Browsing by Subject "deltaic facies"

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Cyfrowy model deltowej asocjacji facjalnej na przykładzie grup Ecca i Beaufort (nadgrupa Karoo) w południowo-zachodniej części Botswany, Afryka południowa
(Data obrony: 2011-07-26) Radwański, Lechosław
Wydział Geologii, Geofizyki i Ochrony Środowiska
The objective of this thesis was to create a digital 3D model representing the deltaic facies of the Karoo Supergroup (Carboniferous-Jurrasic) in the south-western part of Botswana. It is the first work of this kind. Creating the model was done with the use of the Petrel software application owned by the Schlumberger Company. The input data consisted of a series of cores obtained from drilling operations conducted in south-west Botswana. As a result a simple model of the Karoo Ecca-Beaufort succession has been created. The boreholes intersected only the uppermost part of the underlying complex of glaciogenic Karoo sediments known as the Dwyka group and did not reach the basement rocks. Due to the small number of boreholes and their disadvantageous locations only a simple model, which gives general insight in to the structure of the Ecca and Beaufort units, could have been created. However, the results enabled to show the general time–space relations and lateral thickness changes of the distinguished lithostratigraphic divisions. These relations reveal the main subsidence zones, their changes and links between subsidence and the facies variability of the sediments. The facies variations were controlled by the evolution of the main supply system and depositional zones within the delta. The detrital material was derived from the north (beyond the research area) and was transported towards the south. During the early phase of the Ecca sedimentation main zones of deposition were defined by the topography of the marine basin. The basin bottom was covered with glaciogenic sediments (the Dwyka Group) in which two major depressions were interpreted – most likely glacial valleys. They are located in the northern part of the area and extended from north to south. During the main phase of the delta development, proximal coarse grained sediments of delta channels and sandy lobes were filling up these depressions causing local subsidence, most likely by loading into thick complex of glaciogenic mudstones and siltstones. Between delta channels, interchannel sediments were deposited in delta-top lakes and swamps. The last sedimentation phase resulted in a vast deposit of fine-grained material (Beaufort Group) – muds and silts of lacustrine origin with minor fluvial fine-grained sands.