Examples of Turbidity Current Channelization in the Modern Seafloor : Environments, Causes and Products

Gamberi, Fabiano; Dalla Valle, Giacomo; Rovere, Marzia

Under certain circumstances, unconfined turbidity currents flowing above a featureless seafloor can evolve to form channelization downslope. Although studied through modelling, outcrop and modern examples, the processes by which an unconfined turbidity current develops channelization are not completely understood, neither is their signature in the stratigraphic record. The modern seafloor offers a good opportunity to observe the products of channelization of unconfined turbidity currents. In this paper, by means of an analysis of multibeam and chirp data, collected in a variety of turbidite systems in the Tyrrhenian Sea, we show modern settings where channelization of unconfined turbidity currents occurs and we investigate its causes. Beyond channel mouth unconfined flow regions, channelization is often connected upslope with scours, while, it forms fan lobe channels that have different shape and depth of incision downslope. Channelization also occurs in unconfined turbidity flows that build levees. In this case, it mainly develops in the outside of channel bends. The results are straight erosional channels that cut the levees and can deposit small lobate bodies at the base of the overbank wedge, or channelized overbank splay deposits. In the levees, channelization also takes place exploiting the troughs of sediment waves. Channelization is also observed at the base of seamounts, forming restrictions to unconfined flows in the distal areas of basin plain lobes. Finally, channelization is observed where unconfined flows cross intraslope steps along connected tortuous corridors. The causes of channelization are related to seafloor topography; the examples show that channelization takes place through the focussing of the lower part of turbidity currents into discrete seafloor areas. Gradient variations, even if very subtle, and barriers to the free spreading of turbidity flows due to lateral slopes, are the main causes for the observed cases of channelization. The shape and the behaviour of the channels are also largely controlled by variations of the seafloor gradient. The resulting different geomorphic elements can be used as analogues for the prediction of reservoir geometry and heterogeneity in similar environments.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013