本文選題：蘭州盆地 + 晚中新世�。� 參考：《山西師范大學》2017年碩士論文

【摘要】：蘭州盆地的位置處于青藏高原的東北部,它是一個季風區(qū)交匯區(qū)域,也是一個干旱區(qū)域過渡帶。大規(guī)模的發(fā)展良好的晚新生代地層在該盆地內(nèi)被發(fā)現(xiàn),而且該盆地內(nèi)發(fā)現(xiàn)了較多的古人類遺址和哺乳動物化石,且對第四紀地質(zhì)學等方面有著較為大的影響。近年來,運用磁性地層學,生物地層學及綜合手段進行了研究的開展,使我們加深了對高原盆地的一些問題的認識,如動物群的年代框架問題。目前,對蘭州盆地的研究主要集中在哺乳動物化石、植物孢粉化石和沉積學的研究之中,但對第四紀以來的古環(huán)境演化研究相對薄弱。本文通過運用巖石磁學方法和環(huán)境磁學方法對蘭州盆地晚中新世河湖相沉積物的巖石磁進行研究,對該地區(qū)的晚中新世的氣候特征和湖湘沉積物的礦物形成機制進一步挖掘;通過高溫下的磁學性質(zhì)的變化特征分析其所揭示的古氣候意義,為該地區(qū)進行巖石磁學工作提供一定的文獻支持。實驗結果如下:(1)磁化率與磁性礦物的類型密切相關。第三紀蘭州盆地的紅色泥巖層大體磁化率都呈現(xiàn)出較低的值。亞鐵磁性礦物和鐵磁性礦物是是沉積物中磁化率變化的主要成因。但是由于磁性礦物含量不高,所以磁化率值普遍較低。(2)泥巖樣品的ARM、SIRM、HIRM等磁學指標都比砂巖高,說明泥巖中的磁性礦物總含量比砂巖要高。在泥巖樣品中,同時含有高矯頑力和低矯頑力磁性礦物,且低矯頑力磁性礦物對其剩磁的貢獻高于高矯頑力組分,磁性礦物以SP和PSD顆粒為主;砂巖樣品磁性礦物含量比泥巖低,其高級頑力組分和低矯頑力組分對其剩磁都有貢獻。(3)漫反射二階導數(shù)的波段強度反映出本文中砂巖的I425和I535的值比較顯著,而泥巖中的I425和I535的值相對偏小,這就表明在砂巖中的赤鐵礦和針鐵礦要比泥巖中的含量多。通過對泥巖與砂巖的Hm/(Gt+Hm)的值與其深度進行了分析,得出距離對砂巖和泥巖的的影響成不顯著相關,擬合度很低。并且根據(jù)前人的研究,認為Hm/(Gt+Hm)可以為氣候的一個指標,而且Hm/Gt能更加有效的作為氣候的指示指標。(4)砂巖的形成環(huán)境是河道沉積物,磁性礦物發(fā)生了溶解,導致磁化率相對較低;泥巖的形成環(huán)境為湖相,分析可能是由地表徑流從裸露地表帶來的碎屑物質(zhì),磁性礦物含量及種類與物源有著緊密的關系。
[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.
【學位授予單位】：山西師范大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P512.2;P584

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