8 - Deep-water Sedimentary Systems: process to product

Define a deep-marine depositional system

Predominantly clastic sedimentary systems which lie at depths greater than that of the continental-shelf to slope break, or, beneath the influence of wave and storm action.

• Largely inaccessible, and built by processes that are predominantly active during sea-level lowstands.

• Still active during the present highstand, albeit with a reduced magnitude and frequency of event occurrence; bu tthe destructive nature of flows within them renders them difficult, or impossible, to monitor.

What is the impact of source to sink context on deep water sedimentary systems?

From high relief to lower relief

Active vs passive margin

• passive margins take lots of time to reach the sea with fine sediment, form large fans

• active margins have high relief and a short time for sediment to reach the coast, small, radial, coarse submarine fans

  

How do highstand vs lowstand climate impact shelf morphology?

What is the scale of observations in deep-water sedimentary systems?

What are the affects of slope topography in deep-water sedimentary systems?

What are the features of channelised (open) slopes in deep-water sedimentary systems?

• Conduits for sediment transfer to ocean floor: bypass

• More active at low sea level stands when shelf exposed

  

What are the features of submarine canyons in deep-water sedimentary systems?

• Erosional valleys cut into continental shelf

• Long term bypass conduits

• Most terrestrial sediment is delivered though canyons to the deep sea floor

• Steep, v-shaped profile

• Dominated by gravity currents: slides, slumps, debris flows and turbidity currents

• Often transiently filled with coarse grained bypass lag deposits, and finally finally with mud.

  

What are the features of submarine channels in deep-water sedimentary systems?

• Long-term conduits for the transfer of sediment to basin floor fans

• Can be aggradational (levee-confined) or erosional (erosionally-confined), and often a mix of the two

• Formed by turbidity currents

• Reduced density contrast means that levees can be very large compared to fluvial channels

  

• Feed large volumes of sediment from the shelf to the deep ocean floor

• Can be >1000km long & continue on gradients <0.1° at several km depth

• Major features on Earth’s surface

• Commonly highly sinuous and superficially similar to fluvial channels

What are the features of levees in deep-water sedimentary systems?

• Levees build from repeated overspill from the channel, by turbidity currents which are passing through.

• Can be hundreds m high and km wide

• Dominated by turbidity currents, and built from thin-bedded turbidites

  

What are the features of external and internal levees in deep-water sedimentary systems?

External

• Inner levee deformation

• Laterally extensive beds

• Predictable N:G and bed thickness

• Well organised stacking patterns

• Lack of erosional structures

• Simple waning flows

• Divergent and down slope aligned palaeoflow

  

Internal

• Minor deformation associated with thalwegs

• Some beds pinch out over short distances

• Unpredictable N:G and bed thickness?

• Less-organised stacking patterns

• Erosional structures common

• Complex flow waxing and waning signature

• Complex palaeoflow history

  

What are the features of lobes in deep-water sedimentary systems?

• Distributive

• Terminal parts of deep-water sedimentary systems

• Downstream fining and thinning of deposits

• Dominated by  turbidity currents and hybrid flows in their distal parts

• In the ancient subsurface, the control on shapes and facies distribution is poor and depositional models have been found to be too simple. Focus has been on submarine channels rather than distributive systems.