高屏峽谷極上游區域峽谷侵蝕與泥貫入體活動之交互關係研究;Interaction of canyon erosion and mud diapir activity in the uppermost Kaoping submarine canyon

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Title:	高屏峽谷極上游區域峽谷侵蝕與泥貫入體活動之交互關係研究;Interaction of canyon erosion and mud diapir activity in the uppermost Kaoping submarine canyon
Authors:	蔡仲霖;Tsai, Chung-Lin
Contributors:	地球科學學系
Keywords:	高屏峽谷;峽谷溢流;泥貫入體;邊坡滑移
Date:	2019-07-25
Issue Date:	2019-09-03 14:49:00 (UTC+8)
Publisher:	國立中央大學
Abstract:	海底峽谷為陸上沉積物進入深海的主要通道，在沉積物從源到匯的系統中扮演著重要的角色。台灣西南外海的高屏峽谷始於陸上高屏溪，流經高屏陸棚和斜坡最後沒入馬尼拉海溝。每年台灣西南部受到劇烈天氣變化(例如：颱風)帶來的強降雨經由高屏溪將高濃度沉積物帶入高屏峽谷，並在峽谷源頭部分形成濁流或異重流。前人透過傳統反射震測搭配水深地形來研究高屏峽谷整個流域的地形與構造，並認為在峽谷上游的濁流引發邊坡崩塌並形成U型谷的特徵，但由於傳統震測震源較為低頻的限制，對於近海床淺層地層幾乎無解析能力。因此，本研究透過使用較高解析度的電火花放電反射震測法，針對高屏溪出海口至小琉球之間的高屏峽谷極上游，產生濁流的源頭的區域，蒐集二十條電火花反射震測資料並進行資料分析。其資料分析結果顯示，本研究的研究區域根據震測相分析可以大致區分為五種震測相：低水位體系、末次冰期(Last Glacial Maximun; LGM)侵蝕面、海進體系、高水位體系及泥貫入體。其中，低水位體系具有強反射且連續性高向海的進積構造，而海進體系則是強反射且連續性高的水平地層。另外，海進體系與低水位體系間呈現交角不整合，震測反射相為強反射且連續性良好，可推測該不整合面應為末次冰期之侵蝕面。另外，覆蓋於海進體系之上的則是反射強度及連續性均較弱的進積構造，推測應為高水位體系沉積。綜合比較峽谷南北兩側地形及地層構造，可發現相較於峽谷西北側，近小琉球區域峽谷東南側邊坡處於峽谷攻擊面，地形平均較北側低窪約四十公尺，地形呈現U型凹陷，該處地層中的高水位體系完全缺失，僅剩數十公尺薄層海進體系存在，此表示峽谷東南側應長年遭受侵蝕。另外，該處同時可觀察到泥貫入體出露至地表形成泥火山，泥貫入體的活動也使得峽谷南側邊坡易於崩塌。因此，綜合上述觀察，本研究認為在高屏峽谷極上游區域，峽谷西北側應處於穩定堆積環境，而峽谷東南側應長年受峽谷濁流溢流的沖刷下，為侵蝕環境。而泥貫入體引致邊坡崩塌的沉積物亦可能為濁流的來源之一。;As a major pathway of the sediment transportation to deep sea, submarine canyon plays an important role on the source-to-sink, terrestrial-to-marine dispersal system. Kaoping submarine canyon (KPSC) is located on southwestern offshore Taiwan. It originates from the Kaoping River (KPR) mouth through the Kaoping shelf and slope then merges to the northeastern Manila Trench. Because of the dramatic climate change in the southern Taiwan (e.g. strong typhoon triggers flooding or moonson), huge amount of highly concentrated sediments carried by KPR into KPSC may develop turbidity current or hyperpycnal flow in the canyon head. Aithough previous studies using traditional reflective seismic and bathymetry to understand the morphology and structures in KPSC region, and they indicated that slope failures is caused by turbidity current and formed U-shaped valley in the upper canyon. Due to limitation of the seismic source (i.e. central frequency is 50 Hz), near seafloor sedimentary seqences cannot be revealed. We rather used alternative and high resolution marine geophysical exploration method, sparker reflective seismic method in this study. Twenty seismic sections were acquired and analyzed across and prepenticular to the uppermost Kaoping submarine canyon in particular focusing on the area of turbidity current occorence. The results show that five basic standard seismic stratigraphic sequences were identified : (1) Lowstand System Tract (LST); (2) Transgreesive System Tract (TST); (3) Highstand System Tract (HST); (4) Last Glacial Maximun (LGM) uncomformity and (5) Mud diapirism. The LST is characterized high amplitude, continuous and propagating toward to sea, the TST is also high amplitude, continuous but parallel to the seafloor. The LGM is high amplitude and continuous as an angular uncomformity beteen LST and TST. The HST is instead lowest amplitude and dis-continuous amongst the study area. Furthermore, about 40 meters and U-shaped depression was identified in the southern bank of the canyon with respect to the northern bank, HST was gone with thin LST in the southern bank, which indicates a strong and continuous erosion occurred in the south. We suggested that may be the result of canyon overbanking flow erosion. In addition, mud diapirsim also caued slope failure and seafloor depression in the south. The deposits of the slope failure may be one of the sources on turbidity current.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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