对临夏盆地1Ma以来地层中的石英砂所作的扫描电镜分析表明,风成砂一直存在,并在8Ma和6～Ma时含量最高.最大颗粒的平均粒径在(1.5～3.6)/2.6Ma达0.4mm,3.6～2.6Ma之后显著下降.前者表明3.6～2.6Ma以前,近源风沙作用一直存在,并在8Ma和6～Ma达到最盛;后者表明第四纪以来,远源风沙沉积盛行,可能反映了青藏高原在3.6～2.6Ma急剧隆起和与之相关的大气环流的改变.
Atotal of 55 samples were taken from the Tertiary red earth and Quaternary lacustrine deposits and loess for Linxia Basin for the analysis of quartz type and content using electron probe microanalyzer. The eolian sand contents appeared two high values at about 8Ma and 6-5Ma respectively. The mean size of quartz grains was about 0.4mm during the 15-3. 6/2. 6 Ma period and dropped down to 0.1mm dramatically after 3. 6-2. 6Ma. These results mean the eolian deposition reached its maximum at 8 Ma and 6-5 Ma respectively. Since the Quaternary, the local eolian deposition was decreased significantly and disappeared which was replace by dust deception from far source, suggesting the uplift of Qinghai-Xizang Plateau and the change of air circulation.
[1] Rea D K. The paleoclimate record provided by eolian deposition inthedeep sea:The geologic history of wind[J]. Reviews of Geophysics, 1994, 32: 159-195.
[2] 丁仲礼,孙继敏,朱日祥,等.黄土高原红粘土成因及上新世北方干旱化问题[J].第四纪研究,1997,(2):147～157.
[3] 丁仲礼,孙继敏,杨石岭,等.灵台黄土-红粘土序列磁性地层及粒度记录[J].第四纪研究,1998,(1):86～92.
[4] 孙东怀,刘东生,陈明扬,等.中国黄土高原红粘土序列的磁性地层年代与气候记录[J].中国科学,1997,27(3):265～270.
[5] 孙东怀,陈明扬,John Shaw,等.晚新生代黄土高原风尘堆积序列的磁性地层年代与古气候记录[J].中国科学,1998,28(1):79～84.
[6] QuadeJ, CerlingTE, Bowman J R. Development of Asian monsoon revealed by marked ecological shift during the LastestMiocene in north Pakistan[J]. Nature, 1989, 342: 163-166.
[7] Prell W L, Kutzbach J R. Senitivity of the Indian monsoon to forcing parameters and implications for its evolution [J].Nature,1992, 360:647-652.
[8] 陈发虎,方小敏,牟昀智,等.扫描电镜所揭示的安宁砂的特征及成因[J].兰州大学学报(自然版),1987,23(4):137～141.
[9] Li Ji-Jun, Fang Xiao-Min, Rob Van der Voo, et al. Magnetostratigraphy dating of river terraces: Rapid and intermittent incision by the Yellow River of the northeastern margin of the Tibetan Plateau during the Quaternary[J]. Journal of GeophysicalResearch, 1997,102(B5):10 121-10 132.
[10] 方小敏,李吉均,朱俊杰,等.甘肃临夏盆地新生代地层年代测定与划分[J].科学通报,1997a,42(14):1457-1471.
[11] 方小敏,奚晓霞,李吉均,等.中国西部晚中新世气候变干事件的发现及意义[J].科学通报,1997b,42(23):2 521-2524.
[12] 马玉贞,李吉均,方小敏.临夏地区30.6～5.0 Ma红层孢粉植物群与气候演化记录[J].科学通报,1998,43(3):301～304.
[13] 谢又予.中国石英砂表面结构特征图谱[M].北京:海洋出版社1995.
[14] KrinsleyDandDonahueJ. Atlas of Quarts Sand Surface Texture[M]. New York:cambridge University Press, 1973.91.
[15] 方小敏.青藏高原东部边缘及邻区马兰黄土成因与来源的初步研究[J].中国科学,(B辑),1994,24(5):539～546.
[16] Bagnold A. Experiment on Gravity-free Dispersion of LargeSolid Sphere in a Newtonian Fluid under Shear[J]. Proc. Soc.ofLondon, 1954, 225A:49-63.
[17] 董光荣,王贵勇,陈惠忠,等.中国沙漠形成、演化与青藏高原隆升的关系[A].青藏高原研究会(编).青藏高原与全球变化研讨会论文集[C].北京:气象出版社,1995.
[18] 张云翔,陈丹玲,薛祥煦,等.中国北部5.3Ma动物群的年龄分布特征与气候恶化事件[J].科学通报,1997,42(7):734～736.
[19] 张彭熹.青藏高原盐湖几个有关地质问题的讨论[A].张彭喜(编).青海柴达木盆地晚新生代地质与环境演化[C].北京:科学出版社,1986.
[20] Hsu K J, Montadert L, Bemouilli D.History of the Mediterranean salinity crisis[J]. Nature, 1977,267:399-403.
