| Project/Area Number |
07640615
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Tohoku University |
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Principal Investigator |
KAIHO Kunio Tohoku University, Institute of Geology and Paleontology, Faculty of Science, Associate professor, 大学院・理学研究科, 助教授 (00143082)
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| Co-Investigator(Kenkyū-buntansha) |
KAJIWARA Yoshimichi Tohoku University, Institute of Geoscience, University of Tsukuba, Professor, 地球科学系, 教授 (80015578)
FUJIMAKI Hirokazu Tohoku University, Institute of Petrology and mineralogy, Faculty of Science, Pr, 大学院・理学研究科, 教授 (90133933)
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| Project Period (FY) |
1995 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1996: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1995: ¥900,000 (Direct Cost: ¥900,000)
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| Keywords | Mass extinction / Diversification / Stable carbon isotopes / Foraminifera / Sulfarisotopes / Clay minerals / 白亜紀 / 第三紀境界 / 微古生物学 / 地球化学 / 環境変動 / 古海洋学 |
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| Research Abstract |
Twenty kinds of geochemical and foraminiferal analyzes were conducted on samples collected at closely spaced intervals spanning the Gretaceous/Tertiary (K/T) boundary at Caravaca, Spain. Rapid reduction in difference between a delta^<13>C value of carbonate fine fraction (<10mum) and that of benthic foraminifera and in carbonate content at the K/T boundary implies rapid mass mortality in the pelagic organisms and significant reduction of flux of organic carbon from the surface water to the sea floor in the intermediate water. A decrease in dissolved oxygen level evidenced by sulfur isotope ratios of sulfide and sulfate, hydrogen and oxygen indices, and benthic foraminiferal oxygen indices coincided with the delta^<13>C event. Ratios of kaolinite/illite increased in threefold in the basal 1cm Danian and oxygen isotope ratio of carbonate fine fraction decreased in 1.2% in the basal 2cm Danian. Both indicate that warming occurred in the atmosphere and surface water slightly later (0to-1ky
… More
r) than the delta^<13>C and low dissolved oxygen events. Recovery in difference between delta^<13>C of carbonate fine fraction and that of benthic foraminifera started from the planktonic foraminiferal zone Pla (ca.5kyr after the K/T boundary) which implies increases in oceanic primary productivity and in flux of organic matter from the surface water to the sea floor.
The phylogeny of deep-sea calcareous trochospiral benthic foraminiferal genera exhibits major diversifications in the early Aptian to early Albian (118-110 Ma) and Turonian to early Maastrichtian (91-71 Ma) , subsequent to two major mid-Cretaceous anoxic events. No distinct diversification of calcareous trochospiral genera occurred during the latest Cretaceous to Holocene. The timing of major diversifications among deep-sea foraminiferal faunas differs from early Cenozoic diversifications experienced by terrestrial and pelagic faunas. This suggests that different paleoenvironmental causes affected the evolution of deep-sea foraminifera and surface dwelling faunas (mammalia and planktonic foraminifera) , over the past 120m.y.
I analyzed the stratigraphic distribution of the maximum diameter of the largest deep-water (>1500m water depths) calcareous trochospiral benthic foraminiferal test in samples representing the past 120m.y. Average values of the maximum diameter for 2m.y.intervals show a general trend of increasing test size, which has doubled since Early Cretaceous time, including fluctuations with six minima and six maxima, the latter being 1.2 to 3 times greater. It is significant that the fluctuations correspond to changes in global climate and in deep-water dissolved oxygen conditions. This latter synchronism indicates that deep-sea foraminiferal test size was likely controlled by fluctuations in the level of dissolved oxygen or related factors in the deep ocean caused by global climatic changes. Less
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