Deltas, shelf margins and the generation of turbidites
|Location||International Geological Congress,oslo 2008|
|Author||Steel, Ron۱; Olariu, Cornel۲; Petter, Andrew۱|
|Holding Date||08 October 2008|
Rivers and deltas are the major feeders for the accretion of shelf margins, and ultimately for the generation of turbidites and the growth of submarine fan systems. Shelves aggrade and grow basinwards by the systematic spread of sediment from laterally shifting and basinward migrating strandplains and deltas during regression and by a similar sediment spreading during transgression from estuaries and barrier-lagoon systems. Such increments of shelf growth occur on time scales of a 100ky or less during Icehouse periods and probably a few 100ky in Greenhouse intervals. These are also the fundamental time scales of stratigraphic sequences, as the transit of deltas to the shelf edge, the potential delivery of deepwater sediment to slope and basin floor and the subsequent transgression of the shelf are the basic components of clastic stratigraphic sequences.
The growth of the slope and base-of-slope components of margins by turbidites and mass flow processes is driven largely by sediment supplied from the shelf edge by deltas and rivers, but also fashioned by the consequent instability of the slope and the growth of faulting and salt/mud movement as the margin accretes. The margin receives turbidite successions from the conventional ’lowstand’ sytems driven by relative sea-level fall, especially in Icehouse times. However, turbidite successions may also be emplaced, even when shelves are wide, by high sediment-supply delta systems, without significant falls of sea level. The prediction of thick turbidite successions on margins depends of the interplay of sea-level, supply and climate drives.