黄土高原西部红粘土岩石磁学性质及其指示的亚洲内陆中中新世气候变化特征

摘要

对黄土高原西部庄浪红粘土进行详细岩石磁学分析表明,沉积物磁性由磁铁矿和赤铁矿主导,并且含有一定量的磁赤铁矿.中中新世大暖期红粘土中磁铁矿、磁赤铁矿含量显著升高；中中新世大暖期前后红粘土中的磁铁矿含量相对较低,赤铁矿相对含量较高,但并未显示较强的磁赤铁矿信息.磁性矿物的整体粒径表现为以SP,SD和PSD颗粒为主,MD颗粒较少.庄浪红粘土磁化率在16.5 ～ 13.8Ma出现峰值,与当时的夏季风强盛、降水丰富、成壤作用较强造成的亚铁磁性矿物相对含量增加密切相关.在全球气候变暖的中中新世大暖期,综合庄浪岩石磁学特征以及陆地和海洋的其他证据可以推测当时东亚冬、夏季风可能同时增强.%Heqing Basin(26°27' - 26°46'N, 100°08' ~ 100°17'E) is a Late Cenozoic north-south oriented pull-apart basin near the northwestern margin of the Yunnan-Guizhou Plateau. The Basin is located at the southeastern margin of the Tibetan Plateau and belongs to the terminal of Hengduan Mountains.rnThe local climate is dominated by Indian monsoon. Therefore,the continuous and thick sediments in the basin make it a perfect continental record for evolution of Indian summer monsoon. The Heqing drill core was obtained in the centre of the Heqing Basin. Using the internal lining method, recovery of the HQ drill core (26°33'43. 1"N, 100°10'14. 2"E;2200m) which has an accumulative depth of 665. 83m reaches up to 96. 7%. The lake sediments mainly consist of horizontally laminated greyish-green calcareous clay and silty clay with thin-bedded silt and fine sand layers, except two intervals of sand layers with fine gravels. With the equal interval of 50cm, we obtained 1368 samples from the drill core and chose 108 from different depositional units for detailed rock magnetic measurements.rnBased on detailed rock magnetic measurements like magnetic susceptibility versus high/low temperature curves, thermal demagnetization curve, hysteresis loops and FORC diagrams, we have investigated the magnetic properties of Heqing core lacustrine sediments. Magnetic measurements showed that sediments from the lower section (before 1.8Ma) of the core contain both magnetite and greigite while sediments from the upper section ( after 1. 8Ma) contain magnetite only.