East–west contrasts in Holocene coastal geomorphic evolution of the Nakdong River delta, South Korea

This study examines Holocene sea-level rise and associated coastal and estuarine geomorphic evolution of the Nakdong River delta, South Korea, with a particular focus on east–west variations in depositional environments. Previous studies have largely reconstructed delta development based on north–south-oriented sediment cores, implicitly assuming along-axis uniformity. However, the Nakdong River estuary is characterized by an asymmetrical incised-valley morphology that extends farther eastward, suggesting spatially heterogeneous geomorphic responses to Holocene transgression and delta progradation. To address this gap, we analyzed sediment cores collected along an east–west transect across the estuarine valley, integrating chronological constraints and detailed sedimentary facies analysis. Preliminary results reveal a marked contrast in Holocene geomorphic evolution between the two sides of the valley. Thick Pleistocene deposits persist in the western valley, indicating limited accommodation creation, whereas early Holocene inundation and sediment accumulation commenced earlier in the eastern valley. By ~7 ka, marine influence had expanded across the entire valley, reflecting regional sea-level rise. Notably, prodelta and delta-front facies indicative of active delta progradation and shoreline advance are restricted to the eastern valley, suggesting preferential delta growth controlled by inherited valley morphology. In contrast, the western valley is dominated by tidal-flat and salt-marsh facies, implying a geomorphic setting characterized by lateral sediment trapping and restricted shoreline progradation. These east–west contrasts highlight the importance of valley-scale geomorphology in modulating coastal response to Holocene sea-level rise. This study provides new insights into the spatial variability of deltaic geomorphic evolution in a tide-influenced estuary and contributes to a broader understanding of Holocene coastal landscape development in East Asian river deltas.