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
One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method w...One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.展开更多
The mechanism of sedimentary transition from the Cretaceous black shales to the oceanic red beds is a new and important direction of Cretaceous research. Chemical sequential extraction is applied to study the burial r...The mechanism of sedimentary transition from the Cretaceous black shales to the oceanic red beds is a new and important direction of Cretaceous research. Chemical sequential extraction is applied to study the burial records of reactive phosphorus in the black shale of the Gyabula Formation and oceanic red beds of the Chuangde Formation, Southern Tibet. Results indicate that the principal reactive phosphorus species is the authigenic and carbonate-associated phosphorus （CAP） in the Gyabula Formation and iron oxides-associated phosphorus （FeP） in the Chuangde Formation which accounts for more than half of their own total phosphorus content. While the authigenic and carbonate-associated phosphorus （CAP） is almost equal in the two Formations; the iron oxidesassociated phosphorus is about 1.6 times higher in the Chuangde Formation than that in the Gyabula Formation resulting in a higher content of the total phosphorus in the Chuangde Formation. According to the observations on the marine phosphorus cyde in Modern Ocean, it is found that preferential burial and regeneration of reactive phosphorus corresponds to highly oxic and reducing conditions, respectively, leading to the different distribution of phosphorus in these two distinct type of marine sediments. It is the redox-sensitive behavior of phosphorus cycle to the different redox conditions in the ocean and the controlling effects of phosphorus to the marine production that stimulate the local sedimentary transition from the Cretaceous black shale to the oceanic red beds.展开更多
Harrat Al-Birk volcanics are products of the Red Sea rift in southwest Saudi Arabia that started in the Tertiary and reached its climax at ~ 5 Ma.This volcanic field is almost monotonous and is dominated by basalts th...Harrat Al-Birk volcanics are products of the Red Sea rift in southwest Saudi Arabia that started in the Tertiary and reached its climax at ~ 5 Ma.This volcanic field is almost monotonous and is dominated by basalts that include mafic-ultramafic mantle xenoliths(gabbro,websterite,and garnet-clinopyroxenite).The present work presents the first detailed petrographic and geochemical notes about the basalts.They comprise vesicular basalt,porphyritic basalt,and flow-textured basalt,in addition to red and black scoria.Geochemically,the volcanic rock varieties of the Harrat Al-Birk are low- to medium-Ti,sodic-alkaline olivine basalts with an enriched oceanic island signature but extruded in a within-plate environment.There is evidence of formation by partial melting with a sort of crystal fractionation dominated by clinopyroxene and Fe-Ti oxides.The latter have abundant titanomagnetite and lesser ilmenite.There is a remarkable enrichment of light rare earth elements and depletion in Ba,Th and K,Ta,and Ti.The geochemical data in this work suggest Harrat Al-Birk basalts represent products of watersaturated melt that was silica undersaturated.This melt was brought to the surface through partial melting of asthenospheric upper mantle that produced enriched oceanic island basalts.Such partial melting is the result of subducted continental mantle lithosphere with considerable mantle metasomatism of subducted oceanic lithosphere that might contain hydrous phases in its peridotites.The fractional crystallization process was controlled by significant separation of clinopyroxene followed by amphiboles and Fe-Ti oxides,particularly ilmenite.Accordingly,the Harrat Al-Birk alkali basalts underwent crystal fractionation that is completely absent in the exotic mantle xenoliths(e.g.Nemeth et al.in The Pleistocene Jabal Akwa A1 Yamaniah maar/tuff ring-scoria cone complex as an analogy for future phreatomagmatic to magmatic explosive eruption scenarios in the Jizan Region,SW Saudi Arabia 2014).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This work is supported by the National Key Basic Research Program （2006CB701406）；Natural Science Foundation of China for Youth （40403003） ；Key Project of the Natural Science Foundation of China （40332020）, and is a contribution to IGCP 463.
文摘One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.
基金supported by the Natural Science Foundation of China for Youth(40403003)National Key Basic Research Program(2006CB701406)Key Project of Natural Science Foundation of China(40332020),and is a contribution to IGCP 463/555.
文摘The mechanism of sedimentary transition from the Cretaceous black shales to the oceanic red beds is a new and important direction of Cretaceous research. Chemical sequential extraction is applied to study the burial records of reactive phosphorus in the black shale of the Gyabula Formation and oceanic red beds of the Chuangde Formation, Southern Tibet. Results indicate that the principal reactive phosphorus species is the authigenic and carbonate-associated phosphorus （CAP） in the Gyabula Formation and iron oxides-associated phosphorus （FeP） in the Chuangde Formation which accounts for more than half of their own total phosphorus content. While the authigenic and carbonate-associated phosphorus （CAP） is almost equal in the two Formations; the iron oxidesassociated phosphorus is about 1.6 times higher in the Chuangde Formation than that in the Gyabula Formation resulting in a higher content of the total phosphorus in the Chuangde Formation. According to the observations on the marine phosphorus cyde in Modern Ocean, it is found that preferential burial and regeneration of reactive phosphorus corresponds to highly oxic and reducing conditions, respectively, leading to the different distribution of phosphorus in these two distinct type of marine sediments. It is the redox-sensitive behavior of phosphorus cycle to the different redox conditions in the ocean and the controlling effects of phosphorus to the marine production that stimulate the local sedimentary transition from the Cretaceous black shale to the oceanic red beds.
基金funded by the Deanship of Scientific Research(DSR),King Abdulaziz University,Jeddah,under Grant No.(D1435-710-145)
文摘Harrat Al-Birk volcanics are products of the Red Sea rift in southwest Saudi Arabia that started in the Tertiary and reached its climax at ~ 5 Ma.This volcanic field is almost monotonous and is dominated by basalts that include mafic-ultramafic mantle xenoliths(gabbro,websterite,and garnet-clinopyroxenite).The present work presents the first detailed petrographic and geochemical notes about the basalts.They comprise vesicular basalt,porphyritic basalt,and flow-textured basalt,in addition to red and black scoria.Geochemically,the volcanic rock varieties of the Harrat Al-Birk are low- to medium-Ti,sodic-alkaline olivine basalts with an enriched oceanic island signature but extruded in a within-plate environment.There is evidence of formation by partial melting with a sort of crystal fractionation dominated by clinopyroxene and Fe-Ti oxides.The latter have abundant titanomagnetite and lesser ilmenite.There is a remarkable enrichment of light rare earth elements and depletion in Ba,Th and K,Ta,and Ti.The geochemical data in this work suggest Harrat Al-Birk basalts represent products of watersaturated melt that was silica undersaturated.This melt was brought to the surface through partial melting of asthenospheric upper mantle that produced enriched oceanic island basalts.Such partial melting is the result of subducted continental mantle lithosphere with considerable mantle metasomatism of subducted oceanic lithosphere that might contain hydrous phases in its peridotites.The fractional crystallization process was controlled by significant separation of clinopyroxene followed by amphiboles and Fe-Ti oxides,particularly ilmenite.Accordingly,the Harrat Al-Birk alkali basalts underwent crystal fractionation that is completely absent in the exotic mantle xenoliths(e.g.Nemeth et al.in The Pleistocene Jabal Akwa A1 Yamaniah maar/tuff ring-scoria cone complex as an analogy for future phreatomagmatic to magmatic explosive eruption scenarios in the Jizan Region,SW Saudi Arabia 2014).
