Sedimentology and geochemistry of the glaciogenic late Proterozoic Rapitan iron-formation in Canada

The Rapitan iron-formation in the Northwest Territories and Yukon of Canada was formed between 755 and 730 Ma. The mineralogy and major element geochemistry is very simple and is distinctly different from that of most major banded iron-formation types of Archean and Early Proterozoic age. The rare earth element chemistry appears to be much less distinctly influenced by hydrothermal input into an ocean system than that of these earlier sequences. This suggests a hydrothermal input that was highly diluted by ocean waters at Rapitan time. The sedimentologic setting of the formation strongly suggests an origin as part of glaciomarine conditions. The iron-formation was deposited during a major transgressive event with a rapid rate of sea-level rise during an interglacial period. The occurrence, during Late Proterozoic time, of several, mineralogically and chemically very similar iron-formations worldwide that are in close association with major glaciogenic sequences, and paleomagnetic data for that same period which suggest widespread continental glaciers within a few degrees of the equator, lead to the concept of a "snowball-type Earth'; an earth that would have resembled a highly reflective "snowball' with floating pack ice over most of the ocean surface. -from Authors