Control of Quaternary sea‐level changes on gas seeps

Abstract

Gas seeping to the seafloor through structures such as pockmarks may contribute significantly to the enrichment of atmospheric greenhouse gases and global warming. Gas seeps in the Gulf of Lions, Western Mediterranean, are cyclical, and pockmark "life" is governed both by sediment accumulation on the continental margin and Quaternary climate changes. Three-dimensional seismic data, correlated to multi-proxy analysis of a deep borehole, have shown that these pockmarks are associated with oblique chimneys. The prograding chimney geometry demonstrates the syn-sedimentary and long-lasting functioning of the gas seeps. Gas chimneys have reworked chronologically constrained stratigraphic units and have functioned episodically, with maximum activity around sea level lowstands. Therefore, we argue that one of the main driving mechanisms responsible for their formation is the variation in hydrostatic pressure driven by relative sea level changes.

Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait

“…Importantly, gas chimneys, regardless of their position along the ridge, show evidence of buried pockmarks or mounds (i.e., indicators of paleoseepage) [ Plaza‐Faverola et al ., ; Riboulot et al ., ] identified by truncation of reflections through chimney conduits at specific stratigraphic intervals (Figures and ). Nonetheless, the internal geometry of chimneys at each Vestnesa segment suggests dissimilar seepage evolution (Figures and ).…”

“…For resolving the causes of more regular seepage, improved chronostratigraphic constraints for the Pleistocene glacial‐interglacial periods are needed locally at Vestnesa Ridge. Nevertheless, its manifestation as stacked pockmarks intercalated with the periods of inactivity (Figure ) makes these fluid escape features comparable to those from the mid‐Norwegian margin, the Hikurangi Margin, Congo Basin, and the Gulf of Lions, where a link between periodicity and glacial‐interglacial cycles has been documented [e.g., Andresen and Huuse , ; Davy et al ., ; Riboulot et al ., ; Plaza‐Faverola et al ., ].…”

“…Episodic seepage at the updip termination of the GHSZ near the shelf break has been attributed to seasonal gas hydrate dissociation controlled by temperature variations [e.g., Berndt et al ., ; Phrampus and Hornbach , ; Skarke et al ., ; Westbrook et al ., ]. Longer‐term seepage periodicity (>10,000 years) has been attributed to pressure changes governed by processes associated with glacial‐interglacial cycles like sea level fluctuations, changes in sedimentation rates, and ice loading/unloading [e.g., Chand et al ., ; Davy et al ., ; Plaza‐Faverola et al ., ; Riboulot et al ., ] as well as fault reactivation mechanisms [e.g., Plaza‐Faverola et al ., ; Roberts and Carney , ; Zühlsdorff and Spiess , ]. Recent studies demonstrate the influence of inherited structural deformation, tectonic stresses, and fluid dynamics on modern margin evolution [ Autin et al ., ; Zoback et al ., ; Armitage et al ., ; Terakawa et al ., ].…”

“…Methane emissions from ocean floors are a global phenomenon often recognized by the presence of seafloor morphologies (e.g., pockmarks and mounds) and acoustic flares, which indicate rising gas bubbles in the water column [e.g., King and Maclean, 1970]. Pockmark fields are frequently documented in gas hydrate provinces [e.g., Vogt et al, 1994;Riedel et al, 2002;Hovland et al, 2005;Gay et al, 2006;Skarke et al, 2014] as well as from shallow seafloors (<200 m) outside the gas hydrate stability zone (GHSZ) [e.g., Hasiotis et al, 1996;Judd et al, 2002;García-García et al, 2006;Canet et al, 2010;Riboulot et al, 2014]. The geological settings in which seepage has been identified vary from passive margins [e.g., Berndt et al, 2005], active pull-apart basins [e.g., Canet et al, 2010], subduction margins [e.g., Barnes et al, 2010], epicontinental seas [e.g., Chand et al, 2012], and mixed compressional and shear deformation regimes [e.g., Plaza-Faverola et al, 2014].…”

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

“…Present day sea level is ~130 -140 m above the LGM levels (Fairbanks, 1989;Clark & Tarasov, 2014;Lambeck et al, 2014). This introduces pressure changes on the order of 10 -15 atmospheres in subjacent marine sediments that may be important in relatively shallow water depths (e.g., Riboulot et al, 2014) but would less affect sediments at depths 3 -4 km below sea level in the Mediterranean Sea. The observation that mud volcanoes are more active during falls in sea level by Xing & Spiess (2015) is likely a function of increased permeability in the carrier systems and migration routes (Römer et al, 2016) rather than significant pressure-driven changes in GHSZ thickness.…”