Based on the analysis of sedimentary facies and chemical index of alteration(CIA) in Nanhua and Ediacaran Systems in the southwest of Tarim Block,some features of glacial records in Neoproterozoic become more clear.Si...Based on the analysis of sedimentary facies and chemical index of alteration(CIA) in Nanhua and Ediacaran Systems in the southwest of Tarim Block,some features of glacial records in Neoproterozoic become more clear.Six sedimentary facies have been divided in the study area,including alluvial fan facies,lacustrine facies,glacial facies,littoral facies,neritic facies,and lagoonal facies,showing that this area underwent a process from continent to marine,with mainly littoral and neritic sedimentation.Two cold events have been recognized by analysis of CIA values in the study area,called Bolong and Yutang glaciation,respectively.They present as thick-layer tillite deposition in the Bolong Formation and thin-layer tillite deposition in the Yutang Formation,respectively.The Bolong glacial period in the study area can be correlated to the Yulmeinak glacial period in Aksu area,Tereeken glacial period in Qurugtagh area,and the Nantuo glacial period in South China,which is equivalent to the universally acknowledged Marinoan glacial period.The Yutang glacial period can be correlated to the Hankalchough glacial period in Qurugtagh,which is equivalent to Gaskers glaciation in Newfoundland.展开更多
Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from t...Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from these shales,together with the yielded conodonts and chitinozoans etc.,permits a refined correlation of the rocks.Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions,and the successful identification of the new graptolite material from a few drill cores within the basin,we are able to update our knowledge of the Ordovician in the regions,and draw some conclusions:(1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions,which correspond to the Nemagraptus gracilis Zone,may be related to a global sea-level rise during this time interval.(2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag(also spelled as Quruq Tagh) region in east-ern Tianshan Mountains,spanning Tremadocian to mid-Katian(D.spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression.The black shales of the D.spiniferus Zone may even extend into the central Tarim Basin.(3) Three different bio-and litho-facies belts(Bachu:carbonate platform and reef belt;Kalpin-Aksu:marginal platform and upper slope belt;Wushi:slope belt) are recognized in the northwestern Tarim Basin.(4) The internationally well-correlated Saergan black shale,which has been considered to possess high potential for hydrocarbon source rock,may possess a restricted distribution in the Kalpin and Aksu areas.展开更多
基金supported by National Natural Science Foundation of China (Grant Nos. 40972126 & 40821002)
文摘Based on the analysis of sedimentary facies and chemical index of alteration(CIA) in Nanhua and Ediacaran Systems in the southwest of Tarim Block,some features of glacial records in Neoproterozoic become more clear.Six sedimentary facies have been divided in the study area,including alluvial fan facies,lacustrine facies,glacial facies,littoral facies,neritic facies,and lagoonal facies,showing that this area underwent a process from continent to marine,with mainly littoral and neritic sedimentation.Two cold events have been recognized by analysis of CIA values in the study area,called Bolong and Yutang glaciation,respectively.They present as thick-layer tillite deposition in the Bolong Formation and thin-layer tillite deposition in the Yutang Formation,respectively.The Bolong glacial period in the study area can be correlated to the Yulmeinak glacial period in Aksu area,Tereeken glacial period in Qurugtagh area,and the Nantuo glacial period in South China,which is equivalent to the universally acknowledged Marinoan glacial period.The Yutang glacial period can be correlated to the Hankalchough glacial period in Qurugtagh,which is equivalent to Gaskers glaciation in Newfoundland.
基金supported by Chinese Academy of Sci-ences (Grant Nos. KZCX2-EW-111 and KZCX2-YW-Q05-01)China Geological Survey (Grant No.1212011120116)
文摘Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions,and some of them may serve as potential hydrocarbon source rocks.The present study of the Ordovician graptolite fauna from these shales,together with the yielded conodonts and chitinozoans etc.,permits a refined correlation of the rocks.Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions,and the successful identification of the new graptolite material from a few drill cores within the basin,we are able to update our knowledge of the Ordovician in the regions,and draw some conclusions:(1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions,which correspond to the Nemagraptus gracilis Zone,may be related to a global sea-level rise during this time interval.(2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag(also spelled as Quruq Tagh) region in east-ern Tianshan Mountains,spanning Tremadocian to mid-Katian(D.spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression.The black shales of the D.spiniferus Zone may even extend into the central Tarim Basin.(3) Three different bio-and litho-facies belts(Bachu:carbonate platform and reef belt;Kalpin-Aksu:marginal platform and upper slope belt;Wushi:slope belt) are recognized in the northwestern Tarim Basin.(4) The internationally well-correlated Saergan black shale,which has been considered to possess high potential for hydrocarbon source rock,may possess a restricted distribution in the Kalpin and Aksu areas.
