IS THERE A TECHNIQUE FOR THE DETERMINATION OF SEDIMENTATION RATES BASED ON CALCIUM CARBONATE CONTENT? : A COMPARATIVE STUDY ON THE SOUTHEASTERN BRAZILIAN SHELF

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In this paper we evaluate the utilization of the sedimentation rate values obtained by the carbonate content technique (Fukue et al., 1996, 1999) as compared with those obtained by traditional radiometric techniques (^<210>Pb_<XS>, ^<137>Cs and radiocarbon), using sediment samples from the Southeastern Brazilian shelf. Our results indicate that the sedimentation rates calculated by the calcium carbonate content technique do not show any significant differences from those obtained from ^<137>Cs and ^<210>Pb_<XS> but do reveal a significant difference from radiocarbon estimates. Nevertheless, no significant correlation was obtained in the comparisons between ^<137>Cs, ^<210>Pb_<XS> and calcium carbonate. Thus it would seem that the calcium carbonate technique may be used for raw estimates of sedimentation rates. Taking a carbonate level which can be correlated with a tsunami that occurred in 1542 as well as the peak activity of ^<137>Cs in 1963-1965 as age references we obtained an average value for the calcium carbonate precipitation rate for the study area which is close to that given by Fukue et al. (1996, 1999). Nevertheless our results suggest that the assumption of a single carbonate precipitation value may be too generic to be taken as valid for the calculation of sedimentation rates.
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