SEA-LEVEL CHANGE FOLLOWING THE MARINOAN SNOWBALL EARTH DEGLACIATION

Marinoan cap carbonates are thought to represent deposition during the glacioeustatic sea-level rise associated with a ‘Snowball Earth’ deglaciation (Hoffman et al., 1998). However, facies associations within some syn-deglacial Marinoan successions suggest that regional regression punctuated these transgressive sequence tracts (Hoffman and Macdonald, 2010; Rose and Maloof, 2013). A number of questions arise from stratigraphic studies that highlight the need to couple sequence stratigraphic observations with numerical models of post-Snowball sea-level change. For instance, what is the plausible range of geographic variability in regional sea-level change driven by the deglaciation? Is this geographic variability a strong function of the duration of the deglaciation? Can a local geological inference of the magnitude of transgression provide a robust estimate of the globally averaged (eustatic) sea-level rise associated with the deglaciation? What circumstances could lead to a pronounced regional regression during glacioeustatic transgression?

In this talk, we explore the spatial and temporal variability of sea-level change during Snowball deglaciation and its aftermath using a gravitationally self-consistent theory that accounts for the deformational, gravitational and rotational perturbations to sea level on a viscoelastic Earth model. We apply the theory to the case of a model Marinoan Snowball deglaciation on a generalized Ediacaran paleogeography with a synthetic continental ice-sheet distribution. We demonstrate that the sea-level change following a rapid (2 kyr), synchronous collapse of Snowball ice cover would exhibit significant geographic variability, including local sea-level records characterized by syn-deglacial sea-level fall or stillstand. Moreover, asynchronous melting and longer-duration deglaciation phases (5 – 200 kyr) introduce further complexity into the predicted timing and geometry of the computed sea-level change, including zones of syn-deglacial regression followed by transgression and the possibility of deposition that is not limited to the deglaciation phase. These results suggest that sea-level change recorded by strata capping Snowball glaciogenic units may reflect a far more complicated trajectory than previously thought.