| dc.description.abstract | Interaction between sediment-processes and autogenic deformation is often lacking empirical analogues. Autogenic deformation is caused internally in a system, it is different from external or allogenic processes such as plate tectonics or crustal thinning. For deformation in delta bodies, the gravitational disequilibrium can be the cause of autogenic deformation. In this study autogenic tectonics are achieved in an analogue flume model by generating a prograding delta superimposed on a weak substrate (SGM-36 silicon putty). To investigate the role that the weak substrate has on autogenic deformation several experimental runs are conducted, each with varying parameters. 1) substrate thickness 2) rate of progradation, 3) intermittency. The presence of a weak substrate leads to the deformation of the delta clinoform, which leads to the subsidence of the delta and a rotation of the clinoform base. Subsidence and uplift are driven by flow in the weak substrate. At the delta toe a peripheral bulge forms due to local thickening of the substrate. With ongoing constant progradation, the zone of deformation shifts along the profile, and only after a period of non-deposition a distinct peripheral bulge forms at the delta toe.
Particle tracing (PIV-analysis) revealed more insight in the development of deformation over time. It reveals a typical subsidence pattern as experienced by an area along the delta profile: 1) as the delta approaches uplift become predominant, with a maximum rate of uplift at the delta toe. 2) uplift changes to a phase of accelerated subsidence, which is a result of the loading by forest deposits. 3) once the basin is fully filled with sediment, a passive phase of subsidence is following, where subsidence rates slowly converge towards zero.
The initial thickness of the weak substrate affects the amount of subsidence and the significance of deformation. A clear relationship between substrate thickness and total subsidence is seen.
A set of intermittency experiments showed that the passive subsidence phase continues during a period of non-deposition, causing ongoing subsidence at topset region and a retreat of the shoreline, while ongoing uplift at the delta toe causes a significant development of the peripheral bulge. During a long period of non-deposition, subsidence leads to drowning of the delta plain and shoreline retreat. After reintroduction of sediment supply the delta progradation resumes, and the drowned delta plain and peripheral bulge are covered by new deposits. Eventually a new peripheral bulge forms at the delta toe.
Intermittency with a consistent frequency of periods of deposition and non-deposition lead to the equal spacing of (buried) peripheral bulges.
Insights on autogenic subsidence derived from this study, will contribute to our understandings of the dynamics of the subsurface in delta regions. Which can be a crucial topic when it comes to understanding vulnerable submerging delta regions. | |
