利用洞穴石笋的δ^(18)O和δ^(13)C重建3000a以来北京地区古气候和古环境——石花洞研究系列之三  

ISOTOPE STUDIES OF SHIHUA CAVE—Ⅲ:RECONSTRUCTION OF PALEOCLIMATE AND PALEOENVIRONMENT OF BEIJING DURING THE LAST 3 000 YEARS FROM δ 18 O AND δ 13 C RECORDS IN STALAGMITE

作　　者：李红春[1] 顾德隆[1] 陈文寄[2] 李铁英 

机构地区：[1]美国南加州大学地质科学系 [2]国家地震局地质研究所 [3]北京地质调查所

出　　处：《地震地质》1997年第1期77-86,共10页Seismology and Geology

摘　　要：首次提出用石笋中稳定同位素记录重建由降雨量和降水气团同位素组成所反映的古气候历史，从而为研究高分辨率的古季风气候信息开辟了新的途径。利用Ｈｅｎｄｙ准则、洞穴温度、研究区水系的δ１８ＯＨ２Ｏ值以及温度公式，证实了同位素分析结果的可靠性，ＣａＣＯ３－Ｈ２Ｏ之间存在同位素平衡分馏。对采自石花洞的石笋样品进行了分辨率约为２５ａ的δ１８Ｏ和δ１３Ｃ的分析测量，从而得到３０００ａ以来。Unlike low resolution (>1 000 years) δ 18 O record which mostly indicates temperature change in the past, variations of high resolution (<100 years) δ 18 O record of stalgmite mainly reflect changes in rainfall and the isotopic compition of moisture source in the study area. The δ 13 C value of speleothem is mainly controlled by isotope composition of soil CO 2that consists of isotopic composition of C 3and C 4plants. The C 3/C 4ratio is strongly correlated with climatic change. When the δ 18 O and δ 13 C shift to more negative values, the ratio of C 3/C 4indicates wet climate increased precipitation, development of forest. All those climatic conditions may indicate summer monsoon strengthening in the study area. This thoutht provides a new approach to reconstruct high resolution paleomonsoon records. We have first demonstrated this new idea throughout a series studies in Shihua Cave, Beijing. A 12.5cm stalagmite was subsampled at 1mm interval (～25 years resolution) and 109 samples were collected for δ 18 O and δ 13 C analyses. Using Hendy rule, cave temperature and δ 18 O H 2O , we have illustrated the isotopic equilibrium between precipitated calcite and its parent solution and the reliability of our measurement. The δ 18 O and δ 13 C records provide climatic information during the past 3 000 years in Beijing. Our results show that there are six apparently climatic cycles during the last 3 000 years in Beijing. The wet periods were peaked at 2 860, 2 350, 1 850, 1 480, 790 and 150 yr B.P., respectively, with a time step about 500 years. After 600 yr B.P. , all of the δ 13 C values show much heaiver than 3ka mean values. We suspect that this change in C 3/C 4ratio (de forest) was influenced by human activity also. There is a good agreement in the comparisons of the paleoclimate interpreted from the speeothem δ 18 O and δ 13 C records with historical records of temperature and p

关 键 词：古气候 古环境分析 稳定同位素 石花洞 石笋 

分 类 号：P532[天文地球—古生物学与地层学] P531[天文地球—地质学]