Fig. 1: Palaeogeographic setting and stratigraphic correlation of Sturtian iron formations in the South China Block.

a Palaeogeographic reconstruction of the South China Block (SCB) during the late Neoproterozoic Era, showing the distribution of Sturtian-aged iron formations (IFs) in the region^{5,8,21,51,52,54,106}; 1 (Sanjiang IF); 2 (Tongdao IF); 3 (Jiangkou IF); 4 (Qidong IF); and 5 (Xinyu IF). The inset shows the geographic locality of the Yangtze Block. The shelf is subdivided into inner and outer regions. Within the broader slope-to-basin environment, an inferred deep-water sub-basin is delineated, reflecting relatively greater water depth (Supplementary Information). This palaeogeographic framework is primarily informed by previous regional interpretations, including stratigraphic, sedimentological, and lithofacies features, and remains provisional in nature (see main text and SI for a detailed discussion of its limitations). Symbols for IFs and submarine uplifts are not to scale and are exaggerated for illustrative purposes. b Representative stratigraphic columns illustrating the correlation of the studied IFs with the waxing and waning cycles of the Sturtian glaciation in the SCB^{5,8,19,21,51,52,53}. The thicknesses of the IFs, manganese formations, and intervening dolostone layers in the Fulu Formation, as well as the pebble-free siltstone, sandstone, and shale layers in the Nantuo Formation, are exaggerated for illustrative purposes and do not accurately represent their true dimensions.