New Intra-Channel Architecture Within Sinuous Amazon Slope Channel Revealed by a 3-D Seismic Study

Takeshi Nakajima¹, Jeffrey Peakall², William D. McCaffrey², and Philip Thompson^3
1National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
²University of Leeds, Leeds, United Kingdom
³University of Aberdeen, Aberdeen, United Kingdom

There has been a long term debate as to whether submarine channels have the same processes and morphological features as fluvial channels. For examples, flow stripping and nested mounds on the outer corners of channel bends have been proposed as unique to submarine channels. The aims of this study are to describe for the first time intra-channel seismic architecture that is unique to sinuous submarine channels and to provide new insights into physical models of turbidity currents. This study is based on interpretation of 3D seismic data of sinuous channels in the upper slope of the Amazon Fan, offshore Brazil.

We identify a novel architectural element in channel-fill deposits at outer corners of bend apices or slightly downstream of apices in tight meander loops. This architecture is up to 1.5 km wide and up to 150 m thick. The architecture has bar-like feature and its reflectors dip 1 - 10 degrees towards the inner bend of the meander loop. Thus the dip direction of reflectors of this architecture is reverse to that of fluvial point bars or lateral accretion packets. This type of architectural element is found only in the final channel-fill of tight meander loops (radius of curvature < 2 km) of aggradational, narrow (aspect ratio < 20) channels and never occurs in broad, low-sinuosity and less aggradational channels. This architectural element may have been formed as a result of a combination of flow volume reduction and enhanced deposition on the outside of the bend by flow super-elevation while erosion was suppressed due to the low competence of flow in the final aggradational channel phase. The result has significant implications for hydrocarbon reservoir prediction.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas