Contrasting slope channel styles on a prograding mud-prone margin

Abstract

The Pleistocene slope clinoform succession of the Pescara Basin foredeep (Central Adriatic Basin, Italy) has been investigated combining the analysis of the rollover point trajectories with 2D seismic facies analysis and 3D seismic geomorphology approach and visualization techniques. The study documents two different types of slope clinoforms, each of which is characterized by a specific slope turbidite system with distinctive morphologies, internal geometries and architectural elements.Type 1 clinoforms are characterized by rectilinear, slope-confined gullies which develop during a phase of margin growth. Type 1 clinoforms are characterized by a rise of the trajectories of the rollover points, which can be indicative of intervals of relative sea level rise. In type 1 clinoforms most of the coarse-grained sediments are stored in the shelf. The slope-confined gullies barely indent the shelf break, are not connected to rivers, and develop thin (<30 m) frontal splays at the base of the slope. All these evidences indicate that the gullies are inefficient pathways to transfer sandy sediment basinward. The gully depressions are net-erosional and also the inter-gully sectors are sites of dominant sediment bypass. The infill deposit of the gullies consists of channel-wide high-amplitude reflectors (HARs) wedging-out downslope. The origin of the slope-confined gullies is interpreted to be linked to mass wasting processes affecting the upper slope and the shelf-edge during conditions of relative sea level rise. Longshore drifts and storm-driven turbidity currents rework the outer shelf, promoting the maintenance of gully systems, which become filled during the ensuing high-stand of the sea level.Type 2 clinoforms are characterized by a negative trajectory of the rollover points, and develop during a lowering of the sea level and during lowstand periods. Type 2 clinoforms develop sinuous, aggradational slope channels which are river-connected, with incised valleys that supply sediment directly to the head of the slope channel. The slope channels are fed through sustained turbidity currents possibly associated with hyperpycnal flows. Type 2 slope channels develop in a net-aggradational setting, forming erosive based channel-fill deposits about 150 m thick which are characterized by high-amplitude reflectors (HARs). Type 2 slope channels are able to transfer larger amount of sediment to the basin, comparing with type 1 gullies, as the presence of thick (∼150 m) channelized frontal–splay complexes seems to confirm. The combination of 2D and 3D data analysis has lead to the reconstruction of a sedimentological model which has the potential to be applied as analogue for seismic or outcrop-based studies of slope channels in supply-dominated, mud-prone margins.