Paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite

Details Paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite Paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite

Mar 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51..631w&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 51, Issue 3, pp.631-644

Physics

15

Scientific paper

Rare earth element concentrations in biogenic apatite of conodonts, fish debris and inarticulate brachiopods were determined in over 200 samples from Cambrian to modern sediments. Tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory, interexperiment or interspecies related variations clearly show that no resolvable fractionation of REE occurs. Incorporation of REE in biogenic apatite of Recent fish debris occurs near the sediment-water interface soon after deposition and reflects characteristics of seawater. The original REE signature apparently survives subsequent burial and diagenesis. Cerium variations in fish debris from modern environments are controlled by redox potential. Ce is fractionated by co-precipitation with metallic oxides under oxidizing conditions. This fractionation produces a negative Ce anomaly (Ce anom ) in seawater that is reflected in the sedimented fish debris. Conversely, no fractionation of Ce occurs under reducing conditions, resulting in Ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions. Extrapolation of observations of the redox control of Ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower Paleozoic and Lower Triassic oceans, whereas in the upper Paleozoic, the world ocean was generally oxidizing.

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