.42130206,41302076)the Ministry of Science and Technology of the People’s Republic of China(MOST)Special Fund+1 种基金the State Key Laboratory of Continental Dynamics,Northwest University(No.201210128)the Major Scientific and Technological Projects of Changqing Oilfield(No.ZDZX-2021-03)。
文摘Early Cambrian organic-rich shales in the Yangtze Plate are key shale gas exploration targets in China,but their sedimentary environments are not well understood.This lack of knowledge complicates the evaluation of these targets and associated risks.Assessing shale depositional environments is also challenging due to the fine-grained nature of the sediments and subtle compositional variations.Herein,marine black shales of the Lower Cambrian Shiyantou(SYT)Formation(Fm)and Yu'anshan(YAS)Fm are investigated through a series of experiment,including thin sections,scanning electron microscopy,and major and trace elements analysis.Results show that five lithofacies can be identified in the SYT and YAS shales:(1)calcareous mudstone;(2)wavy-laminated sand,silt,and clay bearing mudstone;(3)laminated and massive mudstone;(4)planar-laminated pyritic mudstone,and(5)thin bedded sand and siltstone.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of SYT Fm are 57.03%,12.74%,4.20%,3.97%,3.93%,3.35%,1.09%,0.68%,0.28%,and 0.05%,respectively.Average content of major elements SiO_(2),Al_(2)O_(3),MgO,Fe_(2)O_(3),K_(2)O,CaO,Na_(2)O,TiO_(2),P_(2)O_(5),and MnO of Yu'anshan Fm are 54.93%,14.52%,5.26%,6.00%,3.77%,3.88%,0.15%,0.63%,0.19%,and 0.10%,respectively.Samples from SYT Fm are enriched in Li,V,Cr,Co,Zr,Cs,and U relative to Upper Continental Crust(UCC)and most of shale samples from YAS Fm are enriched in Li,V,Co,and U relative to UCC.The marine black shales are deposited in dynamic anoxic to oxic environment in upper Yangtze Plate,which indicated the seabed had already oxidized in the Cambrian Stages 2 and 3.The Chemical Index of Alteration(CIA)values ranged 51.84–79.46 indicate a warm and humid climate in the 2 stages.These findings are consistent with the region's paleogeography and previous studies.They hold significance for sedimentologists,paleontologists,and other researchers involved in petroleum geology.
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financially supported by the National Natural Science Foundation of China(No.42472334)DeepEarth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2024ZD1004208)the China Postdoctoral Science Foundation(No.2025M771774)。
文摘Although significant progress has been made in micromechanical characterization and upscaling of homogeneous materials,systematic investigations into deposition-controlled micro–macro rheological relationships in heterogeneous sedimentary soft rocks remain limited,particularly concerning timedependent viscous parameter upscaling.This study investigates six typical fluvial and lacustrine microfacies from the Ordos Basin,China,including riverbed lag,natural levee,floodplain lake,point bar,sheet sand,and shallow lake mud.Mineral composition and microstructure are characterized,and nanoindentation creep tests quantify viscoelastic properties.A micro–macro upscaling method that transforms the time-domain Burger model into the frequency domain and utilizes three traditional homogenization schemes:dilute approximation,Mori-Tanaka,and self-consistent methods,for comparative estimation of macroscopic rheological parameters is proposed.Microstructural analysis demonstrates distinct fabric patterns controlled by depositional energy.Floodplain lake and sheet sand microfacies show superior rheological stability due to dense quartz skeletons,whereas riverbed lag and shallow lake mud perform poorly,caused by skeleton relaxation and clay-dominated slip,respectively.The point bar microfacies exhibits a“rigid-soft hybrid”behavior,with high long-term stability but reduced transient stability.Comparatively,the frequency-domain upscaling framework developed in this study,incorporating the Mori-Tanaka scheme,demonstrates satisfactory agreement with experimental data,validating its capability to predict macroscopic viscoelastic properties from microstructural features.
文摘The study area belongs to the north Afghanistan having complex tectonic setting, because of separation of the Afghanistan plate from Pangea in Early Permian and its subsequent northward journey and collision with Eurasian plate. The rock exposed in the area belongs to Paleozoic, Mesozoic to Quaternary with Proterozoic basement. Particularly the Permian succession of Afghanistan is rich in fusulinids (larger foraminifera), is age diagnostic, provides strong biostratigraphic tool for the Permian deposits, and has paleobiogeographic applications. The Bamian zone of north Afghanistan has good exposure to Middle Permian and is designated as Bolula and Khaja Ghar Formation is undertaken in this study. The Bolula Formation overlies the greenschist and basalts, composed mainly of carbonate rocks (Dolostone and limestone), having massive limestone, with some quartz and secondary calcite vein in the succession. The intermittent siliciclastic wedges within the carbonate succession are identified as input within the platform with tectonic pulses in the hinterland. Bolula and Khaja Ghar succession is divided into 8 lithofacies ( Facies A to H) and 6 carbonate Facies viz. Sparry calcites limestone, Micritic limestone, Fossiliferous limestones (Biomicrite), Peloidal limestone (Fecal pellets), Interlaminated micritic and sparite limestone, and sandy limestone (micritic). The Bolula and Khaja Ghar Formation in the Bamian area have deposited in a shallow marine shelf environment because of predominance of carbonate rocks and presence of shallow-water marine fossils including fusulinids, small benthic foraminifera, algae, bivalve, brachiopods fragments, corals and bryozoans, etc. In the Bamian zone the unconformity between Upper Carboniferous and Lower Permian;indicates extensive gap in sedimentation, traceable to many parts of Afghanistan as unconformity or tectonic contact is considered here as sequence boundary.
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.
