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Structural Controls from Slope Deposition in the Amazon Fan

Silva, Carlos M.1; Paton, Douglas 1; McCaffrey, William D.1; Butler, Robert 2
1 University of Leeds, Leeds, United Kingdom.
2 University of Aberdeen, Aberdeen, United Kingdom.

This study investigates the influence of structural controls on deep water channel evolution at both a regional and a reservoir scale. Structural controls on slope deposition are based on 3-D seismic interpretation of the upper slope of the Amazon Fan. Two main packages are identified and are separated by an erosional unconformity. The lower package is characterized by dominantly concordant seismic reflections that are deformed by folds and related faults while the upper package is composed of a heterogenic arrangement of seismic facies, and is less strongly deformed.

The deformation, which is more prominent in the lower package, occurs from the outer shelf to the study area in the upper slope (~150 km) and to sediment depths of more than 5000 m below the sea floor. The lower-package deformation is characterized by three N-S trending thrust-cored anticlines that have an approximately northeasterly sense of vergence. Within the package growth strata and pre-growth strata are defined using stratal geometries. Canyon-like channels with dimensions up to 2600 m wide and 220 m deep are incised into the pre-growth strata. Isopach maps reveal that the structures were active during channel emplacement and they also provide insight into how the active structures functioned as topographic barriers to the channel and also as relative lows, driving the channel direction on the slope.

Contrasting, a local mass transport deposit (MTD) occurs locally and is adjacent to the base of the levee of this system. This MTD slid down the flank of the previous channel-levee system toward the active channel. This deformation was likely to be a result of the different mechanical behaviour between the clay-prone levee (which failed) and the underlying sandy high amplitude reflection package (HARP) possibly augments by fluids trapped in the HARP, creating a “detachment surface” in the interface between the levee and the subjacent HARP.

On a reservoir scale, the data resolution of the upper package enables us to consider the architecture of the internal stacking pattern of the channel systems. The channel is adjacent to the frontal flank of a syn-depositional deforming fold and is characterised by an erosive basal channel overlain by three sub-vertically stacked channel-levees. The architecture of this stacking pattern is related to the degree of deformation on the adjacent structure and hence provides a predictive insight into structural controls on channel-levee architecture.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009