以共和盆地东部风成沉积剖面(MS剖面)磁化率为依据,运用四次回归方程重建了剖面形成时的年均气温和降水量,确定近12 ka以来共和盆地年均温度-0.37℃~5.09℃,多年平均温度为2.5℃,降水量267.91~ 550.77 mm,多年平均降水量为418.62 mm。对常量元素氧化物(SiO_2、Al_2O_3和Fe_2O_3)含量进行分析,结果表明:1)古土壤层SiO_2含量均低于风成砂层,Al_2O_3和Fe_2O_3含量均高于风成砂层;2)风成砂层SiO_2含量S_3>S_5>S_1, Al_2O_3和Fe_2O_3含量S_5>S_3>S_1,揭示S_3层形成时期冷干,S_5层次之,S_1层干旱程度较弱;土壤层SiO_2含量S_4> S_2>S_6, Al_2O_3和Fe_2O_3含量为S_6>S_2>S_4,表明S_6形成时期气候温湿,S_2层次之,S_4层温湿程度较低;3)分层氧化物变异系数大小表明S_2和S_6层形成时气候波动剧烈,S_1和S_3层形成时期气候较稳定。以常量元素氧化物含量、温度和降水为依据,结合14C测年,重建了近12 ka以来共和盆地环境演变过程:11.9 ka BP以前为凉干期,11.9-9.7 ka BP为温湿期,9.7-8.0 ka BP为冷干期,8.0-4.8 ka BP为暖湿期,4.8-2.9 ka BP为凉干期,2.9 ka BP以来为温润期。马四剖面记录的环境演变过程与青藏高原其他区域环境演变过程具有相似性,表明共和盆地环境演变与区域环境变化具有同步性。
英文摘要:
Paleoenvironmental conditions in the eastern part of the Gonghe Basin since 12 Ka are reconstructed on the basis of magnetic susceptibility data and 14C dates from aeolian deposits. The results show that, since 12 Ka, annual average temperatures of the Gonghe Basin were between 0.37 and 5.09°C, with a mean of 2.5°C,and annual average precipitation was between 267.91 and 550.77 mm, with a mean of 418.62 mm. Oxide analysis shows that: 1) The SiO_2 content is lower, and the Al_2O_3 and Fe_2O_3 contents are higher, in ancient soil layers than in aeolian sand layers; 2) In ancient soil layers, the SiO_2 content shows a pattern of S_3>S_5>S_1,whereas the Al_2O_3 and Fe_2O_3 contents follow a pattern of S_5>S_3> S_1, revealing that S_3 records coldest and driest conditions followed by S_5 and then and Si. In aeolian sand layers, the SiO_2 content follows a pattern of S_4> S_2>S_6, whereas the Al_2O_3 and Fe_2O_3 contents follow a pattern of S_6 >S_2> S_4, revealing that S_6 records the warmest and most humid conditions, followed by S_2 and then S_4; 3) The variation coefficients of the layered oxide indicate that the climatic fluctuations were strong as recorded in S_2 and S_6,and much more stable in Si and S_3. Based on oxide contents, paleotemperatures, and paleoprecipitation levels, the environmental history of the Gonghe Basin since 12 Ka can be divided into the following periods: cool-dry period before 11.9 ka BP, warm-wet period of 11.9-9.7 ka BP, cold-dry period of 9.7-8.0 ka BP, warm-wet optimum period of 8.0-4.8 ka BP, cool-dry period of 4.8-2.9 ka BP, and warm-humid period of since 2.9 ka BP. The environmental history of the Gonghe Basin is similar to that of other regions in the Qinghai-Tibet plateau.