兰州盆地晚中新世河湖相沉积物的岩石磁学性质

发布时间：2018-06-08 02:13

本文选题：兰州盆地 + 晚中新世　；参考：《山西师范大学》2017年硕士论文

【摘要】：兰州盆地的位置处于青藏高原的东北部,它是一个季风区交汇区域,也是一个干旱区域过渡带。大规模的发展良好的晚新生代地层在该盆地内被发现,而且该盆地内发现了较多的古人类遗址和哺乳动物化石,且对第四纪地质学等方面有着较为大的影响。近年来,运用磁性地层学,生物地层学及综合手段进行了研究的开展,使我们加深了对高原盆地的一些问题的认识,如动物群的年代框架问题。目前,对兰州盆地的研究主要集中在哺乳动物化石、植物孢粉化石和沉积学的研究之中,但对第四纪以来的古环境演化研究相对薄弱。本文通过运用岩石磁学方法和环境磁学方法对兰州盆地晚中新世河湖相沉积物的岩石磁进行研究,对该地区的晚中新世的气候特征和湖湘沉积物的矿物形成机制进一步挖掘;通过高温下的磁学性质的变化特征分析其所揭示的古气候意义,为该地区进行岩石磁学工作提供一定的文献支持。实验结果如下:(1)磁化率与磁性矿物的类型密切相关。第三纪兰州盆地的红色泥岩层大体磁化率都呈现出较低的值。亚铁磁性矿物和铁磁性矿物是是沉积物中磁化率变化的主要成因。但是由于磁性矿物含量不高,所以磁化率值普遍较低。(2)泥岩样品的ARM、SIRM、HIRM等磁学指标都比砂岩高,说明泥岩中的磁性矿物总含量比砂岩要高。在泥岩样品中,同时含有高矫顽力和低矫顽力磁性矿物,且低矫顽力磁性矿物对其剩磁的贡献高于高矫顽力组分,磁性矿物以SP和PSD颗粒为主;砂岩样品磁性矿物含量比泥岩低,其高级顽力组分和低矫顽力组分对其剩磁都有贡献。(3)漫反射二阶导数的波段强度反映出本文中砂岩的I425和I535的值比较显著,而泥岩中的I425和I535的值相对偏小,这就表明在砂岩中的赤铁矿和针铁矿要比泥岩中的含量多。通过对泥岩与砂岩的Hm/(Gt+Hm)的值与其深度进行了分析,得出距离对砂岩和泥岩的的影响成不显著相关,拟合度很低。并且根据前人的研究,认为Hm/(Gt+Hm)可以为气候的一个指标,而且Hm/Gt能更加有效的作为气候的指示指标。(4)砂岩的形成环境是河道沉积物,磁性矿物发生了溶解,导致磁化率相对较低;泥岩的形成环境为湖相,分析可能是由地表径流从裸露地表带来的碎屑物质,磁性矿物含量及种类与物源有着紧密的关系。
[Abstract]:The Lanzhou basin is located in the northeastern part of the Qinghai Tibet Plateau. It is a confluence area of the monsoon region and a transitional zone in the arid region. The large and well developed late Cenozoic strata are found in the basin, and many ancient human sites and mammalian fossils are found in the basin, and the Quaternary geology and other aspects are found in the basin. In recent years, the use of magnetic stratigraphy, biostratigraphy and comprehensive methods has been carried out, which has deepened our understanding of some of the problems in the Plateau Basin, such as the age frame of the fauna. At present, the study of the Lanzhou basin is mainly concentrated on mammalian fossils, plant palynological fossils and Sedimentology. The study of the Paleoenvironment evolution since the Quaternary is relatively weak. By using the methods of rock magnetism and environmental magnetism, this paper studies the rock magnetism of the late Miocene River lacustrine sediments in the Lanzhou basin, and further excavates the climatic characteristics of the late Miocene and the mineral formation mechanism of the lake and Hunan sediments in this area. The change characteristics of magnetic properties under high temperature are analyzed and the paleoclimate significance is revealed. The results are as follows: (1) the magnetic susceptibility is closely related to the type of magnetic minerals. The gross magnetization of the red mudstone layer in the Lanzhou basin in the third period shows a lower value. Sexual minerals and ferromagnetic minerals are the main causes of the change of susceptibility in the sediments. But because of the low magnetic mineral content, the magnetic susceptibility values are generally low. (2) the ARM, SIRM, HIRM and other magnetic indexes of the mudstone samples are higher than those of sandstone, indicating that the total content of magnetic minerals in the mudstone is higher than that in sandstone. The magnetic minerals with low coercivity and coercive force are higher than the high coercive force components. The magnetic minerals are mainly SP and PSD particles; the magnetic mineral content of the sandstone samples is lower than the mudstone. The high coercive component and the low coercive force component contribute to the remanence of the magnetic minerals. (3) the band intensity reflection of the two order derivative of diffuse reflection is reflected. The values of I425 and I535 in the sandstone are relatively significant, while the value of I425 and I535 in the mudstone is relatively small, which indicates that the hematite and goethite in the sandstone are more than those in the mudstone. By analyzing the value and depth of the Hm/ (Gt+Hm) of the mudstone and sandstone, the influence of distance on the sandstone and mudstone is not significant. Hm/ (Gt+Hm) can be an indicator of climate and Hm/Gt can be more effective as a indicator of climate. (4) the formation environment of sandstone is river sediment, the magnetic minerals are dissolved and the magnetization rate is relatively low; the formation environment of mudstone is lake facies, analysis may be possible. It is the clastic material brought about by surface runoff from bare surface. The content and type of magnetic minerals are closely related to the source.
【学位授予单位】：山西师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P512.2;P584

【参考文献】