5 Isotopic Composition of Seawater
105
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Fig. 5.13. Curves of published Sr and C isotopic data across the Precambrian / Cambrian
boundary. Above: SE. Siberia from Brasier et al. (1994)and authors mentioned in figure;
below: W. Mongolia t'rom Brasier et al. (1996) and Shields ( 1996}. Comparison of the two
sets of curves reveals isotopic features in the Mongolian data set not apparent in Siberia.
(Brasier et al., 1996) conclude that there may be an unconformity in the boundary, sections
of Siberia, ~hich might mask the true, more gradual course or the Cambrian explosion.