The nature and evolution of deep‐sea channel systems

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Abstract
A distinction is drawn between sea‐floor canyons, which are incised into bedrock, and fan valleys and deep‐sea channels, which are cut in unconsolidated sediment. The formation of continental margin canyons/fans and deep‐sea channels is an inevitable consequence of continental margin rifting and sea‐floor subsidence. Such submarine sediment transport systems are amongst the longest‐lived physiographic features on earth, with the Bounty Channel system being more than 50 Myr old. Many deep‐sea channels form the distal part of ocean‐margin sediment transport systems, being incised 100–350 m into ocean‐floor sediments, traversing great distances over the ocean‐basin floor, and generally terminating on an abyssal plain. The course of each deep‐sea channel is, however, unique. Channel locations are controlled primarily by inherited basement relief, and, during their evolution, by rates and patterns of lithospheric subsidence and sedimentation. In the early stages of ocean‐basin formation, deep‐sea channels may issue from the axial parts of marginal rifts, or directly from slope canyon‐fan systems. As an ocean basin widens, margin‐connected channels may become trapped within the strip of oldest (and therefore deepest) oceanic crust at the continent/ocean interface, and will therefore be margin‐parallel features. In some cases, as for the Cascadia Channel, channels may escape from the ocean‐margin deep, bypassing the spreading ridge via a fracture zone. Deep‐sea channels and their associated sediments are influenced also by global sea‐level change, by rate of turbidity current generation from the headward continental margin, by rates of pelagic sediment supply, by differential levee development consequent upon the Coriolis effect, and by the operation of deep‐sea current systems with their associated sediment drifts. The survival of deep‐sea channels as long‐lived features necessitates that rates of long‐term subsidence at the channel terminus exceed sediment accumulation.