The saline lacustrine deposit of the Oligocene Lower Ganchaigou Formation is the main source rock for the Western Qaidam Basin,NW China.In this study,abundant highly branched isoprenoids with 25 carbon atoms (C25HBI) ...The saline lacustrine deposit of the Oligocene Lower Ganchaigou Formation is the main source rock for the Western Qaidam Basin,NW China.In this study,abundant highly branched isoprenoids with 25 carbon atoms (C25HBI) were detected in the upper section of the Lower Ganchaigou Formation.C25HBI is a biomarker for diatoms,and can provide information regarding biogeochemical processes during production and preservation of sedimentary organic matter.The carbon isotopic values of C25HBI in these source rocks were in the range of-18‰ to-20‰.The relative enrichment in 13C of C25HBI suggests that these isoprenoids were derived from diatom blooms.In this case,the diatoms used HCO3-as an additional carbon source to dissolved CO2 in water column due to their high biological productivity.Conversely,the diatom blooms indicated an abundant nutrient supply to the environment and high primary productivity.Thus,the occurrence of 13C-enriched C25HBI could be an ideal marker for good source rocks.The decreased concentration of CO2(aq) in the water column induced by diatom blooms can result in an enrichment in 13C of organic matter synthesized by primary producers.This may be a possible reason for the occurrence of 13C-enriched organic matter in the Cenozoic source rocks of the Western Qaidam Basin.Previous studies have shown that the high carbon number n-alkanes sourced from diatoms have no carbon preference.Hence,the sources of n-alkanes in regional source rocks are complex,and should be considered when discussing the sources of organic matter in future studies.展开更多
Although the distribution of mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans(MTTCs) is well understood as an indicator of water salinity,their origin and formation mechanism are still ambiguo...Although the distribution of mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans(MTTCs) is well understood as an indicator of water salinity,their origin and formation mechanism are still ambiguous and under debate.In this paper,abnormally high levels of MTTCs were detected in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin.Using a two-step column chromatography method,the MTTCs and naphthalenes were separated from other aromatic compounds and concentrated in one fraction,so that the stable carbon isotope compositions of these compounds could be accurately measured.Similar carbon isotope ratios for the mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans in a given sample suggest the MTTCs may share the same biological source(s).The MTTCs from the Western Qaidam Basin have similar carbon isotope compositions to primary producer-derived pristane and phytane.However,the ? 13C values for the MTTCs showed significant differences with other primary producers-derived biomarkers(e.g.C27 and C29 steranes),probably indicating a distinct microalgae source from specific niches for the MTTC compounds.We speculate that the MTTCs distribution patterns may be controlled by the water chemistry dynamics in niches,which,in turn,is affected by hypersaline bottom water.展开更多
Due to the importance of the Gloeocapsomorpha Prisca(G.prisca)-enriched source rocks,which belong to Kukersite-type source rocks in the Lower Paleozoic Ordovician strata,it has received great attentions during the pet...Due to the importance of the Gloeocapsomorpha Prisca(G.prisca)-enriched source rocks,which belong to Kukersite-type source rocks in the Lower Paleozoic Ordovician strata,it has received great attentions during the petroleum exploration as to whether there are the Kukersite-type source rocks developed in the major hydrocarbon source strata of the Upper and Middle Ordovician in the Tarim Basin.Using pyrolysis-gas chromatography-mass spectrography to analyse kerogens from source rocks in the limemud mound with moderate maturity,study reveals that there are the Kukersite-type source rocks in the Ordovician strata of the Tarim Basin.The pyrolysis products showed a low content of>n-C19normal alkanes with a significant odd-even predominance between n-C13and n-C17,long-chain alky substituted alkylbenzene and alkylthiophene isomers and distinctive distribution of 5-Nalkyl-1,3-Benzenediol and its homologous.Based on the geographic environment characteristics of G.Prisca,the molecular distributions of crude oil from the Lower Paleozoic petroleum systems in the Tarim Basin and characteristics of kerogen pyrolysis products from the Middle and Upper Ordovician source rocks,the results suggested that it is less possible to develop the G.Prisca-enriched Kukersite-type source rocks in the major hydrocarbon source rocks in the Middle and Upper Ordovician strata in the Tarim Basin.However,the benthic macroalga and planktonic algae-enriched source rocks are the main contributors.展开更多
Using molecular geochemical data from infrared spectrometer and pyrolysis gas chromatography-mass spectrometry, this paper investigates the petroleum generation characteristics of Jurassic coal measures from Kuche dep...Using molecular geochemical data from infrared spectrometer and pyrolysis gas chromatography-mass spectrometry, this paper investigates the petroleum generation characteristics of Jurassic coal measures from Kuche depression, Tarim Basin, NW China. The results showed that the Jurassic coaly rocks with medium maturity (R0%: 0.8-1.1) were enriched in gas-prone functionalities (-CH3) and low molecular weight pyrolysates (【nC21), indicating that the coaly rocks from Kuche depression were gas/condensate prone at the stages of middle to high maturation, and it was further supported by the oil/source correlation from well Yinan 2 in this region.展开更多
基金supported by the National Natural Science Foundation of China (40972093)the National Special Program of Oil and Gas in China (2008ZX05008-002-001)+1 种基金the Natural Science Foundation of Zhejiang Province (R5080124)the Fundamental Research Funds for the Central Universities
文摘The saline lacustrine deposit of the Oligocene Lower Ganchaigou Formation is the main source rock for the Western Qaidam Basin,NW China.In this study,abundant highly branched isoprenoids with 25 carbon atoms (C25HBI) were detected in the upper section of the Lower Ganchaigou Formation.C25HBI is a biomarker for diatoms,and can provide information regarding biogeochemical processes during production and preservation of sedimentary organic matter.The carbon isotopic values of C25HBI in these source rocks were in the range of-18‰ to-20‰.The relative enrichment in 13C of C25HBI suggests that these isoprenoids were derived from diatom blooms.In this case,the diatoms used HCO3-as an additional carbon source to dissolved CO2 in water column due to their high biological productivity.Conversely,the diatom blooms indicated an abundant nutrient supply to the environment and high primary productivity.Thus,the occurrence of 13C-enriched C25HBI could be an ideal marker for good source rocks.The decreased concentration of CO2(aq) in the water column induced by diatom blooms can result in an enrichment in 13C of organic matter synthesized by primary producers.This may be a possible reason for the occurrence of 13C-enriched organic matter in the Cenozoic source rocks of the Western Qaidam Basin.Previous studies have shown that the high carbon number n-alkanes sourced from diatoms have no carbon preference.Hence,the sources of n-alkanes in regional source rocks are complex,and should be considered when discussing the sources of organic matter in future studies.
基金supported by the National Natural Science Foundation of China (40972093)the National Special Program of Oil and Gas in China (2011ZX05008-002)+1 种基金the Natural Science Foundation of Zhejiang Province (R5080124)the Fundamental Research Funds for the Central Universities
文摘Although the distribution of mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans(MTTCs) is well understood as an indicator of water salinity,their origin and formation mechanism are still ambiguous and under debate.In this paper,abnormally high levels of MTTCs were detected in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin.Using a two-step column chromatography method,the MTTCs and naphthalenes were separated from other aromatic compounds and concentrated in one fraction,so that the stable carbon isotope compositions of these compounds could be accurately measured.Similar carbon isotope ratios for the mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans in a given sample suggest the MTTCs may share the same biological source(s).The MTTCs from the Western Qaidam Basin have similar carbon isotope compositions to primary producer-derived pristane and phytane.However,the ? 13C values for the MTTCs showed significant differences with other primary producers-derived biomarkers(e.g.C27 and C29 steranes),probably indicating a distinct microalgae source from specific niches for the MTTC compounds.We speculate that the MTTCs distribution patterns may be controlled by the water chemistry dynamics in niches,which,in turn,is affected by hypersaline bottom water.
基金supported by the National Oil and Gas Special Fund of China(2011ZX05008-002-15)the National Natural Science Foundation ofChina(41172112)
文摘Due to the importance of the Gloeocapsomorpha Prisca(G.prisca)-enriched source rocks,which belong to Kukersite-type source rocks in the Lower Paleozoic Ordovician strata,it has received great attentions during the petroleum exploration as to whether there are the Kukersite-type source rocks developed in the major hydrocarbon source strata of the Upper and Middle Ordovician in the Tarim Basin.Using pyrolysis-gas chromatography-mass spectrography to analyse kerogens from source rocks in the limemud mound with moderate maturity,study reveals that there are the Kukersite-type source rocks in the Ordovician strata of the Tarim Basin.The pyrolysis products showed a low content of>n-C19normal alkanes with a significant odd-even predominance between n-C13and n-C17,long-chain alky substituted alkylbenzene and alkylthiophene isomers and distinctive distribution of 5-Nalkyl-1,3-Benzenediol and its homologous.Based on the geographic environment characteristics of G.Prisca,the molecular distributions of crude oil from the Lower Paleozoic petroleum systems in the Tarim Basin and characteristics of kerogen pyrolysis products from the Middle and Upper Ordovician source rocks,the results suggested that it is less possible to develop the G.Prisca-enriched Kukersite-type source rocks in the major hydrocarbon source rocks in the Middle and Upper Ordovician strata in the Tarim Basin.However,the benthic macroalga and planktonic algae-enriched source rocks are the main contributors.
文摘Using molecular geochemical data from infrared spectrometer and pyrolysis gas chromatography-mass spectrometry, this paper investigates the petroleum generation characteristics of Jurassic coal measures from Kuche depression, Tarim Basin, NW China. The results showed that the Jurassic coaly rocks with medium maturity (R0%: 0.8-1.1) were enriched in gas-prone functionalities (-CH3) and low molecular weight pyrolysates (【nC21), indicating that the coaly rocks from Kuche depression were gas/condensate prone at the stages of middle to high maturation, and it was further supported by the oil/source correlation from well Yinan 2 in this region.
