Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous R...Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous Region,China.As a result,one positive and two negative carbon isotope excursions in the studied section were iden-tified.The δ13Ccarb values reached the maximum negative excursion(N1:-12.39‰) at the basal of the Yuertusi For-mation,and then increased to P1.After P1,δ13Ccarb values sharply decreased to about-7.06‰(N2) in the studied section.The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections,such as the Laolin section,the Xiaotan section and the Anjiahe section of the Yangtze Platform.It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage,and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation(Meishucun Formation) of the Yangtze Platform.The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites suc-cessions at the basal of the Yuertusi Formation.The δ13Ccarb negative excursion N1 is just across the PC/C boundary,and may be related to certain biomass extinction due to anoxic sedimentary environment,transgression and/or the oceanic overturn.The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cam-brian.展开更多
As a useful approach for hydrocarbon exploration, the sequence stratigraphy has been commonly accepted. The concepts of sequence and parasequence provide a state-of-the-artframework for studying the distribution and c...As a useful approach for hydrocarbon exploration, the sequence stratigraphy has been commonly accepted. The concepts of sequence and parasequence provide a state-of-the-artframework for studying the distribution and characters of depositional system, and analyzing the occurrence, distribution, characteristics of source, reservoir and seal-play elements. The newly-developed geochemical-sequence stratigraphy focuses mainly on the occurrence, distribution and characters of source rocks and reservoir hydrocarbons within a chronostratigraphic framework. Integrated with sequence stratigraphy, geochemistry can be used to study the source rock potential within a sequence stratigraphic framework and to describe the characteristics of hydrocarbons accumulated in reservoirs, which were predicted by way of sequence stratigraphy. The concept of geochemical-sequence stratigraphy was proposed by Peters et al. (2000). Constructing a reliable sequence stratigraphic framework is the basis of geochemical-sequence stratigraphic study although it is not the main goal. High-resolution biomarker analysis is critical to the construction of a geochemical-sequence stratigraphic model. The geochemical-stratigraphic study involves mainly: (1) the distribution and geochemical characteristics of source rocks within a sequence chronostratigraphic framework; (2) the geochemical features of source rocks with relative sea (lake)-level change; (3) to predict if these reservoirs bear hydrocarbons and their geochemical features; (4) to be used to construct the time-stratigraphic framework. This paper also summarizes the lake basin types, and introduces their facies associations, source potential and organic geochemical features. At the end, the authors offer some suggestions about how to carry out geochemical-sequence stratigraphic study in lacustrine strata.展开更多
The Neoproterozoic Era includes some of the most largest ice ages in the geological history. The exact number of glaciations is unknown, though there were at least two events of global glaciation. Neoproterozoic glaci...The Neoproterozoic Era includes some of the most largest ice ages in the geological history. The exact number of glaciations is unknown, though there were at least two events of global glaciation. Neoproterozoic glacial deposits in the Kuruktag Mountain, Xinjiang, western China have proven that there had occurred three discrete Neoproterozoic glaciations. Diamictite units occurred in the Bayisi, Tereeken, and Hankalchough formations, carbonate units were recognized among the diamictites and immediately overlied the Bayisi, Tereeken and Hankalchough diamictites. Carbonates at the top of the Bayisi Formation are characterized by the dolo-sility stones with negative δ13C values ranging from -4.10‰ to -8.17‰ (PDB), comparable to the Sturtian cap carbonates that overlie the Sturtian glacial deposits from other Neoproterozoic sequences. Carbonates overlying the Tereeken Formation are characterized by the pinkish cap dolostones (ca. 10 m thick) with negative δ13C values ranging from -2.58‰ to -4.77‰ (PDB), comparable to the Marinoan cap carbonates. The cap is also characterized by tepee-like structures, barite precipitates and pseudomorphous aragonite crystal fan limestones. Carbonates at the top of the Hankalchough Formation are characterized by subaerial exposure crust (vadose pisolite structure, calcareous crust structure) dolostones with negative δ13C values ranging from -4.56‰ to -11.45‰ (PDB) and the calcareous crust dolostones, implying that the Hankalchough cap carbonates differ from either the Sturtian or Marinoan cap carbonates in sedimentary environment and carbon isotopic composition. In addition, it is suggested the Hankalchough glaciation belongs to a terrestrial glaciation and it is the third largest glaciation during the Neoproterozoic period on the Tarim platform.展开更多
文摘Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous Region,China.As a result,one positive and two negative carbon isotope excursions in the studied section were iden-tified.The δ13Ccarb values reached the maximum negative excursion(N1:-12.39‰) at the basal of the Yuertusi For-mation,and then increased to P1.After P1,δ13Ccarb values sharply decreased to about-7.06‰(N2) in the studied section.The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections,such as the Laolin section,the Xiaotan section and the Anjiahe section of the Yangtze Platform.It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage,and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation(Meishucun Formation) of the Yangtze Platform.The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites suc-cessions at the basal of the Yuertusi Formation.The δ13Ccarb negative excursion N1 is just across the PC/C boundary,and may be related to certain biomass extinction due to anoxic sedimentary environment,transgression and/or the oceanic overturn.The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cam-brian.
文摘As a useful approach for hydrocarbon exploration, the sequence stratigraphy has been commonly accepted. The concepts of sequence and parasequence provide a state-of-the-artframework for studying the distribution and characters of depositional system, and analyzing the occurrence, distribution, characteristics of source, reservoir and seal-play elements. The newly-developed geochemical-sequence stratigraphy focuses mainly on the occurrence, distribution and characters of source rocks and reservoir hydrocarbons within a chronostratigraphic framework. Integrated with sequence stratigraphy, geochemistry can be used to study the source rock potential within a sequence stratigraphic framework and to describe the characteristics of hydrocarbons accumulated in reservoirs, which were predicted by way of sequence stratigraphy. The concept of geochemical-sequence stratigraphy was proposed by Peters et al. (2000). Constructing a reliable sequence stratigraphic framework is the basis of geochemical-sequence stratigraphic study although it is not the main goal. High-resolution biomarker analysis is critical to the construction of a geochemical-sequence stratigraphic model. The geochemical-stratigraphic study involves mainly: (1) the distribution and geochemical characteristics of source rocks within a sequence chronostratigraphic framework; (2) the geochemical features of source rocks with relative sea (lake)-level change; (3) to predict if these reservoirs bear hydrocarbons and their geochemical features; (4) to be used to construct the time-stratigraphic framework. This paper also summarizes the lake basin types, and introduces their facies associations, source potential and organic geochemical features. At the end, the authors offer some suggestions about how to carry out geochemical-sequence stratigraphic study in lacustrine strata.
基金the National Natural Science Foundation of China （Grant No. 400462001） the Ministry of Science and Technology of China （2002CCC02600）+2 种基金 the Guizhou Provincial Excellent Talent Foundation （2002-013） the Postdoctoral Scientific Foundation of China （20033209） the Guizhou Provincial President＇s Funds （2004-233）.
文摘The Neoproterozoic Era includes some of the most largest ice ages in the geological history. The exact number of glaciations is unknown, though there were at least two events of global glaciation. Neoproterozoic glacial deposits in the Kuruktag Mountain, Xinjiang, western China have proven that there had occurred three discrete Neoproterozoic glaciations. Diamictite units occurred in the Bayisi, Tereeken, and Hankalchough formations, carbonate units were recognized among the diamictites and immediately overlied the Bayisi, Tereeken and Hankalchough diamictites. Carbonates at the top of the Bayisi Formation are characterized by the dolo-sility stones with negative δ13C values ranging from -4.10‰ to -8.17‰ (PDB), comparable to the Sturtian cap carbonates that overlie the Sturtian glacial deposits from other Neoproterozoic sequences. Carbonates overlying the Tereeken Formation are characterized by the pinkish cap dolostones (ca. 10 m thick) with negative δ13C values ranging from -2.58‰ to -4.77‰ (PDB), comparable to the Marinoan cap carbonates. The cap is also characterized by tepee-like structures, barite precipitates and pseudomorphous aragonite crystal fan limestones. Carbonates at the top of the Hankalchough Formation are characterized by subaerial exposure crust (vadose pisolite structure, calcareous crust structure) dolostones with negative δ13C values ranging from -4.56‰ to -11.45‰ (PDB) and the calcareous crust dolostones, implying that the Hankalchough cap carbonates differ from either the Sturtian or Marinoan cap carbonates in sedimentary environment and carbon isotopic composition. In addition, it is suggested the Hankalchough glaciation belongs to a terrestrial glaciation and it is the third largest glaciation during the Neoproterozoic period on the Tarim platform.
