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.