Dimensions and architecture of late Pleistocene submarine lobes off the northern margin of East Corsica


  • Present address: Canada-Nova Scotia Offshore Petroleum Board, Halifax, NS, Canada


Sandy lobe deposits on submarine fans are sensitive recorders of the types of sediment gravity flows supplied to a basin and are economically important as hydrocarbon reservoirs. This study investigates the causes of variability in 20 lobes in small late Pleistocene submarine fans off East Corsica. These lobes were imaged using ultra-high resolution boomer seismic profiles (<1 m vertical resolution) and sediment type was ground truthed using piston cores published in previous studies. Repeated crossings of the same depositional bodies were used to measure spatial changes in their dimensions and architecture. Most lobes increase abruptly down-slope to a peak thickness of 8 to 42 m, beyond which they show a progressive, typically more gradual, decrease in thickness until they thin to below seismic resolution or pass into draping facies of the basin plain. Lobe areas range from 3 to 70 km2 and total lengths from 2 to 14 km, with the locus of maximum sediment accumulation from 3 to 28 km from the shelf-break. Based on their location, dimensions, internal architecture and nature of the feeder channel, the lobes are divided into two end-member types. The first are small depositional bodies located in proximal settings, clustered near the toe-of-slope and fed by slope gullies or erosive channels lacking or with poorly developed levées (referred to as ‘proximal isolated lobes’). The second are larger architecturally more complex depositional bodies deposited in more distal settings, outboard more stable and longer-lived levéed fan valleys (referred to as ‘composite mid-fan lobes’). Hybrid lobe types are also observed. At least three hierarchical levels of compensation stacking are recognized. Individual beds and bed-sets stack to form lobe-elements; lobe-elements stack to form composite lobes; and composite lobes stack to form lobe complexes. Differences in the size, shape and architectural complexity of lobe deposits reflect several inter-related factors including: (i) flow properties (volume, duration, grain-size, concentration and velocity); (ii) the number and frequency of flows, and their degree of variation through time; (iii) gradient change and sea floor morphology at the mouth of the feeder conduit; (iv) lobe lifespan prior to avulsion or abandonment; and (v) feeder channel geometry and stability. In general, lobes outboard stable fan valleys that are connected to shelf-incised canyons are wider, longer and thicker, accumulate in more basinal locations and are architecturally more complex.