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浙江沿海全新世海滩岩基本特征及其古地理意义 预览 被引量:5

BASIC FEATURES OF HOLOCENE BEACHROCKS ALONG THE COAST IN ZHEJIANG PROVINCE AND ITS PALAEOGEOGRAPHIC SIGNIFICANCE
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摘要 浙江沿海全新世海滩岩是正处于中亚热带的海滩岩,迄今已发现有13处,主要出露于两侧为基岩岬角的小海湾潮间带中部的沙滩上,^14C年龄主要为2705a±160aBP-6485a±210aBP.通过多学科手段的综合研究,初步探讨了其基本特征及古地理意义。研究结果表明,受海水作用影响产生的颗粒(如生活于潮间带-潮下带的贝类壳体及其碎片、近岸底栖的有孔虫和介形虫等生物碎屑、花岗岩岩屑等)、颗粒支撑结构及文石针胶结物是其最重要特征。在其形成过程中,适宜该地貌如处于有砂砾滩的小海湾中,充足的经海蚀搬运束的陆源岩屑、石英、长石,大量的海洋生物碎屑作为物源,合适的颗粒粒径.适中的水动力,基本稳定或缓慢下降的海面及较高的气温等,都是有利的条件。在海滩岩形成时期,浙江中,北部地区沿岸线基本稳定,或略微缓慢向海推进。东海沿岸流不是如今这种低温水团,其水温应比现今高5—6℃,最少应高2℃,而其低盐度性质则古今基本一致。同时,热带扩展到浙江中、北部地区,或者当时的气候分带性不如现今这么明显。 There are Holocene beachrocks exposed on the sandy beach of the mid-intertidal zone in thirteen coves between rock headlands along the coast in Zhejiang Province. Except for Lianyungang beachrock, Zhejiang beachrocks are the northernmost ones found in China, located in the middle subtropic.The age from data of 14C is from 2 705 a±160 a BP to 6 485 a±210 a BP. Its basic features and palaeogeo-graphic significance were discussed. Results of the study indicate that the grains ( shells and their frag-ments of in tertidal-neritic bivalves, gastropods, foraminiferas and ostracods, and clasts of granite, etc.) which are produced by marine processes,grain-supported texture and aragonite as the cement are the most important features of the beachrocks. Favourable geomorphologic landscape, such as in a cove with sandy beach, sufficient supplies of grains including terrigenous detritus, quartz, feldspar, and a large amount of bioclasts, moderate grain size and hydrodynamic conditions , stable sea level and high temperature influ-ence the formation of the beachrocks. During formation of the beachrocks, the coast-line of the middle-northern part of Zhejiang Province was basically stable, and Donghai Sea longshore current was not the low temperature current like the present.Its temperature was about 5-6°(at least 2°C)higher than the pr-esent, whereas it was the low salinity current like the present. Zhejiang Province belonged to the tropical climate zone,or climatic zonation was not distinct at that time.
作者 江大勇 杨守仁 Jiang Dayong Yang Shouren( Department of Geology, Peking University, Beijing 100871)
出处 《古地理学报》 CAS CSCD 1999年第1期 61-67,共7页 Journal of Palaeogeography
基金 国家自然科学基金:“中国南部全新世海滩岩中的生物群的古生态古环境研究”,4917207 国家教委高校博士点基金:“闽浙全新世海滩岩及其动物群与定量古气候的探索”,930015
关键词 浙江 奎新世 古地理 海滩岩 出露特征 Zhejiang, Holocene, beachrocks, palaeogeography
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