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Accueil du site → Doctorat → Allemagne → 2020 → Fluvio-aeolan interaction and early diagenetic processes, Sossus sand formation, Namibia

Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) 2020

Fluvio-aeolan interaction and early diagenetic processes, Sossus sand formation, Namibia

Feder Amelie

Titre : Fluvio-aeolan interaction and early diagenetic processes, Sossus sand formation, Namibia

Fluvioäolische Interaktion und frühdiagenetische Prozesse, Sossus Sand Formation, Namibia

Auteur : Feder Amelie

Université de soutenance  : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)

Grade : Doktorgrades Dr. rer. nat. 2020

Résumé partiel
Aeolian sandstones have ideal initial conditions to provide good reservoirs, but their reservoir properties are strongly depended on the evolution of the sandstone through time. Diagenesis can either foster or destroy porosity and permeability and therefore rules over the reservoir quality. Early and burial diagenetic processes in aeolian sandstones have been studied extensively, however the drivers of early diagenesis - spatial facies distribution and initial sediment composition - have been neglected. The depositional environment determines the facies distribution, which in turn influences the initial sediment composition. This controls the location of early diagenetic features in the sediments, which defines the pathways for fluid movement during burial diagenesis. The interaction with rivers introduces a heterogeneity into dune fields and changes the depositional facies and sediment compositions. This thesis illuminates the fluvial aeolian interaction, the spatial distribution of the resulting sedimentary facies, sediment composition and their influence on early diagenesis. The study has been conducted in the Namib Desert with its aeolian Sossus Sand Formation as it is a prime example for fluvial aeolian interaction. The ephemeral Tsauchab River enters the dune field, is dammed between the dunes and disembogues in an inter-dune mud pool called ‘vlei’. The various aeolian and fluvial processes generate a complex interplay of sedimentary deposits. In a first step a workflow was developed to classify satellite images into sedimentary facies. The map was created by combining remote sensing with observations and samples from the field. A WorldView3 image of four visible to near-infrared and eight short wave infra-red with a resolution of 7.5 m was used to generate the map. The best classification results have been achieved by combining a principal component analysis, band ratios, as well as geomorphological and texture indices. After the preprocessing a principal component analysis was applied to reduce dimensionality and filter noise. Band ratios for clays and iron oxide were calculated to highlight spectral differences based on the mineralogy. Additionally the Topographic Position Index and slope were applied to include the spatial features of the facies and texture statistics are derived from a Gray Level Co-Occurrence Matrix to include the textural features of the facies. The supervised classification algorithm “random forest” used these calculations together with field data for validation to propose the facies distribution. Based on the remote sensed map, the Sossus area was subdivided into six facies : modern aeolian sand, deflation surface, mud pool/mud drapes, heavy mineral lag, aeolian reworked fluvial sediment, and fossil dune remnant.


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