【作者】 黄永波；

【导师】 戴霜；

【作者基本信息】 兰州大学 ， 第四纪地质学， 2010， 硕士

【摘要】 温室效应造成的全球变暖已成为本世纪最大的全球性环境问题,在自然与人为因素的叠加作用下,全球土地沙漠化问题正变得越来越严重。白垩纪作为距今最近的“温室地球”时期,对该时期的沙漠演化展开系统研究对认识现代沙漠形成演变具有重要意义。鄂尔多斯盆地白垩纪沙漠是白垩纪横贯我国西北-东南沙漠带的重要组成部分。本文通过对鄂尔多斯盆地南部下白垩统志丹群下段(宜君组、洛河组及环河—华池组,厚420.23米)钻孔岩芯高分辨率高精度的磁性地层研究,结合沉积环境分析,发现岩石原生(特征)剩磁的携带矿物为赤铁矿及部分磁赤铁矿；获得了25个正极性柱和25个负极性柱,结合已有的生物化石资料,将其与GTS2004的M5n至M16n相对应,获得志丹群下部的磁性地层年代为142.06—129.73Ma；岩芯钻获的志丹群各组磁性地层年龄分别为宜君组142.06—141.48Ma、洛河组141.48—133.94Ma及环河—华池组133.94—129.73Ma；志丹群下段沉积环境为冲积扇相、河流相、沙漠相及滨浅湖相,沙漠沉积物发育于洛河组,起止时代为141.48—135.37Ma。通过对沉积物磁化率测量结合前人孢粉资料分析显示,发现志丹群下段沉积物反映的气候环境与早白垩世全球温度变化具有很好的相关性,气候总体显示为干热环境,以133.94Ma界可分为两个阶段：早期相对温干阶段(142.06—133.94Ma),后期相对暖湿阶段(133.94—129.73Ma)。风成砂沉积层序及磁化率值变化特征显示早白垩世鄂尔多斯盆地南部沙漠经历了三次发育→扩张→消亡的阶段,发育的年代分别为：141.48—140.64Ma；139.51—137.84Ma；136.26—135.37Ma.更多还原

【Abstract】 Global warming resulted from greenhouse effect has already become the most serious global environmental problem in the present century, owing to the natural factor and human disturbance, land desertification around the desert is becoming more and more serious. Cretaceous is the latest typical greenhouse Earth state, thus the systematic research on the desert evolution in these period is of great significance to understand the modern desert.The desert in the Ordos Basin is an important part of desert belt across China continent in the Cretaceous. In this study, based on the high resolution magnetostratigraphy of lower Cretaceous-Zhidan Group in the southern of Ordos Basin, it could be inferred that the original remnant magnetic-carrying minerals are mainly hematite and somewhat maghemite, there are 25 long normal polarity zones and 25 short reversed zones in Zhidan Group with a thickness of about 420.23m, including Yijun Formation, Luohe Formation and Huanhe-huachi Formation. Combined with the obtained biological fossil data, the observed polarity zones could be reasonably correlated with the M5n through M16n of GTS2004, thus yield the age control of lower Zhidan Group between 142.06 Ma and 129.73 Ma, then the ages of Yijun Formtion, Luohe Formation and Huanhe-huachi Formation are 142.06-141.48 Ma, 141.48-133.94 Ma and 133.94-129.73 Ma, respectively. The deposition environment of the lower Zhidan Group is alluvial fan, fluvial, desert and shore-shallow lake facies, while the desert deposition is in the Luohe Formation between 141.48 Ma and 135.37 Ma.Based on the measurement of magnetic susceptibility and the previously obtained pollen data in sediments, we found that the climate environment inferred from sediments of the lower Zhidan Group has a better correlation with global temperature change in early Cretaceous and it shows a arid and heat condition on the whole. Its climate change could be further divided into two substages:the early relative arid and warm substage (142.06 Ma-133.94 Ma), the last relative humid and warm subsage (133.94 Ma-129.73 Ma). Three stages are reconstructed in Ordos Basin at early Cretaceous based on the magnetic susceptibility feature and the location of anemoarenyte, they are development, expansion and subduction, correspondingly to 141.48 Ma-140.64Ma,139.51 Ma-137.84 Ma and 136.26 Ma-135.37 Ma.更多还原