摘要:
四川茂县较场剖面厚101.1m,其中湖相沉积厚98.0m,为一套浅黄色-灰色的粉砂、粘土质粉砂和粉砂质粘土层。古地磁测试显示,除2个样品的磁偏角显示负极性外,其余样品的磁偏角全部为正,属布容正极性时,没有出现B/M界线。根据该套地层的岩性、岩相和所处的地貌部位,可以和云南金沙江谷地的龙街组对比,推测其开始沉积的时代为100~120 kaBP.另外,距顶4.0 m处光释光年龄为16.7±1.2 kaBP,推测其结束于10kaBP.湖相沉积历时约100kaBP,是岷江流域出露的末次(间)冰期以来厚度最大的剖面之一。
Abstract:
The Jiaochang section in Maoxian County,Sichuan Province,is 101.1 m thick,in which lacustrine sediments are 98.0 m thick,consisting of light yellow-gray silt,clayey silt and silty clay.Paleomagnetic measurements indicate that all the samples show normal polarity except two samples that have negative magnetic declination.The magnetic polarity belongs to Brunhes normal polarity and the B/M boundary is absent.According to the lithology,lithofacies and landform location,the strata can be correlated with the Longjie Formation in the Jinsha River valley,Yunnan.So it is inferred that the sediments began deposition at 100-120 ka BP.In addition,the optically stimulated luminescence(OSL) age is 16.7±1.2 ka BP at 4.0 m below the surface of the sediments,so it is inferred that the deposition ended at 10 ka BP according to calculation.The deposition of the lake sediments lasted for(100,000) years.The section is one of the exposed thickest sections since the last glaciation(deglaciation) in the Minjiang River valley.
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