北京地区末次冰消期气候环境变化记录的初步研究

对北京房山县长沟镇附近埋藏末次冰消期湖沼沉积物层序和岩性变化的观测资料，以及１４Ｃ测年、孢粉分析、磁化率、有机碳δ^１３Ｃ值和有机质含量等测定资料的综合研究表明：１)约１３０００ａＢ．Ｐ．以前本区气候相当干冷，植被稀疏；２)约１３０００～１２１００ａＢ．Ｐ．气候明显变暖，植被日趋繁茂，出现针叶－落叶阔叶林；３)约１２１００～１００００ａＢ．Ｐ．气候波动相当显著，十分不稳定，并在约１１６００～１１３００ａＢ．Ｐ．和约１０９５０～１０４８０ａＢ．Ｐ．气候明显向干冷逆转；而在这两个气候逆转之间出现相对湿润或温湿的气候。这一短期气候变化与北大西洋地区有相似之处，又有差异。

CLIMATIC CHANGES AND THEIR ENVIRONMENTAL EFFECTS DURING THE LAST DEGLACIATION IN BEIJING AREA

This paper reports a recent research on climatic and environmental evolution at Changgouzhen(38°32′N,115°47′E)area,60km southwest of Beijing city during the Last Deglaciation.It is delivered from the sedimental sequence consisting of about 4m lacustrine sediments overlaid by a 4m pluvial and slop washed loessic deposits with two Holocen paleosols.This lacustrine sequence can be divided into four stratigraphic units as follows.  14C dating of 13 peat and organic mud samples collected from depth 820m to 480m indicates that the lacustrine sediments were deposited during the period from 13 000a B.P. to ca 10 000a B.P.On the basis of pollen spore analyses,magnetic susceptibility and organic content measurements of more than 70 samples taken from the profile of the sequence,it can be observed that the climatic and environmental evolution at the study area underwent the following episodes during the Last Deglaciation:(1)dry and cold with poor vegetation befor 13 000a B.P.;(2)during 13 000￣12 100a B.P.a warme and wetter climate,with the vegetation of luxuriant together with needle leaved and deciduous broad leaved trees;(3)during 12 100￣11 300a B.P. an unstable climate which fluctuated frequently with a general trend of increasing dryness and coldness,and semi desert environment occurred in 11 600￣11 300a B.P.;(4)during 11 300￣10 950a B.P.a wetter or warmer wetter climate with relatively abundant vegetation;(5)climate reversed again during 10 950￣10 480(or 10 540)a B.P.with the development of desert or semi desert;(6)the vegetation recovered and the climate became warmer afterwards. The short term climate changes in Beijing area during the Last Deglaciation corespond well with that in North Atlantic,but with evident local characteristics.For an example,there was a relative wetter or warmer wetter period(11 300-10 950a B.P.) between two periods of climatic deterioration(11 600￣11 300 and 10 950-10 480a B.P.).