Chapter 18 Abyssal Plain Contourites

Abstract

Publisher Summary Abyssal plain contourites are of great significance for palaeoceanographic reconstructions. Ocean basins in general and abyssal plains in particular contain extensive sheeted depositional systems characterized by many thin-bedded-distal turbidites, rare but very large-scale megaturbidites, and interbedded-hemipelagic and pelagic sediments. This chapter summarizes the characteristics, terminology, and processes involved with abyssal plain contourites. It presents key case studies from different abyssal-plain settings, namely––southern hemisphere basins, northern hemisphere basins, and equatorial abyssal basins. Some general and specific characteristics of different types of abyssal-sediment drift such as large-scale depositional and erosional features are also discussed. Abyssal-drift systems illustrate the combined influence of regional oceanographic conditions and local physiographic constrains of the basins in which they occur. Many ocean basins and abyssal plains are connected by oceanic gateways such as deep channels or valleys. Opening, deepening, and evolution of these gateways are crucial elements in the sedimentary evolution of the basins because they allow the exchange of deep and intermediate water masses, sedimentary processes, and biota distribution. The continental rises and abyssal plains of ocean basins are considered as relatively tranquil environments, the realm of quiet pelagic sedimentation episodically punctuated by down-slope -turbidity-current input. Based on ocean-basin and abyssal-plain deposits around the world, the main factors considered as characteristic are: long-term hydrological conditions, nepheloid layer, large eddies, benthic storms, and the effect of sea-floor obstacles.