等深流岩顧名思義就是沉積物受等深水流影響，而沿著等深線方向持續堆積沈積物。等深流岩的分佈與近海床底流的流向與流速有很大的關係。底流流向會影響到等深流岩沉積物的漂移型態分布，底流流速則會影響到等深流岩的岩性以及海床形貌。透過漂移型態以及海床形貌可以初步了解等深流岩沉積系統的分布。綜觀全球等深流岩之研究，過去幾十年來主要集中在大西洋的被動大陸邊緣，但台灣附近海域過去幾乎沒有等深流岩的研究。然而，在台灣東部縱谷北端海域由米崙台地向海域延伸，地形特徵上有花蓮海脊、花蓮峽谷、新城海脊，此些區域有陸域上的河流如美崙溪及立霧溪的流入。美崙溪由於米崙台地之抬升而往南流至米崙台地南段出海，立霧溪出海口則是連接花蓮峽谷上游。因此，從米崙台地北端延伸入海的花蓮海脊上的沉積物來源可以排除掉陸源的沉積物。此外，區域內同時受黑潮影響，而花蓮海脊頂部的地形也是小於水深300公尺，因此此區域會受黑潮的影響而造成沉積物的侵蝕和搬運而成等深流岩，也成為研究等深流岩之絕佳研究場域。從既有的底質剖面以及高解析反射震測剖面可以發現花蓮海脊北段淺部地層具有等深流岩分開飄移（separated drift）的特徵。而花蓮海脊南段的海床海床表面上有沙溝(sand furrow)之線型特徵。因此，本計畫希望透過海洋地球物理的方法，進一步研究花蓮海脊上等深流岩的分佈，及其沉積物漂移型態和海床表面特徵，藉以了解等深流岩沉積系統之機制。 ;The sediments deposits associated with persistent contour current named contourites. Bottom current pathway and velocity significantly affect the contourite deposition. Bottom current pathway dominates the sediments drift morphology and current velocity changes the lithology and the bed form. Therefore, the sediments drift and the bed form investigation could help understand a contourite deposition system. In the past decades the contourite studies were generally around the passive continental margin of the Atlantic Ocean. Nevertheless, the contourite system around the offshore area of Taiwan was rarely studied, although there is an obviously Kuroshio off eastern Taiwan In the offshore area of the northernmost Lontitudinal Valley, the geological units from south to north consist of Hualien Ridge, the upper reach of the Hualien Canyon and Hsincheng Ridge. The main rivers onshore are Meilun River and Liwu River. Meilun River connected to the submarine canyon to the south of the Milun Tableland while Liwu River transported the sediments into the Hualien Canyon directly. Therefore, the source for the sediments on the Hualien Ridge, which extends from the northern the Milun Tableland, could avoid the terrigenous sediments from Central Range. In contrast, Kuroshio current passes over the Hualien Ridge and the Hualien Ridge is only around 300 m deep. The Hualien Ridge thus provide an excellent location for the contourite study. In the northern Hualien Ridge, we could find the separated drifts based on the sub-bottom profiler and high-resolution seismic profiles. In the southern Hualien, we could observe sand furrow linear structures related to the bottom current based on the side-scan sonar image and the high resolution bathymetric data. In this project we will investigate the sediments drift morphology and bed form on the Hualien Ridge. By using sparker seismic profiles, sub-bottom profiles and side-scan sonar images, we can understand the system of coutourite off eastern Taiwan and the erosion and deposition system related to the mechanism of contourite formation.
