Progradational Units as Recorders of Sedimentary Evolution in the Alaskan North Slope and Gulf of Mexico



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Ripples and clinoforms are progradational units that are commonly found in fluvial to deep-water depositional environments. Ripples have a height of <4 cm, and clinoforms height vary from tens to hundreds of meters. The geometry of these progradational units is a useful indicator of sedimentary processes, and basin configuration and evolution; and are controlled by the relative sea level, sediment supply, and grain size availability. Understanding the relationship between geometry and formative processes is crucial in establishing a predictive quantitative model that can be applied to paleo- and modern- environments. This dissertation concentrates on one tidal and one shallow to deep-water environment:1) modern ripples and flood-tidal delta evolution in the San Luis Pass, Upper Texas coast; and 2) the lower Cretaceous Torok-Nanushuk clinoforms in the Alaskan North Slope. Two different datasets were used: 1) seafloor sediment samples, measured ripple geometries, water depths, satellite and aerial images, and sediment grain size analysis (chapter 2); and 2) 2D and 3D seismic data, well log data, and core data. The San Luis Pass flood-tidal delta is the main sink for sediments eroded from the northeast, updrift Galveston Island, via longshore drift. At 4.3 km from the mouth of the tidal inlet, there is a rapid transition in grain size, from proximal (fine sand) to distal (silt and very fine sand) sediments, related to a decrease in current velocities away from the inlet entrance. Ripple height/ripple wavelength and water depth have a positive correlation. However, the correlation is much stronger for ripple wavelength. The Lower Cretaceous of the Alaskan North Slope is a well-known example of large-scale (600-2500 m depositional relief), constructional, siliciclastic clinoforms. After decompaction, the seismically-imaged slope angles vary between 2.7°-6.9°. Decompaction is an important step in the analysis of these clinoforms as it allows for a more accurate interpretation of geometries and shelf-edge trajectories. The 3D seismic analysis demonstrates along strike geometry variations of the clinoform packages related to sediment source location and basin morphology. Integration of clinoform geometries, log and core data, thickness, geomorphological features, and shelf-edge trajectories facilitated the development of a predictive model of sediment bypass and accumulation.



Clinoforms, Alaskan North Slope, Decompaction, Slope angles, Shelf-edge trajectories, Graded, Erosional, Current ripples, Ripple wavelength, Ripple height, Sediment grain size, Flood-tidal delta, Hurricane Harvey


Portions of this document appear in: Ramon-Duenas, Carolina, Kurt W. Rudolph, Peter A. Emmet, and Julia S. Wellner. "Quantitative analysis of siliciclastic clinoforms: An example from the North Slope, Alaska." Marine and Petroleum Geology 93 (2018): 127-134.