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Sedimentology, stratigraphy and architecture of the Nicobar Fan (Bengal–Nicobar Fan System), Indian Ocean: Results from International Ocean Discovery Program Expedition 362

Sedimentology, stratigraphy and architecture of the Nicobar Fan (Bengal–Nicobar Fan System), Indian Ocean: Results from International Ocean Discovery Program Expedition 362
Sedimentology, stratigraphy and architecture of the Nicobar Fan (Bengal–Nicobar Fan System), Indian Ocean: Results from International Ocean Discovery Program Expedition 362
Drill sites in the southern Bay of Bengal at 3°N 91°E (International Ocean Discovery Program Expedition 362) have sampled for the first time a complete section of the Nicobar Fan and below to the oceanic crust. This generally overlooked part of the Bengal–Nicobar Fan System may provide new insights into uplift and denudation rates of the Himalayas and Tibetan Plateau. The Nicobar Fan comprises sediment gravity‐flow (SGF) deposits, mostly turbidites, that alternate with hemipelagite drapes and pelagite intervals of varying thicknesses. The decimetre‐thick to metre‐thick oldest pre‐fan sediments (limestones/chalks) dated at 69 Ma are overlain by volcanic material and slowly accumulated pelagites (0.5 g.cm‐2.kyr‐1). At Expedition 362 Site U1480, terrigenous input began in the early Miocene at ca 22.5 Ma as muds, overlain by very thin‐bedded and thin‐bedded muddy turbidites at ca 19.5 Ma. From 9.5 Ma, sand content and sediment supply sharply increase (from 1‐5 to 10–50 g.cm‐2.kyr‐1). Despite the abundant normal faulting in the Nicobar Fan compared with the Bengal Fan, it offers a better‐preserved and more homogeneous sedimentary record with fewer unconformities. The persistent connection between the two fans ceased at 0.28 Ma when the Nicobar Fan became inactive. The Nicobar Fan is a major sink for Himalaya‐derived material. This study presents integrated results of International Ocean Discovery Program Expedition 362 with older Deep Sea Drilling Project / Ocean Drilling Program / International Ocean Discovery Program sites that show that the Bengal–Nicobar Fan System experienced successive large‐scale avulsion processes that switched sediment supply between the Bengal Fan (middle Miocene and late Pleistocene) and the Nicobar Fan (late Miocene to early Pleistocene). A quantitative analysis of the submarine channels of the Nicobar Fan is also presented, including their stratigraphic frequency, showing that channel size/area and abundance peaked at ca 2 to 3 Ma, but with a distinct low at 3 to 7 Ma: the intervening stratigraphic [sub]unit was a time of reduced sediment accumulation rates.
Bengal Fan, Indian Ocean, IODP Expedition 362, Nicobar Fan, sediment gravity flow, submarine fan, Sunda Subduction Zone
0037-0746
Pickering, Kevin T.
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Pouderoux, Hugo F.A.
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McNeill, Lisa
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Backman, Jan
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Chemale Jr., Farid
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Kutterolf, Steffen
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Milliken, Kitty L.
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Mukoyoshi, Hideki
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Henstock, Timothy
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Stevens, Duncan E.
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Parnell, Charlie
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Dugan, Brandon
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Pickering, Kevin T.
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Pouderoux, Hugo F.A.
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McNeill, Lisa
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Backman, Jan
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Chemale Jr., Farid
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Kutterolf, Steffen
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Milliken, Kitty L.
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Mukoyoshi, Hideki
1b2ca6a3-9b9c-4f69-b99b-5b88708e836c
Henstock, Timothy
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Stevens, Duncan E.
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Parnell, Charlie
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Dugan, Brandon
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Pickering, Kevin T., Pouderoux, Hugo F.A., McNeill, Lisa, Backman, Jan, Chemale Jr., Farid, Kutterolf, Steffen, Milliken, Kitty L., Mukoyoshi, Hideki, Henstock, Timothy, Stevens, Duncan E., Parnell, Charlie and Dugan, Brandon (2019) Sedimentology, stratigraphy and architecture of the Nicobar Fan (Bengal–Nicobar Fan System), Indian Ocean: Results from International Ocean Discovery Program Expedition 362. Sedimentology. (doi:10.1111/sed.12701).

Record type: Article

Abstract

Drill sites in the southern Bay of Bengal at 3°N 91°E (International Ocean Discovery Program Expedition 362) have sampled for the first time a complete section of the Nicobar Fan and below to the oceanic crust. This generally overlooked part of the Bengal–Nicobar Fan System may provide new insights into uplift and denudation rates of the Himalayas and Tibetan Plateau. The Nicobar Fan comprises sediment gravity‐flow (SGF) deposits, mostly turbidites, that alternate with hemipelagite drapes and pelagite intervals of varying thicknesses. The decimetre‐thick to metre‐thick oldest pre‐fan sediments (limestones/chalks) dated at 69 Ma are overlain by volcanic material and slowly accumulated pelagites (0.5 g.cm‐2.kyr‐1). At Expedition 362 Site U1480, terrigenous input began in the early Miocene at ca 22.5 Ma as muds, overlain by very thin‐bedded and thin‐bedded muddy turbidites at ca 19.5 Ma. From 9.5 Ma, sand content and sediment supply sharply increase (from 1‐5 to 10–50 g.cm‐2.kyr‐1). Despite the abundant normal faulting in the Nicobar Fan compared with the Bengal Fan, it offers a better‐preserved and more homogeneous sedimentary record with fewer unconformities. The persistent connection between the two fans ceased at 0.28 Ma when the Nicobar Fan became inactive. The Nicobar Fan is a major sink for Himalaya‐derived material. This study presents integrated results of International Ocean Discovery Program Expedition 362 with older Deep Sea Drilling Project / Ocean Drilling Program / International Ocean Discovery Program sites that show that the Bengal–Nicobar Fan System experienced successive large‐scale avulsion processes that switched sediment supply between the Bengal Fan (middle Miocene and late Pleistocene) and the Nicobar Fan (late Miocene to early Pleistocene). A quantitative analysis of the submarine channels of the Nicobar Fan is also presented, including their stratigraphic frequency, showing that channel size/area and abundance peaked at ca 2 to 3 Ma, but with a distinct low at 3 to 7 Ma: the intervening stratigraphic [sub]unit was a time of reduced sediment accumulation rates.

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Pickering_et_al-2019-Sedimentology - Accepted Manuscript
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Accepted/In Press date: 27 December 2019
e-pub ahead of print date: 28 December 2019
Keywords: Bengal Fan, Indian Ocean, IODP Expedition 362, Nicobar Fan, sediment gravity flow, submarine fan, Sunda Subduction Zone

Identifiers

Local EPrints ID: 436904
URI: http://eprints.soton.ac.uk/id/eprint/436904
ISSN: 0037-0746
PURE UUID: 97b09d0a-8185-468b-b0c8-1628c6c4314a
ORCID for Timothy Henstock: ORCID iD orcid.org/0000-0002-2132-2514

Catalogue record

Date deposited: 13 Jan 2020 17:34
Last modified: 05 Jan 2021 05:01

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