Lowstand slope channels of the Itilli succession (Maastrichtian-Lower Paleocene), Nuussuaq, West Greenland

The Maastrichtian-Lower Paleocene Itilli slope succession of Nuussuaq, West Greenland consists of an at least 2.5 km thick turbidite succession, composed of mudstone, thinly interbedded sandstone and mudstone, chaotic beds, amalgamated sandstone and giant-scale cross-bedded sandstone. The amalgamated and giant-scale cross-bedded sandstones were deposited in 1-2 km wide slope channels draining basin-margin source areas. The chaotic beds invariably underlie undisturbed channel fill sandstones suggesting that initially channels were excavated largely by retrogressive slumping of unstable slope mudstones. Retrogressive slumping was followed by intense channel excavation with continued scouring of channel base and walls before deposition of channel fills from high-density turbidity currents. It is suggested that destabilisation of the slope mudstones was triggered by drops in relative sea-level, associated with increased sediment deposition on the slope. Sequence stratigraphic concepts have been applied to the Itilli slope succession. The chaotic beds are related to the forced regressive wedge systems tract. The sequence boundary is placed at the erosional unconformity separating the chaotic beds from the overlying channel sandstone turbidites and it represents the lowest point of relative sea-level fall. The channel fill represents the lowstand prograding wedge systems tract and the transgressive systems tract. Poorly developed highstand systems tract deposits include thinly interbedded sandstones and mudstones and are probably also represented in the redeposited material in the chaotic beds.