内蒙古苏尼特左旗中新世晚期孢粉记录干旱事件

A Study of the Late Miocene Dry Event Based on Sporo-Pollen Variations in Sunitezuoqi, Inner Mongolia

对中中新统通古尔组和上覆地层宝格达乌拉组的40个孢粉样品的分析表明通古尔期晚期形成环境较早期温湿,在通古尔期向宝格达乌拉期过渡期间,灌木和草本植物花粉由19·7%增加到46%,而乔木植物花粉总数由69·5%下降为34·7%,松蒿比(A/C)由4突降为0·64,标志着干旱事件的开始。将该地区的古地磁、哺乳类化石和孢粉资料与前人研究进行对比,结果显示干旱事件发生在晚中新世约8·5Ma,这一事件在华北具有广泛的可比性。

The sporo-pollen variations of Mid-Miocene Tonggur Formation and overlying Baogeda Ula Formation indicate that late Mid-Miocene was wetterand warmer than early Mid-Miocene in Sunitezuoqi,Inner Mongolia. A dry event occurred in the transitional period from Mid-Miocene to Late-Miocene at about 8.5 Ma, when grass and shrub pollens increased from 19.7% to 46%, tree pollens decreased from 69.5% to 34.7%, and the Pinus/Arlemisia ratio (A/C) decreased from 4 to 0.64 in this area. The paleomagnetism along Section PM-01 indicates a correlation between C5An and C4r in the standard polarity, with an age range of 12.5～12 Ma and a late stage of 8.5Ma. Widespread arid and semi-arid areas occurred in North China and Northwestern China since 8.5Ma of Late Miocene, and the dry event in North China at 8.5 Ma was related to the lift of the Himalayas and the red clay in the tableland. An extensive correlation of dry events in North China at 8.5 Ma is supported by sporo-pollen data.