【作者】 徐永；

【导师】 岳乐平；

【作者基本信息】 西北大学 ， 地球环境科学， 2010， 博士

【摘要】 黄土高原新近纪红粘土堆积蕴含着丰富的古环境变化信息,它真实而详细地记录了东亚季风的发展演化过程和亚洲内陆干早化的历史,对进一步探讨青藏高原的隆升以及全球气候变化提供了载体。在黄土高原东部粉尘堆积的起始时间和西部秦安地区相差较大,而且直接不整合覆盖在中生代砂岩之上,所以粉尘堆积的研究有利于了解黄土高原东部鄂尔多斯地块中上新世的构造运动。黄土高原的红粘土堆积被普遍认为是风成堆积,所以较老的风成堆积可以为季风的早期演化和长尺度的古气候变迁提供证据。在吕梁山前红粘土堆积中时常夹杂有砂砾石层、湖相层和化石层等典型的水成物质,这些物质良好地记录了晚新生代以来吕梁山山前盆地的演化,中上新世黄土高原的生态环境及气候变化事件。在详细调查研究区新近纪地层的基础上,选择了位于吕梁山西麓中部的石楼,复兴和卫家洼3个红粘土剖面,对其进行详细的岩石磁学、磁极性地层、粒度、磁化率、沉积速率、古生物等方面的工作,并和北部保德和府谷地区的红粘土堆积进行对比,研究吕梁山西麓红粘土的古地磁年代、沉积环境、形成过程等,进而探讨吕梁山以及鄂尔多斯地块晚新生代的沉积演化,黄土高原中-上新世的环境变迁。吕梁山西麓红粘土上部颜色较深,呈深红棕色或紫红色,成壤作用较强,较下部质地均一,纯净。下部颜色稍浅,呈浅棕红色、淡红色、黄色,其间常夹杂有灰白色砂层、砂砾石层,灰绿色、灰白色的湖相层和数层化石层。这套红土序列的起始年龄集中在7-11Ma。野外岩性特征以及粒度、磁化率、石英颗粒的微形态等方面的研究表明石楼地区红粘土和黄土高原其他地区典型红粘土堆积显示出相似或者相同的特征,判断石楼地区红粘土为风成沉积,而详细的磁性地层研究显示其底界年龄约为11Ma,这是黄土高原东部发现最老的风成物质。复兴和卫家洼红粘土的下部则含有粗颗粒物质,甚至砂层、砂砾石层,磁化率也极低,部分层段还有层理等明显水流作用的痕迹,表明其形成过程中有水流作用的参与。根据红粘土的粒度、磁化率和沉积速率的变化,结合岩性特征和古生物化石,我们将东亚季风演化分为出现并剧烈波动(11.0-8.0Ma),相对加强(8.0-6.5Ma),极度变化(6.5-4.8Ma)和进一步增强(4.8-2.6Ma)四个阶段。更多还原

【Abstract】 Neogene red clay deposits in the Chinese Loess Plateau (CLP) contain much paleoclimate information. They detailedly recorded the evolution of the East Asian monsoon and the history of aridity of the East Asian inland area, and furtherly provided the information of uplift of Qinghai-Xizang Tibetan and global climate change. The eolian deposits in the eastern CLP are of great significance to understand the tectonic movements of Ordos block in the Miocene and Pliocene because they directly covered unconformabally on Mesozoic sandstone basement and had significant different basal ages compared with the eolian dust in the western CLP. The red clay deposits in the CLP are considered to be eolian origin, so older red clay deposits contain information of early paleomonsoon evolution and paleoenvironment change. In the piedmont of Luliang Mountains, the red clay deposits always interbedded with sand-gravel layers, lacustrine strata and fossil layers. These layers are extremely important to find out the evolution of the piedmout of Luliang Mountains, ecological environment and climate change events of CLP in the Neogene.Based on carefully investigate of the Neogene strata in the western piedmont of Luliang Mountains, Shilou, Fuxing and Weijiawa three red clay profile were chose, and other sections in Baode and Fugu were also chose for comparison. The rock magnetism, magnetic polarity stratigraphy, particle-size, magnetic susceptibility, sedimentation rate, biological fossil etc. were studied to discuss the age, sedimentary environment, formation processes of red clay deposits in the western piedmont of Luliang Mountains, and further explore the tectonic movements of Luliang Mountains and Ordos block in the late Cenozoic, and the environmental changes of the CLP in the Miocene and Pliocene.The upper part of red clay in western piedmont of Luliang Mountains show redder color, which demonstrate deep reddish-brown or purplish red, stronger soil character and purer texture than the lower part. The lower part which display light reddish-brown, light red and yellow color, always interbedded with grayish white sands, sand-gravel layers and grayish-green lacustrine strata. The basal age of the red clay in western piedmont of Luliang Mountains were centralized at 7-11 Ma. Field deposit characteristics, particle-size, magnetic susceptibility, quartz particle micromorphology, and comparison with other sections revealed that the Shilou red clay are eolian origin, and this is the oldest red clay deposit found so far on the eastern CLP. However, the lower part of Fuxing and Weijiawa red clay exhibit water transportation or transformation evidence with coarse particle size, lower susceptibility etc. Furthermore, several layers display obvious characteristics of water flow action, such as bedding or burying of fossils. By comparing lithologic features, particle size distribution, magnetic susceptibility, deposition rate and biological fossils of red clay sequence in western piedmont of Liiliang Mountains, the paleomonsoon evolution from 11 to 2.6 Ma can be divided into four stages:largely fluctuated stage (11.0-8.3 Ma), relatively strengthen period (8.3-6.5 Ma), extremely changed stage (6.5-4.9 Ma) and further intensified period (4.9-2.6 Ma).更多还原