La-Ce and Sm-Nd systematics of siliceous sedimentary rocks: A clue to marine environment in their deposition
- University of Tokyo (Japan)
La-Ce isotopic data, together with Sm-Nd isotopic data, were determined on siliceous sedimentary rocks (cherts) in order to elucidate the rare earth element (REE) character of their sources and the nature of their depositional environments. The cherts studied are a late Archean chert from the Gorge Creek Group in the Pilbara block of Western Australia, Triassic cherts from central Japan, and Cretaceous and Paleogene deep-sea cherts from the central Pacific and the Caribbean Sea. The Archean chert from the Gorge Creek Group shows chondritic Ce and Nd isotope ratios at its sedimentation age which indicate that its sources had a time-integrated chondritic REE pattern. Triassic cherts from Japan have initial Ce and Nd isotope ratios that show a direct derivation from their continental source. On the other hand, for Cretaceous and Paleogene deep-sea cherts having negative Ce anomalies in their REE patterns, two different sources for Ce and Nd are revealed from their initial Ce and Nd isotope data: Ce from long-term light-REE-depleted oceanic volcanic rocks and Nd from light-REE-enriched continental rocks. The reverse nature observed for deep-sea cherts is considered to be a reflection of their depositional environment far from a continent. These results confirm that the La-Ce isotope system is highly useful in determining the nature and cause of Ce anomalies observed in marine sedimentary rocks such as chert.
- OSTI ID:
- 5657105
- Journal Information:
- Geology; (USA), Vol. 19:4; ISSN 0091-7613
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHERT
DEPOSITION
ISOTOPE RATIO
CARIBBEAN SEA
CERIUM ISOTOPES
COMPARATIVE EVALUATIONS
CRETACEOUS PERIOD
GEOCHEMISTRY
GEOLOGIC HISTORY
JAPAN
LANTHANUM ISOTOPES
MEASURING METHODS
NEODYMIUM ISOTOPES
PACIFIC OCEAN
PERFORMANCE TESTING
PRECAMBRIAN ERA
RARE EARTHS
SAMARIUM ISOTOPES
SAMPLING
SEDIMENTARY ROCKS
SOURCE ROCKS
TERTIARY PERIOD
TRIASSIC PERIOD
WESTERN AUSTRALIA
ASIA
ATLANTIC OCEAN
AUSTRALASIA
AUSTRALIA
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
ELEMENTS
GEOLOGIC AGES
ISOTOPES
MESOZOIC ERA
METALS
RARE EARTH ISOTOPES
ROCKS
SEAS
SURFACE WATERS
TESTING
580000* - Geosciences