| dc.description.abstract | The Kenting Plateau is characterized by unusual low relief surfaces that straddle the topographic crest of the northern Manila accretionary prism off southern Taiwan at 400-700 m water depth. Multibeam bathymetric data, reflection seismic data, Acoustic Doppler Current Profiler (ADCP) data, Acoustic Split-Beam Echosounder (EK60) data, surface grab samples, and sediment cores were collected in and around the Plateau to identify evidence of erosion in the Kenting Plateau and understand how the morphological evolution has been influenced by submarine erosion over geological time scales. The most distinctive feature on the Kenting Plateau is a 3 km x 7 km bean-shaped flat elevated platform (Kuroshio Knoll) revealed by multibeam bathymetry. Seismic data show almost no reflections beneath the seafloor and erosional truncations at the seafloor, especially in the Plateau′s eastern half, evidencing widespread erosion. The P-wave velocity of the gravels recovered from the top of the Plateau ranges from 2.2 to 4 km/s. After comparing the velocity with the borehole data from nearby basin the burial depth of the parent rocks was found to be around 2 to 4 km below the seafloor, indicating that the parent rocks have been uplifted and gravels were formed due to erosion of the Plateau. Sand content of the sediment cores decreases away from the Plateau, suggesting that sediment transport is effective in this area with high energy deposition, thereby accumulating coarse sediments on the Plateau and removing fine particles away from it. The presence of a dune field migrating northward of the Plateau, parallel to Kuroshio Current also evidences active sediment transport in the area. The Kuroshio Current velocity observed from the ADCP data is very high, reaches up to 1.8 m/s on top of the Kuroshio Knoll (SE domain). We thus interpret that the observed intense erosion is caused by the Kuroshio Current. The higher sedimentation rate and coarser in grain size during sea level lowstand (20,000-12,000 yrs BP) suggests that the erosion was more intense during the glacial period in compared to that of deglacial period (< 12,000 yrs BP) as seen from the MD97-2145 core.
There is a prevalent development of mud volcanoes and mud diapirs in the northern part of the plateau whereas the southern part is mostly comprised of erosional surfaces with lithified rocks. Numerous mud volcanoes and mud diapirs (>10) are found in the northern domain of the plateau, leading to an irregular topography which is in sharp contrast with the southern domain. The base and top of the mud volcanoes range from 450-900 m and 260-400 m, respectively, below the sea level. A few mud volcano edifices show abrupt slope ranging from ~8 to ~20 degree suggesting the mud flow is active and viscous. EK-60 data demonstrate a 200 m gas flare through the top of one of the mud volcanos, revealing that some of the mud volcanos are active. A few mud volcanos are collapsed and further eroded away by the strong Kuroshio current around the plateau. The formation of mud diapirs and volcanoes in the study area is attributed to the overpressure in sedimentary layers, compressional tectonic forces and gas-bearing fluids. The uplift of the Kenting Plateau is partially due to isostatic rebound caused by sediment removal through erosion and compression of the accretionary wedge. Submarine erosion is predominant throughout the Plateau, and along with the diapiric intrusion, it controls the geomorphology of the Plateau. | en_US |