Did gas-hydrate dissociation promote slope instability in the western Black Sea since the end of the last glacial period?

Submarine landslides constitute major marine and coastal geohazards, causing damage to marine infrastructures or even provoking tsunamis. For many authors, gas hydrate dissociation represents an effective triggering mechanism in generating sedimentary instabilities. In the Romanian upper slope of the Black Sea, failure headscarps are observed in an active gas-seep province close to the gas hydrate occurrence zone acting as an effective seal preventing gas from reaching the seafloor (Popescu et al., 2007; Riboulot et al., 2017). Through a chronostratigraphic interpretation of a large multi-resolution geophysical database, the aim of this article is, for a key period extending from the last glacial period (ca. 33.5–17 ka BP) to the present day, to test the claim of a sudden and instantaneuous scenario developed by Kennett et al. (2003), which argue that hydrate dissociation can trigger large-scale landslides on submarine continental margins. Our results show that pronounced gas hydrate dissociation in the Black Sea in response to rapid environmental changes since the last glacial period (Riboulot et al., 2018), does not appear to be the exclusive and main triggering factor of the observed slope failures. This statement is supported by new dating of successive failure events put forward in this study, and the fact that the current and past modelled free gas and hydrate interfaces are much deeper than the basal shear surfaces of instabilities. Alternatively, we suggest that high sedimentation rates, falling hydrostatic pressure, and gas exsolution linked to rapid sea-level lowering are probably the most significant preconditioning factors to consider. Seismic activity cannot be ruled out, given the proximity of active faults on the outer shelf.