The Late Precambrian and Cambrian were periods of marked global change
in the biosphere with the appearance and rapid radiation of skeletali
zed metazoans. However, the changes in atmosphere and oceanic environm
ents that may have accompanied this evolutionary episode remain largel
y unresolved. In this contribution carbonate samples from Lower Cambri
an sections in eastern Siberia are used to construct a composite Sr is
otope curve across the Nemakit-Daldynian-Tommotian boundary (the forme
r Precambrian-Cambrian boundary in Siberia). The results show a signif
icant fall in seawater Sr-87/Sr-86 ratios across this interval. This d
ecrease is placed in context by the construction of a new seawater Sr
curve for the late Neoproterozoic to early Ordovician, compiled from t
hese data and those available in previous publications. The ocean-atmo
sphere interactions recorded by the marked variation in seawater Sr im
mediately preceding and during the Cambrian potentially record short-t
erm (15-20 Ma) hydrothermal events punctuating an overall increase in
terrestrial weathering rates, although further research is needed to c
onfirm this conclusion.