EVIDENCE FOR AUTOGENIC FORCING OF SNOWBALL GLACIOMARINE SEDIMENTATION

The Sturtian and Marinoan snowball Earth glaciations of the Cryogenian are instances of the runaway ice-albedo feedback in Earth’s climate system, providing examples of dramatic climate variability in our planetary history. The drivers of sedimentary variability in records of these events remain contested, with hypotheses including tectonic, climatic, and autogenic forcings. We turn to the modern analogue of Antarctic glaciomarine sedimentation to help test the climatic, specifically, orbital, hypothesis. Using a novel Bayesian age modelling approach, we probabilistically constrain the compensation time and length scales of glaciomarine sedimentation recorded by the ANDRILL AND-2A Antarctic sediment core. We argue that the compensation length scale is set by the amplitude, 30–36 m, of orbitally forced Neogene glacioeustasy, providing a reference value from the best modern analogue for sub-ice shelf glaciomarine sedimentation. Then, using hundreds of bed traces on high resolution drone imagery of the well-exposed glaciomarine stratigraphy of the Marinoan snowball Ghaub Formation along Fransfontein Ridge in Namibia, we independently estimate a compensation length scale of roughly 6 m. This smaller value is inconsistent with Cenozoic-style glacioeustatic variability, and, given a constant tectonic environment during deposition, suggests instead the role of autogenic variability in driving glaciomarine sedimentary variability.