Wonsuck Kim

Long-period cyclic sedimentation with constant tectonic forcing in an experimental relay ramp

It is widely believed that cyclic sedimentation in active tectonic basins is caused by external forcing such as sea-level cycles, episodic tectonic events, or variation in sediment supply due to climate change. Here we present a case of cyclic sedimentation in an experiment subject to constant fault slip rate and sediment discharge with no base-level fluctuation. The experiment was designed to study sedimentation in a simplified extensional relay ramp system. Reorganization of the fluvial channel network in a cyclic manner caused local variation in sediment supply to the hanging-wall basin, where subsidence was maximized, and resulted in autogenic appearance and disappearance of a lake associated with 90° rotation of paleocurrent direction and delta formation. Comparing an early phase of the experiment using no external forcing (i.e., no tectonic movement or base-level change) with the following main phase of the experiment (i.e., including subsidence in an extensional relay ramp pattern) shows that the characteristic time scale for channel mobility was five times longer during the phase with subsidence than during the previous phase without subsidence. Active fault slip imposed a new, longer time scale for autogenic dynamics by establishing a linked tectonic-sedimentation system. Scaling the experimental results to field length and time scales suggests that comparable autogenic cycles would produce 10–20-m-thick strata on time scales of 105 yr, comparable to observed cases attributed to allogenic effects.

An enthalpy method for moving boundary problems on the earth's surface

Purpose – To present a novel moving boundary problem related to the shoreline movement in a sedimentary basin and demonstrate that numerical techniques from heat transfer, in particular enthalpy methods, can be adapted to solve this problem.Design/methodology/approach – The problem of interest involves tracking the movement (on a geological time scale) of the shoreline of a sedimentary ocean basin in response to sediment input, sediment transport (via diffusion), variable ocean base topography, and changing sea level. An analysis of this problem shows that it is a generalized Stefan melting problem; the distinctive feature, a latent heat term that can be a function of both space and time. In this light, the approach used in this work is to explore how previous analytical solutions and numerical tools developed for the classical Stefan melting problem (in particular fixed grid enthalpy methods) can be adapted to resolve the shoreline moving boundary problem.Findings – For a particular one‐dimensional case,...

Effects of in-phase and out-of-phase sediment supply responses to tectonic movement on the sequence development in the late Tertiary Southern Ulleung Basin, East (Japan) Sea

Stratigraphic inverse modeling using the SEDPAK stratigraphic simulator established the size of the physical parameters that together controlled the development of the stratal patterns in the late Tertiary Ulleung Basin, East (Japan) Sea. The modeling results provided a quantitative geohistory of the basin. This included the dimension of variations in rates of tectonic subsidence (or uplift) and sediment supply. Input variables were based on the ages and geometries of strata determined from well and seismic interpretations and the given base-level control of the Haq et al. eustatic curve. The simulation results indicate that changes in the rate of sediment supply clearly correlate with local back-arc tectonic events that occurred both with (out-of-phase) and without (in-phase) a time lag associated with the local tectonic movements. The initial package of the basin stratigraphy was generated by an in-phase response of sediment supply to back-arc spreading in the Early and Middle Miocene, during which a high rate of sediment supply caused a series of downlap surfaces onto which strata prograding northward. In contrast, the basin experienced an out-of-phase response to the sediment supply during the second stage of basin growth, a back-arc closure characterized by rapid uplift, thrusts, and folds during the Late Miocene. In the latter case, the time lag in sediment supply response, caused by sediment trapping behind the thrust zone, produced transgressive surfaces and halted basin growth, and then gradually forced the shelf front to migrate basinward as the sediment supply slowly increased in response to the further tectonic uplift.