Modern Sedimentary Mechanisms and Evolution of Extreme Event Layers Offshore Southwestern Taiwan

Taiwan is located in the western Pacific typhoon corridor and the Pacific Ring of Fire, where typhoons and earthquakes frequently happen, making submarine geohazards prone to occur. As the second longest river in Taiwan, the annual sediment load of the Gaoping River averages approximately 35.61 million tons, making it the dominant contributor of terrestrial sediments offshore southwestern Taiwan. Su et al. (2018) pointed out that the sedimentation rate in most areas offshore southwestern Taiwan is less than 0.5 cm/year, and the upper continental slope in the northern part is relatively more stable compared to the southern part. Natural disasters significantly influence sediment distribution and sedimentation processes off the southwestern Taiwan. In 2005, Typhoon Haitang caused heavy rainfall, leading to the rapid transport of large amounts of suspended materials from the Gaoping River to the offshore area of southwestern Taiwan. Based on the radionuclides data published by Huh et al. (2009), a distinct Typhoon Haitang event layer can be observed, and the high-activity layer associated with the 1963 global fallout can also be identified. In this study, we intend to integrate the findings of Huh et al. (2009) regarding the application of radionuclides with 13 box core samples collected in 2023 from the same locations (the shelf and slope areas on the northern and southern sides of the Gaoping Canyon). We aim to utilize the multi-tracer approach and grain size distribution to assess modern sedimentary event records, sediment transport pathways, and potential disaster risks offshore southwestern Taiwan. Additionally, we plan to analyze the correlation of sedimentary sequences across different coring sites, as well as their temporal variations in sedimentary records at the same site. The current results indicate a positive correlation between sediment porosity and water depth. Grain size analysis shows that the median grain size and sorting decrease as water depth increases. The higher sand content observed on the northern shelf is due to northward coastal currents and overflow effects at the canyon head. Future research will focus on investigating hydrodynamic differences across various layers to better understand sedimentary dynamics over the past two decades. This study will further examine how bioturbation affects radioactive dating results, which will help to establish a more accurate chronological model for sedimentary records.

 

References

Chih-An Huh, Hui-Ling Lin, Saulwood Lin, Ya-Wen Huang, Modern     accumulation rates and a budget of sediment off the Gaoping (Kaoping) River, SW Taiwan: A tidal and flood dominated depositional environment around a submarine canyon, Journal of Marine Systems, Volume 76, Issue 4, 2009, Pages 405-416, ISSN 0924-7963, https://doi.org/10.1016/j.jmarsys.2007.07.009

Su, C.-C., S.-T. Hsu, H.-H. Hsu, J.-Y. Lin, and J.-J. Dong, 2018: Sedimentological characteristics and seafloor failure offshore SW Taiwan. Terr. Atmos. Ocean. Sci., 29, 65-76, doi: 10.3319/TAO.2017.06.21.01