Submarine slope morphology as a control on the development of sand-rich turbidite depositional systems: 3D seismic analysis of the Kyrre Fm (Upper Cretaceous), Maloy Slope, offshore Norway

摘要

Three-dimensional seismic and well data are integrated to investigate the geometry and controls on a series of sand-rich slope systems in the Kyrre Fm (Upper Cretaceous) on the Maloy Slope, offshore Norway. Slope systems were fed by sediments eroded from mainland Norway to the east and transported across a relatively narrow shelf into four canyons developed at the shelf edge. These canyons were not formed through erosional or mass-wasting processes during the Late Cretaceous, but represent a series of underfilled canyons developed during an earlier, Late Jurassic erosional phase. Channels, which are commonly arranged into laterally or vertically stacked channel complexes, were fed sediment through the shelf-edge canyons and may be associated downslope with small terminal fans. The canyons and their associated depositional systems were not active synchronously, with a clear southward migration of the active depositional systems. On the slope, syn-depositional topography was formed via: (i) differential compaction of mudstone-rich strata across underlying Late Jurassic canyons which resulted in the formation of a series of E-W-trending structural lows; and (ii) differential compaction of mudstone-rich strata across the underlying Late Jurassic fault blocks which resulted in N-W-trending structural highs. Both of these features had a variable influence on the incision, fill and overall spatial distribution of slope channels/channel complexes and associated fans. A large fan which overlies the shelf-edge canyons and associated downslope depositional systems represents the final depositional unit within the study area. The fan effectively 'seals' the underlying shelf-edge canyons, suggesting it was not supplied by sediment routed through the canyons. The results of this study support previous studies which indicate that shelf-edge canyons may be a first-order control on the location of sand-rich, turbidity current-fed depositional systems on submarine slopes. Furthermore, this study demonstrates that differential compaction may be a key control on slope morphology in submarine settings and the associated topography can markedly influence depositional patterns.