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
Tonle Sap sedimentary basin was considered a favorable geological condition for hydrocarbon accumulation in the onshore Cambodia. Two exposure outcrops in Battambang province, called Somlout and Takream, were selected...Tonle Sap sedimentary basin was considered a favorable geological condition for hydrocarbon accumulation in the onshore Cambodia. Two exposure outcrops in Battambang province, called Somlout and Takream, were selected to represent sediments in this basin. The sedimentology and geochemistry studies provide insights into the depositional environment of sediments using field investigation, lithological, sedimentological, paleontological, and geochemical analysis. The redox condition, water column, and depositional setting were analyzed by plotting the ratio of V vs. Cr, Uauthigenic vs. V/Cr, Sr vs. Ba, Ca vs. (Fe + Ca), and Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> vs. Al<sub>2</sub>O<sub>3</sub>/(Al<sub>2</sub>O<sub>3</sub> + Fe<sub>2</sub>O<sub>3</sub>) diagram. Moreover, these diagrams can be used to predict depositional conditions as well. Based on the results, Somlout and Takream comprise calcareous shale and limestone facies. The geochemical analysis showed that Somlout calcareous shale samples were deposited in the dysoxic freshwater of the lake setting during the regression, while Somlout limestones and Takream were deposited in high salinity seawater, oxic condition of shallow-marine water. In addition, Somlout limestones consist of fragmental fusulinid foraminifera, bivalve shelve, and bryozoan, which suggest a barrier environment. Meanwhile, Teakream consists of fine-grained calcareous shale, and lime-mudstone, which are presented to form in the quiet marine setting of the lagoon environment. Therefore, the Tonle Sap basin sediments were deposited in the Somlout area’s barrier and lake environment, and the lagoon environment for Takream.展开更多
A set of organic-rich shales of the upper Permian Longtan Formation,which is widely developed in the northeastern part of the Sichuan Basin,is a key formation for the next step of exploration and development.At presen...A set of organic-rich shales of the upper Permian Longtan Formation,which is widely developed in the northeastern part of the Sichuan Basin,is a key formation for the next step of exploration and development.At present,most studies on this set of formations have focused on the reservoir characteristics and reservoir formation mechanism of the shales,and basic studies on the palaeoenvironment and organic matter(OM)enrichment mechanism have not been fully carried out.In this paper,we recovered the sedimentary palaeoenvironment by mineralogical,elemental geochemical and organic geochemical analyses,and explored the enrichment mechanism of OM under the constraints of palaeoenvironmental evolution.The shales can be divided into two stages of sedimentary evolution:compared with the shales of the Lower Longtan Formation,the shales of the Upper Longtan Formation are relatively rich in quartz,poor in clay and carbonate minerals,and the OM type changes from typeⅢto typeⅡ_(2).The depositional environment has undergone a change from sea level rise,from warm and wet climate to dry and cold climate,and from oxygen-poor condition restricted to open reduction environment;the land source input has decreased,the siliceous mineral content has increased,the biological productivity has improved,and the deposition rate has changed from high to low.A depositional model was established for the shales of the Longtan Formation,reflecting the differential reservoir formation pattern of organic matter.For the Lower Longtan Formation shales,the most important factors controlling OM content are terrestrial source input and deposition rate,followed by paleoclimate and paleooxygen conditions.For the Upper Longtan Formation shales,the most important controlling factor is paleo-productivity,followed by sedimentation rate.The depositional model constructed for the Upper and Lower Longtan Formation shales can reproduce the enrichment of organic matter and provide a basis for later exploration and development.展开更多
As a repository of REE,the Paleoproterozoic phosphorite of the Aravalli Basin in India is explored time to time.Paleoproterozoic phosphorite deposits of the Sallopat sub-basin Banswara district of the Aravalli Supergr...As a repository of REE,the Paleoproterozoic phosphorite of the Aravalli Basin in India is explored time to time.Paleoproterozoic phosphorite deposits of the Sallopat sub-basin Banswara district of the Aravalli Supergroup show moderate REE concentrations much lower than that of average marine phosphorites.Different ratios and PAAS-normalized REE distribution patterns reflect MREE enrichment over LREE and HREE in these phosphorites.MREE enrichment confirmed by(Sm/Yb)Nversus(Sm/Pr)Nrelationship and attributed to the selective uptake by cyanobacteria and mixing of riverine inputs.Y/Ho,La/Ce and Er/Nd ratios confirm that the REE in Sallopat phosphorites might have been affected by the argillaceous terrigenous and plagioclase-rich sediments probably derived from Banded Gneissic Complex.Diagenetic modeling indicates that REE were concentrated during early diagenetic processes with limited weathering influence.Moderate negative to low Ce anomaly depicts oxic to sub-oxic conditions of seawater due to oxidation of Ce^(3+)to Ce^(4+)whereas Eu^(3+)reduced to Eu^(2+)indicating positive Euanomaly and reducing conditions as well during the deposition.These anomalies may be due to the stratified restricted marine environment of upwelling and mingling of organic-rich anoxic deep water with oxic upper seawater prior to the formation of phosphorite deposits in the embayment.Enrichment of REE in Sallopat phosphorite relies on various physico-chemical conditions.These phosphorites may have been formed in restricted marine water which was influenced by extra clastic sediment input carried out by fluvial systems.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 carb...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
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
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
Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from t...Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from the grain size analysis indicates that the Ngrayong sediments are classified as sand or muddy sands. They are very fine- to medium-grained (phi values: 1.67 to 3.35), moderately- to well-sorted (standard deviation: 0.19 to 0.57), strongly fine-skewed to strongly coarse-skewed (skewness values: 4.82 to −5.97), and very platykurtic to very leptokurtic (kurtosis values: 0.36 to 2.41). Sandstone samples show unimodal grain size distribution. The sediments are interpreted to be transported in all three modes-traction, saltation and suspension, however, suspension and rolling are the major processes during transportation. Discriminant functions indicate diversity in the depositional environment for the sandstones. However, shallow marine is regarded as the dominant depositional environment. The preponderance of fine-grained sediments and lack of coarse sands suggest low to moderate energy conditions during deposition of Ngrayong sediments.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
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
Permian rocks in Kalmard block are recognized with Khan Group, enjoying various characteristics in different outcrops. This group is made up of three informal formations, namely Chili, Sartakht and Hermez. Middle Perm...Permian rocks in Kalmard block are recognized with Khan Group, enjoying various characteristics in different outcrops. This group is made up of three informal formations, namely Chili, Sartakht and Hermez. Middle Permian deposits (Sartakht formation) are composed chiefly of sandstone and carbonate rocks. This formation is composed of 58.6 m sandstone and dolomitic limestone in the Bakhshi section. Lower Permian carbonate deposits (Chili formation) unconformably underlie this formation while lateritic paleosols of upper Permian (Hermez formation) are depicted overlying an erosional unconformity above this formation. According to lithologic and microscopic investigations, the deposits of Sartakht formation can be divided into 2 siliciclastic petrofacies and 12 carbonate microfacies. Field observations, along with microscopic examinations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the rocks of the studied formation. Vertical changes of microfacies and depth variation curve point to the high thickness of the microfacies of lagoon and shoal environments and low thickness of the microfacies of tidal flat and open marine environments. The carbonate-siliciclastic sequence of Sartakht formation is made up of a third-order depositional sequence, separated from carbonate depositions of lower Permian (Chili formation) and lateritic paleosols of upper Permian by type 1 sequence boundary (SB1). Siliciclastic deposits include LST system tract, and carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. Sartakht formation rocks in Bakhshi section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the south of Paleotethys Ocean. The depositional sequence identified in Sartakht formation points to the age of middle Permian, conforming to middle Absaroka II supersequence. The upper erosional boundary between Sartakht and Hermez formations conforms to the global-scale sea level fall.展开更多
Deposits of Lower Carboniferous rocks in Kalmard block are recognized by Gachal informal formation, showing various characteristics in different outcrops. Lower Carboniferous deposits (Gachal formation) are composed c...Deposits of Lower Carboniferous rocks in Kalmard block are recognized by Gachal informal formation, showing various characteristics in different outcrops. Lower Carboniferous deposits (Gachal formation) are composed chiefly of carbonate, evaporite and siliciclastic rocks. This formation is composed of 198 m sandstone, limestone and dolomite as well as a small amount of shale, marl and gypsum in the Madbeiki section. This formation unconformably underlies Precambrian metamorphic deposits (Kalmard formation) while lateritic soils of lower Permian (Chili formation) are depicted overlying an erosional unconformity above this formation. According to lithologic and microscopic investigations, the deposits of Gachal formation can be divided into 1 siliciclastic petrofacies, 1 evaporite microfacies and 16 carbonate microfacies. Field observations, along with microscopic examinations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the rocks of the studied formation. Vertical changes of microfacies and depth variation curve indicate the high thickness of the microfacies of tidal flat, lagoon and shoal environments and low thickness of the microfacies of open marine environment. The carbonate-evaporite-siliciclastic sequence of Gachal formation is made up of three third-order depositional sequence, separated each other by type 1 sequence boundary (SB1). Siliciclastic and evaporite deposits include LST system tract, and carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. Gachal formation rocks in Madbeiki section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the southern Paleotethys Ocean. The depositional sequence identified in Gachal formation points to the age of Lower Carboniferous, conforming to upper Kaskaskia super sequence. The upper erosional boundary between Gachal and Chili formations conform to the global-scale sea level fall.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
The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settingshave distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate prov...The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settingshave distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances,depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of theclastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin areenriched in silica (SiO2=66.48-80.51%), and their ΣREE are 30-130 times of that of chondrite with remarkable Euanomalies. In discriminating diagrams of Eu/Eu* vs ΣREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/Eu*=1, on the right of the line Eu/Eu*/ΣREE=1 and under the line La/Yb)N/ΣREE=1/8, which indicates that thedepositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3,FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments in the basin. Analysesalso show that the protolytes of the sediments in the basin were felsic igneous rocks, and the Songliao prototype basin wasin a tectonic setting of an island arc on an active continental margin, with violent sinistral strike-slip.展开更多
A deeper understanding of the mechanisms by which geological factors(depositional environment and tectonic evolution) control the occurrence of coalbed methane(CBM) is important for the utilization of CBM resources vi...A deeper understanding of the mechanisms by which geological factors(depositional environment and tectonic evolution) control the occurrence of coalbed methane(CBM) is important for the utilization of CBM resources via surface-drilled wells and the elimination of coal-methane outbursts, the latter of which is a key issue for coal mine safety. Based on drill core data, high-pressure isothermal adsorption experiments, scanning electron microscopy experiments, mercury intrusion porosimetry, and X-ray diffraction experiments, the impact of the depositional environment and tectonic evolution on CBM occurrence of the II-1 coal seam of the Shanxi Formation in West Henan was analyzed. Results showed that the depositional environment led to the epigenetic erosion of tidal flat coal-accumulating structures by shallow-delta distributary channel strata. This resulted in the replacement of the original mudstonesandy mudstone coal seam immediate roof with fine-to-medium grained sandstones, reducing methane storage capacity. Epigenetic erosion by the depositional environment also increased coal body ash content(from 6.9% to 21.4%) and mineral content, filling the cleat system and reducing porosity, reducing methane storage capacity. The maximum methane adsorption capacity of the coal body reduced from35.7 cm3/g to 30.30 cm3/g, and Langmuir pressure decreased from 1.39 MPa to 0.909 MPa. Hence, the methane adsorption capacity of the coal body decreased while its capacity for methane desorption increased. Owing to the tectonic evolution of West Henan, tectonically deformed coal is common; as it evolves from primary cataclastic coal to granulitic coal, the angle of the diffraction peak increases, d002 decreases, and La, Lc, and Nc increase; these traits are generally consistent with dynamic metamorphism.This is accompanied by increases in the total pore volume and specific surface area of the coal body, further increasing the capacity for methane storage. Increases in micropore volume and specific surface area also increase the ability of the coal body to adsorb methane.展开更多
This paper discussed the petrographic characteristics of No.6 coal from the Xiaoyugou mine,Jungar Coalfield,Ordos Basin,China.10 samples(7 coal,1 parting mudstone and 2 floor mudstone)were analysed by microscopical an...This paper discussed the petrographic characteristics of No.6 coal from the Xiaoyugou mine,Jungar Coalfield,Ordos Basin,China.10 samples(7 coal,1 parting mudstone and 2 floor mudstone)were analysed by microscopical and geochemical methods.Four maceral compositions and several associated elements parameters were selected as indicators and corresponding diagrams were drawn to explicate the sedimentary environment.The results indicate that the maceral is dominated by vitrinite and minerals are mainly kaolinite in the No.6 coal.The sedimentary facies vary from barrier island system to tidal-flat which is a deposition process of water body shallowing and the coal-forming plants are herbs and woody plants formed in swamps.展开更多
The Asmari Formation is a thick carbonate sequence of the Oligocene-Miocene in the Zagros Basin, southwest of Iran. This formation is located in Bandar Abbas and Coastal Fars regions on the following two sections: Ang...The Asmari Formation is a thick carbonate sequence of the Oligocene-Miocene in the Zagros Basin, southwest of Iran. This formation is located in Bandar Abbas and Coastal Fars regions on the following two sections: Anguro anticline (west-northwest of Bandar Abbas) and Gavbast anticline (southwest of Lar County). The Asmari Formation has diameters of 68 and 26 m in the Anguro and Gavbast sections, respectively. This formation is composed of limestone, dolomitic limestone and an altered form of marl. Based on the results of petrographic analyses, 7 facies were identified in the Anguro and Gavbast sections in the study region. The facies were deposited on the following 3 belts: tidal flat (MF 1 - 3), lagoon (MF 4 - 5) and open marine (MF 6, 7). According to evidence such as the gradual change of microfacies, the lack of main reef barriers, and the lack of slumping and sliding features, the Asmari Formation was formed in a marine environment of carbonate homoclinal ramp type. This environment is composed of the following two subenvironments: the inner ramp and the middle ramp. The comparison of the facies identified in the Anguro and Gavbast sections indicates that Gavbast section is mainly composed of lagoon facies. Moreover, the Anguro section demonstrates more facies diversity than Gavbast section.展开更多
Early Permian deposits in north of Kalmard region recognize with formal group of Khan;they have various features in the different place. This group includes four different formations from lower to the upper part: Chil...Early Permian deposits in north of Kalmard region recognize with formal group of Khan;they have various features in the different place. This group includes four different formations from lower to the upper part: Chili, Sartakht and Hermez. These formations consist of carbonate rocks. Chili Formation has 104 m, thickness in Darin section and consists of limestone with intermediates of shale and marland sandstone. Lower boundary of this formation is disconformable with Gachal formation. The upper boundary is separated by unconformity from the upper part Sartakht formation according to the lithological characters and microscopic studies, cause identifications of beach, intertidal, open and semi-restricted lagoon, shoals and bar and open marine sub-environ- ments for the Chili Formation. Vertical changes of microfacies and depth changes curve show much more thickness of shoals and bar microfacies, and little thickness of open and semi-re- stricted lagoon and open marine microfacies. Deposits of Chili Formation in Darin section deposited in the gentle gradient Homoclinal ramp in the south of Paleotethys Ocean. Two depositional sequences have been identified in this formation, based on recognized Fusulinid, show age of Sakmarian, which has adaptation with Lower Absaroka III.展开更多
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.
文摘Tonle Sap sedimentary basin was considered a favorable geological condition for hydrocarbon accumulation in the onshore Cambodia. Two exposure outcrops in Battambang province, called Somlout and Takream, were selected to represent sediments in this basin. The sedimentology and geochemistry studies provide insights into the depositional environment of sediments using field investigation, lithological, sedimentological, paleontological, and geochemical analysis. The redox condition, water column, and depositional setting were analyzed by plotting the ratio of V vs. Cr, Uauthigenic vs. V/Cr, Sr vs. Ba, Ca vs. (Fe + Ca), and Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> vs. Al<sub>2</sub>O<sub>3</sub>/(Al<sub>2</sub>O<sub>3</sub> + Fe<sub>2</sub>O<sub>3</sub>) diagram. Moreover, these diagrams can be used to predict depositional conditions as well. Based on the results, Somlout and Takream comprise calcareous shale and limestone facies. The geochemical analysis showed that Somlout calcareous shale samples were deposited in the dysoxic freshwater of the lake setting during the regression, while Somlout limestones and Takream were deposited in high salinity seawater, oxic condition of shallow-marine water. In addition, Somlout limestones consist of fragmental fusulinid foraminifera, bivalve shelve, and bryozoan, which suggest a barrier environment. Meanwhile, Teakream consists of fine-grained calcareous shale, and lime-mudstone, which are presented to form in the quiet marine setting of the lagoon environment. Therefore, the Tonle Sap basin sediments were deposited in the Somlout area’s barrier and lake environment, and the lagoon environment for Takream.
基金the General Fund of the National Natural Science Foundation of China(Grant No.42272184)National Natural Science Foundation of China(Grant Nos.42230311 and 91755215)for their support of this paper。
文摘A set of organic-rich shales of the upper Permian Longtan Formation,which is widely developed in the northeastern part of the Sichuan Basin,is a key formation for the next step of exploration and development.At present,most studies on this set of formations have focused on the reservoir characteristics and reservoir formation mechanism of the shales,and basic studies on the palaeoenvironment and organic matter(OM)enrichment mechanism have not been fully carried out.In this paper,we recovered the sedimentary palaeoenvironment by mineralogical,elemental geochemical and organic geochemical analyses,and explored the enrichment mechanism of OM under the constraints of palaeoenvironmental evolution.The shales can be divided into two stages of sedimentary evolution:compared with the shales of the Lower Longtan Formation,the shales of the Upper Longtan Formation are relatively rich in quartz,poor in clay and carbonate minerals,and the OM type changes from typeⅢto typeⅡ_(2).The depositional environment has undergone a change from sea level rise,from warm and wet climate to dry and cold climate,and from oxygen-poor condition restricted to open reduction environment;the land source input has decreased,the siliceous mineral content has increased,the biological productivity has improved,and the deposition rate has changed from high to low.A depositional model was established for the shales of the Longtan Formation,reflecting the differential reservoir formation pattern of organic matter.For the Lower Longtan Formation shales,the most important factors controlling OM content are terrestrial source input and deposition rate,followed by paleoclimate and paleooxygen conditions.For the Upper Longtan Formation shales,the most important controlling factor is paleo-productivity,followed by sedimentation rate.The depositional model constructed for the Upper and Lower Longtan Formation shales can reproduce the enrichment of organic matter and provide a basis for later exploration and development.
文摘As a repository of REE,the Paleoproterozoic phosphorite of the Aravalli Basin in India is explored time to time.Paleoproterozoic phosphorite deposits of the Sallopat sub-basin Banswara district of the Aravalli Supergroup show moderate REE concentrations much lower than that of average marine phosphorites.Different ratios and PAAS-normalized REE distribution patterns reflect MREE enrichment over LREE and HREE in these phosphorites.MREE enrichment confirmed by(Sm/Yb)Nversus(Sm/Pr)Nrelationship and attributed to the selective uptake by cyanobacteria and mixing of riverine inputs.Y/Ho,La/Ce and Er/Nd ratios confirm that the REE in Sallopat phosphorites might have been affected by the argillaceous terrigenous and plagioclase-rich sediments probably derived from Banded Gneissic Complex.Diagenetic modeling indicates that REE were concentrated during early diagenetic processes with limited weathering influence.Moderate negative to low Ce anomaly depicts oxic to sub-oxic conditions of seawater due to oxidation of Ce^(3+)to Ce^(4+)whereas Eu^(3+)reduced to Eu^(2+)indicating positive Euanomaly and reducing conditions as well during the deposition.These anomalies may be due to the stratified restricted marine environment of upwelling and mingling of organic-rich anoxic deep water with oxic upper seawater prior to the formation of phosphorite deposits in the embayment.Enrichment of REE in Sallopat phosphorite relies on various physico-chemical conditions.These phosphorites may have been formed in restricted marine water which was influenced by extra clastic sediment input carried out by fluvial systems.
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
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.
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Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from the grain size analysis indicates that the Ngrayong sediments are classified as sand or muddy sands. They are very fine- to medium-grained (phi values: 1.67 to 3.35), moderately- to well-sorted (standard deviation: 0.19 to 0.57), strongly fine-skewed to strongly coarse-skewed (skewness values: 4.82 to −5.97), and very platykurtic to very leptokurtic (kurtosis values: 0.36 to 2.41). Sandstone samples show unimodal grain size distribution. The sediments are interpreted to be transported in all three modes-traction, saltation and suspension, however, suspension and rolling are the major processes during transportation. Discriminant functions indicate diversity in the depositional environment for the sandstones. However, shallow marine is regarded as the dominant depositional environment. The preponderance of fine-grained sediments and lack of coarse sands suggest low to moderate energy conditions during deposition of Ngrayong sediments.
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>
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.
文摘Permian rocks in Kalmard block are recognized with Khan Group, enjoying various characteristics in different outcrops. This group is made up of three informal formations, namely Chili, Sartakht and Hermez. Middle Permian deposits (Sartakht formation) are composed chiefly of sandstone and carbonate rocks. This formation is composed of 58.6 m sandstone and dolomitic limestone in the Bakhshi section. Lower Permian carbonate deposits (Chili formation) unconformably underlie this formation while lateritic paleosols of upper Permian (Hermez formation) are depicted overlying an erosional unconformity above this formation. According to lithologic and microscopic investigations, the deposits of Sartakht formation can be divided into 2 siliciclastic petrofacies and 12 carbonate microfacies. Field observations, along with microscopic examinations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the rocks of the studied formation. Vertical changes of microfacies and depth variation curve point to the high thickness of the microfacies of lagoon and shoal environments and low thickness of the microfacies of tidal flat and open marine environments. The carbonate-siliciclastic sequence of Sartakht formation is made up of a third-order depositional sequence, separated from carbonate depositions of lower Permian (Chili formation) and lateritic paleosols of upper Permian by type 1 sequence boundary (SB1). Siliciclastic deposits include LST system tract, and carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. Sartakht formation rocks in Bakhshi section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the south of Paleotethys Ocean. The depositional sequence identified in Sartakht formation points to the age of middle Permian, conforming to middle Absaroka II supersequence. The upper erosional boundary between Sartakht and Hermez formations conforms to the global-scale sea level fall.
文摘Deposits of Lower Carboniferous rocks in Kalmard block are recognized by Gachal informal formation, showing various characteristics in different outcrops. Lower Carboniferous deposits (Gachal formation) are composed chiefly of carbonate, evaporite and siliciclastic rocks. This formation is composed of 198 m sandstone, limestone and dolomite as well as a small amount of shale, marl and gypsum in the Madbeiki section. This formation unconformably underlies Precambrian metamorphic deposits (Kalmard formation) while lateritic soils of lower Permian (Chili formation) are depicted overlying an erosional unconformity above this formation. According to lithologic and microscopic investigations, the deposits of Gachal formation can be divided into 1 siliciclastic petrofacies, 1 evaporite microfacies and 16 carbonate microfacies. Field observations, along with microscopic examinations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the rocks of the studied formation. Vertical changes of microfacies and depth variation curve indicate the high thickness of the microfacies of tidal flat, lagoon and shoal environments and low thickness of the microfacies of open marine environment. The carbonate-evaporite-siliciclastic sequence of Gachal formation is made up of three third-order depositional sequence, separated each other by type 1 sequence boundary (SB1). Siliciclastic and evaporite deposits include LST system tract, and carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. Gachal formation rocks in Madbeiki section are deposited in a low-angle homoclinal ramp, mostly in the inner ramp, located in the southern Paleotethys Ocean. The depositional sequence identified in Gachal formation points to the age of Lower Carboniferous, conforming to upper Kaskaskia super sequence. The upper erosional boundary between Gachal and Chili formations conform to the global-scale sea level fall.
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.
文摘The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settingshave distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances,depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of theclastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin areenriched in silica (SiO2=66.48-80.51%), and their ΣREE are 30-130 times of that of chondrite with remarkable Euanomalies. In discriminating diagrams of Eu/Eu* vs ΣREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/Eu*=1, on the right of the line Eu/Eu*/ΣREE=1 and under the line La/Yb)N/ΣREE=1/8, which indicates that thedepositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3,FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments in the basin. Analysesalso show that the protolytes of the sediments in the basin were felsic igneous rocks, and the Songliao prototype basin wasin a tectonic setting of an island arc on an active continental margin, with violent sinistral strike-slip.
文摘A deeper understanding of the mechanisms by which geological factors(depositional environment and tectonic evolution) control the occurrence of coalbed methane(CBM) is important for the utilization of CBM resources via surface-drilled wells and the elimination of coal-methane outbursts, the latter of which is a key issue for coal mine safety. Based on drill core data, high-pressure isothermal adsorption experiments, scanning electron microscopy experiments, mercury intrusion porosimetry, and X-ray diffraction experiments, the impact of the depositional environment and tectonic evolution on CBM occurrence of the II-1 coal seam of the Shanxi Formation in West Henan was analyzed. Results showed that the depositional environment led to the epigenetic erosion of tidal flat coal-accumulating structures by shallow-delta distributary channel strata. This resulted in the replacement of the original mudstonesandy mudstone coal seam immediate roof with fine-to-medium grained sandstones, reducing methane storage capacity. Epigenetic erosion by the depositional environment also increased coal body ash content(from 6.9% to 21.4%) and mineral content, filling the cleat system and reducing porosity, reducing methane storage capacity. The maximum methane adsorption capacity of the coal body reduced from35.7 cm3/g to 30.30 cm3/g, and Langmuir pressure decreased from 1.39 MPa to 0.909 MPa. Hence, the methane adsorption capacity of the coal body decreased while its capacity for methane desorption increased. Owing to the tectonic evolution of West Henan, tectonically deformed coal is common; as it evolves from primary cataclastic coal to granulitic coal, the angle of the diffraction peak increases, d002 decreases, and La, Lc, and Nc increase; these traits are generally consistent with dynamic metamorphism.This is accompanied by increases in the total pore volume and specific surface area of the coal body, further increasing the capacity for methane storage. Increases in micropore volume and specific surface area also increase the ability of the coal body to adsorb methane.
文摘This paper discussed the petrographic characteristics of No.6 coal from the Xiaoyugou mine,Jungar Coalfield,Ordos Basin,China.10 samples(7 coal,1 parting mudstone and 2 floor mudstone)were analysed by microscopical and geochemical methods.Four maceral compositions and several associated elements parameters were selected as indicators and corresponding diagrams were drawn to explicate the sedimentary environment.The results indicate that the maceral is dominated by vitrinite and minerals are mainly kaolinite in the No.6 coal.The sedimentary facies vary from barrier island system to tidal-flat which is a deposition process of water body shallowing and the coal-forming plants are herbs and woody plants formed in swamps.
文摘The Asmari Formation is a thick carbonate sequence of the Oligocene-Miocene in the Zagros Basin, southwest of Iran. This formation is located in Bandar Abbas and Coastal Fars regions on the following two sections: Anguro anticline (west-northwest of Bandar Abbas) and Gavbast anticline (southwest of Lar County). The Asmari Formation has diameters of 68 and 26 m in the Anguro and Gavbast sections, respectively. This formation is composed of limestone, dolomitic limestone and an altered form of marl. Based on the results of petrographic analyses, 7 facies were identified in the Anguro and Gavbast sections in the study region. The facies were deposited on the following 3 belts: tidal flat (MF 1 - 3), lagoon (MF 4 - 5) and open marine (MF 6, 7). According to evidence such as the gradual change of microfacies, the lack of main reef barriers, and the lack of slumping and sliding features, the Asmari Formation was formed in a marine environment of carbonate homoclinal ramp type. This environment is composed of the following two subenvironments: the inner ramp and the middle ramp. The comparison of the facies identified in the Anguro and Gavbast sections indicates that Gavbast section is mainly composed of lagoon facies. Moreover, the Anguro section demonstrates more facies diversity than Gavbast section.
文摘Early Permian deposits in north of Kalmard region recognize with formal group of Khan;they have various features in the different place. This group includes four different formations from lower to the upper part: Chili, Sartakht and Hermez. These formations consist of carbonate rocks. Chili Formation has 104 m, thickness in Darin section and consists of limestone with intermediates of shale and marland sandstone. Lower boundary of this formation is disconformable with Gachal formation. The upper boundary is separated by unconformity from the upper part Sartakht formation according to the lithological characters and microscopic studies, cause identifications of beach, intertidal, open and semi-restricted lagoon, shoals and bar and open marine sub-environ- ments for the Chili Formation. Vertical changes of microfacies and depth changes curve show much more thickness of shoals and bar microfacies, and little thickness of open and semi-re- stricted lagoon and open marine microfacies. Deposits of Chili Formation in Darin section deposited in the gentle gradient Homoclinal ramp in the south of Paleotethys Ocean. Two depositional sequences have been identified in this formation, based on recognized Fusulinid, show age of Sakmarian, which has adaptation with Lower Absaroka III.
