11:30 AM - 11:45 AM
[HDS11-09] A Study on Paleoenvironmental Changes Around DP Lagoon
Keywords:DP Lagoon, Paleoenvironmental changes, Ka-teng Harbor, X-ray fluorescence (XRF) analysis, AMS radiocarbon datin
The "abrupt rise of water in Ka-teng Harbor", recorded in the Taiwan Gazetteer (Taiwan Caifangce), has been suggested as a tsunami event in 1781, possibly triggered by an earthquake or a submarine landslide. This record has been considered the only credible historical evidence of a tsunami in southwestern Taiwan. However, no geological evidence currently supports this claim.
To investigate the authenticity of this record, this study drilled eight sediment cores, each approximately 12 meters deep, in the southeastern part of Dapeng (DP) Lagoon, in areas that were reclaimed before the 20th century. Six cores were collected from inland areas, while two were obtained from the barrier island. The cores were further classified into lithofacies units based on sedimentary characteristics and X-ray fluorescence (XRF) analysis. Additionally, selected samples were sent for AMS radiocarbon (14C) dating to establish age models for the cores.
The results reveal that the six inland cores primarily contain muddy sediments interspersed with several sand layers, whereas the two cores from the barrier island are mainly composed of sand. The basal sediments of the inland cores are generally dated to around 1.5 ka, with sandy layers consistently found in deposits younger than 0.3 ka. The presence of these coarser grains within an otherwise stable depositional environment suggests high-energy events, particularly those corresponding to the "abrupt rise of water in Ka-teng Harbor". However, these sandy deposits consist of fine to very fine sand with yellowish mottled textures and lack marine indicators such as shell fragments, suggesting a fluvial rather than marine origin.
Therefore, we conclude that the sandy layers at the top of the six inland cores likely represent geological records of extensive flooding and river discharge directly into DP Lagoon following river diversions between the 1700s and 1800s. This conclusion is further supported by Qing Dynasty maps.
To investigate the authenticity of this record, this study drilled eight sediment cores, each approximately 12 meters deep, in the southeastern part of Dapeng (DP) Lagoon, in areas that were reclaimed before the 20th century. Six cores were collected from inland areas, while two were obtained from the barrier island. The cores were further classified into lithofacies units based on sedimentary characteristics and X-ray fluorescence (XRF) analysis. Additionally, selected samples were sent for AMS radiocarbon (14C) dating to establish age models for the cores.
The results reveal that the six inland cores primarily contain muddy sediments interspersed with several sand layers, whereas the two cores from the barrier island are mainly composed of sand. The basal sediments of the inland cores are generally dated to around 1.5 ka, with sandy layers consistently found in deposits younger than 0.3 ka. The presence of these coarser grains within an otherwise stable depositional environment suggests high-energy events, particularly those corresponding to the "abrupt rise of water in Ka-teng Harbor". However, these sandy deposits consist of fine to very fine sand with yellowish mottled textures and lack marine indicators such as shell fragments, suggesting a fluvial rather than marine origin.
Therefore, we conclude that the sandy layers at the top of the six inland cores likely represent geological records of extensive flooding and river discharge directly into DP Lagoon following river diversions between the 1700s and 1800s. This conclusion is further supported by Qing Dynasty maps.