Uranium-234 anomalies in corals older than 150,000 years

Journal Article · Thu Aug 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90115-L· OSTI ID:6912920

Bard, E ^[1]; Fairbanks, R G; Zindler, A ^[2]; Hamelin, B ^[3]; Hoang, C T ^[4]

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1. CNRS-CEA, Gif-sur-Yvette (France) Columbia Univ., Palisades, NY (United States)
2. Columbia Univ., Palisades, NY (United States)
3. Columbia Univ., Palisades, NY (United States) Univ. Aix-Marseille III (France)
4. CNRS-CEA, Gif-sur-Yvette (France)

The authors present new precise U-Th ages of well-preserved coral specimens collected from the island of Barbados, West Indies, and the atoll of Mururoa, French Polynesia. Their new data confirm the ages attributed to oxygen isotope stage 7 in the framework of the Milankovitch theory. By using thermal ionization mass spectrometry (TIMS), it is also possible to quantify precisely the [sup 234]U/[sup 238]U ratios in corals. Samples older than 150 kyr B.P. are shown to be characterized by significant excesses of [sup 234]U relative to the uranium isotopic composition expected if the corals grew in present-day sea water. Assuming that the [sup 230]Th-ingrowth ages are accurate, these anomalies translate into high initial [sup 234]U/[sup 238]U ratios: about 1.2 at 200 kyr and up to 1.5 at about 450 kyr B.P. They propose that the anomalies result from both diagenetic addition and replacement of U and possibly from global changes in the [sup 234]U/[sup 238]U composition of the sea water through time. The [sup 234]U anomalies cast doubt on the accuracy of the classical [sup 230]Th-ingrowth dating method in old corals, and in particular for the use of measured [sup 234]U/[sup 238]U ratios alone to date corals older than 150 kyr.

• OSTI ID: 6912920
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:8; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACCURACY
ACTINIDE ISO
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
ANIMALS
BARBADOS
CHEMICAL ANALYSIS
CNIDARIA
COELENTERATA
CORALS
EVEN-EVEN NUCLEI
GEOLOGIC STRUCTURES
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
INVERTEBRATES
ISLANDS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LESSER ANTILLES
MAGNESIUM 28 DECAY RADIOISOTOPES
MASS SPECTROSCOPY
NEON 24 DECAY RADIOISOTOPES
NUCLEI
OCEANIA
PALEOCLIMATOLOGY
PALEONTOLOGY
QUANTITATIVE CHEMICAL ANALYSIS
RADIOISOTOPES
REEFS
SPECTROSCOPY
SPONTANEOUS FISSION RADIOISOTOPES
THORIUM 230
THORIUM ISOTOPES
URANIUM 234
URANIUM ISOTOPES
WEST INDIES
YEARS LIVING RADIOISOTOPES