Architecture and evolution of shelf-margin clinoforms developed in a back-arc tectonic setting: Insights from quantitative analysis on the south-west shelf margin of the Ulleung Basin

Abstract

Geophysical and geological research in the Ulleung Basin has been ongoing since the 1970s, involving continuous seismic acquisition and multiple well-drilling projects. This study utilized an integrated quantitative approach with conventional seismic interpretation based on recent trends to understand the history of the shelf-margin development and individual controls that may have influenced each period in the Ulleung Basin. Quantitative analysis was conducted by measuring the progradation (P_se), aggradation (A_se) and sediment influx (Fc) of individual shelf margins in seven dip-oriented seismic profiles, and calculating the shelf-edge gradient (α_se) and the P/A ratio. Based on these data and the ratio of accommodation to sediment supply (A/S ratio), which was interpreted from the stratal stacking pattern, five shelf-edge trajectory types were defined and assigned to each shelf margin. By considering individual controls (eustatic fluctuations, sediment supply and tectonic events), we defined the three evolution intervals of the Ulleung Basin during the Middle Miocene to Late Miocene (15 to 6.5 Ma): (1) the upper Middle Miocene (15 to 11.63 Ma) characterized by a moderate sediment supply and high aggradation margin induced by rapid subsidence, (2) the lower Upper Miocene (10.8 to 10 Ma) as a high sediment supply and low aggradation margin associated with reworked sediments from the uplifted Dolgorae Thrust and (3) the uppermost Miocene (9.2 to 6.5 Ma) characterized by a low sediment supply and low aggradation margin experiencing sediment starvation. A comparison with worldwide continental margins indicated that the Ulleung Basin formed under a relatively low rate of progradation (low sediment supply; 4.79 km/Myr) and a high rate of aggradation (high shelf accommodation; 361.04 m/Myr) condition. The SW margin of the Ulleung Basin provides a unique example of understanding stratigraphic architecture variations under changing stress regimes of back-arc setting (extensional to compressional) and understanding of individual controls that influence margin development.