Slip Sliding Away: Enigma of Large Sandy Blocks Within a Gas-Bearing Mass Transport Deposit, Offshore Northwestern Greenland

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 (162 mi) 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 largeMTDblocks and provides constraints on the basin development and petroleum prospectivity of northeast Baffin Bay. AUTHORS David R. Cox ~ Department of Earth and Environmental Sciences, The University of Manchester, Manchester, United Kingdom; david.cox@manchester.ac.uk David R. Cox joined The University of Manchester in 2016 as a Ph.D. student after working for 2 years in the oil industry. His Ph.D. research is focused on the impacts of glaciation on Arctic petroleum systems, encompassing topics such as seismic geomorphology, fluid flow, gas hydrates, reservoir characterization, basin modeling, and shallow hazard analysis. Mads Huuse ~ Department of Earth and Environmental Sciences, The University of Manchester, Manchester, United Kingdom; mads.huuse@manchester.ac.uk Mads Huuse is professor of geophysics at The University of Manchester. He received his Ph.D. from Aarhus University in 1999 and joined Manchester in 2009 to lead the seismic interpretation group. His interests include basin fill, temperature, diagenesis, gas hydrates, reservoir and seal characterization, and fluid flow. His interests also include seismic geomorphology of glaciated basins and margins. Andrew M. W. Newton ~ Department of Earth and Environmental Sciences, The University of Manchester, Manchester, United Kingdom; A.Newton@qub.ac.uk Andrew M. W. Newton received his Ph.D. in seismic geomorphology of glaciated margins from The University of Manchester in 2017. After a short postdoctoral, he joined Queen’s University Belfast as an independent research fellow and remains a visiting researcher at Manchester. His current research interests include using seismic geomorphology to understand subsurface evolution, paleoclimate, and fluid flow. Paul Gannon ~ Cairn Energy, PLC, Edinburgh, United Kingdom; Paul.Gannon@ cairnenergy.com Paul Gannon is a geoscientist working for Cairn Energy, PLC, as part of the Norwegian North Sea exploration team, based in Stavanger Norway, and previously as part of the North Copyright ©2020. The American Association of Petroleum Geologists. All rights reserved. Gold Open Access. This paper is published under the terms of the CC-BY license. Manuscript received January 11, 2019; provisional acceptance March 21, 2019; revised manuscript received May 23, 2019; final acceptance October 3, 2019. DOI:10.1306/10031919011 AAPG Bulletin, v. 104, no. 5 (May 2020), pp. 1011–1043 1011