Scour in large braided rivers and the recognition of sequence stratigraphic boundaries

J.L. Best, Philip Ashworth

Research output: Contribution to journalArticle

Abstract

Alluvial scour into shallow marine sediments may be caused by the incision of a river adjusting to a new base level 1–4 following a fall in sea level. The identification of such erosion surfaces1–3 has therefore been pivotal in the reconstruction of past sea-level changes from ancient sedimentary sequences1–14. Here we report data from a study of the Jamuna river, Bangladesh, one of the world's largest modern braided rivers15, which illustrate that bed scour associated with channel confluences and bends alone can be substantial—as much as five times greater than the mean channel depth. Indeed, the basal erosion surfaces produced by such deep scours have characteristics similar to those of boundaries in some ancient sedimentary sequences that have been assumed to result from sea-level fall1–14, potentially leading to radically different interpretations of past variation in base level and climate. We suggest that, to discount unambiguously the influence of fluvial scour in ancient sediments, the erosive boundary should be greater than five times the mean channel depth and extend for distances greater than the floodplain width. Ideally, it should be traceable between different basins.
Original languageEnglish
Pages (from-to)275-277
Number of pages3
JournalNature
Volume387
Publication statusPublished - 15 May 1997

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stratigraphic boundary
braided river
sequence boundary
scour
sea level
erosion
confluence
sedimentary sequence
river
sea level change
marine sediment
floodplain
climate
basin
sediment

Cite this

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abstract = "Alluvial scour into shallow marine sediments may be caused by the incision of a river adjusting to a new base level 1–4 following a fall in sea level. The identification of such erosion surfaces1–3 has therefore been pivotal in the reconstruction of past sea-level changes from ancient sedimentary sequences1–14. Here we report data from a study of the Jamuna river, Bangladesh, one of the world's largest modern braided rivers15, which illustrate that bed scour associated with channel confluences and bends alone can be substantial—as much as five times greater than the mean channel depth. Indeed, the basal erosion surfaces produced by such deep scours have characteristics similar to those of boundaries in some ancient sedimentary sequences that have been assumed to result from sea-level fall1–14, potentially leading to radically different interpretations of past variation in base level and climate. We suggest that, to discount unambiguously the influence of fluvial scour in ancient sediments, the erosive boundary should be greater than five times the mean channel depth and extend for distances greater than the floodplain width. Ideally, it should be traceable between different basins.",
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Scour in large braided rivers and the recognition of sequence stratigraphic boundaries. / Best, J.L.; Ashworth, Philip.

In: Nature, Vol. 387, 15.05.1997, p. 275-277.

Research output: Contribution to journalArticle

TY - JOUR

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AU - Best, J.L.

AU - Ashworth, Philip

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AB - Alluvial scour into shallow marine sediments may be caused by the incision of a river adjusting to a new base level 1–4 following a fall in sea level. The identification of such erosion surfaces1–3 has therefore been pivotal in the reconstruction of past sea-level changes from ancient sedimentary sequences1–14. Here we report data from a study of the Jamuna river, Bangladesh, one of the world's largest modern braided rivers15, which illustrate that bed scour associated with channel confluences and bends alone can be substantial—as much as five times greater than the mean channel depth. Indeed, the basal erosion surfaces produced by such deep scours have characteristics similar to those of boundaries in some ancient sedimentary sequences that have been assumed to result from sea-level fall1–14, potentially leading to radically different interpretations of past variation in base level and climate. We suggest that, to discount unambiguously the influence of fluvial scour in ancient sediments, the erosive boundary should be greater than five times the mean channel depth and extend for distances greater than the floodplain width. Ideally, it should be traceable between different basins.

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