白银盆地中新世末沙丘岩及其古沙漠与古环流重建

野外调查、室内样品分析及区域地层对比表明,广布于甘肃白银盆地的巨厚层发育大型交错斜层理的浅黄色固结砂岩是典型的沙丘岩,主要沉积于中新世末至上新世初,代表弱固定性沙漠,风系属行星西风,但盛行古风向分为SW至WNW两支,既不同于早白垩世鄂尔多斯盆地盛行NE向信风及W向行星西风,也不同于现代本区在东亚季风环流影响下盛行N、NNE及NE向冬季风的情况.这可能指示当时青藏高原已经隆升到海拔1 000～3 000 m,引起西风环流在高原南北两侧发生季节性摆动绕流,而同期蒙古高压系统的作用不明显.

Reestablishment of Palaeodesert and Palaeoclimate based on Dune Rocks of Later Tertiary in the Baiyin Basin, Gansu Province, China

There are extensively distributed concreted rocks, colored with brownish yellow, developed with cross\|bedding layers in the Baiyin basin of Gansu province. Based on analysis of aeolian characteristics of sedimentary structures, grain\|size distribution, and micro\|features of quartz grains, the rocks are determined as dune rocks. The layer of dune rocks is upon the series of brownish alluvial\|pluvial facies layers of the Early Tertiary. The alluvial-pluvial facies layers were deposited upon the erosion surface formed in the beginning of the Tertiary and under the Quaternary loess layer. Maybe it was of the Later Tertiary, corresponding to the drought event of later Tertiary found in the Linxia basin, south of the Lanzhou city. The palaeoclimate in which the dune rocks formed may similar to the modern semiarid desert. The composition of calcium carbonate in the rocks and silicon dioxides deposited on the surfaces of quartz sands showed that dunes might have experienced stabling periods. The palaeowind directions can be generally grouped into two parts: one is northwest, and the other southwest. Only small part is west. This maybe caused by the palaeo\|planetary\|west\|wind influenced by the uplifting of Qinghai-Tibetan Plateau with general height of about 1000 to 3000 m above sea level in that period. In the other hand, the influences of the palaeo-anticyclone\|cell of Asian Mongolia were not clear in the same epoch