渭河中上游地区全新世气候不稳定性初步研究

Primary Study on the Environmental Instability During Holocene in the Upper and MiddleReaches of Weihe River

在野外宏观分析的基础上,对甘肃省天水市北道全新世黄土剖面以2 cm为间距密集采样,并对所有样品进行了磁化率测定和粒度分析.通过对各气候指标的分析认为,研究区全新世以来的气候演化表现为不稳定性和阶段性,其中全新世早期升温过程中,发生了历时约千年之久的气候恶化事件.全新世中期在总体温暖的背景下,曾产生过多次气候波动,其中以6 000～5 000 a B.P最为显著,其次为7 300～6 900 a B.P以及4 000～3 600 a B.P间.3100 a B.P之后,古季风再次发生大规模重组,气候趋于干冷.

A Holocene loess-palaeosol profile in Tianshui city,Gansu province,was studied by field investigation and laboratory analysis of grain-size(GZ) and measurement of magnetic susceptibility(MS).These records indicated that the climatic environment of Holocene in studied area was unstable.During the early Holocene,a climatic deterioration phase had broken the anathermal process.In the middle Holocene,although the weather was warm and moist as a whole,it fluctuated several times,especially in 6 000～5 000 a B.P.which is represented by loess L_(x)lying between S_(01)and S_(02).7 300～6 900 a B.P and 4 000～3 600 a B.P were in the next place.After 3 100 a B.P,the palaeo-monsoon recombined on a large scale again,and the climate entered into a relatively dry and rain shortage period.