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Tesi etd-11192018-142549

Tipo di tesi
Tesi di laurea magistrale
Evolution of Neogene deposits in the Brazilian Equatorial margin: A 3D Seismic Interpretation Approach
Corso di studi
relatore Dott. Iacopini, David
relatore Dott. Maselli, Vittorio
Parole chiave
  • image processing
  • seismic attribute
  • 3D seismic interpretation
Data inizio appello
Data di rilascio
Riassunto analitico
In recent years, high resolution 3D seismic data have been used in morphological studies of submarine depositional systems. This technique represents a powerful tool to investigate, from a qualitative and a quantitative point of view, the seabed and the subsurface in deep-water areas across the globe. <br>The present work focuses on the study of Neogene up to modern deposits in the Mundau basin (Brazilian Equatorial margin), where a high resolution 3D seismic data allowed the identification, on the actual seafloor and in the subsurface, of the following morphological features: <br><br>- A main drainage system composed by three large canyons eroding the seafloor from the shelf break and toward the upper continental rise; <br>- A minor drainage system shaping the areas located between the major channels and comprising a system of gullies located along the slope, a series of circular depressions organized randomly or in trains of discrete depressions along the entire dataset a series of landslide related features and sediment waves fields. <br><br>The employment of techniques of image processing involving seismic traces amplitude modification using seismic attributes, complex trace seismic attributes and Variance and Dip Illumination attributes, allowed to deal with a large volume of data and facilitated the 3D seismic interpretation of the area. <br>Based on the study of previous works on the genesis of the submarine canyon systems, and on the quantitative observation of the modern seafloor, this work suggests a mechanism for the evolution of the study area as the continuous interplay between gravity-driven flows and retrogressive erosion processes. Indeed, gravity-driven flows (e.g. turbidity currents) combined with a retrogressive erosion mechanism triggered by localized geological weaknesses (e.g landslides, sediment under consolidation, oversteepening slope), are thought to be responsible for the formation of canyons and their evolution in three different evolutionary stages: a youthful stage, a transitional stage and a mature stage. Within this framework, the identified and mapped slope failures scars, along the slope, are representative of the preliminary stage of canyons evolution, the gullies are interpreted as transitional morphological features characterizing the second stage, while the major canyons visible on the seafloor represent the last evolutionary stage. Furthermore, through the measurement and the study of quantitative parameters, as channel gradient, height, and width, we demonstrate that the slope gradient combined with temporal and spatial variation of the gravity flows volume are the major factors affecting the canyons morphology. <br>The interest in this area is also increased by the presence of circular topographic depressions at the seafloor, found as isolated features or trains of discrete depressions. The mechanisms responsible for the genesis of this features are thought to be similar to the processes which lead to the formation of sediment waves. According to this hypothesis, the observed circular depressions and sediment waves origin as a result of erosion/deposition mechanisms, related to gravity currents, which create an undulating topography on a preexistent irregular seabed: erosion occurs when gravity flows accelerate on steep slopes, while deposition occurs when slope angles decrease and the gravity current decelerates. <br>We can conclude that the project here presented demonstrates the important role played by a 3D seismic interpretation approach on the study of areas characterized by a high geological complexity.