Seismic investigation uncovers formation and spatial distribution of seafloor erosional features on the Changjiang (Yangtze) River subaqueous delta

Abstract

River deltas face erosional challenges driven by global changes and human activities leading to diminished sediment supply. Despite extensive researches on erosional processes within the Changjiang River subaqueous delta (CRSD), there exists a knowledge gap concerning the comprehensive spatial distribution of erosional features throughout the CRSD. This study addresses this gap by utilizing a substantial dataset of high-resolution chirp data to analyze the characteristics, distributions, and stratigraphic terminations of seafloor erosional features within the CRSD. The results unveil an expansive erosion area spanning approximately 2900 km², occurring at depths ranging from 10 to 40 m in the modern CRSD. These erosional features manifest as extensive truncations, low-relief scoured seafloor, and cut-and-fill structures, distributed variably across the CRSD. Particularly noteworthy is the identification of an alignment between the suspended sediment front and a 20 m water depth erosional area along the deltaic coast. Erosion in this area is dominated by truncations, extending ∼ 10 km in width, and followed by scoured (several hundred meters wide and ∼ 1–2 m deep on average) seafloor. Slope gradient also influences erosion, with cut-and-fill structures (2 km wide and around 5 m deep) that we attribute to sediment gravity flows are identified on steeper slopes offshore of North Channel. Beyond the 20 m water depth, extensive truncations spanning approximately 20 km wide and lead to outcrops of older strata. The spatial distribution of erosional features, coupled with river outlets and subsurface structure, suggests joint influences from reduced riverine sediments, estuarine engineering, wave actions, and tidal regimes. These findings emphasize the primary impact of sediment discharge reduction and underscore the collective influence of various anthropological and natural factors in shaping the spatial distribution of erosional features across different water depths in the subaqueous delta. Insights from this study contribute to a deep understanding of erosional processes and the ongoing evolution of erosional degradation in deltaic systems worldwide.