METHANE-GENERATED(QUESTIONABLE) POCKMARKS ON YOUNG, THICKLY SEDIMENTED OCEANIC-CRUST IN THE ARCTIC - VESTNESA-RIDGE, FRAM STRAIT

Acoustic backscatter imagery in the Fram strait (between Greenland and Spitzbergen) reveals a 1-3-km-wide, 50-km-long belt of approximately 50 pointlike backscatter objects decorating the approximately 1300-m-d eep crest of Vestnesa Ridge, a 1->2 km thick sediment drift possibly u nderlain by a transform-parallel oceanic basement ridge (crustal ages approximately 3-14 Ma). A 3.5 kHz seismic-reflection profile indicates that at least some objects are pockmarks approximately 100-200 m in d iameter and 10-20 m deep. The pockmarks (possibly also mud diapirs) ma y have been formed by evolution of methane generated by the decomposit ion of marine organic matter in the Vestnesa ridge sediment drift. The ridge may be underlain by an anticlinal carapace of methane-hydrate c alculated to be 200-300 m thick, comparable to the hydrate thickness m easured just to the south. The rising methane would collect in the rid ge-crest trap, intermittently escaping to the sea floor. This hypothes is is supported by multichannel evidence for bright spots and bottom-s imulating reflectors in the area. The pockmark belt may also be locate d above a transcurrent fault. Sediment slumps on the flanks of Vestnes a ridge and northeast of Molloy ridge may have been triggered by plate -boundary earthquakes and facilitated by methane hydrates.