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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Africa
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Central Africa
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Gabon
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Oklo (2)
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commodities
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metal ores
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uranium ores (2)
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mineral deposits, genesis (1)
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petroleum (1)
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elements, isotopes
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carbon
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C-13/C-12 (4)
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organic carbon (2)
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isotope ratios (3)
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isotopes
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stable isotopes
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C-13/C-12 (4)
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O-18/O-16 (2)
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metals
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manganese (1)
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oxygen
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O-18/O-16 (2)
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geologic age
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Precambrian
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upper Precambrian
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Proterozoic
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Great Oxidation Event (1)
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Paleoproterozoic
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Francevillian (7)
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metamorphic rocks
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metamorphic rocks
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metasedimentary rocks (1)
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minerals
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silicates
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orthosilicates
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nesosilicates
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zircon group
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thorite (1)
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sheet silicates
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chlorite group
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chlorite (1)
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illite (1)
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Primary terms
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Africa
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Central Africa
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Gabon
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Oklo (2)
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-
-
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carbon
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C-13/C-12 (4)
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organic carbon (2)
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clay mineralogy (1)
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economic geology (2)
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geochemistry (1)
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inclusions
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fluid inclusions (2)
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isotopes
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stable isotopes
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C-13/C-12 (4)
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O-18/O-16 (2)
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-
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metal ores
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uranium ores (2)
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-
metals
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manganese (1)
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-
metamorphic rocks
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metasedimentary rocks (1)
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metasomatism (1)
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mineral deposits, genesis (1)
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oxygen
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O-18/O-16 (2)
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paleobotany (1)
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paleontology (1)
-
petroleum (1)
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Precambrian
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upper Precambrian
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Proterozoic
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Great Oxidation Event (1)
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Paleoproterozoic
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Francevillian (7)
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-
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sea-level changes (1)
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sedimentary rocks
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clastic rocks
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black shale (1)
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sandstone (3)
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sedimentary structures (1)
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waste disposal (1)
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sedimentary rocks
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sedimentary rocks
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clastic rocks
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black shale (1)
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sandstone (3)
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-
-
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sedimentary structures
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sedimentary structures (1)
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Francevillian
The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi-Jatuli event: REPLY
The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi-Jatuli event: COMMENT
The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi-Jatuli event
Carbonaceous substances in Oklo reactors—Analogue for permanent deep geologic disposal of anthropogenic nuclear waste
Abstract Seventeen known natural nuclear fission reactors sustained criticality in hydrothermally altered low-grade metasedimentary rocks of the Proterozoic Franceville Series ca. 1968 ± 50 Ma. About half of these reactors contain only traces of carbonaceous substances, and in these, fission products including strontium, cesium, rubidium, and boron migrated away from the reactors and were nearly completely lost. The others are rich in carbonaceous substances, particularly solid, partly graphitized bitumen and kerogen, as well as liquid oil in fluid inclusions. In these carbonaceous substance–rich reactors, uranium and fissiogenic isotopes are held in uraninite, which became enclosed in liquid bitumen during criticality and was subsequently fixed when the bitumen solidified. The preservation of liquid oil in fluid inclusions for over two billion years suggests that time is not a parameter that controls petroleum degradation. This is viewed as a potentially important aspect in engineered nuclear waste containment projects. Likewise, because of the hydrophobic qualities of solid bitumen, its inducible plasticity, and its capability of conversion to nonflammability, it deserves serious consideration for use in permanent deep geologic disposal sites. Indications are that at Oklo, Gabon, carbonaceous substances have combined to restrain the migration of radionuclides and limit the extent to which migration occurs. The strength of the Oklo analogue lies in the fact that it represents more extreme conditions than those likely to be met in a deep geologic repository. The carbonaceous substance–rich reactors of Oklo stand as time-tested analogues for anthropogenic nuclear waste containment strategies.