Stages of Construction of the Distal Lobes of the Amazon Deep Sea Fan

Isabelle Jegou¹, Bruno Savoye¹, Laurence Droz², and C. Pirmez^3
1 IFREMER, Plouzane, France
² UMR6538 Domaines Oceaniques, Plouzane, France
³ Shell International E&P Inc, Houston, TX

In giant turbidite systems, distal lobes correspond to the most distal depocentres at the termination of the system. Their architecture is not well known due to a distal position at very important water depth (around 5000 m). The term of "lobe" generally describes a depocentre with a lobated shape, apparently non channelized and located at the extremity of a channel. This schematic view seems to be too simple; our results demonstrate that the architecture is much more complex. How is the termination of the Amazon channel-levee system (the last active system)? New and quality data are available on the distal part of the Amazon deep-sea fan (Survey Lobestory IFREMER) including bathymetric and side-scan sonar data (EM12), 3.5 kHz profiling, multitrace high resolution seismic-reflection profiles and tens of cores collected on the distal lobe area. The complex stratigraphic framework of the distal lobe area of the Amazon deep-sea fan allowed to identify 7 channel-levee systems with their distal lobes (chronologically 1F, 1E, 1D, 1C, 1B, 1A and Amazon) formed between 14 ky and 9 ky. The distal lobes of the Amazon system built on older channel-levee systems; it induces a strong interaction with the pre-existent morphology. During the deposition of the Amazon lobes, two phases are identified with first, the progradation of the system with deposition of two lobes, followed by the retrogradation and the deposition of a third lobe which marks the death of the system. The internal geometry of these last lobes describes stacking retrogressive units.