西昌大箐梁子组形成时代及沉积环境  

AGE AND SEDIMENTARY ENVIRONMENT OF THE DAQINGLIANGZI FORMATION IN XICHANG

作　　者：傅建利[1] 赵志中[1] 李朝柱[1] 王书兵[1] 陈永生[2] 蒋复初[1] 姚海涛[1] 王燕[1] 乔彦松[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国地质大学,北京100083

出　　处：《第四纪研究》2007年第4期620-631,共12页Quaternary Sciences

基　　金：国家地质调查局地质调查项目(批准号:200312300034);国家自然科学基金项目(批准号:40302036和40302025)资助

摘　　要：对大箐梁子剖面进行了系统的磁性地层学研究和孢粉分析。磁性地层结果显示,剖面中B/M界线出现于32·6m处,剖面下部出现了C1r.2r-1n极性事件;本次测试结合已有研究成果表明,大箐梁子组形成于1·256～0·195MaB·P.。孢粉记录反映在此期间该区经历了凉湿(1·256～1·180MaB·P.)—暖干,后期偏潮湿(1·18～0·94MaB·P.)—暖湿(0·94～0·66MaB·P.)—温湿(0·66～0·59MaB·P.)—凉干(0·59～0·40MaB·P.)—干旱(0·400～0·195MaB·P.)的6个气候演变阶段,揭示出5次明显气候转型事件。通过与青藏高原和黄土高原地区不同或相同季风环流系统中其他剖面气候特征的比较,探讨了气候转型的控制因素。分析结果表明大箐梁子剖面环境演变过程主要受青藏高原“昆黄运动”阶段性隆升与全球气候变化控制,同时也受该区季风环流的复杂性、特殊的地貌部位等区域环境的影响。The Daqingliangzi Formation is an accumulation of fluvial-lacustrine sediments and consisted of gravel, sand, sand powder clay, clay and peat units, which lies in Daqingliangzi, southeast of Xichang City of Sichuan Province of China. The studied model section is 69.4m thick and the samples were taken every 30 ～ 50cm distance to get 97 paleomagnetic samples and 97 powder and granularity samples from the Daqingliangzi Formation. Stepwise thermal demagnetization up to 685℃ was performed on all 97 samples using a TD-48 thermal demagnetizer with a temperature step. of 20 ～ 50℃. Measurements were made using a 2G-755 three-axis cryogenic magnetometer. The results show that the Daqingliangzi section was formed between the Brunhes normal zone and the Matuyama reversed zone and the M/B line is confined at a depth of 32.6m. According to the Canda＇s polarity time scale, the C1n-1, Clr. 1n and Clr. 2r-1n subzones sequentially occur at the depth of 16.6 ～ 17.5m, 48. 5 ～ 55.6m and 62.8 ～ 64. 0m. Extrapolation with this accumulation rate yields a basal age of about 1. 256 ～ 0. 195MaB. P. at the Daqingliangzi Formation. In total 6 change stages have been recognized for the pollen record of the past 1. 061MaB. P. （1. 256 ～ 0. 195MaB. P. ） ： （ 1 ） The pollen concentration of 1. 256 ～ 1. 180MaB. P. was low and pollen assemblage was dominated by Betula, Tsuga and Polypodium, suggesting that the climate was cool and humid. （2） During 1.18 ～ 0.94MaB. P., the climate was changed from temperate and dry to wet, with meadow mixed with scattered woods. （3） The climate during 0. 94 ～0. 66MaB. P. was temperate and wet, and a constant broadleaved forest was developed, dominated by Castanopsis and Lithocarpus, with increasing percentage of Picea and Tsuga. （4） During 0.66 ～ 0.59MaB. P., the climate turned to warm and wet and the shrub was mixed with scattered woods. （5） During 0. 59 ～ 0. 40MaB. P. the mountainous coniferous forest was mixed with broadleaved forest and the vegetation

关 键 词：磁性地层 孢粉分析 环境演变 季风环流 青藏高原 

分 类 号：P539.3[天文地球—古生物学与地层学]