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Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk

Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk
Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk
Geomorphic features such as drifts, sediment waves and channels have been documented in the Upper Cretaceous of north-west Europe. These features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns. Chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition. There is limited knowledge on the processes that govern nannofossil ooze mobility, thus forcing uncertainty onto numerical models based on sedimentological observations. This article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes. A fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity. Erosion characteristics, labelled as erosion types, vary with total bed porosity (?) and applied shear stress (?0). High-porosity ooze (? >80%) is characterized by constant erosion rates (Em). At ? <77%, however, erosion characteristics showed greater variance. Surface erosion was typically followed by transitional erosion (with asymptotically decreasing Em), and stages of erosion with constant, and exponential erosion rates. The estimated erosion thresholds (?c) vary from ca 0·05 to 0·08 Pa for the onset of surface erosion and up to ca 0·19 Pa for the onset of constant erosion (? of 60 to 85%). Variability of deposition thresholds (?cd) from ca 0·04 to 0·13 Pa reflects the influence of variable suspended sediment concentration and ?0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation. Additionally, deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity. Lastly, slow sediment transport without resuspension occurred in high-porosity ooze as surface creep, forming low-relief sedimentary features resembling ripples. This process represents a previously undescribed mode of fine-grained nannofossil ooze transport.
Calcareous nannofossil ooze, chalk dynamics, experimental sedimentology, flume, sediment transport, Upper Cretaceous
0037-0746
478-507
Buls, Toms
3bcc11a2-65a1-4763-a2d8-eaad3fca005e
Anderskouv, Kresten
d73bf3d7-49d9-4e21-bcd7-faa74c7c164f
Friend, Patrick
eb5dc541-1021-492a-8c49-670461d4d834
Thompson, Charlie
2a304aa6-761e-4d99-b227-cedb67129bfb
Stemmerik, Lars
5d086c91-48fe-4f0f-8ea6-70160838eee0
Buls, Toms
3bcc11a2-65a1-4763-a2d8-eaad3fca005e
Anderskouv, Kresten
d73bf3d7-49d9-4e21-bcd7-faa74c7c164f
Friend, Patrick
eb5dc541-1021-492a-8c49-670461d4d834
Thompson, Charlie
2a304aa6-761e-4d99-b227-cedb67129bfb
Stemmerik, Lars
5d086c91-48fe-4f0f-8ea6-70160838eee0

Buls, Toms, Anderskouv, Kresten, Friend, Patrick, Thompson, Charlie and Stemmerik, Lars (2017) Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk. Sedimentology, 64 (2), 478-507. (doi:10.1111/sed.12311).

Record type: Article

Abstract

Geomorphic features such as drifts, sediment waves and channels have been documented in the Upper Cretaceous of north-west Europe. These features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns. Chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition. There is limited knowledge on the processes that govern nannofossil ooze mobility, thus forcing uncertainty onto numerical models based on sedimentological observations. This article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes. A fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity. Erosion characteristics, labelled as erosion types, vary with total bed porosity (?) and applied shear stress (?0). High-porosity ooze (? >80%) is characterized by constant erosion rates (Em). At ? <77%, however, erosion characteristics showed greater variance. Surface erosion was typically followed by transitional erosion (with asymptotically decreasing Em), and stages of erosion with constant, and exponential erosion rates. The estimated erosion thresholds (?c) vary from ca 0·05 to 0·08 Pa for the onset of surface erosion and up to ca 0·19 Pa for the onset of constant erosion (? of 60 to 85%). Variability of deposition thresholds (?cd) from ca 0·04 to 0·13 Pa reflects the influence of variable suspended sediment concentration and ?0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation. Additionally, deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity. Lastly, slow sediment transport without resuspension occurred in high-porosity ooze as surface creep, forming low-relief sedimentary features resembling ripples. This process represents a previously undescribed mode of fine-grained nannofossil ooze transport.

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Buls et al 2016_Sedimentology_resub_May2016.pdf - Accepted Manuscript
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More information

Accepted/In Press date: 18 June 2016
e-pub ahead of print date: 22 October 2016
Published date: 1 February 2017
Keywords: Calcareous nannofossil ooze, chalk dynamics, experimental sedimentology, flume, sediment transport, Upper Cretaceous
Organisations: Ocean and Earth Science

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Local EPrints ID: 397083
URI: https://eprints.soton.ac.uk/id/eprint/397083
ISSN: 0037-0746
PURE UUID: 6d2b11d2-025b-4e54-a960-700b10d3f309

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Date deposited: 20 Jun 2016 10:56
Last modified: 03 Feb 2018 05:02

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Author: Toms Buls
Author: Kresten Anderskouv
Author: Patrick Friend
Author: Lars Stemmerik

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