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Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar

Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar
Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar
The depositional stratigraphy of within-channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular ‘unit’ bars and complex ‘compound’ bars), as well as the infill of individual channels (herein termed ‘channel fills’). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within-channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1Æ3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (<1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground-penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grainsize trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object-based models of sandy braided river alluvial architecture
alluvial architecture, channel fill, compound bar, sandy braided river, unit bar
0037-0746
1860-1883
Ashworth, P.
35b182f7-9428-4369-a223-f618aaecd7ea
Sambrook Smith, G.
acda4878-9c23-4db6-8dbd-90f78491e216
Best, J.
2ebf0cce-d0ad-4c5a-b459-8098240dc9ae
Bridge, J.
0dc8d8dc-3de4-429d-ad41-70bd267cca85
Lane, S.
34c98a43-fc8b-48ab-8459-81a00e90df17
Lunt, I.
dedaef9a-03f5-4ee0-8e09-e3be91fe7bda
Reesink, A.
e9a3724d-3430-4fad-b85e-b27ed7343e53
Simpson, C.
b96008f9-2a11-4695-b717-5f49ffa12b52
Thomas, R.
6814ea6d-818e-4088-882f-2b87f0147d2a
Ashworth, P.
35b182f7-9428-4369-a223-f618aaecd7ea
Sambrook Smith, G.
acda4878-9c23-4db6-8dbd-90f78491e216
Best, J.
2ebf0cce-d0ad-4c5a-b459-8098240dc9ae
Bridge, J.
0dc8d8dc-3de4-429d-ad41-70bd267cca85
Lane, S.
34c98a43-fc8b-48ab-8459-81a00e90df17
Lunt, I.
dedaef9a-03f5-4ee0-8e09-e3be91fe7bda
Reesink, A.
e9a3724d-3430-4fad-b85e-b27ed7343e53
Simpson, C.
b96008f9-2a11-4695-b717-5f49ffa12b52
Thomas, R.
6814ea6d-818e-4088-882f-2b87f0147d2a

Ashworth, P., Sambrook Smith, G., Best, J., Bridge, J., Lane, S., Lunt, I., Reesink, A., Simpson, C. and Thomas, R. (2011) Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar. Sedimentology, 58 (7), 1860-1883.

Record type: Article

Abstract

The depositional stratigraphy of within-channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular ‘unit’ bars and complex ‘compound’ bars), as well as the infill of individual channels (herein termed ‘channel fills’). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within-channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1Æ3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (<1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground-penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grainsize trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object-based models of sandy braided river alluvial architecture

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Accepted/In Press date: 23 February 2011
Published date: December 2011
Keywords: alluvial architecture, channel fill, compound bar, sandy braided river, unit bar
Organisations: Earth Surface Dynamics

Identifiers

Local EPrints ID: 382023
URI: https://eprints.soton.ac.uk/id/eprint/382023
ISSN: 0037-0746
PURE UUID: f01f9482-3881-4edb-9c7a-4036fba3c783

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Date deposited: 19 Oct 2015 12:04
Last modified: 21 Oct 2017 17:36

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Contributors

Author: P. Ashworth
Author: G. Sambrook Smith
Author: J. Best
Author: J. Bridge
Author: S. Lane
Author: I. Lunt
Author: A. Reesink
Author: C. Simpson
Author: R. Thomas

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