TY - BOOK
T1 - Physical behaviour of calcareous nannofossil ooze and effects of clay and organic matter on pelagic sediment stability: experimental approach using laboratory flumes
AU - Buls, Toms
N1 - Ph.d.-grad opnået ved mundtligt forsvar 27. oktober 2017
PY - 2017/7/17
Y1 - 2017/7/17
N2 - This thesis explores the subject of physical behaviour of ancient calcareous nannofossil ooze that eventually
formed kilometre-thick Upper Cretaceous chalk succession over vast areas of NW Europe and more than 65
Ma years later forms valuable hydrocarbon and ground-water reservoirs. This thesis is unique as it uses a
“hands-on” approach utilising experimental sedimentology methods studying ancient sediment mobility.
This would provide better constraints on the strength of the bottom currents of the Late Cretaceous Chalk
Sea, potentially lead to improvement of chalk depositional models and interpretation of paleocirculation
patterns from the sediment record. In order to achieve the goals of the project, a method to produce
calcareous nannofossil ooze was developed and tested allowing acquiring an unconsolidated and unlithified
analogue of the chalk. The method, by freezing and thawing, disaggregated the Upper Cretaceous chalk from
onshore Denmark to its primary components. Further investigations testing the texture, grain-size, microand
nannofossil preservation using backscatter electron microscopy and image analysis confirmed the
effectiveness of the method.
Further studies tested the erosional and depositional behaviour of the produced experimental nannofossil
ooze utilising laboratory flumes. These experiments observed general decrease of calcareous nannofossil
ooze mobility with decreasing bed porosity and with increasing concentration of clay and organic matter
within the studied bed porosity range (85–60 %). A transition from simple to complex erosional behaviour
has been identified mostly when bed porosity decreases below 80 %. This complex erosion required
definition of multiple erosion thresholds. Typically, erosion thresholds were increasing with decreasing bed
porosity and increasing clay and organic matter concentration. Erosion rates displayed a positive correlation
with bed porosity and negative correlation with clay and organic matter. The onset of constant erosion
(characterised by constant erosion rates), was identified as the most reliable parameter that responded
consistently with changes of bed properties (e.g. changing clay, organic matter concentration). Overall bed
porosity decrease and higher concentrations of clay and organic matter seemed to more affect the erosion
rate decrease than the erosion threshold increase.
Clay and organic matter significantly increased the pelagic ooze bed stability, however clay was generally
less effective in bed stabilisation compared to organic matter. Extracellular polymeric substances (EPS)
organic matter was a more potent stabiliser than the other used marine particulate organic matter proxy
sourced from cultivated phytoplankton.
Experiments at sub-erosion threshold current velocities identify potential alternative sediment transport mode
in the form of “surface creep“ in high porosity beds (> 80 %).
The deposition experiments observed potential calcareous nannofossil ooze aggregation and flocculation, a
fact that has previously been identified in chalk sedimentology literature as of unlikely occurrence.
Agreement between the results of earlier flume studies using modern pelagic ooze and the current research
project allow to apply the results from this PhD project not only exclusively for modelling sediment transport
of ancient calcareous nannofossil ooze but also for modern day calcareous pelagic sediments.
AB - This thesis explores the subject of physical behaviour of ancient calcareous nannofossil ooze that eventually
formed kilometre-thick Upper Cretaceous chalk succession over vast areas of NW Europe and more than 65
Ma years later forms valuable hydrocarbon and ground-water reservoirs. This thesis is unique as it uses a
“hands-on” approach utilising experimental sedimentology methods studying ancient sediment mobility.
This would provide better constraints on the strength of the bottom currents of the Late Cretaceous Chalk
Sea, potentially lead to improvement of chalk depositional models and interpretation of paleocirculation
patterns from the sediment record. In order to achieve the goals of the project, a method to produce
calcareous nannofossil ooze was developed and tested allowing acquiring an unconsolidated and unlithified
analogue of the chalk. The method, by freezing and thawing, disaggregated the Upper Cretaceous chalk from
onshore Denmark to its primary components. Further investigations testing the texture, grain-size, microand
nannofossil preservation using backscatter electron microscopy and image analysis confirmed the
effectiveness of the method.
Further studies tested the erosional and depositional behaviour of the produced experimental nannofossil
ooze utilising laboratory flumes. These experiments observed general decrease of calcareous nannofossil
ooze mobility with decreasing bed porosity and with increasing concentration of clay and organic matter
within the studied bed porosity range (85–60 %). A transition from simple to complex erosional behaviour
has been identified mostly when bed porosity decreases below 80 %. This complex erosion required
definition of multiple erosion thresholds. Typically, erosion thresholds were increasing with decreasing bed
porosity and increasing clay and organic matter concentration. Erosion rates displayed a positive correlation
with bed porosity and negative correlation with clay and organic matter. The onset of constant erosion
(characterised by constant erosion rates), was identified as the most reliable parameter that responded
consistently with changes of bed properties (e.g. changing clay, organic matter concentration). Overall bed
porosity decrease and higher concentrations of clay and organic matter seemed to more affect the erosion
rate decrease than the erosion threshold increase.
Clay and organic matter significantly increased the pelagic ooze bed stability, however clay was generally
less effective in bed stabilisation compared to organic matter. Extracellular polymeric substances (EPS)
organic matter was a more potent stabiliser than the other used marine particulate organic matter proxy
sourced from cultivated phytoplankton.
Experiments at sub-erosion threshold current velocities identify potential alternative sediment transport mode
in the form of “surface creep“ in high porosity beds (> 80 %).
The deposition experiments observed potential calcareous nannofossil ooze aggregation and flocculation, a
fact that has previously been identified in chalk sedimentology literature as of unlikely occurrence.
Agreement between the results of earlier flume studies using modern pelagic ooze and the current research
project allow to apply the results from this PhD project not only exclusively for modelling sediment transport
of ancient calcareous nannofossil ooze but also for modern day calcareous pelagic sediments.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01010815520&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Physical behaviour of calcareous nannofossil ooze and effects of clay and organic matter on pelagic sediment stability: experimental approach using laboratory flumes
PB - Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen
ER -
