Browsing by Subject "Submarine channels"
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Item Quantifying the sedimentology, stratigraphy and morphodynamics of submarine channels(2012-05) Fernandes, Anjali Mary; Mohrig, David; Steel, R. J.; Kim, Wonsuck; Fulthorpe, Craig; Henriksen, SverreThis dissertation examines how turbidity currents interact with submarine channels. Turbidity currents display exaggerated super-elevation at the outer banks of channel bends, because they have low excess densities relative to the ambient sea-water. Low-velocity zones form where flows separate from the inner banks. In a high-resolution seismic volume, I mapped 226 inclined surfaces associated with bank-attached bars in 16 channel bends of 2 buried sinuous channels. Position and geometries of bars indicate construction from suspended sediment in flow separation zones. Concave-bank benches, first identified in rivers where they are built from fully-suspended sediment deposited within flow separation zones in channel bends, comprise approximately 19% of this dataset. Bars have high median slopes (10°-11°) and occupy less than 30% of channel width. Associated channels migrated a median distance of less than 70% of the channel width and incised 20-30% of the channel depth. These bars are therefore interpreted to have formed during sediment bypass or weak erosion. I have analyzed the sedimentology and stratigraphy of a well-exposed channel complex, in the Permian Brushy Canyon Formation, west Texas. A steeply-inclined set of fine-grained sandstone beds (median dip=10°) at the margin of the channel complex is interpreted as deposits of a bank-attached bar. Beds are characterized by sub- to super-critically climbing ripple-lamination, planar stratification and trough cross-stratification. Paleo-transport directions are at high angles, 20-120°, to the dip azimuths of interpreted bar surfaces. Geometries of bounding surfaces, sedimentation styles and grain-size data were used to construct a facies model for suspension-dominated, bank-attached bars, built within flow-separation zones in submarine channels. I designed physical experiments to examine how erosional turbidity currents evolve channel- bend topography. Time-lapse bathymetry maps capture the evolution of raised benches tied to sedimentation within flow separation zones and erosion outside of separation zones. Erosional currents showed sensitivity to local conditions. The pattern of erosion was connected to roughness elements such as bend curvature and scours on the bed. Turbidity current run-up at the outside of bends produced a greater aerial extent of side-wall erosion than is commonly seen in incisional rivers.Item Seismic-based geomorphology of a mixed carbonate siliciclastic shelf-to-basin submarine drainage system, Miocene, Browse Basin, Northwest Shelf of Australia(2020-08-14) Zeng, Leo Young; Janson, XavierRecent studies revealed that carbonate slopes can have similar architectural elements as their siliciclastic counterparts. This study uses a large regional 3D seismic dataset to map and quantify carbonate and mixed carbonate-siliciclastic slope architectural elements to generate an updated model of these slope systems. The research area of this project is the upper slope to toe-of-slope region of Miocene carbonates in the Browse Basin of the NW Shelf of Australia covering a total of over 25,000 km² in area. This slope can be divided into three components: (1) a low angle transition between carbonate platform margins and the upper slope; (2) a steep upper slope riddled with low-sinuosity, line-fed canyons; and (3) a low angle lower slope with a mix of sinuous channel-levee systems, mass transport deposits, and slope fans. The slope channels were sourced from large carbonate platforms along the shelf. Slope architectural elements, such as canyons, channel-levee systems, mass transport deposits, and fans, were imaged to extract geomorphic data such as length, gradient, aspect ratio, and sinuosity. Canyons are defined as channels between 0.5 to 1.5 km wide and 80 to 250 m deep that are relatively straight (sinuosity of 1.00-1.14) and set upon the steeper gradients of the upper slope (2.4° - 11°). Some canyons transformed downstream into channel-levee systems, which are narrower and shallower and more sinuous (1.05-1.30), developing on a slope angle of 1.2° - 4.6°. In many cases, the evolution of canyons into channel-levee systems can be clearly observed in seismic data in the middle-outer slope. The development of the channel-levee systems in the lower slope is controlled by slope gradient and concavity. The channel-levee system can be eroded by large mass transport deposits. This high-resolution regional 3D seismic dataset provides an excellent example of a carbonate slope to toe-of-slope morphology that can be used to generate an updated model of such systems and provide a new analogue for exploring other carbonate slope and basin environments.Item Submarine channel curvature and migration distance : a study of Joshua Channel with implications for sinuous submarine channel geomorphology and deepwater reservoir connectivity(2020-08-14) Altman, Indre; Sylvester, Zoltán; Mohrig, DavidThe nature of plan-view migration in submarine channels is a subject of debate among researchers, and of significance to oil and gas investment in deepwater prospects. Early work has suggested that common features in fluvial channels such as downstream migration are rare or absent in deepwater reservoirs, and that relationships between geometric attributes of submarine channels do not compare to those in fluvial channels. This study explores whether curvature and migration in sinuous submarine channels are correlated, in a similar manner to rivers in the Amazon, where a recent study has found that variance in curvature explains 57% of variance in migration rate. Using bathymetric and seismic data from the Joshua Channel in the Eastern Gulf of Mexico, this study find that variance in curvature explains approximately 52% of variance in migration distance. In addition, the lag between curvature and migration is similar to that found in rivers when scaled to thalweg width. Lastly, a qualitative financial discussion of reservoir connectivity highlights the importance of understanding submarine channel kinematics.