The d 13C values of Lower Cretaceous Aptian-Albian platform-type carbonates in the Cuoqin Basin, North Tibet vary between 2.48 and 5.46. The mean value is 3.93. The values are not only provided with positive excursion...The d 13C values of Lower Cretaceous Aptian-Albian platform-type carbonates in the Cuoqin Basin, North Tibet vary between 2.48 and 5.46. The mean value is 3.93. The values are not only provided with positive excursion, but also 1.17 higher than those of con-temporaneous pelagic carbonates which possess pretty high d 13C values. The origin is ap-proached. During the oceanic anoxic events, a great number of organisms were rapidly buried, causing the increase of the d 13C value of oceanic total dissolved carbon (TDC) and generally promoting the values of marine carbonates. After that, owing to the organisms undergoing dif-ferent isotopic fractionation in the paleo-ocean with stratified structure, d 13C values of shallow sea carbonate were obviously higher than those of pelagic carbonates.展开更多
The Mid-Cretaceous interval has been recognized as a crucial period in Earth’s history,and a number of studies on Neo-Tethyan successions illustrate intense evolutions in the nature of Mid-Cretaceous ocean chemistry,...The Mid-Cretaceous interval has been recognized as a crucial period in Earth’s history,and a number of studies on Neo-Tethyan successions illustrate intense evolutions in the nature of Mid-Cretaceous ocean chemistry,sea level,and marine faunal communities.However,much less investigations have been conducted in the Sistan Ocean,in the eastern Neo-Tethys.Here,the Nimbolook Section(Lut Block,central Iran)has provided an opportunity to address these shortcomings and provide a better understanding of the paleoenvironmental changes in this region.The biostratigraphic analysis and age interpretation of the Nimbolook Section have been performed in earlier investigations by means of planktonic foraminifera,ammonites and calcareous nannofossils.This provides a reliable age framework for the chemostratigraphic interpretations.In the Nimbolook Section,the δ^(13)C stratigraphy was carried out on a total of 41 samples,which ranged between -3.26‰and 2.86‰ with an average of 1.09‰(standard deviation=1.15‰),and expanded within the upper Aptian to lower Cenomanian stages.However,there is a prominent negative shift at the base of the section,accompanied by episodes of sea-level fluctuations.Notably,according to the age-diagnostic calcareous nannofossils records,this carbon isotope negative shift(0.88‰ to -3.26‰)straddle between late Aptian and early Albian ages.Furthermore,these new chemostratigraphic observations could be interpreted as being the coeval data from the reference well-studied successions in the other parts of the world,tentatively reflecting the oceanic anoxic event(OAE)1b.展开更多
A biostratigraphic study was carried out in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. The Lower ...A biostratigraphic study was carried out in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. The Lower Cretaceous shallow-water limestones on the northeast of Shiraz contains abundant and diversified orbitolinid foraminifera. A biostratigraphy, based on the orbitolinid taxa and their distribution, is proposed for the Aptian and Albian deposits in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. Three orbitolinid biozones have been recognized: 1) Palorbitolina lenticularis Assemblage Zone in the Lower Aptian;2) Mesorbitolina parva Total Range Zone in the Late Aptian;3) Orbitolina (Mesorbitolina) texana Assemblage Zone in the uppermost Aptian-lower Albian, the body of strata being characterized by a distinctive assemblage of Orbitolina (Mesorbitolina) texana and O. (M.) parva. The following taxa are the most abundant: Mesorbitolina texana, Mesorbitolina parva, Orbitolina sp., Pseudocyclammina lituus, Pseudochrysalidina conica, Pseudochrysalidina cf. arabica, Pseudocyclammina hedbergi, Praechrysalidina infracretacea, Cuneolina pavonia, Dictyocunus arabicus, Iraqia simplex, Vercosella laurentii, Protomarssonella trochus, Nautiloculina oolithica, and calcareous algae such as Salpingoporella dinarica, Trinocladus tripolitanus, Terquemella sp. and Lithocodium aggregatum-Bacinella irregularis.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49772124)the China National Petroleum Corporation (Grant No. 970204-04-01).
文摘The d 13C values of Lower Cretaceous Aptian-Albian platform-type carbonates in the Cuoqin Basin, North Tibet vary between 2.48 and 5.46. The mean value is 3.93. The values are not only provided with positive excursion, but also 1.17 higher than those of con-temporaneous pelagic carbonates which possess pretty high d 13C values. The origin is ap-proached. During the oceanic anoxic events, a great number of organisms were rapidly buried, causing the increase of the d 13C value of oceanic total dissolved carbon (TDC) and generally promoting the values of marine carbonates. After that, owing to the organisms undergoing dif-ferent isotopic fractionation in the paleo-ocean with stratified structure, d 13C values of shallow sea carbonate were obviously higher than those of pelagic carbonates.
基金partly financed by the University of Birjand,Iran.
文摘The Mid-Cretaceous interval has been recognized as a crucial period in Earth’s history,and a number of studies on Neo-Tethyan successions illustrate intense evolutions in the nature of Mid-Cretaceous ocean chemistry,sea level,and marine faunal communities.However,much less investigations have been conducted in the Sistan Ocean,in the eastern Neo-Tethys.Here,the Nimbolook Section(Lut Block,central Iran)has provided an opportunity to address these shortcomings and provide a better understanding of the paleoenvironmental changes in this region.The biostratigraphic analysis and age interpretation of the Nimbolook Section have been performed in earlier investigations by means of planktonic foraminifera,ammonites and calcareous nannofossils.This provides a reliable age framework for the chemostratigraphic interpretations.In the Nimbolook Section,the δ^(13)C stratigraphy was carried out on a total of 41 samples,which ranged between -3.26‰and 2.86‰ with an average of 1.09‰(standard deviation=1.15‰),and expanded within the upper Aptian to lower Cenomanian stages.However,there is a prominent negative shift at the base of the section,accompanied by episodes of sea-level fluctuations.Notably,according to the age-diagnostic calcareous nannofossils records,this carbon isotope negative shift(0.88‰ to -3.26‰)straddle between late Aptian and early Albian ages.Furthermore,these new chemostratigraphic observations could be interpreted as being the coeval data from the reference well-studied successions in the other parts of the world,tentatively reflecting the oceanic anoxic event(OAE)1b.
文摘A biostratigraphic study was carried out in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. The Lower Cretaceous shallow-water limestones on the northeast of Shiraz contains abundant and diversified orbitolinid foraminifera. A biostratigraphy, based on the orbitolinid taxa and their distribution, is proposed for the Aptian and Albian deposits in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. Three orbitolinid biozones have been recognized: 1) Palorbitolina lenticularis Assemblage Zone in the Lower Aptian;2) Mesorbitolina parva Total Range Zone in the Late Aptian;3) Orbitolina (Mesorbitolina) texana Assemblage Zone in the uppermost Aptian-lower Albian, the body of strata being characterized by a distinctive assemblage of Orbitolina (Mesorbitolina) texana and O. (M.) parva. The following taxa are the most abundant: Mesorbitolina texana, Mesorbitolina parva, Orbitolina sp., Pseudocyclammina lituus, Pseudochrysalidina conica, Pseudochrysalidina cf. arabica, Pseudocyclammina hedbergi, Praechrysalidina infracretacea, Cuneolina pavonia, Dictyocunus arabicus, Iraqia simplex, Vercosella laurentii, Protomarssonella trochus, Nautiloculina oolithica, and calcareous algae such as Salpingoporella dinarica, Trinocladus tripolitanus, Terquemella sp. and Lithocodium aggregatum-Bacinella irregularis.
