摘要
杭州西湖三面环山,东接沿海平原,不仅风景秀丽驰名中外,而且其特殊的地貌形态吸引着科学工作者的注意。自从竺可桢教授指出西湖按成因类型属于“礁湖”(即泻湖)以来,已有不少文章从地貌角度论及西湖的由来,大多认为它是由海湾—泻湖演变而成。然而,能为西湖形成和演变历史提供确凿证据的,还是西湖的地层及其中所含的化石。为此,我们对西湖湖滨两个钻孔和杭州市区一个钻孔进行了微体古生物分析,结果证明:在第四纪期间,西湖经历了山间谷地—淡水湖—早泻湖—海湾—晚泻湖—淡水湖的演变过程。今日的西湖,是冰后期海面上升与河口泥沙堆积作用的产物。
Unconsolidated sediments more than 30 m in thickness were penetrated by two drilling bores on the shores of"West Lake,Hangzhou city,Zhejiang Province.Synthesized quantitative micropaleontologieal analysis of these sediments shows that they contain abundant foraminiferids,ostracods,molluscs,thecamoebians,echinoid spines,diatoms,oospore membranes of Chara and some shieldform fossils.Based on the faunal composition,diversity H(S)of foraminiferids,as well as sedimentological and palynolo-gical data,it is concluded that the West Lake was formed as a result of postglacial transgression,and five stages of its geologic history are recognized as follows:1.Mountain valley and fresh-water ponds stage.Pleistocene.No fossils were found,(fig.4a)2.Early lagoon stage.Early Holocene(Praeboreal and Boreal phases,7,000-10,000 years B.P.).With euryhaline foranis only.Diversity H(S)=0.4-0.5.Brackish water to oligohaline(fig.4b).Two fossil horizons may be established:(1)Corbicula japonica sandaiformis-Ammonia tepida-Sinocytheridea horizon;(2)A.tepida-Haplophragmoides canariensis horizon.3.Bay stage.Middle Holocene(Atlantic and Sub-boreal phases,about 7,000-2,500 years B.P.).With both brackish-water and.small-sized open-sea forams.H(S)>1.Brackish water(fig.4c).Four fossil horizons:(1)Ammonia tepida-Cribrononion spp.horizon;(2)A.tepida-Trochammina inflata horizon;(3)T.inflata horizon;(4)A.tepida-Pseudononionella variabilis horizon.4.Late lagoon stage.Late Holocene(early Sub-atlantic phase,about 2,500-1,500.years B.P.).The passage into sea was gradually barred by estuary deposition(fig.4d).Foraminiferal fauna consists of two species only:Ammonia tepida and Elphidium nakanokawaense.Diversity H(S)=0.6.Brackish water with very low salinity.5.Present West Lake stage.Late Holoeene(late Sub-atlantic phase,last 1,500 years).Fresh water.Barren of forams.The Holoeene paleogeographic curve of West Lake(fig.1)is representative of the sea coast of eastern China and is in agreement with the postglacial sea-level changes of the world oceans,with the exception that apparent regression occured in the late Holoeene as a estuarine deposition.The marine transgressive horizons in the Quaternary formations of the sea coast of eastern China correlate well with warm(interglacial)phases and are of great use in Quaternary stratigraphy.
作者
汪品先
叶国樑
卞云华
Wang Pinxian;Ye Guoliang;Bian Yunhua(Tongji University;The Sixth Mineral Exploring Team of Zhejiang Province)
出处
《海洋与湖沼》
1979年第4期373-382,408,共11页
Oceanologia Et Limnologia Sinica
