Diagenesis of fossil coral skeletons: Correlation between trace elements, textures, and [sup 234]U/[sup 238]U
- California Inst. of Technology, Pasadena (United States)
A comparative study of Pleistocene fossil coral skeletons and of modern coral skeletons was carried out using petrographic and trace element analyses on a suite of Pleistocene samples that had previously been studied from [sup 234]U, [sup 230]Th, and U-[sup 230]Th ages (Chen et al. 1991). Evidence of a range of diagenetic changes can be recognized by optical (OM) and scanning electron microscopy (SEM). Using an electron microprobe and SEM, concentrations of Na, S, Sr, and Mg were measured. No other trace elements were detected. Na, S, and Mg contents of the matrix, the fibrous micropores, and radiating needles are highly variable and well correlated. High concentrations of Na, S, and Mg were found in modern living corals with lower concentrations in fossil corals and fibrous micropores, and the lowest value in the radiating needles. The reason for the correlations of Na, S, and Mg and crystal chemistry and the response to diagenesis of these trace elements is not understood. The average concentrations of Na, S, and Mg for each sample, when plotted against the whole coral initial [delta][sup 234]U, are generally correlated (Chen et al., 1991). As all these diagenetic changes involve the recystallization and deposition of aragonite, the authors infer that the geologic site of diagenesis both for forming the secondary aragonitic phases and for the enhancement of the [sup 234]U content in the fossil corals was the marine environment. It is possible that the textural and Na, S, and Mg trace element contents of fossil corals be used to ascertain the reliability of fossil coral skeletons for U-[sup 230]Th dating. The basic problem of identifying a priori unaltered coral skeletons for [sup 230]Th dating is not yet resolved. 64 refs., 16 figs., 5 tabs.
- OSTI ID:
- 6943512
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:2; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ACTINIDE ISO
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALKALI METALS
ALKALINE EARTH METALS
ALPHA DECAY RADIOISOTOPES
ANIMALS
ARAGONITE
CARBONATE MINERALS
CHEMICAL ANALYSIS
CHEMISTRY
CNIDARIA
COELENTERATA
CORALS
CORRELATIONS
DEPOSITION
DIAGENESIS
ELECTRON MICROPROBE ANALYSIS
ELECTRON MICROSCOPY
ELEMENTS
EVEN-EVEN NUCLEI
FOSSILS
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
INVERTEBRATES
ISOTOPES
MAGNESIUM
MAGNESIUM 28 DECAY RADIOISOTOPES
METALS
MICROANALYSIS
MICROSCOPY
MINERALS
NEON 24 DECAY RADIOISOTOPES
NONDESTRUCTIVE ANALYSIS
NONMETALS
NUCLEI
RADIOISOTOPES
SCANNING ELECTRON MICROSCOPY
SODIUM
SPONTANEOUS FISSION RADIOISOTOPES
STRONTIUM
SULFUR
THORIUM 230
THORIUM ISOTOPES
URANIUM 234
URANIUM ISOTOPES
YEARS LIVING RADIOISOTOPES