台灣西南海域高屏峽谷下游段之沉積物分布與峽谷演進

Abstract

過去研究對於高屏海底峽谷整個區域已經有一定程度的了解，然而對於下游部分是否有海底沖積扇以及峽谷下游曲流的環境和演進尚未有明確的結果和解釋。本研究目的在於提供過去較缺乏資料的下游段新的地質資訊，並且驗證海底扇的存在與否以及建立一個曲流可能的演進過程。 本研究使用多頻道反射震測資料來分析，運用「層序分析」為主要解釋震測剖面資料的觀念，觀察各震測相特徵並且辨識層序邊界，發現本研究區域於峽谷下游頭部存在一海底扇，主要可分成「水道堆積物」、「溢堤堆積物」、以及「峽谷底部堆積物」3種沉積物，並且可分成4個時期討論。藉由沉積物於各個時期沉積的情形，推論包括前人指出的褶皺「R3.4」(Lin et al., 2008)以及本研究新發現的「褶皺A」和「褶皺B」的活動時期，加以由震測剖面上觀察到古峽谷的分布情形，進一步推論峽谷與水道於各個時期的行經路徑。 沉積物由陸地經由高屏海底峽谷輸送，於高屏海底峽谷下游堆積形成海底扇，峽谷兩側斜坡盆地將沉積物限制於其中，峽谷本身也受構造影響而以曲流方式行進，因此海底扇形貌上與一般情形略有不同。

The Kaoping Submarine Canyon offshore southwestern Taiwan has been widely studied, however, the submarine fan distribution and the cause of canyon meandering of the Kaoping Submarine Canyon lower section are still unclear. The purposes of this study are to investigate the sediment distribution of the submarine fan and to develop a model for canyon meandering process. In this study, multi-channel seismic reflection data are analyzed by using the “Sequence analysis” approach. The submarine fan sediment can be classified into 3 types: “channel deposits”, “overbanking deposits”, and “Canyon thalweg”. We have identified 4 deposition stages from seismic sequence analysis. The active stages of Fold R3.4, Fold A, and Fold B have all affected the development of the submarine fan. Further with analyzing the paleo-canyon and paleo-channle on the seismic profiles, evolution of the canyon and channel has been established in this study. Sediments has been transported from land to deep sea and deposited at lower section Kaoping Submarine Canyon. Two slope basins confine the overbanking sediments. Canyon is meandering due to the activities of Folding. Therefore, the shape of submarine fan is different from general cases.