西峰剖面有机质记录的黄土高原L_6-L_1古湿度演变  

Paleohumidity Evolution in Loess Plateau Recorded by Organic Matter in Xifeng Loess Section

作　　者：贾蓉芬[1] 彭先芝[1] 

机构地区：[1]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广东广州510640

出　　处：《地理科学》2004年第6期693-697,共5页Scientia Geographica Sinica

基　　金：国家自然科学基金项目(49291100)和(40073029)资助。

摘　　要：对甘肃西峰黄土剖面L6～L1层段162块样品进行了(Rock-Eval)2+PLUS分析,获得了TOC和热解烃的含量,以及有机质最高热解峰温(Tmax)的数据,并以与下降水有关的有机质和与蒸发水有关的矿物包裹有机质之比估算了古湿度的分布。结果表明,古土壤层的湿度比相邻黄土层的大,湿度的变化范围为47%～80%,其中湿度最大的层段为S5上部,次之为S1,湿度最小的层段为L6,次之为L4,L2-S1-L1层段的古湿度变化与陕西渭南剖面的相当层位具有很好的对应性。上述结果与黄土研究中常用的矿物粒度分析、CaCO3、Fe2+和Fe3+及磁化率等方法的测定结果具有良好的可比性。西峰剖面L6-S5-L4层段有机质和湿度的变化都很大,反映大气环流在这段时间异常活跃,具有热湿事件或黄土高原气候变化的边界特征。而在L4以来,特别是L4-S3-L3层段,湿度变化幅度相对较稳定,总的趋势向湿度减小方向发展,而在S2以后湿度演变有增大的趋势。162 samples collected from Xifeng section, Gansu Province have been analyzed by Rock-Eval + PLUS(quick analyzer of organic matter). The data were gained that include total organic carbon(TOC)and pyrolysis hydrocarbon(pHC_1 and pHC_2), as well as the temperature of the most organic matter pyrolyzed(Tmax℃).Paleohumidity has been calculated by formula Qq=pHC_(2-1)/(pHC_(2-2))+(pHC_(2-2)). Here pHC_(2-1 )is hydrocarbon pyrolyzed at 300-500℃,which presents organic matter combined with organism residue in sample and correlated to supergene water, rain or other surface water in the area,pHC_(2-2) is hydrocarbon pyrolyzed at 500-600℃,which presents organic matter combined with special secondary carbonate and correlated to evaporation water. The calculated result shows that the paleohumidity is bigger in the paleosol layer than that in the adjacent loess layers. The range of paleohumidity in the section is 47%-80%, the highest is in S_(5-1),the secondary is in S_1, the lowest is in L_6,the secondary is in L_4。The paleohumidity change of L_2-S_1-L_I in Xifengg section could correlate with the same layers in Weinan section of Shaanxi Province, Which could compared with the results of mineral partial size, content of CaCO_3, iron changes of Fe^(2+) and Fe^(3+), as well as susceptibility used often in the research on loess section. The paleohimidity evolution in Xifeng section shows that during L_6-L_4 layers, the paleohumidity changed intensively, it means that the general circulation of atmosphere was very activity and may be reflect an event of hot-humidity or the climatic boundary of the dry and humid general circulations. After L_4,special in L_4-L_2 layers, the amplitude of paleohumidity changes to gentle , and the trend of humidity to decrease, but since S_2 the trend of the humidity have changed to increase.

关 键 词：西峰黄土剖面 有机质 古湿度 热解结合烃 Rock—Eval 

分 类 号：P531[天文地球—古生物学与地层学]