Submarine Lobes Deposited Off the Northern Margin of East Corsica Over the Last 60 k.y.r.—Relationship Between Outer Shelf Evolution and Lobe Architecture from Ultra-High Resolution Seismic Profiles

Mark E. Deptuck¹, David J. W. Piper², Bruno Savoye³, and Anne Gervais^4
1 current address: Turbidite Research Team, Shell International E & P, Houston, TX
² Geological Survey of Canada (Atlantic), N/A,
³ IFREMER, 29280 Plouzané, France
⁴ Géosciences , Université de Rennes 1,

A total of 20 'lobes' were mapped using ultra-high resolution boomer seismic profiles. Repeated crossings of the same depositional bodies were used to measure spatial changes in their dimensions, geometry and architecture. Most lobes increase abruptly down-slope to a peak thickness, beyond which they show a systematic, typically more gradual, decrease in thickness until they thin to below seismic resolution or pass into draping facies of the basin plain. A wide range of lobe dimensions is observed. They cover areas ranging from 3 to 70 km2 and have total lengths that vary from about 2 to greater than 14 km. Together these observations indicate wide variations in transport efficiency and size of sediment gravity flows. Based on their location, dimensions, internal architecture, and nature of the feeder channel, the lobes are divided into two populations: 1) small lobes located in proximal settings on the slope or near the toe-of-slope; 2) larger composite lobe bodies deposited in more distal settings, outboard from leveed fan-valleys.

Correlation of lobe stratigraphy to shelf-edge deltas indicates that the larger muddier composite lobes were deposited during the falling stage in sea level (to -110 m) with contemporaneous outer levee deposition. In contrast, the smaller and sandier lobes were deposited during the latest lowstand to early rise in sea level and were fed by erosive and more ephemeral non-leveed gullies and channels. What accounts for this departure from traditional sequence stratigraphic models for fan development? We believe that the processes by which sediment is sorted on the shelf, and ultimately triggered and transported as sediment-gravity flows down the slope, is an important control on lobe architecture. In contrast to direct river input during periods of falling sea level, reworking of sediment on the outer shelf during early transgression pre-sorted material resulting in poorly efficient, smaller flows.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005