Subaqueous delta Sequence Stratigraphy in the western Taiwan: Insights from High-Resolution Seismic Reflection Data

The Zhuoshui River is one of Taiwan’s largest sediment suppliers, and thick subaqueous deposits archive past geological events. To understand variability in the paleoclimate and active fault-slip cycles in the drainage area, subtle stratigraphic signals within these deposits may reveal recent processes relevant to human society. Here we utilize high-resolution sparker seismic data to investigate the subaqueous delta accumulated off Changhua since the Holocene maximum flooding surface (MFS), to establish millennial- and centennial-scale sequence stratigraphy, and to decipher delta evolution and potential controlling factors.

We acquired single-channel sparker data with a dominant frequency of 500 Hz and an initial vertical resolution of ~50 cm, penetrating to a depth of ~100-150 meters below seafloor. After deconvolution, the vertical resolution is improved to ~30 cm, enabling identification of subtle stratigraphic signals. Based on terminations, including toplap and downlap, we integrate (1) subdividing underwater deltaic sediments into several depositional periods, (2) estimating progradation directions and Wheeler diagrams, and (3) demonstrating trajectories of clinoform rollover points to examine spatiotemporal changes in sediment distribution.

The delta deposits can be subdivided into five stratigraphic units bounded by toplap/downlap, and northwestward progradation directions are broadly subparallel to the modern Zhuoshui and Wu River trends, supporting a wave-reworked, river-fed subaqueous delta model. We interpret systematic alongshore shifts of the depocenter as reflecting avulsion-related course changes of the palaeo-Zhuoshui and palaeo-Wu rivers, which caused north–south migration of sediment delivery points. Wheeler-diagram patterns and rollover-point trajectories suggest sequence-scale changes approximately ~2 kyr and ~centennial timescales in average integrated onshore radiocarbon chronologies, potentially linked to climate variability and episodic onshore fault activity. These findings provide new evidence linking land–sea sediment-routing systems and offer a framework for disentangling the complex couplings between tectonics, climate, and surface processes in high-sediment-yield margins.

 

keywords

subaqueous delta; sequence stratigraphy; high-resolution seismic reflection; Taiwan Strait