Complex sentence: The stratigraphic thickness averages about, consisting mainly of an interbedded sequence of chert, jasper and magnetite with smaller proportions of hematite, pyrite and volcanic tuff; this suggests that volcanic eruptions were simultaneous with deposition of the banded iron formation.
Split into simpler sentences: The stratigraphic thickness averages about, consisting mainly of an interbedded sequence of chert, jasper and magnetite with smaller proportions of hematite, pyrite and volcanic tuff. This suggests that volcanic eruptions were simultaneous with deposition of the banded iron formation.