Recognition of cyclic steps in sandy and gravelly turbidite sequences, and consequences for the Bouma facies model
Recognition of cyclic steps in sandy and gravelly turbidite sequences, and consequences for the Bouma facies model
Preservation of cyclic steps contrasts markedly with that of subcritical-flow bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south-eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft-sediment deformation (flames) preserved in coarse-tail normal-graded structureless deposits (Bouma Ta), while near-horizontal, massive to stratified top-cut-out turbidite beds are found further down the stoss side of the bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens-shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top-cut-out turbidite beds. The facies that characterize these bedforms have traditionally been described as turbidite units in idealized vertical sequences of high-density turbidity currents, but have not yet been interpreted to represent bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far.
Bouma sequence, cyclic steps, high-density turbidity current, hydraulic jump, supercritical-flow bedforms, traction carpet, turbidite facies
2268-2290
Postma, George
9f590b3e-32fb-4959-b63b-d25dc07c4463
Kleverlaan, Kick
6d888202-9752-485b-916c-d4c04e57a936
Cartigny, Matthieu J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
December 2014
Postma, George
9f590b3e-32fb-4959-b63b-d25dc07c4463
Kleverlaan, Kick
6d888202-9752-485b-916c-d4c04e57a936
Cartigny, Matthieu J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
Postma, George, Kleverlaan, Kick and Cartigny, Matthieu J.B.
(2014)
Recognition of cyclic steps in sandy and gravelly turbidite sequences, and consequences for the Bouma facies model.
Sedimentology, 61 (7), .
(doi:10.1111/sed.12135).
Abstract
Preservation of cyclic steps contrasts markedly with that of subcritical-flow bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south-eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft-sediment deformation (flames) preserved in coarse-tail normal-graded structureless deposits (Bouma Ta), while near-horizontal, massive to stratified top-cut-out turbidite beds are found further down the stoss side of the bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens-shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top-cut-out turbidite beds. The facies that characterize these bedforms have traditionally been described as turbidite units in idealized vertical sequences of high-density turbidity currents, but have not yet been interpreted to represent bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far.
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More information
Accepted/In Press date: 4 August 2014
Published date: December 2014
Keywords:
Bouma sequence, cyclic steps, high-density turbidity current, hydraulic jump, supercritical-flow bedforms, traction carpet, turbidite facies
Organisations:
Marine Geoscience
Identifiers
Local EPrints ID: 367688
URI: http://eprints.soton.ac.uk/id/eprint/367688
ISSN: 0037-0746
PURE UUID: 6301bfc6-34fe-45f1-af0c-f2a5e43f53c5
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Date deposited: 05 Aug 2014 10:58
Last modified: 14 Mar 2024 17:34
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Contributors
Author:
George Postma
Author:
Kick Kleverlaan
Author:
Matthieu J.B. Cartigny
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