iPlex Lunch spring-2015

The Snowball Earth hypothesis posits that two global glaciation events in the Neoproterozoic entombed the Earth and that continental ice sheets reached paleo-equatorial latitudes (Kirschvink, 1992). Cap carbonates are thought to represent marine deposition atop formerly glaciated margins during the glacioeustatic sea-level rise accompanying a Snowball Earth deglaciation (Hoffman et al., 1998; 2007). Inferences of globally coherent sea-level rise in the vicinity of rapidly melting ice sheets conflicts with insights from geodetic and geophysical models of the Plio-Pleistocene ice age that predict that the decay of ice sheets results in a sea-level change characterized by significant geographic variability, including pronounced sea-level fall in the vicinity of rapidly melting ice sheets driven by elastic/gravitational effects and viscoelastic crustal deformation (post-glacial rebound).

In this talk, I present lithofacies observations and a sequence stratigraphic analysis of the Noonday Dolomite, Death Valley region, CA, a ~ 635 Ma Marinoan-equivalent cap carbonate. This analysis reveals complex post-Snowball sea-level change, including a large amplitude sea-level fall that punctuated the post-glacial transgression. I speculate on the mechanisms responsible for the observed sea-level change using a gravitationally self-consistent theory that accounts for the gravitational and deformational perturbations to sea level on a viscoelastic Earth model. I apply the theory to model a Marinoan Snowball deglaciation across a generalized Ediacaran paleogeography with a synthetic ice sheet distribution (Creveling and Mitrovica, 2014). I conclude that either a hiatus in melt-water flux or a rapid, local collapse of Snowball ice sheets can reconcile the sea-level fall observed in the Noonday Dolomite. Further I conclude that globally distributed syn-deglacial transgression over formerly glaciated margins provides strong evidence for ‘Snowball’-scale ice volumes that contribute to a sea-level rise that overwhelms local dynamic effects.