台湾海峡北部两侧海阶之研究

海岸阶地的形成是海平面变动、地壳变动或两者共同作用之结果．研究海阶不仅可印证推论古气候、往昔海平面变化及地壳变动状况，更可藉以了解各区域间变动的差异，全盘了解大地构造的意义，同时，小规模的海阶变动，常与地震活动伴生，研究海阶可作为判读地震周期的依据之一，所以，世界各地位于地壳活动带的国家对于海阶的形态与演育过程均作详细的调查及研究．位于台湾海峡北部两侧的台湾西北部以及马祖、金门等海岸地区，都有海阶的分布．透过阶地分布、地形特征与阶序对比，同时，利用世界海阶对比基图找出该地区的地壳隆升率与海阶可能形成的年代，并藉以了解各区域间变动的差异．前述地区的海阶大致上可分成高位与低位2群，高位海阶分布的高度在15～275m之间，上覆红壤层，为晚更新世时期产物；低位海阶分布的范围较小，高度较矮，大部分分布于海滩与高位阶地末端阶崖问，沿着海岸呈带状分布，阶面大多无红壤层覆盖，海拔在10m以下．组成的物质多以砾石及砂为主，属于全新世时期的产物，即近1万年以来全球高海水位时期（第四纪最后一次冰期结束后）所形成．利用海阶对比基图与已有的定年数据，辅以地形地貌及堆积物特征比较，获得各段阶地之平均隆升率，台湾西北部之观音山北部沿海、客雅溪口南岸、后龙溪口南岸3个地区，分别是2．1mm／a、2．2mm／a、2．15mm／a，数值相近，显示该区之地盘隆升率及海平面变动状况大致相同；仅新竹山子顶沿海地盘隆升率较小，为1．4mm／a．此表示，台湾岛的海阶变化不仅受到海平面变动的影响，尚受到区域性地壳隆升的控制．马祖与金门地区的隆升率则分别为1．6mm／a、1．3mm／a，由于该区仅受新华夏断裂构造的控制，因此，其活动的幅度相对而言较台湾为小．

Research of Marine Terraces on the Both Sides of Northern Taiwan Straits

As influenced by eustatic changes and tectonic movements, marine terraces are considered as indicators of regional tectonic, paleo-climate ＆ sea-level variations as well as crust movements. Based on aerial photographic interpretation, field survey and data analysis, this study finds that： 1 ） Classified and correlated by the continuity of altitude and the extension of terrace surface, two types of marine terraces in the study area can be indentified. One is Pleistocene terraces, with heights in the range of 15 - 275 m and being covered with thick laterite. The other belongs to Holocene terraces, the heights of which are mostly below 10 m and mainly distribute along the coastal lowlands, consisting of sand and gravels ; 2） Based on dating, elevation, erosion mode and deposit feature, the uplift rate of marine terraces in Northwestern Taiwan, Matsu area and Kinmen area can reflect regional lectonie activities and sea level variations. The rate on Shinchu coast is 1.4 ram/a, and the rates on the north coast of Kuanyin Voh＇ano, the south coast of Keya river estuary and tile south coast of Houlongriver estuary are 2. 1 mm/a, 2.2 mm/a and 2. 15 mm/a, respectively. The uplift rate on Hsinchu coast is smallest, perhaps being influenced by the distribution of Hsinchu subsidence area. The rates of Matsu area and Kinmen area are 1.6mm/a and 1.3 mm/a. Inlluenced by the New China Tectonic Movements, the movement scale of the study area is smaller than whole Taiwan.