The impact of climate controlled frequency variations in sediment supply on basin margin architecture
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In the general sequence stratigraphic model, variations in icehouse delta architecture are solely influenced by variations in accommodation space which is dominantly controlled by eustatic variations. However, there is an ongoing debate on the importance of climate variations. These climate variations might control discharge changes and therefore sediment flux variations towards a delta, adding another potentially important control on delta architecture. To create a better understanding on the effects of climate, six analogue flume models with different discharge scenarios are generated. These are subsequently analysed by roll-over point migration-, parasequence- and system tract-analyses to examine the importance of the discharge component in delta architecture. For these analyses video imaging, 3D digital height models and lacquer peels are used. In this thesis, specifically the effects of discharge frequency variations on icehouse delta architecture are examined. The effects of discharge are quantified with a newly developed representation of roll-over point migration. Significant discharge frequency related offsets from eustatically forced roll-over point migration patterns are observed. These offsets can be explained by a discharge frequency variation control on the sediment flux that works in two separate ways; 1) by directly increasing or decreasing stream power via discharge variations, therefore in- or decreasing sediment carrying capacity, resulting in a correlation with the discharge curve; 2) by rapidly altering the equilibrium slope during high frequency discharge variations, therefore increasing or decreasing stream power and sediment carrying capacity, resulting in a correlation to the discharge gradient curve. The latter control is only significant when the discharge induced disequilibrium is dominant over eustatically induced disequilibria. This situation is observed during periods of extreme frequency and amplitude variations in discharge. The addition of a climate component would moderately increase the predictive power of the sequence stratigraphic model. However, including this parameter poses a major challenge because of its complexity. The experimental results predominantly confirm the general opinion that the rate of eustatic change provides the dominant control on delta architecture. Therefore the Exxon sequence stratigraphic model does not need modification to incorporate the effects of discharge frequency variations on the sediment flux.