Snowball Earth
An alternative mechanism for banded iron formations in the Snowball Earth era suggests the iron was deposited from metal-rich brines in the vicinity of hydrothermally active rift zones due to glacially-driven thermal overturn. The limited extent of these BIFs compared with the associated glacial deposits, their association with volcanic formations, and variation in thickness and facies favor this hypothesis. Such a mode of formation does not require a global anoxic ocean, but is consistent with either a Snowball Earth or Slushball Earth model.