Evolution of the 87Sr/86Sr composition of Neoproterozoic seawater
The limited availability and low resolution of biostratigraphic and radiometric data in the Precambrian necessitate using marine chemostratigraphy to correlate and integrate the fragmentary stratigraphic record. We present a new composite record of the strontium isotope composition of seawater during the Neoproterozoic (1000–542 Ma) Era that is linked to a high-resolution δ13C (carbonate) compilation. The 87Sr/86Sr record consists predominantly of new and previously published data from carbonate-rich successions in northwest Canada, Svalbard, and northern Namibia. Published data from other late Neoproterozoic successions are conservatively included to fill in the Ediacaran Period (635–542 Ma). Consistent with previous compilations, the resulting strontium isotope record shows a systematic rise in 87Sr/86Sr throughout the Neoproterozoic, from as low as 0.7055 at the beginning of the era to greater than 0.7085 towards the end. Though the record remains poorly resolved and time-calibrated, it appears that declines, inflections, and rapid changes in 87Sr/86Sr all correspond to major biogeochemical or climatic events. However, this record supports neither a tight coupling between δ13C and 87Sr/86Sr via continental erosion nor widespread mountain-building as the main driver for increasing 87Sr/86Sr compositions during the Neoproterozoic. Rather, the steady rise in 87Sr/86Sr during the Neoproterozoic corresponded to the break-up of the supercontinent Rodinia.