Record of Rapid Sea Level Rise during Deglaciation of the Marinoan Snowball Earth

Deglaciation of the Marinoan ( 635 Ma) Snowball Earth is recorded, in part, within a unique 30-50 m thick, tidal-rhythmite siltstone unit in the upperElatina Formation in South Australia.The unit contains a complete daily record of sedimentation driven by a combination of tidal currents and wind-driven waves. The tidal currents produced cm-scale packages of 12-15 pairs of mm-thick silt and muddy silt laminae that systematically vertically thicken and thin. The packages were previously interpreted to represent spring-neap tide cycles. These laminae also record two scales of generally symmetrical ripples. Larger bedforms (heights of 1.5-2 cm) preserve lamination typical of combined-flow ripples, and gradual vertical shifts, including reversals in cross-stratification orientations. These features and others indicate reversals in migration direction and suggest deposition under a combination of reversing tidal currents and waves. Smaller 2D ripples ( 0.5 mm high) are oriented perpendicular to the large ripples, and paleohydraulic analysis indicates that they formed under wind-driven waves in water depths of 8-28 m. Ripple spacing remained nearly constant through 16 m of sedimentary strata, which were deposited in 96 yrs, as constrained by the tidally bundled laminae. To maintain a near-constant water depth, increased accommodation space must have matched our calculated (decompacted) sediment accumulation rate of 28 cm yr^-1, which rules out slower processes of compaction or tectonic subsidence. Our analysis instead indicates a rate of sea level rise during Marinoan Snowball Earth deglaciation that was several orders of magnitude greater than present rates of sea level rise.