台灣西南外海增積岩體高屏峽谷之地形與沉積特徵;Morpho-sedimentary features of the Gaoping Canyon System in the accretionary wedge off SW Taiwan

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Title:	台灣西南外海增積岩體高屏峽谷之地形與沉積特徵;Morpho-sedimentary features of the Gaoping Canyon System in the accretionary wedge off SW Taiwan
Authors:	張立;Chang, Li
Contributors:	地球科學學系
Keywords:	高屏峽谷;高屏斜坡;濁流;異重流;沉積物;Gaoping Canyon;Gaoping Slope;Turbidity Current;Hyperpycnal Flow;Sediment
Date:	2021-07-09
Issue Date:	2021-12-07 11:44:58 (UTC+8)
Publisher:	國立中央大學
Abstract:	高屏海底峽谷源頭與高屏溪出海口相連。發生颱風或地震事件時，高屏溪帶來的陸源沉積物以及地震引發的海底山崩，都可能形成濁流，將沉積物傳輸至深海。未發生颱風或地震時，沉積物從河口向外散佈並暫時堆積在高屏陸棚、上部高屏斜坡與高屏峽谷源頭內。地震、颱風事件、或是海床氣體逸出造成的擾動，皆有可能導致沉積物再次懸浮或觸發海底山崩、形成濁流，將沉積物向下部斜坡及高屏峽谷下游輸送。除了有豐沛的沉積物來源，活躍的馬尼拉增積岩體造成此區複雜的地形，在沉積物傳輸與高屏峽谷演育上也扮演了重要的角色。本研究使用多音束水深資料、沉積物岩心、反射震測剖面以及海床底質剖面，探討高屏峽谷沿線的地形、沉積物分佈以及構造活動之間的關係。在高屏溪出海口附近的峽谷源頭所採的岩心中，觀察到因陸上洪氾事件所形成的異重流沉積物。研究資料顯示，濁流在上游主要受限於高屏峽谷內，位於峽谷兩側的砂質沉積物比例分布主要受深度控制。高屏峽谷中游的路徑筆直，峽谷中游上段主要是搬運的環境。峽谷西側平台的沉積物以泥質為主，其來源主要為上部高屏斜坡的濁流所產生之霧濁層；濁流在中游主要仍受限於高屏峽谷內，只有南側平台南端可能有溢流現象。高屏峽谷下游的峽谷路徑蜿蜒，下游上部在地形與震測剖面中可見此區峽谷兩側具有向上堆積的「堤岸」特徵，且曲流狀峽谷經歷側向遷移。濁流在此處較容易溢出峽谷堤岸，沉積於峽谷兩側的深海盆地，峽谷兩側有大量的海底山崩崖；峽谷西側15公里外、高出峽谷周圍深海盆地170公尺的海脊上的岩心中也含有濁流事件層。下游下部在一系列隆起的海脊間發育，一開始蜿蜒於海脊之間，接著穿過數個海脊，最後與澎湖峽谷一同匯入馬尼拉海溝。;The head of Gaoping Submarine Canyon (GPC) is connected with the river mouth of the Gaoping River. When extreme events such as typhoons and earthquakes, river floods and submarine landslides around the GPC may generate turbidity currents and transport sediments to the downstream of GPC and the deep South China Sea. The terrestrial sediments will spread from the river mouth and temporarily deposited on the Gaoping Shelf, upper Gaoping Continental Slope or at the head of GPC during fair weather conditions. Extreme events or the gas emission on the sea bed may resuspend the sediments or even trigger submarine landslides and turbidity currents move downward of the Gaoping Slope, and/or downstream of GPC. Nepheloid layers can also be generated and transport downward at the same time. Aside from the abundant sediment supply, the tectonic activities of the Manila accretional wedge form the complex topography in this area, which plays an important role in affecting sediment dispersal and the development of GPC. In this research, multi-beam bathymetry data, sediment cores, multi-channel seismic profiles and sub-bottom profiles are applied to analyze the relationship among the topography, sediment distribution and tectonic activities along the GPC. The upper reach of GPC is a meandered channel without depositional levee. We call the margin of the canyon as the “canyon margin”. Hyperpycnites generated after the onshore floods were recorded at the head of GPC. After passing through the Xiaoliuqiu Bend, GPC develops in between the mud-diapiric ridges. Turbidity currents in the upper reach is restricted inside the canyon. The canyon course of the middle reach is straight, the upper-middle reach is interpreted as erosive setting with bypassing turbidity currents. The platform on the west of the middle reach is dominated by muddy sediments, the turbidity currents are mainly restricted in the canyon as well. The only possible point of overspill is the south margin of the platform on the south of the middle reach. The meandered lower reach consists of two segments. The upper-lower reach has depositional levees and experienced lateral channel migration. A lot of slump scarps scattered along both sides of the canyon. The height of canyon walls is relatively low, turbidity currents spill over the levees easily and deposited in the slope basins. Turbidites are found on a submarine ridge 170 meters above the surrounding seafloor and 15 kilometers away from the canyon margin. The lower-lower reach develops through a series of submarine ridges, initially meandered between two ridges, then cuts through few ridges and finally merges with the Manila Trench.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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