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 km 2 (162 mi 2 ) 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.

Repeated ice streaming on the northwest Greenland continental shelf since the onset of the Middle Pleistocene Transition

“…These features are interpreted as MSGLs due to their morphology (Spagnolo et al, 2014) and similarity to MSGLs observed on the local seafloor and buried on other glaciated margins (e.g. Andreassen et al, 2007;Dowdeswell et al, 2006;Montelli et al, 2017;Rea et al, 2018).…”

“…Switches in ice stream pathways on continental shelves between different glacial maxima have been observed on the mid-Norwegian margin, where new cross-shelf troughs were formed through the erosive action of ice (Dowdeswell et al, 2006). In contrast to the mid-Norwegian margin, the available data in Melville Bugt do not show evidence of buried cross-shelf troughs.…”

Geohazard detection using 3D seismic data to enhance offshore scientific drilling site selection

“…A shallow coring program was carried out in 2012, but no exploration wells have been drilled. Since then, the identification of a large potential gas reservoir (Cox et al, 2020a) and widespread evidence for shallow gas and gas hydrates (Cox et al, 2020b) further support an active petroleum system, thus underscoring the need for a geohazard assessment study prior to drilling.…”

“…This included the physical character of anomalies, which were often isolated bright spots or brightening along single horizons ( Fig. 8), as well as their spatial and stratigraphic distribution, which was widespread within all levels of the post-rift stratigraphy (mu-D to -A) and focussed around the Melville Bay Ridge (Cox et al, 2020b). The seismic amplitude range of the bright anomalies was also analysed to aid amplitude extractions.…”

“…Bright fluid anomalies were identified hosted within inclined, likely sandy, strata that terminate abruptly at a certain depth beneath the seabed (Fig. 9) (Cox et al, 2020b). This level, characterized by a dim, negative amplitude reflection that cuts across the stratigraphic layering in a manner that mirrors the seabed topography, represents a bottom-simulating reflector (BSR).…”