PhD defence: Toms Buls – Københavns Universitet

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PhD defence: Toms Buls

Toms Buls defends his thesis,

Physical behaviour of calcareous nannofossil ooze and effects of clay and organic matter on pelagic sediment stability: experimental approach using laboratory flumes

Professor Lars Stemmerik, SNM
Associate Professor Kresten Anderskouv, IGN

Assessment Committee:
Senior Researcher Peter Frykman, GEUS
Lecturer Esther Sumner, National Oceanographic Centre Southampton - UK
Professor Thorbjørn J. Andersen (chair), IGN

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. 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 %). 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 was generally less effective in bed stabilisation compared to organic matter. Extracellular polymeric substances (EPS) organic matter was a more potent stabiliser than the marine particulate organic matter proxy sourced from the 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.

The thesis is available for inspection at the PhD administration office, 04.1.413.