中国风成黄土及其形成下限研究

A study of eolian loess and its lower boundary in China

“中国岩漠·砾漠·沙漠·黄土分布与主风向关系图”显示西北地区的第四纪黄土堆积是以风力为主的综合因素所形成，即就地起沙，近沙成土，一定地域的黄土在物源上隶属于一定地区的沙漠。黄土高原及新疆天山、昆仑山北麓的黄土地层结构的综合对比研究表明，典型风成黄土在不同地域和不同地貌单元上最早开始堆积的层位基本上是一致的，即均始于所有黄土剖面中的下粉砂层（Ｌ＿（１５））。该层以下的第四纪沉积类型因地而异，为非黄土沉积（湖相、冲洪积相及火山岩相等）。由黄土高原各代表性剖面的磁性地层学研究及新疆于田黄土下伏的安山玄武岩的同位素年龄测定获得黄土层开始堆积的时代为早更新世晚期，约１．２ＭａＢ．Ｐ。风成黄土的开始堆积是与黄土南缘各造山带（昆仑山、天山、祁连山及秦岭等）强烈的新构造隆升并产生区域环境效应有成因联系。这一更新世早期的事件层位得到了古生物学、新构造学、地貌学及地外物体高速撞击地球表面所产生的玻璃陨石等事件的佐证。

As clearly indicated by the Atlas of the relationships of Chinese rocky deserts, gravel deserts, deserts and loess with the main wind directions compiled by the author and others, the widely distributed thick loess deposits in Northwest China is mainly controlled by wind and many other multiple factors. A comprehensively comparative study of the texture of loess strata in Loessial Plateau, Tianshan Mt. and northern piedmont of Kunlun Mt. of Xinjiang shows that they are of the same horizon in the earliest deposits of the typical eolian loess in different regions and different geomorphic units, that is, all of them started at the lower siltstone (L15) in the loess sections. However the deposits below them are quite different. The time of the lower siltstone deposit is of late Early Pleistocene,i. e. 1. 2Ma B. P. , by means of the magnetostratigraphical study of all the typical sections in Loessial Plateau and repeatedly isotopical dating of the andesitic basalt below the loess stratum in Yutian county of Xinjiang. The start of eolian loess deposit has a genetic relationship with the intensively neotectonic uplifting of the orogenic belts (such as Kunlun Mt., Tianshan Mt., Qilian Mt. and Qinling Mt., ect. ) and their regional environment variation. In the meantime, this Pleistocene event stratum is notably coincident with events of paleontology, neotectonics, geomorphology and tektite formed by impact of outspace flying objects.