Fig. 1.

Variation in Nd- and Fe-isotope compositions in the Dales Gorge member BIF sampled over different length and timescales. (Left and Center) Coupled Nd- and Fe-isotope data are from bulk sample solution analyses, and (Right) Fe-isotope data of hematite and magnetite are from in situ laser ablation analysis. The absolute age (2.50–2.45 Ga) and duration [50 million years (My)] of the Dale Gorge member BIF are suggested in ref. 24. The durations of BIF macroband 16 and the 7-cm drill core sample are estimated using a sedimentation rate of 50–63 m/Ma based on assuming that the finest scale banding (microbands) reflects annual or varve-like bands (SI Appendix, section 3); this assumption produces a sedimentation rate similar to that calculated using the total sediment thickness of a 50-My depositional interval.