20000年来郑州地区湖沼沉积与环境演变研究

A STUDY OF LACUSTRINE AND PALUSTRINE SEDIMENTS AND ENVIRONMENTAL CHANGES IN ZHENGZHOU REGIONS DURING THE PAST 20000 YEARS

本文通过圃田、大河村和张五寨等钻孔和剖面岩性、粒度、磁化率、抱粉和化学元素等环境指标分析,结合AMS l4C和释光年代标尺,探讨20000年来郑州地区古湖沼沉积与环境演变特征。结果表明,郑州地区在15000-13000 yr BP和8900-2600 yr BP主要发育湖泊或沼泽沉积,其余时期为河漫滩和洪水沉积或文化层堆积。然而不同地点沉积序列虽然基本相同,但是沉积介质始末时间和延续时段略有差异。古湖泊可能为通江湖泊,洪水期水量剧增,湖盆扩大连成一片;枯水期分散为众多小湖塘,仅在低洼地区残留成河道型水域。受气候变干和人类大规模开垦影响,晚全新世湖沼最终消亡。这个沉积背景可能与郑州地区晚更新世晚期以来不同时期主导的沉积介质变化有关。

By the environmental proxies,such as lithology,grain size,magnetic susceptibilities,pollen and chemical elements,combining with AMS 14C and luminescence dating from B2*-PT core of Putian,JS-005-DHC core of Dahe Village,the outcrop and Bl-ZWZ core of Zhangwuzhai,this paper has analyzed the palaeolake sediments and environmental changes in Zhengzhou regions during the past 20000 years.The results indicate that it was mainly lacustrine and palustrine sediments at〜15000—13000 yr BP and〜8900—2600 yr BP,while flood and floodplain deposits or thick cultural layers in the rest time.Though the sedimentary sequence is basically the same among that of Putian,Dahe Village and Zhangwuzhai,but timing and duration of the deposits are slightly different.The ancient lakes may have been seasonal and connected with the river,exhibiting flood surging,lake expanding,water-level suddenly rising in rainy season and only appearing in low-lying regions in dry season.Because it has become dry and the massive reclamation of human kind,ancient lakes and bogs turned shallow,eventually died out in the late Holocene.This may has been related with major sedimentary changes in Zhengzhou regions in the different periods of the latest Pleistocene.