SUBMARINE FAN

OLEH :1. Arifin (12011048) 2. Dantie Claudia (12011007)3. M. Indra Nugraha (12011004)4. M. Najib (12011035)5. Oddy Adnan (12011056) 6. Pandu Prawira (12011085)SUBMARINE FANSubmarine Fan DefinitionA submarine fan is a body of sediment on the sea floor deposited by mass-flow processes that may be fan-shaped, but more elongate, lobate geometries are also common.

The morphology and depositional character of submarine fan systems are strongly controlled by the composition of the material supplied, particularly the proportions of gravel, sand and mud present.

Depositional Environments ona Submarine Fan.

The term submarine fan is restricted to fan-shaped bodies that are deposited by mass-flow, mainly turbidity current processes.

A submarine fan could form of any clastic material,but the larger fans are all composed of terrigenous clastic material supplied by large river systems.Architectural elements of submarinefan systems The supply of carbonate sediment is rarely focused at discrete points along the continental slope: submarine fans composed of carbonate material are therefore rarely formed, and most carbonate turbidites are associated with slope-apron systems.

Submarine fan channels form distinct elements on the fan surface and may have levees associated with them: these channels may incise into, or pass distally into, depositional lobes, which are broad, slightly convex bodies of sediment.

Submarine channels and leveesSubmarine fan channels are variable in size: some of the larger modern examples are several tens of kilometres wide and over a thousand metres deep, and in the stratigraphic record there are submarine fan channels with thicknesses of up to 170m and 20 km across (Macdonald & Butterworth 1990).Architectural Elements on Submarine Fans (1)The proportions of different architectural elements on submarine fans are determined by the dominant grain size deposited on the fan.Architectural Elements on Submarine Fans (2)

Thick sandstone beds deposited in a channel in the proximal part of a submarine fan complex.Most of an individual turbidity flow is confined to the channel but the upper, more dilute part of the flow may spill out of the channel laterally. The overbank flow from the channel contains fine sand, silt and mud and this spreads out as a fine grained turbidity current away from the channel to form a submarine channel levee.Bouma Sequence and Levee Turbidite

The levee turbidites consist of the upper parts of Bouma sequences (Tce and Tde) and they thin away from the channel margin with a low-angle, wedge-shaped geometry.Depositional lobesAt the distal ends of channels the turbidity currents spread out to form a lobe of turbidite deposits that occupies a portion of the fan surface.An individual lobe is constructed by a succession of turbidity currents that tend to deposit further and further out on the lobe through time.A simple progradational geometry results if fan deposition is very ordered, with each turbidity current event of approximately the same magnitude and each depositing progressively further from the mouth of the channel.

Turbidite sheetsTurbidite sheets are deposits of turbidity currents that are not restricted to deposition on a lobe but have spread out over a larger area of the fan. they are thin, fine-grained turbidites characterised by Bouma divisions Tce and Tde with little or no organisation into patterns or trends in grain size and bed thickness.Submarine fan systemsSubmarine fan systemsSubmarine fan systems are commonly divided into upper fan (inner fan), mid-fan and lower fan (outer fan). - The upper fan is dominated by channel and levee complexes- The mid-fan by depositional lobes - The lower fan by sheets.

Inner fan. Submarine fanchannel filled with thick conglomerateand sandstone turbiditesInner Fan. Thin-bedded levee depositsMid-fan. Channel on lobeMid-fan. Coarsening-up succession of sandy turbditesDistal fan. Thin, fine-grained turbiditesGravel-rich systems

Facies model for a gravel-rich submarine fan: typically found in front of coarse fan deltas, the fan is small and consists mainly of debris flows.Sand-rich systems

Facies model for a sand-rich submarine fan: sand-rich turbidites form lobes of sediment that build out on the basin floor, with switching of the locus of deposition occurring through time.Mixed sandmud systems

Facies model for a mixed sandmud submarine fan: the lobes are a mixture of sand and mud and build further out as the turbidites travel longer distances.Muddy systems

Facies model for a muddy submarine fan: lobes are very elongate and most of the sand is deposited close to the channels.Ancient submarine fan systems(additional)The type of depositional system can be assessed by considering the ranges of the grain sizes of the material and the distribution of channel, levee, lobe and sheet facies. Because of the size of most submarine fan systems, the beds exposed will often represent only a very small part of a whole system, even if the outcrop extends for tens of kilometres or more.

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