--> Controls from Submarine Slope Channel-Levee Deposition in Amazon Fan, Silva, Carlos M.; Paton, Douglas; McCaffrey, William D., #90100 (2009)

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Controls from Submarine Slope Channel-Levee Deposition in Amazon Fan

Silva, Carlos M.1
 Paton, Douglas1
 McCaffrey, William D.1

1University of Leeds, Leeds, United Kingdom.

The upper slope deposits of Amazon Fan consist of a combination of stacked channel-levee systems intercalated with mass transport deposits, and ponded sheet-like sand rich deposits (high amplitude reflections packets - HARPs). Based on the interpretation of a 3D seismic survey located in water depths of about 1000 to 2000 m and covering an area of 2300 km2 on the upper slope of the Amazon Fan, three upslope-stacked channel-levee systems of Pleistocene age can be distinguished. Each channel disperses obliquely down the slope, resulting in levee size asymmetry, with the downslope levee of greatest size. Upslope stacking of successive channels results from a sequence of avulsions on the upslope levees, with the bathymetric influence of the older channel levee system interpreted to dictate the slope-oblique orientation of the new channel. The channel levees are architecturally distinct. In the lowest system, the channel becomes more sinuous and narrower upward and presents an upstream-migrating backfill sequence terminating as the channel became plugged due to clay deposition. In the middle system, the channel becomes both less sinuous and wider upward and the channel is filled by longitudinally continuous reflectors sub-parallel to the channel axis. These reflectors overspill the levee to form the uppermost layers of the adjacent HARPs - whereas HARPs were absent in the oldest channel-levee architecture. Vary patterns of sediment flux variation can possibly account for these different styles of architectural development. As these systems are components of a levee complex which represents deposition during a single glacial period, as defined in previous work of ODP Proceedings, these flux variations may be related to higher frequency of sea level change.

The compressional tectonics that may have influenced the deposition of these sediments is characterised by thrusts and thrust related folds that were formed as a response to gravity-driven listric faults generated in the shelf margin. The uplift promoted by growing anticlines may have created accommodation favouring channel-levee development. In the youngest channel-levee system, this upslope relief and the huge downslope levee caused the channel confinement avoiding the upslope avulsion as it occurred in the lower systems and leading to the sub-vertical stacking of at least four cycles of channel-levee development.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil