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://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122540295205763

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 -