Major shoreline retreat and sediment starvation following Snowball Earth

Abstract

While cap dolostones are integral to the Snowball Earth hypothesis, the current depositional model does not account for multiple geological observations. Here we propose a model that rationalises palaeomagnetic, sequence-stratigraphic and sedimentological data and supports rapid deglaciation with protracted cap dolostone precipitation. The Snowball Earth hypothesis posits that a runaway ice-albedo can explain the climate paradox of Neoproterozoic glacial deposits occurring at low palaeolatitudes. This scenario invokes volcanic degassing to increase atmospheric greenhouse gases to a critical threshold that overcomes the albedo effect and brings the planet back from the ice-covered state. Once this occurs, Earth should shift rapidly from a snowball to an extreme greenhouse. However, cap dolostone units overlying glacial sediments, typically interpreted as transgressive deposits, exhibit multiple magnetic reversals indicating they accumulated in >105 years. By reviewing modern post-glacial systems, sequence stratigraphic concepts and principles of sedimentology, we suggest that cap dolostones are not restricted to the transgression but rather represent sediment starvation following a major landward shoreline migration associated with the demise of Snowball Earth. Thus, the duration in which cap dolostone accumulated is not directly coupled to the timescale of the Snowball Earth deglaciation.