Slip sliding away: Enigma of large sandy blocks within a gas-bearing mass transport deposit, offshore northwestern Greenland

Abstract

The northwestern Greenland margin contains several underexplored sedimentary basins formed by Cretaceous rifting and Cenozoic postrift sedimentation. The basins are thought to contain significant hydrocarbon reserves, although no exploration wells have been drilled to date. This paper reports the discovery of a gas-charged submarine landslide mass transport deposit (MTD) covering 420 km2 (162 mi2) above the Melville Bay ridge (MBR) rift structure. The sedimentary succession that deformed into the MTD was likely deposited within a shallow-marine spit complex developed along the ridge axis extension during the Eocene. The MTD displays landslide characteristics with distinct blocks up to 1 km (3281 ft) wide and 80 m (262 ft) thick that geometrically fit together like a jigsaw puzzle. Clear direct hydrocarbon indicators and velocity estimations suggest the mass transport blocks are composed of highly porous, gas-charged sands intercalated with shale layers and overlain by postslide pelagic mudstones. The reconstruction of all 499 MTD blocks suggests emplacement by bidirectional sliding, triggered by rejuvenation and a southward tilt of the MBR. Sliding most likely occurred slowly along a low-angle decollement surface, with the blocks remaining intact despite not being confined within a typical slide mass. Instead, coherency was likely aided by lithological layering and diagenesis. Gravitational shedding of the steep block margins has created interblock sand accumulations, which may enhance connectivity. This study provides an important analog for significant reservoir occurrence in large MTD blocks and provides constraints on the basin development and petroleum prospectivity of northeast Baffin Bay.