The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shal...The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shales in the Early and Middle Cretaceous respectively, during the last decades. But few people have paid any attention to the set of pelagic redbeds lying on the black shales, not to mention the applications to paleoclimatology and paleoceanography. It is shown by the sedimentary records of redbeds, that they were deposited around the CCD, with both a higher content of iron and much lower concentrations of organic carbon, which implies conditions with a relatively high content of oxygen. Such redbeds occurred in the global oceans, mainly in the Tethyan realm, with different durations of deposition and a climax from the late Santonian to early Campanian. Global cooling and dramatic changes in ocean currents might help to increase the oxygen flux between the atmosphere and ocean, after the large scale organic carbon burial during the Middle Cretaceous, and therefore lead to the oxygenation of deep ocean and so the occurrence of late Cretaceous oceanic redbeds.展开更多
We describe in detail the Miocene to Quaternary paleoceanography of the western equatorial Pacific Ocean based on calcareous nannofossils of Hole 805B. The relative abundance of Discoaster which lived in the lower pho...We describe in detail the Miocene to Quaternary paleoceanography of the western equatorial Pacific Ocean based on calcareous nannofossils of Hole 805B. The relative abundance of Discoaster which lived in the lower photic zone under the stable sea with nutricline and thermocline, decreased step by step at NN5/NN6 and NN10/NN11 boundaries. Al- though the size of Reticulofenestra which is strongly influenced by nutrient, increased five times throughout the section, it drastically decreased in NN4-5 zone, NN10, NN12, and in NN15/NN16 boundary. On the basis of the relationship between Discoaster abundance and Reticulofenestra size change, collapse of the stability of the sea surface in the west- ern equatorial Pacific Ocean progressed step by step throughout the Miocene to Quaternary.展开更多
We investigated the calcareous nannofossils in the western Pacific and Bahama Bank of Caribbean Sea to reconstruct the paleoceanography and correlate with the global events. The absolute abundant of coccolith (number/...We investigated the calcareous nannofossils in the western Pacific and Bahama Bank of Caribbean Sea to reconstruct the paleoceanography and correlate with the global events. The absolute abundant of coccolith (number/g) are gradually increased from NN6 throughout NN19 Zone, while the relative abundance of Discoaster is decreased at Sites 782 in the western Pacific Ocean. The changes of the modal and maximum size of Reticulofenestra which are strongly reflected the collapse of sea surface stability, show four times in 8.8 Ma, 6.4 Ma, 5.4 Ma and 3.75 Ma at Site 782. On the basis of relationship between the changes of maximum sizes of Reticulofenestra and nutrient condition, these eutrophication events are clearly traceable to the western Pacific, Bahama Bank, northwestern Pacific Ocean and to the Indian Ocean. Two paleoceanographic events found in 8.8 Ma and 3.75 Ma are interpreted as change to high nutrient condition resulted in the intensification of Asian Monsoon and closure of Panama Isthmus.展开更多
This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized...This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized as follows.(1)Diatom compositions in sediment record sea surface condition changes in the Bransfield Strait and Cosmonaut Sea,indicating an increase in sea ice cover since the Mid-Holocene for both areas,possibly linked to cold water mass injection from the Weddell Sea ice shelf.(2)Export productivity records from Antarctic marginal seas show a glacial-interglacial variation pattern,with higher and lower productivity during the interglacial and glacial periods,respectively,controlled by both the intensity of Circumpolar Deep Water upwelling and sea ice cover.An overall increase of export productivity from Marine Isotope Stage(MIS)12 to MIS 6 is noticed.(3)Ventilation state of the abyssal Southern Ocean is closely related to global climate change and atmospheric CO_(2) concentrations,with elevated ventilation efficiency during deglacial periods responsible for elevated atmospheric CO_(2) concentrations.(4)Antarctic marine-based ice sheets/glaciers wax and wane in line with global and regional ice volume changes,predominantly subject to oceanic forcing,while land-based ice sheets might only reorganize in specific glacial intervals.Despite significant progress in understanding the role of the Southern Ocean and the Antarctic Ice Sheet within the global climate system,challenges remain in sample collection and research methods.Future studies should aim to collect samples from a broader range of latitudes,ensure higher quality and longer temporal span,resolve dating issues,reconstruct seawater temperature,and focus on reconstructions of Southern Ocean carbon cycling and changes of intermediate to deep water masses.展开更多
基金The research is jointly supported by the Key Project of the National Natural Science Foundation of China(No.40332020)Prophase Special Research of Vital Projects in the Basic Research of the Ministry of Science and Technology of China(No.2001CCA01 800)International Geological Correlation Program(IGCP463/494).
文摘The Cretaceous is among the most unusual eras in the geological past. Geoscience communities have been having great concerns with geological phenomena within this period, for example carbonate platforms and black shales in the Early and Middle Cretaceous respectively, during the last decades. But few people have paid any attention to the set of pelagic redbeds lying on the black shales, not to mention the applications to paleoclimatology and paleoceanography. It is shown by the sedimentary records of redbeds, that they were deposited around the CCD, with both a higher content of iron and much lower concentrations of organic carbon, which implies conditions with a relatively high content of oxygen. Such redbeds occurred in the global oceans, mainly in the Tethyan realm, with different durations of deposition and a climax from the late Santonian to early Campanian. Global cooling and dramatic changes in ocean currents might help to increase the oxygen flux between the atmosphere and ocean, after the large scale organic carbon burial during the Middle Cretaceous, and therefore lead to the oxygenation of deep ocean and so the occurrence of late Cretaceous oceanic redbeds.
文摘We describe in detail the Miocene to Quaternary paleoceanography of the western equatorial Pacific Ocean based on calcareous nannofossils of Hole 805B. The relative abundance of Discoaster which lived in the lower photic zone under the stable sea with nutricline and thermocline, decreased step by step at NN5/NN6 and NN10/NN11 boundaries. Al- though the size of Reticulofenestra which is strongly influenced by nutrient, increased five times throughout the section, it drastically decreased in NN4-5 zone, NN10, NN12, and in NN15/NN16 boundary. On the basis of the relationship between Discoaster abundance and Reticulofenestra size change, collapse of the stability of the sea surface in the west- ern equatorial Pacific Ocean progressed step by step throughout the Miocene to Quaternary.
文摘We investigated the calcareous nannofossils in the western Pacific and Bahama Bank of Caribbean Sea to reconstruct the paleoceanography and correlate with the global events. The absolute abundant of coccolith (number/g) are gradually increased from NN6 throughout NN19 Zone, while the relative abundance of Discoaster is decreased at Sites 782 in the western Pacific Ocean. The changes of the modal and maximum size of Reticulofenestra which are strongly reflected the collapse of sea surface stability, show four times in 8.8 Ma, 6.4 Ma, 5.4 Ma and 3.75 Ma at Site 782. On the basis of relationship between the changes of maximum sizes of Reticulofenestra and nutrient condition, these eutrophication events are clearly traceable to the western Pacific, Bahama Bank, northwestern Pacific Ocean and to the Indian Ocean. Two paleoceanographic events found in 8.8 Ma and 3.75 Ma are interpreted as change to high nutrient condition resulted in the intensification of Asian Monsoon and closure of Panama Isthmus.
基金The National Natural Science Foundation of China under contract Nos 42030401 and 42276077the Open Foundation of State Key Laboratory of Marine Geology,Tongji University under contract No.MGK202207+1 种基金the Open Foundation Project of the Key Laboratory of Polar Geology and Marine Mineral Resources of Ministry of Education,China University of Geosciences (Beijing),under contract Nos PGMR-2024-102 and PGMR-2023-304the Start-up Foundation of Guangdong Ocean University under contract No.060302032110
文摘This review compiles studies on paleoceanographic and paleoenvironmental changes in the high-latitude Southern Ocean during the late Quaternary based on Chinese Antarctic Expeditions.Four major findings are summarized as follows.(1)Diatom compositions in sediment record sea surface condition changes in the Bransfield Strait and Cosmonaut Sea,indicating an increase in sea ice cover since the Mid-Holocene for both areas,possibly linked to cold water mass injection from the Weddell Sea ice shelf.(2)Export productivity records from Antarctic marginal seas show a glacial-interglacial variation pattern,with higher and lower productivity during the interglacial and glacial periods,respectively,controlled by both the intensity of Circumpolar Deep Water upwelling and sea ice cover.An overall increase of export productivity from Marine Isotope Stage(MIS)12 to MIS 6 is noticed.(3)Ventilation state of the abyssal Southern Ocean is closely related to global climate change and atmospheric CO_(2) concentrations,with elevated ventilation efficiency during deglacial periods responsible for elevated atmospheric CO_(2) concentrations.(4)Antarctic marine-based ice sheets/glaciers wax and wane in line with global and regional ice volume changes,predominantly subject to oceanic forcing,while land-based ice sheets might only reorganize in specific glacial intervals.Despite significant progress in understanding the role of the Southern Ocean and the Antarctic Ice Sheet within the global climate system,challenges remain in sample collection and research methods.Future studies should aim to collect samples from a broader range of latitudes,ensure higher quality and longer temporal span,resolve dating issues,reconstruct seawater temperature,and focus on reconstructions of Southern Ocean carbon cycling and changes of intermediate to deep water masses.
