中国东部沿海更新世末期以来海陆变迁的初步认识

PRELIMINARY RECOGNITION OF SEA AND LAND CHANGES ALONG THE EAST COAST OF CHINA SINCE THE TERMINAL PLEISTOCENS

更新世末期以来,中国东部沿海地区经历了海进、海退和相对稳定三个阶段。中全新世中期为海侵鼎盛时期,其海面较现今高2—5m。全新世冰后期是玉木(大理)冰期中的间冰阶,自晚全新世以来,气候开始向新的冰阶缓慢过渡。由CO_2增加所导致的“温室效应”虽然可以减缓这一进程,但目前还不能改变气候发展的自然规律。关于海平面将普通上升5m的预测,尚缺乏令人信服的证据。今后一个时期内,中国东部区域海面和岸线仍将继续保持相对稳定状态,但局部变化将十分明显而频繁,渤海湾西岸等地区,存在着海侵威胁。

Since the therminal Pleistocene, the sea level and coastline along the eastern coast of China have changed greatly. According to stratigraphic, geomorphological and paleontological analyses, the culmination of the Wurm (Dali) glacial stage occurred about 15000a. ago at the end of Pleistocene, when in eastern China sea level was 150-160m lower than the present one and the coast lay on the margin of the present continental shelf. After wards, as the climate got warmer, the region entered the post-glacial stage, when the sea level rose and transgression occurred. In the early Holo-cene, the sea level rose drastically and the sea rapidly invaded the land in the west, and reached the present coast. In the middle part of the Middle Holocene, the climate was warm and humid, the sea level was 2-5m higher than that of today and the transgression reached a climax, with the coastline migrated further inland an far as about 150km from the original one. After the Middle Holocene, the climate became cooler, the rea level slowly declined, accompained by intermittent retrogression. Since the Late Holocene, the sea level has fluctuated to a limited extent and the coast has been basically stable.The sea level fluctuation and marine transgression and regression were results of combined processes of many factors. Apart from that of glacial eustacy caused by the climatic changes, the other factors were the rather local crust rise and fall and sedimentation on land and adjacent sea floors, and also the influence of local isostatic adjustment and human activities. Of these, only the glacio-eustatism was of worldwide and secular nature, which controlled the main process of the eustatic changes, while others, including those related to tectono-eustatism and sedimento-eustatism, only determined the concrete changes in different periods and different areas.In the Holocene post-glacial stage corresponding to the third intergla-cial stage of the Wurm glaciation, its warm cutmination period was in theMiddle Holocene. Since the beginning of Late Holocene, the climate passed to the relatively cold fourth interglacial stage. Althought it is possible that the 'greenhouse effect' due to CO2 increase will interfere with this stage of cooling of the climate, it seems that such an effect cannot basically change the natural law of the climatic development. Hence the inference, that the global sea level will rise to great extent in several decades,is lack of enough evidence. It is likely that the worldwide sea level will, in the main, remain relatively stable within a certain period. The writers hold that there is little possibility that the eastern coast of China will advance or retreat on a large scale, yet various local changes will be apparent and frequent. For instance, there is a severe threat of transgression on the west coast of the Bohai Bay.