Melting the Marinoan Snowball Earth: The impact of deglaciation duration on the sea-level history of continental margins

• Modeled sea-level histories resulting from the deglaciation of Snowball Earth. • Short deglacial durations result in a limited range of sea-level patterns. • Longer deglaciations can drive two distinct intervals of sea-level rise and fall. • Long deglaciation may have contributed to geologic record of the Naukluft Mts. The termination of the Marinoan Snowball Earth (∼635 Ma) represents a significant transition in Earth's climate. Cap carbonate strata, and underlying glaciogenic deposits, record global deglaciation and preserve diverse relative sea-level histories, representing the intersection of global mean sea-level rise with regional forcings such as glacial isostatic adjustment and sedimentation. For example, at cap carbonate outcrops in the Naukluft Mountains of central Namibia, facies transitions reveal two intervals of water-depth deepening and shallowing. While many factors may have contributed to this deglacial pattern of relative sea-level change, here we consider the possibility that this, and other, non-monotonic sea-level histories, were driven by glacial isostatic adjustment. We modeled relative sea-level change due to glacial isostatic adjustment for a globally synchronous and continuous Marinoan deglaciation, and explored how the duration of deglaciation impacts the range of resulting relative sea-level patterns across continental margins. Short Snowball deglaciation durations, on the order of ∼2 kyr, result in exclusive relative sea-level rise, or relative sea-level rise followed by relative sea-level fall but cannot drive two distinct phases of relative sea-level fall. However, longer duration Snowball deglaciations, of ∼10–30 kyr, can drive two distinct intervals of relative sea-level rise and fall across much of the width of a continental margin, which may have contributed to the stratal patterns observed in Naukluft Mountains cap carbonate, though we cannot exclude that the pattern arises from changes in sediment supply or other factors. This work underlines the need for better constraints on the areal distribution and volume of Marinoan ice sheets from field observations, as well as plausible deglacial durations from global climate models.