This paper is a synthetic use of carbon isotope composition,Rock-Eval data,organic petrology,element composition of kerogen,major and trace elements,and biomarker characteristic of the Permian Pingdiquan(P_(2)p)source...This paper is a synthetic use of carbon isotope composition,Rock-Eval data,organic petrology,element composition of kerogen,major and trace elements,and biomarker characteristic of the Permian Pingdiquan(P_(2)p)source rocks in the Wucaiwan sag,Junggar Basin,China as proxies(1)for evaluations of hydrocarbon potential,organic matter(OM)composition and thermal maturity of the OM in the source rocks,(2)for reconstruction of paleodepositional environment,and(3)for analysis of controlling factor of organic carbon accumulation.The P_(2)p Formation developed good-excellent source rocks with thermal maturity of OM ranging from low-mature to mature stages.The OM was mainly composed of C_(3)terrestrial higher plants and aquatic organisms including aerobic bacteria,green sulfur bacteria,saltwater and fresh algae,Sphagnum moss species,submerged macrophytes,Nymphaea,and aquatic pollen taxa.The proportion of terrestrial higher plants decreased and that of aquatic organisms increased from margin to center of the sag.The benthic water within reducing environment and brackishwater column were superposed by periodic/occasional fresh-water influx(e.g.,rainfall and river drain),which led to fresh-water conditions and well oxygenating in the water column during overturn process.The whole study area developed lacustrine source rocks without seawater intrusion.During periodic/occasional fresh-water influx periods with plenty of terrestrial plant inputs,the paleoredox conditions of the sag were relatively oxic in the shallow fresh-water which experienced strong oxidation and decomposition of OM,therefore were not conducive for the OM preservation.However,the overall middle primary productivity made up for this deficiency,and was the main controlling factor on the organic carbon accumulation.A suitable supply from terrestrial inputs can promote biotic paleoproductivity,and a relatively high sedimentation rate can reduce oxidation and decomposition times of OM.On the contrary,during the intervals of the fresh-water influxes,relatively reducing conditions are a more important controlling factor on the OM accumulation in the case that the decrease of the terrestrial biotic source.展开更多
Lignite samples collected from Vastan, Rajpardi and Tadkeshwar lignite mines of Cambay basin （Gujarat） were subjected to organic petrographic investigations and geochemical analyses and the data, thus generated, is ...Lignite samples collected from Vastan, Rajpardi and Tadkeshwar lignite mines of Cambay basin （Gujarat） were subjected to organic petrographic investigations and geochemical analyses and the data, thus generated, is used to reconstruct the paleodepositional history of these lignite sequences. The lignites of Cambay basin dominantly comprise huminite maceral group （71.6%-86.3%） followed by liptinite （10.1%-19.3%） and inertinite （3.6%-11.0%） maceral groups. The mineral matter varies from 9.0% to 20.0%. The petrography based facies model indicates that these lignites have high values of gelification index （GI） and low tissue preservation index revealing a continuous wet condition in the basin and a relatively slower rate of subsidence during the decay of organic matter. On several occasions, during the formation of seams in Tadkeshwar, Rajpardi and Vastan mines, the value of GI exceeded 10 which indicates a forest permanently flooded and the cause of pronounced degree of degradation. However, few sections in Tadkeshwar seam had relatively drier spells of environmental conditions due to fluctuation in the water table as revealed by moderately high content of inertinite macerals. This is specially indicated by the occurrence of funginite which normally thrives in the upper oxy- genated peatigenic layer and indicates prevalence of oxic conditions during plant deposition. Such conditions prevailed during a transgressive phase but there were intermittent fluvial activities also giving rise to supratidal flood plain as reflected in the form of associated carbonaceous shales in the basin.展开更多
基金financially supported by the National Natural Science Foundation of China(NSFC)(No.42202154)the Science Foundation of China University of Petroleum,Beijing(No.ZX20220074)。
文摘This paper is a synthetic use of carbon isotope composition,Rock-Eval data,organic petrology,element composition of kerogen,major and trace elements,and biomarker characteristic of the Permian Pingdiquan(P_(2)p)source rocks in the Wucaiwan sag,Junggar Basin,China as proxies(1)for evaluations of hydrocarbon potential,organic matter(OM)composition and thermal maturity of the OM in the source rocks,(2)for reconstruction of paleodepositional environment,and(3)for analysis of controlling factor of organic carbon accumulation.The P_(2)p Formation developed good-excellent source rocks with thermal maturity of OM ranging from low-mature to mature stages.The OM was mainly composed of C_(3)terrestrial higher plants and aquatic organisms including aerobic bacteria,green sulfur bacteria,saltwater and fresh algae,Sphagnum moss species,submerged macrophytes,Nymphaea,and aquatic pollen taxa.The proportion of terrestrial higher plants decreased and that of aquatic organisms increased from margin to center of the sag.The benthic water within reducing environment and brackishwater column were superposed by periodic/occasional fresh-water influx(e.g.,rainfall and river drain),which led to fresh-water conditions and well oxygenating in the water column during overturn process.The whole study area developed lacustrine source rocks without seawater intrusion.During periodic/occasional fresh-water influx periods with plenty of terrestrial plant inputs,the paleoredox conditions of the sag were relatively oxic in the shallow fresh-water which experienced strong oxidation and decomposition of OM,therefore were not conducive for the OM preservation.However,the overall middle primary productivity made up for this deficiency,and was the main controlling factor on the organic carbon accumulation.A suitable supply from terrestrial inputs can promote biotic paleoproductivity,and a relatively high sedimentation rate can reduce oxidation and decomposition times of OM.On the contrary,during the intervals of the fresh-water influxes,relatively reducing conditions are a more important controlling factor on the OM accumulation in the case that the decrease of the terrestrial biotic source.
文摘Lignite samples collected from Vastan, Rajpardi and Tadkeshwar lignite mines of Cambay basin （Gujarat） were subjected to organic petrographic investigations and geochemical analyses and the data, thus generated, is used to reconstruct the paleodepositional history of these lignite sequences. The lignites of Cambay basin dominantly comprise huminite maceral group （71.6%-86.3%） followed by liptinite （10.1%-19.3%） and inertinite （3.6%-11.0%） maceral groups. The mineral matter varies from 9.0% to 20.0%. The petrography based facies model indicates that these lignites have high values of gelification index （GI） and low tissue preservation index revealing a continuous wet condition in the basin and a relatively slower rate of subsidence during the decay of organic matter. On several occasions, during the formation of seams in Tadkeshwar, Rajpardi and Vastan mines, the value of GI exceeded 10 which indicates a forest permanently flooded and the cause of pronounced degree of degradation. However, few sections in Tadkeshwar seam had relatively drier spells of environmental conditions due to fluctuation in the water table as revealed by moderately high content of inertinite macerals. This is specially indicated by the occurrence of funginite which normally thrives in the upper oxy- genated peatigenic layer and indicates prevalence of oxic conditions during plant deposition. Such conditions prevailed during a transgressive phase but there were intermittent fluvial activities also giving rise to supratidal flood plain as reflected in the form of associated carbonaceous shales in the basin.
