56-8 Erosional modulation of tectonically-controlled shelf-edge migration: Insights from Middle Miocene clinoform successions, Ulleung Basin, East Sea (Japan Sea), Korea

Abstract:

Shelf-edge evolution in tectonically active basins reflects complex interactions between structural deformation, sea-level change, and sedimentary processes. This study investigates Middle Miocene clinoform successions (14.00-12.50 Ma) in the southwestern Ulleung Basin, East Sea, using 3D seismic data to examine how erosional processes modulate structurally-controlled shelf-edge migration patterns. Eight clinothems were identified, showing cyclic alternations between sigmoidal types (ascending trajectories) and thin-top sigmoidal/oblique types (flat-to-descending trajectories), possibly reflecting high-frequency relative sea-level cycles (4th-5th order). A reverse fault system in the southeast of the study area (DS A) formed monocline structure that created differential accommodation along strike. The structure caused reduced accommodation space favoring oblique clinothems in the uplifted proximal area and maintained more space resulting in thin-top sigmoidal clinothems distally. Conventional tectono-stratigraphic models often predict that such uplift enhances shelf-edge progradation, producing arcuate shelf-edge geometry. However, shelf-edge migration remained relatively linear without enhanced shelf-edge migration toward the reverse fault system, contradicting these established models. The interaction between the structural deformation and erosional processes on the shelf margins explains these shelf-edge behaviours.

The structural deformation (DS A) that controlled clinoform type variation also induced slope oversteepening that promoted erosional features at shelf margins within 20 km of this structure. These erosional depressions formed atop sigmoidal clinothems during early stage of sea-level fall, creating additional accommodation at the shelf margin that moderated shelf-edge advance. This "erosional modulation" process represents a compensatory mechanism where uplift-induced oversteepening creates preferential erosion sites that generate offsetting accommodation, preventing the expected translation of structural deformation into margin architecture. The recurrence of this process across multiple stratigraphic cycles suggests that erosional modulation operates as a persistent architectural control rather than independent random events. These findings provide new insights into how erosional processes can modulate shelf-edge evolution, particularly in tectonically active settings, complementing traditional models that assume direct translation of structural deformation into margin architecture.

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