1,721,058 research outputs found
The impact of changes in sediment supply and sea-level on fluvio-deltaic stratigraphy
No full textStudies in stratigraphy are often driven by the predicted climate change and possible gains for the oil and gas industry. Because, at present predictions of the development of future deltaic architecture are insufficient. This thesis addresses the problem of qualitative and quantitative understanding of sedimentary systems in two stages. In the first stage the stratigraphy of Holocene delta deposits of the Kura and Mahakam deltas (respectively in Azerbaijan en Indonesia) are studied. Results from these studies provide insights as an analogue to ancient systems and serve as an example for expected future conditions. The results form the Kura delta show a prominent role for the rapid sea-level change of the Caspian Sea, while the results of Mahakam delta suggest an important role for the eustatic Holocene sea-level curve and the absence of floods of the Mahakam River. Information obtained from studies in a similar context have the potential to reduce uncertainties and increase confidence in models. The second stage of this thesis covers the development of a process-response simulation model to assess the impact of changes in sediment supply and sea-level on fluvio-deltaic stratigraphy. Anticipating on the dominant role of sediment supply on fluvial dominated deltas, a choice is made for a detailed investigation in how to incorporate good estimates of sediment supply in the numerical model, that enable to explore the possibilities of using a probabilistic approach instead of a deterministic output or geostatistical analysis.Civil Engineering and Geoscience
Controls on shallow-marine stratigraphy; a process-response approach
No full textThis thesis is concerned with the interface between land and sea. The interaction of coastal evolution and the sedimentary record, in this case of a wave-dominated coastal system, over geological timescales (< 105 y) is investigated in relation to their forcing parameters such as relative sea-level change, sediment supply, and wave climate. The preserved sediments record the dynamics of the coastal system in stacked but uncomplete sediment packages, which formed as the coastline migrated in landward or seaward direction resulting from erosion and deposition of sand and clay along the shallow parts of the coastal system (< 100 m waterdepth). If we want to understand coastal evolution over geological timescales, we must be able to read or interpret the stratigraphic record. Reconstructing coastal evolution from preserved shallow-marine stratigraphy is very difficult. The sediment record is not complete due to phases of erosion and we know little about past local changes in relative sea level, sediment supply, and wave climate. Also, the individual effects of these variables on coastal evolution and the stratigraphic record are poorly known. As the processes that drive coastal evolution, and therefore the resulting sedimentary record, act over thousands of years it is not possible to simply take measurements and make observations. Nevertheless, the stratigraphic record is the key to understand coastal evolution over geological timecales because it is the only physical evidence. Therefore a two dimensional numerical model has been developed which simulates the processes which are presumably important for coastal evolution and the formation of the stratigraphic record over long timescales. This model, its development and some applications are described in this thesis with the goal of increasing our understanding of coastal dynamics over geological timescales.Civil Engineering and Geoscience
Process-response simulation of fluvio-deltaic stratigraphy
No full textCivil Engineering and Geoscience
Rapid Caspian Sea-level change and its impact on Iranian coasts
No full textThe Late Pleistocene and Holocene evolution as well as recent developments of the southern coast of the Caspian Sea have been studied using remote sensing and core data. This thesis focuses firstly on recent shoreline shifts during the last rapid sea-level cycle between 1929 and 1995, with an amplitude of three meters. Secondly, it shows a reconstruction of past Caspian Sea-level change and palaeoenvironments in an area very sensitive to such changes. A new tentative Holocene Caspian Sea-level curve has been reconstructed, which might help to predict future Caspian Sea-level. Up to now there has been no consensus on the chronology and amplitudes of Holocene Caspian sea-level oscillations due to problems with sampling strategies, absolute dating, relative tectonics, deformation, different datum levels and absence of data on long-term development of Caspian Sea-level.Geoscience & EngineeringCivil Engineering and Geoscience
Numerical modeling of fluvial sediment supply to marine basins
No full textCivil Engineering and Geoscience
Process-based modelling of turbidity-current hydrodynamics and sedimentation
No full textThe production potential of deep-water reservoirs is primarily determined by rock bulk volume, porosity and permeability. Quantification of the geometry and spatial distribution of reservoir sands in deep-water deposits can provide crucial information to assess sand body volume, connectivity and the distribution of permeability baffles. This study aims to investigate the influence of turbidity-current process, sediment composition and basin-floor relief, on the geometry and spatial distribution of reservoir sands in turbidite fans. For this purpose, a process-based model has been developed which simulates turbidity-current flow, erosion, and deposition based on principles of fluid dynamics that can deal with arbitrary basin-floor topography and accommodates various grain sizes. It employs the depth-averaged shallow-water approximation in combination with the Boussinesq approximation for density-driven flow in three dimensions. Sediment transport is modelled by an advection-diffusion type equation, and exchange with the bed is largely based on existing empirical models for sediment entrainment and deposition. The model is solved numerically on a rectangular grid representing topography by means of a second-order finite-difference approximation, and employs a shock-capturing technique to accurately model the discontinuous flow front characteristic of density-driven flows. Results are presented of laboratory-scale model validation tests, in which modelling results are quantitatively and qualitatively compared to experimental data. Laboratory experiments involve small-scale flows interacting with complex topographic features as well as multiple successive flows over the same erodible bed. Results indicate that the model is capable of simulating turbidity-current hydrodynamics and sedimentation with an acceptable degree of accuracy under a wide range of conditions.Civil Engineering and Geoscience
Multi-scale simulation of fluvio-deltaic and shallow marine stratigraphy
No full textSimClast is a basin-scale 3D stratigraphic model, which allows several interacting sedimentary environments. We developed it from 2004 to 2008 at Delft University of Technology and implemented part of the Meijer (2002) code for accounting, loading and storing algorithms. SimClast is a fully plan view 2D, depth-averaged model, allowing the complex interaction between fluvial and wave influences on deltaic and shoreface development to be studied. It focuses on theoretical experiments, as quantitative experiments are intrinsically difficult to recreate in real world settings. Yet there lies the great strength of numerical modelling, as we can improve upon the understanding of these systems by focussing on the process forming and removing the deposits. The modelling applications focus especially on the erosional and nondepositional events as these probably represent the greatest amount of “stratigraphic time”. Short-term, high-resolution processes are coupled with the long-term stratigraphic model by nesting a parameterised version of the high-resolution processes. We extrapolate physical and empirical relationships of the geomorphological development and implement these. A necessary constraint on these long-term models is a relatively large grid sizing (i.e. km scale), as the area to be modelled is on the scale of continental margins and the modelling time is on the scale of many millennia. Areas of special importance are modelled by implementing sub-grid scale processes into a large-scale basin-filling model; this refines the model dynamics and the resulting stratigraphy. Processes included are; fluvial channel dynamics and overbank deposition, river plume deposition, open marine currents, wave resuspension, nearshore wave induced longshore and crosshore transport. This combined modelling approach allows insight into the processes influencing the flux of energy and clastic material and the effect of external perturbations in all environments. Many governing processes work on relatively small scales, e.g. in fluvial settings an avulsion is a relatively localised phenomenon, yet they have a profound effect on fluvial architecture. This means that the model must mimic these processes, but at the same time maintain computational efficiency. Additionally, long-term models use relatively large grid sizing (km scale), as the area to be modelled is on the scale of continental margins. We solve this problem by implementing the governing processes as sub-grid scale routines into the large-scale basin-filling model. This parameterization greatly refines morphodynamic behaviour and the resulting stratigraphy. SimClast recreates realistic geomorphological and stratigraphic delta behaviour in river and wave-dominated settings.GeotechnologyCivil Engineering and Geoscience
Mass-balanced stratigraphy: Data-model comparison within a closed sedimentary system (Adriatic Sea, Italy)
No full textGeotechnologyCivil Engineering and Geoscience
Geological evolution of the Amazonian Craton: Forget about geochronological provinces
No full textGeoscience & EngineeringCivil Engineering and Geoscience
- …
