Controls on shallow-marine stratigraphy; a process-response approach

This 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

Automatic detection of buried channel deposits from dense laser altimetry data

The formation of the current Rhine-Meuse delta mainly took place during the last 12 000 years. Consecutive avulsions, i.e. sudden changes in the course of river channels, resulted in a complicated pattern of sandy channel deposits, surrounded by peat and clay. Knowledge of this pattern is not only interesting from a geohistorical viewpoint, but is also essential when planning and maintaining constructions like roads and dikes. Traditionally, channel deposits are traced using labor intensive soil drilling. Channel deposits are however also recognizable in the polder landscape by small local elevation changes due to differential compaction. The purpose of this research is to automatically map channel deposits based on a structural analysis of high resolution laser altimetry data. After removing infrastructural elements from the laser data, local feature vectors are built, consisting of the attributes slope, curvature and relative elevation. Using a maximum likelihood classifier, 75 million gridded laser points are divided into two classes: buried channel deposits and other. Results are validated against two data sets, an existing paleographic map and a set of shallow drilling measurements. Validation shows that our method of channel deposit detection is hampered by signal distortion due to human intervention in the traditional polder landscape. Still it is shown that relative young deposits (4 620 to 1 700 years Before Present) can be extracted from the laser altimetry data.Remote SensingAerospace Engineerin

Impact of external forcing and catchment response on sediment flux

Geoscience & EngineeringCivil Engineering and Geoscience

Establishing 3d numerical reservoir analogues: Modelling the formation of sand bodies in deltaic environments

The assessment and production of hydrocarbon resources incorporates geological models created from core and wireline well data, as well as seismic data. This data is spatially discrete but is used create a spatially continuous model. However, the heterogeneity within depositional environments is on a smaller spatial scale than the available data resolution. The field data is therefore supplemented with relevant analogue data, often from deposits which differ in various aspects from the actual reservoir being assessed. To improve the correlation between analogues and the reservoir being studied, it is proposed that 3D numerical analogues are used in addition to the current outcrop analogues. These 3D numerical analogues can be created through process based numerical modelling and can more closely match the conditions of the reservoir being studied. In this presentation we propose a workflow to create and implement 3D numerical outcrops. We go on to show an initial stage of a proof of concept for the workflow. It is shown that using the software Delf3D, it is possible to simulate the sand bodies found in deltaic deposits, which can later act as hydrocarbon reservoirs.Geoscience & EngineeringCivil Engineering and Geoscience

Modelling astronomical climate signals in fluvial stratigraphy

Orbital climate forcing is demonstrated to result in cyclic changes as reflected in the catchment, including precipitation, temperature, vegetation, sediment supply and water discharge. All of these are known to largely impact alluvial architecture. Climate change related to the 21-kyr precession cycle was proposed as driver of regularly-alternating river avulsion and overbank phases in the Eocene Willwood Formation of the Bighorn Basin, Wyoming, USA (Abels et al. 2013; 2016). This study aims to explore the conditions that are favourable for these climate cyclic signals to be preserved in the fluvial stratigraphy.Applied Geolog

Modelling orbital climate signals in fluvial stratigraphy

There are certain orbital cycles influencing the relative position and location of the earth towards the sun, resulting in the cyclic insolation received on the earth, which causes climate changes and subsequent environmental response in the catchment, including precipitation, temperature, and vegetation, and so on. Furthermore, such catchment responses induce cyclic variation of source materials, including sediment supply and water discharge in the entry of a fluvial basin. Climate change related to the 21-kyr precession cycle was proposed as the driver of regularly-alternating river avulsion and overbank phases in the Eocene Willwood Formation, Bighorn Basin, Wyoming, USA 1-2. This study aims to simulate the building-up process of fluvial stratigraphy under the action of precession.Applied Geolog

Source to sink reconstruction of a Holocene Fjord‐infill: Depositional patterns, suspended sediment yields, wind‐induced circulation patterns and trapping efficiency for Lake Strynevatnet, inner Nordfjord, Norway

This paper reconstructs the sedimentation volumes and patterns, suspended sediment yields, wind‐induced circulation patterns and sediment trapping efficiency of Lake Strynevatnet, western Norway as an integrated source to sink system. The lake became deglaciated ca 11 ky cal bp, with glacio‐isostatic uplift isolating the basin from the nearby fjord (Nordfjord) ca 9.2 ky cal bp. Based on geophysical data collected in 2010, the upper 15–20 m of Holocene sediment accumulation in the lake was mapped. A sediment body in the centre of the lake indicates a depositional mechanism dominated by suspension sedimentation. The source of this sediment is associated with the adjacent glaciated catchments westward of the lake. Three seismic units were identified based on seismic facies generating an evolutionary model utilizing three depositional units (U1, U2 and U3), in which unit U2 represents the Storegga tsunami event. Unit U3 is further divided into three subunits; U3a, U3b and U3c based on their spatial continuity and subtle downlapping and onlapping relationships. The degree to which wind conditions could have affected the lake depositional patterns were studied utilizing an open‐source coupled hydrodynamic and sediment transport model. The results show that fluvial discharge alone is incapable of generating a circulation pattern in the lake currents. Suspended sediment concentrations in the lake are highest for strong winds. Modelled sediment accumulation on the lake floor shows that mild or absent winds lead to a proximal to distal sediment thickness trend, while strong winds result in uniform sediment thickness. Based on this it is argued that the thickness trends of seismic subunits U3a‐c are related to a variable palaeowind climate. As such, seismic data of lake infills, in combination with numerical modelling, may provide valuable palaeoclimatic information on wind patterns.Applied Geolog

Oblique aggradation: A novel explanation for sinuosity of low-energy streams in peat-filled valley systems

Low-energy streams in peatlands often have a high sinuosity. However, it is unknown how this sinuous planform formed, since lateral migration of the channel is hindered by relatively erosion-resistant banks. We present a conceptual model of Holocene morphodynamic evolution of a stream in a peat-filled valley, based on a palaeohydrological reconstruction. Coring, ground-penetrating radar (GPR) data, and 14C and OSL dating were used for the reconstruction. We found that the stream planform is partly inherited from the Late-Glacial topography, reflecting stream morphology prior to peat growth in the valley. Most importantly, we show that aggrading streams in a peat-filled valley combine vertical aggradation with lateral displacement caused by attraction to the sandy valley sides, which are more erodible than the co-evally aggrading valley-fill. Owing to this oblique aggradation in combination with floodplain widening, the stream becomes stretched out as channel reaches may alternately aggrade along opposed valley sides, resulting in increased sinuosity over time. Hence, highly sinuous planforms can form in peat-filled valleys without the traditional morphodynamics of alluvial bed lateral migration. Improved understanding of the evolution of streams provides inspiration for stream restoration.Applied Geolog

Evaluating alluvial stratigraphic response to cyclic and non-cyclic upstream forcing through process-based alluvial architecture modelling

Formation of alluvial stratigraphy is controlled by autogenic processes that mix their imprints with allogenic forcing. In some alluvial successions, sedimentary cycles have been linked to astronomically-driven, cyclic climate changes. However, it remains challenging to define how such cyclic allogenic forcing leads to sedimentary cycles when it continuously occurs in concert with autogenic forcing. Accordingly, we evaluate the impact of cyclic and non-cyclic upstream forcing on alluvial stratigraphy through a process-based alluvial architecture model, the Karssenberg and Bridge (2008) model (KB08). The KB08 model depicts diffusion-based sediment transport, erosion and deposition within a network of channel belts and associated floodplains, with river avulsion dependent on lateral floodplain gradient, flood magnitude and frequency, and stochastic components. We find cyclic alluvial stratigraphic patterns to occur when there is cyclicity in the ratio of sediment supply over water discharge (Qs/Qw ratio), in the precondition that the allogenic forcing has sufficiently large amplitudes and long, but not very long, wavelengths, depending on inherent properties of the modelled basin (e.g. basin subsidence, size, and slope). Each alluvial stratigraphic cycle consists of two phases: an aggradation phase characterized by rapid sedimentation due to frequent channel shifting and a non-deposition phase characterized by channel belt stability and, depending on Qs/Qw amplitudes, incision. Larger Qs/Qw ratio amplitudes contribute to weaker downstream signal shredding by stochastic components in the model. Floodplain topographic differences are found to be compensated by autogenic dynamics at certain compensational timescales in fully autogenic runs, while the presence of allogenic forcing clearly impacts the compensational stacking patterns.Applied Geolog