Rare earth element distributions in recent and fossil apatite: implications for paleoceanography and stratigraphy

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 1985

OSTI ID:6997073

Wright, J

Rare earth element (REE) distributions in biogenic apatite were determined in over 200 samples from Cambrian to the Recent. Nondestructive instrumental neutron activation analysis techniques were adapted for analysis of low-mass microfossil samples. Tests for chemical contamination, interspecies, interlaboratory and interexperiment variations show that there is no fractionation of REE, so that ratios of rare earths are consistent throughout the entire group of samples. The REE signature of biogenic apatite is acquired after deposition but only at the sediment-water interface and is characteristic of the redox state of the environment of deposition. This original environmental signature is retained through subsequent burial and diagenesis. Cerium has been shown to be the rare earth element that is sensitive to oxidation-reduction variations in marine waters. This cerium variation is stated mathematically and called Ce/sub anom/. Comparison of Ce/sub anom/ in fish debris from different modern redox environments shows that values > -0.10 occur in fish debris deposited under reducing conditions, whereas Ce/sub anom/ values <-0.10 are obtained under oxidizing conditions. Paleoredox studies of Ce/sub anom/ of fossil apatite of conodonts, fish debris and inarticulate brachiopods indicate that significant shifts in the overall redox balance of seawater occurred in ancient oceans. Cambrian through Silurian seas were dominated by anoxia, followed by a gradual change to oxidizing conditions in the Devonian. Oceans remained generally oxidizing throughout the Carboniferous and Lower Permian. In the Upper Permian and Lower Triassic anoxic conditions were again prevalent. This was followed by a return to an oxidizing oceanic environment in the Upper Triassic.

• Research Organization: Oregon Univ., Eugene (USA)
• OSTI ID: 6997073
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
APATITES
CHEMICAL ANALYSIS
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
STRATIGRAPHY
RARE EARTHS
CERIUM
DISTRIBUTION
FOSSILS
INTERFACES
OCEANOGRAPHY
OXIDATION
REDOX POTENTIAL
REDUCTION
SEAWATER
SEDIMENTS
VARIATIONS
CHEMICAL REACTIONS
ELEMENTS
GEOLOGY
HYDROGEN COMPOUNDS
METALS
MINERALS
OXYGEN COMPOUNDS
PHOSPHATE MINERALS
WATER
580400* - Geochemistry- (-1989)
580500 - Oceanography- (1980-1989)