| 摘要: | 高屏峽谷位於台灣西南海域，由高屏溪供給大量的沉積物，並作為沉積物的重要通道將其運輸至馬尼拉海溝。陸源沉積物在峽谷中透過濁流的形式向下游移動，而本研究區域高屏峽谷源頭區為陸源沉積物入海形成濁流的源頭區，在頻繁的濁流事件與深部的泥貫入體活動的雙重影響下，形成豐富且易變的海床與地層形貌。本研究利用16條高解析底拖側掃聲納影像與底質剖面，以及3條高解析電火花反射震測剖面，經過資料處理後配合鄰近區域中的鑽井資料進行近一萬年以來近海床層面解釋，結果顯示峽谷西岸區域可辨識出地層Sw1至Sw9層，以及峽谷東岸區域可辨識出地層Se1至Se8層。經過高解析底質剖面、側掃聲納與電火花反射震測資料並與前人資料綜合分析後，本研究發現儘管今日高屏溪擁有最高的沉積物供應量，過去數千年以來古東港溪流域才是主要的沉積物供應源，並且透過豐富的峽谷支流往高屏峽谷主流輸送沉積物。此外，近岸的近海床砂質地層均可觀察到大規模振幅弱化特徵，此可能為透水層中的地層流體影像，即可能與屏東平原海水入侵或地下水往外海輸送有關。此外，在距今八千年前高屏峽谷西岸曾受到海退期的粗顆粒沉積物溢流侵蝕形成兩條古水道，現今已被沉積物填滿。峽谷西側上拱的泥貫入體造成線型的地形落差也間接導致該古水道的形成。最後，區域的地層中與海床上可辨識出大量的流體相關構造，推測可能為自生碳酸鹽沉積物、泥火山、噴氣、地層間的流體填充、泥貫入體等等，應與區域深部的泥貫入體所提供的流體物質有關。;As an important conduit of sediment transportation in the southwest offshore Taiwan, Gaoping submarine canyon (GPSC) receives a huge amount of terrestrial sediment from the Gaoping river, which transports down to the Manila Trench. The sediment in the GPSC moves in the form of turbidity currents. The study area locates at the head of GPSC, source location of turbidity current showing the most vigorous turbidity current activity compared to the other parts of the canyon. Due to turbidity current erosion and mud diapirism intrusion, the geological structures and seafloor morphology are characterized by strong diversity and variability. Three high resolution sparker seismic profiles and sixteen deep-towed sub-buttom profiles, accompanied by side-scan sonar images were used in this study. After data processing, the sub-bottom profiler (SBP) sections were tied to wells close to coast, identifying the nine geological strata (sequences Sw1 to Sw9) west bank of GPSC and another eight strata (sequences Se1 to Se8) on the east bank.
Integration analysis between high resolution deep towed SBP, side-scan sonar and sparker seismic data with previous hydrogeological wells, we concluded that the paleo-Donggang river could be the dominant sediment supplier for the past thousands of years, despite the Gaoping river being the main one currently. In addition, the sediment could be transported through the canyon by both main canyon and tributaries on the east bank of the GPSC. Moreover, seismic acoustic blanking zones observed in the profiles near the coast could suggest sediment fluid accumulation in the aquifer strata, which may act as a conduit or channel for the seawater and ground water exchange near the coast of Pingtung Plain. On the west bank of the GPSC, two paleo-channels were formed by the erosion caused by coarse-grained sediment during the sea level regression approximately eight thousand years ago. The uplifting of mud diapirism in the area could generate linear seafloor relief and indirectly facilitate the erosion of the paleo-channels. Subsequently, the paleo-channels were filled up later. Additionally, many structures associated with sediment fluid were observed in the seismic profiles and side-scan sonar images. These structures are probably the authigenic carbonate, mud volcanos, mud diapirs, gas plumes, sediment fluid accumulation, etc., all of which could be related to the fluid supplied by mud diapirs in the depths. |
