涠洲岛地貌与第四纪地质特征

FEATURES OF GEOMORPHY AND QUATERNARY GEOLOGY OF THE WEIZHOU ISLAND

涠洲岛是第四纪玄武岩岩浆喷发时在水下堆积而形成的。该岛构造上受东北、西北、东南向断裂的控制,地形南高北低.据分析,南湾是本岛南部被侵蚀破坏后的古火山口残迹,另一火山口位于岛西横路村西北。岛屿地貌特征为南侵北堆,南部从石盘滩向南绕南湾港至西岸海蚀地貌比较发育,常见的有海蚀崖、海蚀洞、海蚀柱、海蚀平台等.北端从横岭向西北转西南到后背塘,海成沙堤十分发育。沙堤呈牛轭状分布,长71cm,宽100～450m,按形态、结构把沙堤分新、老沙堤,老沙堤高6～12m,由于长期吹扬作用,已改变原状,形成凹凸不平砂丘;新沙堤内缘与老沙堤接触且覆盖于老沙堤之上.高2～4m.岛的沿岸珊瑚岸礁相当发育,特别是在北、东部发育最好,南、西部较差.珊瑚岸礁最重要特征是礁源碳酸盐和陆源碎屑的混合沉积作用.其珊瑚礁的形成于3100年前。涠洲岛出露的地层最老的是玄武岩,主要分布于东北海滩,北部及南部沿岸零星露头。其次为火山碎屑岩,火山碎屑岩构成岛屿主体。本岛自第四纪以来、火山活动经历过三个喷发旋回、五次喷发。

The Weizhou Island is piled up under the water when Quaternary basalt magma gushed out The structure of the island is controlled by the faults in direction of NE and SW-SE. Southern part of the island is high and northern low. According to investigation Nanwan Bay is a destroyed andentvolcanic crater. There is another andent crater in northwest of Heng Lu Shan village. The erosion in the South and piling-up in north are obviousgeomorphic features. In the south there are eroded cliffs, cavities, pillars and platforms. In the north shore from Henling to Houbeitang, sand bars are well developed, distributed as a bend, 7km long and 0.1-0.45km wide. Based on the shape and structure, sand bars can be divided into two kinds: old or new ones, the former ones are from 6 to 12 meters high and deformed into some uneven dunes because of the long-period wind blowing. But the new ones, from 2 to 4 meters high, their inner margins are merged with old dunes, and even cover on them. The coral reefs are better developed in northeast, but less in southwest. The mixing accumulation of fringing reef carbonates and terrigenous clastics is important feature of the coral fringing. The coral fringing reef was formed 3100 years ago. In Weizhou Island, the oldest rock is basalt, which distributes mainly on northeast sea shore. The volcanic clastic rock is little younger than the basalt rock. It composes the main part of the island The volcanic activities of this island have been taking place during Quaternary in three cycles and five gushes.