When the Levee Breaks: Collapse of Submarine Channel Levees
The levees that bound many submarine channels on the continental slope and basin floor are prone to large-scale gravitational failure, especially on the steeper slopes facing the channel belt. Such failures typically leave arcuate slide scars on the inner wall of the levee. The kinematics of the deformed zone indicate movement towards the channel, often by rotation along listric failure surfaces. The failed material creates a zone of slide blocks and sheets of semi-coherent material fringing the channel belt, bounding (and possibly inter-stratified with) channel-margin terraces. This creates irregular surface topography that can deflect and reflect turbidity currents within the channel belt, generating locally complex current patterns. The upper surfaces of rotated slide blocks bordering the channel belt may exhibit outward-dipping geometries, which can be mimetic of ‘internal’ or ‘confined’ levees. We present examples from outcrop (late Cretaceous Rosario Formation, Baja California, Mexico), the shallow subsurface (Pleistocene, Foz de Amazonas, equatorial margin of Brazil) and the modern sea-floor (Tyrrhenian Sea) that illustrate this phenomenon and its potential impact on levee and channel margin architecture. The most channel-proximal parts of levees can be sand-prone, and constitute potentially good reservoir. We outline some potential consequences of large-scale levee collapse for performance in these collapsed thin-bedded turbidite reservoirs, and the relationships between levee, collapsed zone, terraces and channel fill.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014