Computer Science
Scientific paper
Jun 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52.1361l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 52, Issue 6, pp.1361-1371
Computer Science
6
Scientific paper
The Ce anomalies found in marine carbonates provide a sensitive indicator for the study of paleo-oceanic redox conditions. The dependency of C Ce (the observed Ce concentration) and CePO 0 4 (the activity of the CePO 4 complex) to the P O 2 , pH and P CO 2 of seawater can be used for deciphering some aspects of the paleo-ocean chemistry, and is: The pH, which is related to P CO 2 , and P O 2 are major factors for controlling the Ce concentration in seawater. Therefore Ce anomalies, Ce A s (Ce observed/Ce interpolated between La and Pr or Nd) serve as indicators for pH (or P CO 2 ) Or P O 2 changes. Nearly uniform Ce abundances found in Pacific ~ 5000 m water columns ( and , 1988) and the Ce A s in ichthyoliths can be explained using this model. A general Ce A shift in sediments from D.S.D.P. Holes 525A, 530A & B, 516, 516F suggest that the entire South Atlantic water redox condition changed from reducing to oxidizing at 56 My. In the North Atlantic, the Galicia Margin samples show a redox change between 132-148 My, indicating active surface currents between the Atlantic ocean and the shallow sea off the Iberian Peninsula. The carbonate samples from D.S.D.P. Hole 316 in the Central Pacific yielded an average Ce A of 0.15 ± 0.01, which is 2-3× the Ce A s observed in deep Pacific seawater by and (1988). The relative enrichment of Ce in these samples is ascribed to coprecipitation of Ce(OH) 4 onto Fe-Mn-O coatings. The striking similarities in the trace element profiles of REE + Sc + Hf + Th and Ce A s and the low U abundances (~0.08 ppm) in many marine carbonates indicate insignificant Ce redox and trace elemental concentration changes for the Pacific ocean over the past 95 My: no significant Ce redox change occurred in the Pacific ocean within ± < 1 My below and above the K / T boundary. One 240 My China limestone, deposited under oxic sedimentary conditions, yielded a Ce A of 0.53. Calculations indicate a P CO 2 of ~1.9× present value prevailed over the ~240 My Tethyan Ocean. U / Th ratios and low U concentrations are diagnostic indicators for obtaining reliable Ce A s in marine carbonates, and perhaps for biogenic apatites and conodonts as well.
Liu George Yong
Miah R. U. M.
Schmitt Roman A.
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