Graphical simulation of clastic margin progradation: Ulleung Basin, offshore Korea

Abstract

The evolution of the southern part of the Ulleung Basin, East Sea (Sea of Japan) is analysed using a two-dimensional computer-based graphical simulation (SEDPAK) on a multichannel seismic profile. Iterative editing of the input data file includes various factors: initial basin configuration, local tectonic behavior, eustatic sea level, and the amounts and direction of clastic sedimentation. The sedimentary succession on the seismic profile can be divided into seven sequences bounded by sequence boundaries. The simulation relatively well reproduces evolving geometry shown on the interpreted seismic profile and burial history of sediments through time. The over 3000-m-thick sedimentary body is composed of sandstone and shale which have been accumulated in deltaic setting and as slumping or turbidites in a shelf-slope setting since the middle Miocene (16.5 Ma). The SEDPAK simulation shows all sequences except for the upper part of Sequence 5 which displays progradational clinoforms and onlapping transgressive units. It well reflects that the simulated sequences were formed during the mature stage of the back-arc basin development since the early Miocene. Scouring by incised valleys occurred extensively after the deposition of Sequence 5 on the margin, most obviously during the lowstand of sea level. Scouring may be related to the late Miocene thrusting and wrenching caused probably by collision of the Bonin Arc with the Amurian Plate. Simulation also shows the evolutionary development of the sedimentary sequences, which can track the burial history of individual layers throughout the run. When the 16.5 Ma surface is assumed to be the initial basin surface (the top of the pre-16.5 Ma sequence), the burial path of the 17.5 Ma to 16.5 Ma sequence reveals that it was at a depth of 3000 m at 12.5 Ma; 3200 to 3900 m at 6.3 Ma; at 3500 to 4200 m at 3.8 Ma; and at 4000 to 4700 m today. In addition, one can follow the burial history at a particular location using the time-depth-elevation plot for a specific column of the output within the simulated section. These features aid in the prediction of sedimentary facies distribution and geothermal history of the sequences.