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The Barra Fan: a bottom-current reworked, glacially-fed submarine fan system

The Barra Fan: a bottom-current reworked, glacially-fed submarine fan system
The Barra Fan: a bottom-current reworked, glacially-fed submarine fan system
On the basis of sedimentary structures, textures and ichofauna, seven depositional facies have been recognised in cores from the Barra Fan region of the Hebrides slope. Sedimentary facies are combined into three genetic groups A–C that represent their primary mode of deposition: (A) sandy to muddy contourite facies A, A1, and A2, which represent an overall coarsening upward sequence caused by an increase in bottom-current velocity over time; (B) disorganised glaciomarine deposits, including the glaciomarine dumpstone of facies B and facies B1 deposited as a result of ice-rafting and glaciomarine sedimentation; and (C) hemipelagite facies C and C1 which are the result of normal marine hemipelagic settling. It is most likely that all contourite facies (A–A2) identified in this study are Holocene (<10,000 y) in age and that the underlying glaciomarine and hemipelagite facies (groups B and C) were deposited during the last glacial period.
In terms of its diverse morphological elements and varied facies, this high latitude submarine fan is truly composite in nature. However, a broad three-stage glacial to post-glacial evolutionary system is recognised, during which different processes and process combinations were dominant. During the last glacial period (low stand system tract), downslope processes, including debris flows and minor turbidity currents, sculpted an irregular slope topography. Little in the way of bottom current activity was evident. Staged deglaciation was accompanied by rising sea level and high sedimentation rates across the region. This created an unstable margin prone to extensive sliding and slumping, that masked any effects of an incipient alongslope current. The present high stand system tract is dominated by a strong slope current that became fully active during the early part of the Holocene. Low sedimentation rates, diminished sediment supply and strong bottom current activity led to development of the sandy contourite sheeted drift system across the mid-slope region. Little downslope movement is evident during this period, so that the slope topography is being slowly smoothed and remoulded by active bottom currents.
BARRA FAN, DEEP SEA FANS, BOTTOM CURRENTS, SEDIMENTARY STRUCTURES
0264-8172
219-238
Armishaw, J.E.
d6ffb179-9e8a-4fce-85c3-d5ef17427804
Holmes, R.W.
bc5a30f0-795b-4c7c-ac35-b5cd3c2a0120
Stow, D.A.V.
434350cd-0ae5-4bb3-b71f-e1da90587f74
Armishaw, J.E.
d6ffb179-9e8a-4fce-85c3-d5ef17427804
Holmes, R.W.
bc5a30f0-795b-4c7c-ac35-b5cd3c2a0120
Stow, D.A.V.
434350cd-0ae5-4bb3-b71f-e1da90587f74

Armishaw, J.E., Holmes, R.W. and Stow, D.A.V. (2000) The Barra Fan: a bottom-current reworked, glacially-fed submarine fan system. Marine and Petroleum Geology, 17 (2), 219-238. (doi:10.1016/S0264-8172(99)00049-5).

Record type: Article

Abstract

On the basis of sedimentary structures, textures and ichofauna, seven depositional facies have been recognised in cores from the Barra Fan region of the Hebrides slope. Sedimentary facies are combined into three genetic groups A–C that represent their primary mode of deposition: (A) sandy to muddy contourite facies A, A1, and A2, which represent an overall coarsening upward sequence caused by an increase in bottom-current velocity over time; (B) disorganised glaciomarine deposits, including the glaciomarine dumpstone of facies B and facies B1 deposited as a result of ice-rafting and glaciomarine sedimentation; and (C) hemipelagite facies C and C1 which are the result of normal marine hemipelagic settling. It is most likely that all contourite facies (A–A2) identified in this study are Holocene (<10,000 y) in age and that the underlying glaciomarine and hemipelagite facies (groups B and C) were deposited during the last glacial period.
In terms of its diverse morphological elements and varied facies, this high latitude submarine fan is truly composite in nature. However, a broad three-stage glacial to post-glacial evolutionary system is recognised, during which different processes and process combinations were dominant. During the last glacial period (low stand system tract), downslope processes, including debris flows and minor turbidity currents, sculpted an irregular slope topography. Little in the way of bottom current activity was evident. Staged deglaciation was accompanied by rising sea level and high sedimentation rates across the region. This created an unstable margin prone to extensive sliding and slumping, that masked any effects of an incipient alongslope current. The present high stand system tract is dominated by a strong slope current that became fully active during the early part of the Holocene. Low sedimentation rates, diminished sediment supply and strong bottom current activity led to development of the sandy contourite sheeted drift system across the mid-slope region. Little downslope movement is evident during this period, so that the slope topography is being slowly smoothed and remoulded by active bottom currents.

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More information

Published date: 2000
Keywords: BARRA FAN, DEEP SEA FANS, BOTTOM CURRENTS, SEDIMENTARY STRUCTURES

Identifiers

Local EPrints ID: 8706
URI: https://eprints.soton.ac.uk/id/eprint/8706
ISSN: 0264-8172
PURE UUID: a6aae622-7de6-4a71-930e-1223ef47f44e

Catalogue record

Date deposited: 25 Aug 2004
Last modified: 17 Jul 2017 17:12

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