| 摘要: | 大陸斜坡介於大陸棚與深海平原之間，為陸緣沉積物往深海輸送的必經路徑。然而，上部大陸斜坡水深介於數十公尺至數百公尺，沉積物在傳輸過程中容易受海水面升降的影響產生週期性的變化。台灣西南外海的東南側高屏斜坡，緊鄰高屏峽谷，上部區域連接高屏陸棚，底部則與馬尼拉海溝相連。前人研究顯示，高屏峽谷極上游區域有強烈的底流侵蝕作用，造成峽谷東側邊坡發生海床侵蝕。而該侵蝕作用所搬運之沉積物的動力行為，與高屏陸坡區域受重力影響的沉積物滑移過程，與海水面變化的關係以及與周邊海流的影響為何，過去均未曾探討，因此，本研究使用高解析多頻道火花反射震測法，針對高屏陸坡區域蒐集九條垂直斜坡走向的測線並進行資料分析。
研究結果顯示，研究區域可辨識出15萬年以來的沉積體系，包括13.5萬年的MIS 6冰期侵蝕面、末次冰盛期(LGM, Last Glacial Maximum)侵蝕面、LGM時期以來的低水位時期(LST, Lowstand System Tract)、海進時期(TST, Transgressive System Tract)、高水位時期(HST, Highstand System Tract)層序。小琉球及相關泥貫入體活動導致鄰近邊坡崩塌嚴重，而其東北方的侵蝕作用可往東南延伸至棚坡邊界。此外東南高屏陸坡的沉積物移動可分成兩種方式，其一是透過重力作用由棚坡邊界往下滑移，自水深100公尺處即可開始觀察到沉積物波，可持續延伸至斜坡中段。另一種形式是斜坡下段泥貫入體或泥火山作用導致邊坡不穩定，而產生大型山崩，這些沉積物會直接堆積在斜坡底部。值得注意的是，研究區域的沉積物波以LST層序及HST層序交界面為滑脫面，表示LST時期的陸緣沉積物深埋可導致高孔隙液壓，容易使沉積物沿著該介面滑移，此可為未來對於研究大陸斜坡邊坡不穩定及沉積物移動的重要參考。
;The continental slope is located between the continental shelf and the deep-sea basin, and is the pathway to transport terrestrial sediments to the deep sea. However, the water depth of the upper continental slope ranges from tens of meters to hundreds of meters, and the sediments are susceptible to periodic changes affecting by sea level change during the sediment transportation process. The southeast Gaoping slope, southwestern offshore Taiwan is adjacent to the Gaoping Canyon, the upper area is connected to the Gaoping shelf, and the bottom is headed to the Manila Trench. Previous studies have shown that there is a strong bottom current up to 1 m/s current speed northeast Xiaoliuchiu islet, causing seabed erosion on the eastern slope of the canyon. The dynamic behavior of the sediments transported by this erosion, the sliding process of the gravity driven sediments in the Gaoping continental slope area, the relationship between the sea level changes, and the influence of the surrounding ocean currents have not been discussed. In this study, we applied high resolution marine sparker seismic method to acquire nine seismic profiles across southeast Gaoping slope, constructing seismic sequence stratigraphy framework since 150 ka.
The results show that the study area can be identified seismic sequence systems over the past 150 ka, including the 135 ka MIS 6 glacial erosion event, the last glacial maximum (LGM, Last Glacial Maximum) erosion event, and seismic sequences Lowstand System Tract (LST), Transgressive System Tract (TST), and Highstand System Tract (HST) sequence since LGM period. The mud diapir uplift adjacent to Xiaoliuchiu islet developed serious resent submarine slope failures, and Xiaoliuchiu channel erosion can be extended east toward middle southeast Gaoping shlef. In addition, the sediment movement of the southeast Gaoping slope can be divided into two categories. First is gravity driven sediment wave along the slope. The sediment wave can be observed since -100 meters, and it can be extended to the middle slope. Second is mud diapir and mud volcano activities in the lower slope caused large scale submarine landslide which failure sediments accumulate at the bottom of the slope. It is worth noting that the sediment wave in the study area sliding along a interface between LST sequence and HST sequence indicating high pore fluid pressure of terrestrial sediments within LST may play a key role to surface sediment gliding. |
