Geochemistry of Neoproterozoic black shales from Svalbard: Implications for oceanic redox conditions spanning Cryogenian glaciations

- Anoxic-ferr. conditions during deposition of Neoproterozoic shales from Svalbard
- Sturtian glaciation not related to oxygenation
- Shelf environments remained anoxic after Marinoan glaciation.
- Oceanic redox structure in Ediacaran becomes similar to Phanerozoic.

We present paleoredox data from black shales from the ca. 835-630 Ma Akademikerbreen and Polarisbreen groups, northeastern Svalbard. These iron speciation, trace metal, and organic carbon data include the first record of ocean redox conditions leading up to the Sturtian glaciation and contribute to the emerging narrative of protracted Neoproterozoic oxygenation. Sampled shales were deposited under dominantly suboxic to anoxic-ferruginous conditions on a stable continental shelf. Together with data from other basins, these data show no evidence of dramatic increases in environmental oxygen levels prior to or following the Sturtian glaciation. Proposed global oxygenation in the aftermath of the Marinoan glaciation did not lead to long-term oxygenation of shelf environments in Svalbard or northwestern Canada. We suggest that this reflects sufficient organic matter loading to maintain suboxic to anoxic water columns on continental margins. In contrast, oxygen concentrations may have been higher in low-productivity zones further offshore, where downwelling of oxygenated surface waters may have even increased oxygen concentrations in the deep ocean.