Mesoarchean banded iron-formation from the northern Yangtze Craton, South China and its geological and paleoenvironmental implications

•The Dujiagou BIFs are of Mezoarchean age and the oldest identified in the Yangtze Craton.•They were deposited predominantly by chemical sedimentation with minute detrital input from the Archean continent.•Iron isotope systematics point to a change in the valence state of iron in magnetite and deposition in an ocean lacking a persistent and pervasive redoxcline.