第四纪以来福建海坛岛北部软质海蚀崖演化过程研究

Geomorphic Evolution of Soft-cliffs since the Quaternary on the North Coast of Haitan Island,Fujian Province

通过对福建海坛岛北部海岸带镜沙、流水等地软质海蚀崖剖面结构与构造的野外观测、分析粒度特征、磁学特征,并参考前人有关南方第四纪年代地层学的研究成果,对海蚀崖地貌演化过程进行了初步研究。结果表明:在末次间冰期的干热气候背景下,在镜沙海岸带发育了风成老红砂沉积,在冰后期气候转型阶段发育了山前冲洪积层,覆盖在剥蚀夷平的老红砂沉积之上,在冰后期以来的海平面波动上升的背景下,波浪、潮汐等海岸动力的长期侵蚀造成海岸线不断向南侵蚀后退,逐渐演变成目前的海蚀崖地貌景观。第四纪早更新世海平面的升降交替,在今流水镇一带堆积了浅海相和陆相交互沉积,构成流水镇连岛沙坝的地貌基础。中更新世晚期以来转变为陆上沉积环境,在历次间冰期干热气候背景下发育了多层老红砂沉积,并在晚冰期以来海平面波动性上升过程中,侵蚀形成流水镇北部的海蚀崖,以波浪-风沙侵蚀作用为主,强烈的波浪侵蚀作用使海蚀崖不断向南侵蚀后退。总体上看,第四纪以来海坛岛北部海岸软质海蚀崖演变过程是由地壳运动、气候变迁、海平面变化、波浪作用等内外营力所驱动的。

In this paper, on the basis of field observation of profile texture and structure of soft-cliff and granulometric and magnetic analysis, and referring to the achievements of Quaternary chronos-tratigraphy in southern China, we focused on judging the geomorphic evolution process of soft-cliffs in Jingsha （JS） and Liushui （LS） on the north coast of Haitan Island of Fujian Province. The results showed in the early geomorphic evolution of soft-cliffs in JS, development of the aeolian ＂Old Red Sand＂ deposits under the background of the hot dry climate in the Last interglacial. Jun Mountain subjected to intense physical weathering and produced a large number of clastic rock under Last Glacial Maximum （LGM） of the cold dry climate, developed piedmont diluvial layer and covered the base level of denudation of ＂Old Red Sand＂ during the climate transition phase of postglacial period. Long- term erosion of wave, tidal power causing shoreline erosion back to the south under the background of rising sea level fluctuations since postglacial, developed into present soft-cliff landscape. The soft-cliff in LS recorded the rise and fall of sea-level alternately during early Pleistocene of Quaternary, LS deposited alternately by shallow sea and continental sediment and composed geomorphic basis of the tiebar. Converted continental sedimentary environment since the late mid-pleistocene and development of multi layers of ＂Old Red Sand＂ deposits under the background of the hot dry climate. LS also developed into soft-cliff landscape under the background of rising sea level fluctuations since late glacial epoch. The geomorphic evolution process of modern times in LS was mainly wave and sand erosion effect and the shoreline erosion back to the south under strong wave erosion. Although the difference of early sedimentary formation process was obvious between JS and LS soft-cliff, the geomorphic evolution process of soft-cliff was similar under the background of rising sea level fluctuations since postglacial. In general, the evolution process of soft-cliff on the north coast of Haitan Island was driven by internal and external force of crustal movement, climatic change, sea-level change and wave action.