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文章通过对西宁盆地谢家剖面上部(620~819m)厚度190m,有精确年代控制且无明显相变的晚渐新世-早中新世的湖相沉积物样品的磁化率系统测量,建立了该区晚渐新世-早中新世高分辨率的磁化率变化序列,揭示高、低频磁化率在约25Ma和21Ma存在两次明显的台阶式长期增大趋势,并在约23.8Ma,21.6Ma和19.8Ma叠加短期峰值,在时间上可能分别对应全球此时的长期变冷趋势及全球性Mi-1.1事件、Mi-1a事件和Mi-1aa事件短暂快速变冷事件,而频率磁化率记录几乎没有变化。代表性样品的系列岩石磁学分析,揭示出沉积物的载磁矿物主要为假单畴(PSD)的磁铁矿,同时可能还存在赤铁矿和针铁矿;磁化率增大主要由假单畴磁铁矿的含量增多引起,而不是通常情况下的成壤作用形成的超顺磁颗粒的增多引起,推测青藏高原东北部隆升导致的侵蚀增强,或干旱化,或两者兼并,可能是导致西宁盆地上述磁化率增强的原因。
By measuring the magnetic susceptibility of the late-Oligocene-Early Miocene lacustrine sediments in the upper part of Xiejia section of Xining basin (620 ~ 819m) and controlled by precise chronology and with no significant phase transition The sequence of late-Oligocene-Early Miocene magnetic susceptibility changes in this area reveals that the high and low frequency magnetic susceptibilities have two obvious long-term stepwise increases at about 25 Ma and 21 Ma, and at about 23.8 Ma, 21.6 Ma and 19.8Ma superimposed short-term peaks may correspond to the global long-term cooling trend at this time and the transient rapid cooling events of the Mi-1.1 event, the Mi-1a event and the Mi-1aa event respectively, while the frequency susceptibility records almost no change at all. A series of rock magnetographic analyzes of representative samples revealed that the magnetite-bearing minerals in the sediments are primarily pseudo- monophasic (PSD) magnetite with the possible presence of hematite and goethite; the increase in susceptibility is mainly dominated by fake The increase of monodomain magnetite rather than the increase of superparamagnetic particles formed by pedogenesis under normal circumstances is the reason for speculation that the erosion caused by the uplift of the northeastern Tibetan Plateau is enhanced or aridified or both, This may be the reason that the above magnetic susceptibility increased in Xining basin.