Petrography, age (uranium-lead zircon), geochemical and isotopic studies of the Sawawin Banded Iron Formation (BIF), Northwestern Saudi Arabia: Implications for understanding Neoproterozoic climate change

The Neoproterozoic Era (1000-544 Ma) was a time of global climate change, hypothesized to range from snowball Earth to a greenhouse climate. Two contrasting models such as the Snowball Earth Hypothesis and the Zipper-Rift model compete to explain such climatic oscillations. The worldwide reappearance of banded iron formations (BIFs) during the Neoproterozoic glacial periods after ∼1 Ga long hiatus is considered to be a key pillar of the snowball Earth hypothesis. Neoproterozoic BIFs can be categorized into the Algoma- and Superior-type is primarily based upon their depositional, tectonic and stratigraphic associations and can help evaluate the role of Neoproterozoic BIF in order to understand the Neoproterozoic climate change controversy.;Neoproterozoic Algoma-type, oxide facies BIF from Wadi Sawawin, NW Saudi Arabia occurs at the eastern edge of a larger BIF basin in the northern part of the Arabian-Nubian Shield (ANS), most of which now is found in eastern Egypt. Study of ANS-BIF provides an opportunity to test the two hypotheses. The age of the Sawawin BIF is constrained between 763+/-25 Ma and 661.5+/-2.3 Ma, consistent with deposition during the broad Sturtian glacial period. Our best estimate is that ANS-BIF was deposited ∼740 Ma ago.;The Sawawin BIF precipitated as chemical sediment. The geochemical signatures of Sawawin and Egyptian BIF suggest that they share characteristics of both modern seawater and hydrothermal vent fluids, suggesting their derivation from a mixture of shallow Black Sea type suboxic seawater with a low-T hydrothermal vent fluid. Neodymium and lead isotopic data suggest that Sawawin BIFs derived its Pb and Nd (and by analogy iron) from mantle sources, most likely through hydrothermal activity. This observation is consistent with both the snowball Earth model and the Zipper Rift model, where hydrothermal inputs are also likely.