Organic remains in late Palaeoproterozoic granular iron formations and implications for the origin of granules

Toward the end of the Palaeoproterozoic era, over 109 billion tonnes of banded (BIF) and granular (GIF) iron formations were deposited on continental platforms. Granules in iron formations are typically sub-spherical structures 0.2 to 10 mm in size, whereas concretions are >10 mm. Both types of spheroids are preserved throughout the sedimentological record. Their formation has typically been interpreted to originate from reworked Fe-rich...