Computer Science
Scientific paper
Jul 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987e%26psl..84..181g&link_type=abstract
Earth and Planetary Science Letters, Volume 84, Issue 2-3, p. 181-196.
Computer Science
21
Scientific paper
The REE content and isotopic composition of Sr and Nd have been determined in fish teeth ranging in age from the Trias to the present and from various localities mostly around the Atlantic. These measurements have been carried out on Selachian and Teleost remains from the same locality in Togo and show no appreciable difference, which suggests, with the help of a mass balance calculation of the Ce anomaly, that diagenetic effects are not responsible for the REE enrichment of biogenic phosphates.
One group of fossil teeth has about 3 times the REE abundances of shale and a shale-normalized pattern with a minimum at Sm: it is thought to reflect deposition in the open-sea environment. A second group has REE concentration about 10 times higher than the first group with either a regular light REE enrichment or, more frequently, a maximum in the middle REE, both being probably indicative of deposition in estuarine or near-shore conditions. The shape of the REE spectra and the size of the Ce anomaly can be used semi-quantitatively to determine the depth of deposition. The results presented here on Late Cretaceous/Eocene fish teeth samples from Morocco reflect an increasing influx of deep waters with a low La/Yb ratio and strong negative Ce anomaly, which agrees well with the evolution of sediment chemistry and microfauna associations.
In contrast, ɛNd is typical of the water mass in which the fish debris decayed. Examples of nearly isolated basins identified with Nd isotopes include the South Atlantic prior to the Lutetian (ɛNd ~ -13.5), the Miocene Persian Gulf (ɛNd = -3.1), and Bolivia during the Late Cretaceous (ɛNd = -12.8). Togo and Guinea-Bissau results suggest that, in the South Atlantic, the meridional oceanic circulation had not started before 45 Ma ago.
Combination of REE and ɛNd data suggests that the assignment of Jurassic-Cretaceous samples measured so far to open-sea water masses is still ambiguous.
Albarède Francis
Cappetta Henri
Grandjean Patricia
Michard Annie
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