The planktic foraminifera of the Chuangde Formation （Upper Cretaceous Oceanic Red Beds, CORBs） as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostra...The planktic foraminifera of the Chuangde Formation （Upper Cretaceous Oceanic Red Beds, CORBs） as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession： a lower unit （the Shale Member） mainly composed of purple （cherry-red, violet-red） shales with interbedded siltstones and siliceous rocks; and an upper unit （the Limestone Member） of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia （Gyangze, Sa＇gya, Sangdanlin, northern Zanskar, etc.）. The fossil contents of the Chuangde Formation in the sections （CORBs） studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation （CORBs） and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe（II）-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.展开更多
The lower part of Fahdene Formation outcropping in northeastern Tunisia is repre- sented by pelagic sequences and characterized by an important siliciclastic fraction that includes ra- diolarian and organic-rich beds ...The lower part of Fahdene Formation outcropping in northeastern Tunisia is repre- sented by pelagic sequences and characterized by an important siliciclastic fraction that includes ra- diolarian and organic-rich beds of Allam Member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam Member is confined to the Microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale depo- sition. The assemblages can be correlated with the radiolarian biochronozone U.A.10-11 indicating an Early Albian to early Middle Albian in age. Radiolarian assemblages composed of species characteris- tic of U.A.10 biochronozone （A. montisserei, D. gracilis） are associated with radiolarian taxa belonging to Costata Zone （U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora）, which can be correlated with Dercourt Member in the Ionian Zone and Paquier level of the Vocontian Basin （southeast of France）. Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa （i.e., Pseudodictyomitrae lodogaensis） compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was dia- chronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAElb which is characterized by the widespread of supraregionnally organic-rich beds in the Mediterranean Tethys basins across the Aptian-Albian transition.展开更多
To enable the lithostratigraphic and biostratigraphie study of the Gurpi Formation, within the ＇Dezak＇ or Globigerina Marl, a stratigraphic section at Booraki, located to the NNW of Shiraz, SW Iran, through the late...To enable the lithostratigraphic and biostratigraphie study of the Gurpi Formation, within the ＇Dezak＇ or Globigerina Marl, a stratigraphic section at Booraki, located to the NNW of Shiraz, SW Iran, through the late Cretaceous was examined. The formation consists of shale and greenish-gray marls interbedded with cream limestone, brown sandstones and siltstones with an exposed thickness of 160 m in the studied section. Samples were taken at regular intervals in all yielding 14 genera and 16 different species of benthic and planktic foraminifera that allowed determination of the age of the beds as Maastrichtian. To examine the paleoecology of the formation, some important ecological factors including water level, salinity, and oxygen regime change during the depositional courses of the formation were analyzed. The density of foraminiferans decreases from the base to top of the Gurpi Formation whereas the ratio of planktic to benthic Foraminifera （i.e., P/B） and proportion of shallow-water fauna increase. These foraminiferal changes indicate an increase and decrease in depth, temperature, salinity and oxygen, respectively, at the base and top of the Formation.展开更多
Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during ...Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during Holocene.To achieve our goals,grain size,total organic carbon,planktic and benthic foraminifera,dinoflagellate cysts have been investigated.Few micropalaentological studies have been done in the studied area and none of them used the combined proxies of benthic foraminifera and dinoflagellate cyst.Theses combined proxies reflects more comprehensive paleoenvironmental view.Biotic and abiotic data have been analysed with multivariate technique including Redundancy Analysis(RDA).Diversity indices such as:Fisher alpha index(α)and Shannon index(H)have been applied.The foraminiferal study yields 9 planktic species and 10 benthic species.Foraminiferal assemblages have low species diversity indices especially at sapropel layer S1.Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding organic poor sediments.Sapropels occur periodically in sedimentary sequences of the last millions years,which have been the subject of extensive previous study.Redundancy Analysis(RDA)yields two groups of foraminiferal assemblages depending on the changes of total organic carbon and clay content.The dinocysts study yields 15 species,the majority of cyst types belonging to the order Gonyaulacales.The association of dinoflagellate cyst shows two depositional phases in the sediment.The sapropel layer S1,with anoxic condition and warmer temperature,is recorded at depth 28-46 cm where heterotrophic taxa dominate and the post-sapropel layer is recorded at depth 0-28 cm;where autotrophic taxa dominate.展开更多
基金supported by the National Basic Research Program of China(973 ProgramGrant No 2006CB701400)the Excellent Teacher study Program(Grant No53200959212)
文摘The planktic foraminifera of the Chuangde Formation （Upper Cretaceous Oceanic Red Beds, CORBs） as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession： a lower unit （the Shale Member） mainly composed of purple （cherry-red, violet-red） shales with interbedded siltstones and siliceous rocks; and an upper unit （the Limestone Member） of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia （Gyangze, Sa＇gya, Sangdanlin, northern Zanskar, etc.）. The fossil contents of the Chuangde Formation in the sections （CORBs） studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation （CORBs） and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe（II）-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.
基金supported by the«le Ministère de L’Enseignement Supérieur et de la Recherche Scientifique» and «Centre des recherches des technologies des eaux–CERTE»
文摘The lower part of Fahdene Formation outcropping in northeastern Tunisia is repre- sented by pelagic sequences and characterized by an important siliciclastic fraction that includes ra- diolarian and organic-rich beds of Allam Member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam Member is confined to the Microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale depo- sition. The assemblages can be correlated with the radiolarian biochronozone U.A.10-11 indicating an Early Albian to early Middle Albian in age. Radiolarian assemblages composed of species characteris- tic of U.A.10 biochronozone （A. montisserei, D. gracilis） are associated with radiolarian taxa belonging to Costata Zone （U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora）, which can be correlated with Dercourt Member in the Ionian Zone and Paquier level of the Vocontian Basin （southeast of France）. Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa （i.e., Pseudodictyomitrae lodogaensis） compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was dia- chronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAElb which is characterized by the widespread of supraregionnally organic-rich beds in the Mediterranean Tethys basins across the Aptian-Albian transition.
文摘To enable the lithostratigraphic and biostratigraphie study of the Gurpi Formation, within the ＇Dezak＇ or Globigerina Marl, a stratigraphic section at Booraki, located to the NNW of Shiraz, SW Iran, through the late Cretaceous was examined. The formation consists of shale and greenish-gray marls interbedded with cream limestone, brown sandstones and siltstones with an exposed thickness of 160 m in the studied section. Samples were taken at regular intervals in all yielding 14 genera and 16 different species of benthic and planktic foraminifera that allowed determination of the age of the beds as Maastrichtian. To examine the paleoecology of the formation, some important ecological factors including water level, salinity, and oxygen regime change during the depositional courses of the formation were analyzed. The density of foraminiferans decreases from the base to top of the Gurpi Formation whereas the ratio of planktic to benthic Foraminifera （i.e., P/B） and proportion of shallow-water fauna increase. These foraminiferal changes indicate an increase and decrease in depth, temperature, salinity and oxygen, respectively, at the base and top of the Formation.
文摘Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during Holocene.To achieve our goals,grain size,total organic carbon,planktic and benthic foraminifera,dinoflagellate cysts have been investigated.Few micropalaentological studies have been done in the studied area and none of them used the combined proxies of benthic foraminifera and dinoflagellate cyst.Theses combined proxies reflects more comprehensive paleoenvironmental view.Biotic and abiotic data have been analysed with multivariate technique including Redundancy Analysis(RDA).Diversity indices such as:Fisher alpha index(α)and Shannon index(H)have been applied.The foraminiferal study yields 9 planktic species and 10 benthic species.Foraminiferal assemblages have low species diversity indices especially at sapropel layer S1.Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding organic poor sediments.Sapropels occur periodically in sedimentary sequences of the last millions years,which have been the subject of extensive previous study.Redundancy Analysis(RDA)yields two groups of foraminiferal assemblages depending on the changes of total organic carbon and clay content.The dinocysts study yields 15 species,the majority of cyst types belonging to the order Gonyaulacales.The association of dinoflagellate cyst shows two depositional phases in the sediment.The sapropel layer S1,with anoxic condition and warmer temperature,is recorded at depth 28-46 cm where heterotrophic taxa dominate and the post-sapropel layer is recorded at depth 0-28 cm;where autotrophic taxa dominate.
