--> ABSTRACT: Relationships between Through-Channel Processes and Overbank Wedge Development in Straight Slope Channels: Examples from the Modern Seafloor (Sicilian Margin, Tyrrhenian Sea), by Gamberi, Fabiano; Rovere, Marzia ; Marani, Michael; Gallerani, Andrea; Leidi, Elisa ; Mercorella, Alessandra; #90142 (2012)

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Relationships between Through-Channel Processes and Overbank Wedge Development in Straight Slope Channels: Examples from the Modern Seafloor (Sicilian Margin, Tyrrhenian Sea)

Gamberi, Fabiano *1; Rovere, Marzia 1; Marani, Michael 1; Gallerani, Andrea 1; Leidi, Elisa 1; Mercorella, Alessandra 1
(1) ISMAR-CNR, Bologna, Italy.

The correlation between the stratigraphy of submarine channel infill and that of their related overbank environment, both in seismic and in outcrop studies, is always challenging. Modelling is amply used to investigate the effects of channel planform on the overbank flow, however, it often concentrates on sinuous or meandering channels. On the contrary, less is known about the influence of the behaviour of through-channel flows on overbank sedimentation patterns in straight channels. This latter issue can be studied using modern examples of submarine channels. Here, we present the interpretation of multibeam bathymetric data and CHIRP seismic profiles of straight submarine slope channels in the Sicilian margin. The study is aimed at showing that downslope variations in through-channel flow behaviour cause modifications in the character of the associated overbank flow wedge. The data show that the gradient of the channels has a great impact on the behaviour of through-channel flows and that a downslope gradient reduction causes the onset of local intrachannel or channel-wide deposition. Gradient variations within the channels are accompanied by a hydraulic jump shown by cyclic steps or by a scoured channel floor. Downslope from the hydraulic jump a different depositional setting characterizes the channels; here flows are slower and thicker and this has a direct consequence on the corresponding overbank wedge development. Where the flow thickening is not enough to produce significant overbank flow, an internal levee is developed and the external levee is smooth and featureless. In other cases, flow thickening is responsible for a larger volume of overbanking flows capable of developing sediment waves on the external levee. Besides flow thickening, the reduction of the relief of the external levee crests, brought about by channel floor aggradation, can also allow the lower and coarser part of the flows to escape the channels. In this case, channelized overbank splays, are formed and scours are also found on large portions of the overbank wedge. This study demonstrates that a close linkage exists between the character of through-channel flows and the structure of the corresponding overbank wedge. The results show that an increase of the aggradational character of a channel infill can be accompanied by a thickening and coarsening of the genetically related overbank deposits.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California