柳林地区新近纪红粘土的岩石磁学研究及古环境意义
发布时间：2018-11-08 14:52
【摘要】：中国黄土高原红粘土作为中国北方新近纪最典型的沉积产物,蕴含着丰富的古气候与古环境变化信息,详细地记录了黄土高原新近纪以来的发展演化历程。黄土高原东缘在地理位置上处于吕梁山西侧,吕梁山的隆升造就了山前砂砾石层堆积,砂砾石层之上以厚层的红粘土为特征,红粘土堆积直接不整合覆盖于中生代砂岩之上,红粘土堆积中常夹杂有砂砾石、化石等典型的水成物质,这些成分良好地指示了新近纪以来吕梁山隆升、黄土高原粉尘堆积的演变记录。中国黄土高原东部、吕梁山西麓的柳林地区正是在这种环境下形成了一套巨厚的红粘土沉积序列。在前人对新近纪红粘土研究的基础上,选择了吕梁山西麓、黄土高原东缘的柳林县卫家洼村红粘土剖面进行详细的岩石磁学研究,通过环境磁学、古地磁学以及磁化率各向异性相结合的方法对该区域加以评估,并进一步探讨新近纪以来吕梁山西麓、黄土高原东缘红粘土粉尘堆积的古环境演变过程。卫家洼红粘土剖面东侧为吕梁山,西侧为黄河,现代地貌属于黄土丘陵沟壑区。该区域经历了强烈的剥蚀作用,地形以中生代基底之上的黄土、红粘土冲沟和山谷为特征,红粘土地层出露较好。卫家洼红粘土剖面厚度约为112m,上覆为黄土-古土壤序列,下未见底。该新近纪地层根据野外岩性特征可分为三段:上段,Om～30m,由深红棕色的红粘土与钙质结核互层为主,表现出比第四纪黄土-古土壤更强的风化作用;下段,81m～112m,为红粘土或砂质粘土夹杂灰白色砂层、砂砾石层,红粘土为浅红棕色,主要由两个从上至下变粗的冲积扇相沉积序列组成;中部过渡段,30m～81m,兼有上下段的岩性特征,部分层位岩性复杂。首先通过K-T曲线、磁滞回线研究表明剖面红粘土的磁性矿物与黄土基本相同,这保证了后面环节的古地磁实验、磁化率各向异性等研究方案实施的可行性和数据结果的准确性;然后通过古地磁学实验得出柳林红粘土剖面记录的地磁极性柱与地磁极性年代表的C3n.1n～C4n.2r相对应,卫家洼红粘土的起始时间可以追溯到8.1Ma左右,并对剖面的三个段位进行年龄区间划分和沉积速率计算,分析不同沉积速率所代表的沉积物源搬运距离、搬运介质以及动力能量的稳定性;最后利用磁化率各向异性研究推断出柳林地区红粘土磁性颗粒的优势取向以及沉积动力方向在不同深度上的表现形式有所差异。结合磁极性地层结果表明,柳林剖面受到吕梁山隆升的影响,沉积古环境分为3个阶段,8.1Ma～7.3Ma红粘土处于水下沉积的阶段,受到由东向西的水流搬运堆积;7.3Ma～5.5Ma主要为西北方向风成粉尘沉积,阶段内部分时期参杂来自东侧吕梁山水流作用的过渡带;5.5Ma以来,磁化率各向异性开始显示完整的风成沉积特征。
[Abstract]:Red clay in the Loess Plateau of China, as the most typical sedimentary product of the Neogene in the north of China, contains abundant information of paleoclimate and paleoenvironment changes, and records in detail the development and evolution of the Loess Plateau since the Neogene. The eastern margin of the Loess Plateau is located on the west side of Luliangshan Mountain. The uplift of Luliangshan has resulted in the accumulation of sand and gravel layer in front of the mountain, which is characterized by thick red clay, which is directly unconformable to Mesozoic sandstone. Typical hydrogenic materials such as gravel and fossils are often mixed in red clay deposits which indicate the evolution of dust accumulation in Luliangshan uplift and Loess Plateau since the Neogene. The Liulin area in the western foot of Luliang Mountain in the eastern part of the Loess Plateau in China formed a set of extremely thick red clay sedimentary sequences in this environment. Based on the previous studies of the Neogene red clay, the red clay profile of Weijiawa village, Liulin County, on the western foot of Luliangshan, the eastern edge of the Loess Plateau, was selected for detailed petromagnetic study, and environmental magnetics was adopted. Paleomagnetism and magnetic susceptibility anisotropy are combined to evaluate the area and to further explore the paleoenvironmental evolution of red clay dust accumulation in the western foot of Luliangshan and the eastern edge of the Loess Plateau since the Neogene. The red clay profile of Weijiawa is Luliangshan to the east and the Yellow River to the west. The modern geomorphology belongs to the loess hilly and gully region. The area experienced strong denudation and the topography was characterized by loess red clay gullies and valleys above the Mesozoic basement. The red clay strata were well exposed. The thickness of Weijiawa red clay section is about 112 m, the upper layer is loess-paleosol sequence, but the bottom is not seen below. According to the characteristics of field lithology, the Neogene strata can be divided into three sections: in the upper section, Om~30m, is mainly composed of crimson brown red clay and calcareous nodules, showing stronger weathering than Quaternary loess paleosol; In the lower section, 81mU 112m, red clay or sandy clay mixed with grayish-white sand layer, sand gravel layer, red clay is light red-brown, mainly composed of two alluvial fan facies sedimentary sequence from top to bottom. There are lithologic characteristics of upper and lower member in the middle transitional section, which is 30 m or 81 m, and some of the strata are complicated. First of all, through K-T curve, hysteresis loop study shows that the magnetic minerals of red clay in section are basically the same as loess, which ensures the paleomagnetic experiment in the latter part. Feasibility of implementation of magnetic susceptibility anisotropy and accuracy of data results; Then through paleomagnetic experiments, the geomagnetic polarity column recorded in the Liulin red clay profile corresponds to the C3n.1n~C4n.2r represented by the geomagnetic polarity year, and the onset time of Weijiawa red clay can be traced back to about 8.1Ma. At the same time, the three sections of the section are divided by age interval and the sedimentation rate is calculated, and the stability of sediment source transport distance, transport medium and dynamic energy represented by different deposition rates is analyzed. Finally, based on the magnetic susceptibility anisotropy, the dominant orientation of the red clay magnetic particles in Liulin area and the different forms of the sedimentary dynamic direction at different depths are inferred. The results of magnetic polar strata show that the Liulin profile is affected by the uplift of Luliangshan and the sedimentary paleoenvironment is divided into three stages. The 8.1Ma~7.3Ma red clay is in the underwater sedimentary stage and is transported and accumulated by the flow from east to west. The 7.3Ma~5.5Ma is mainly eolian dust deposition in the northwest direction, and in some periods it comes from the transitional zone of the eastern Luliangshan flow. Since 5.5Ma, the magnetic susceptibility anisotropy has begun to show the complete characteristics of the aeolian deposition.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P318.41;P532
，
本文编号：2318810
[Abstract]:Red clay in the Loess Plateau of China, as the most typical sedimentary product of the Neogene in the north of China, contains abundant information of paleoclimate and paleoenvironment changes, and records in detail the development and evolution of the Loess Plateau since the Neogene. The eastern margin of the Loess Plateau is located on the west side of Luliangshan Mountain. The uplift of Luliangshan has resulted in the accumulation of sand and gravel layer in front of the mountain, which is characterized by thick red clay, which is directly unconformable to Mesozoic sandstone. Typical hydrogenic materials such as gravel and fossils are often mixed in red clay deposits which indicate the evolution of dust accumulation in Luliangshan uplift and Loess Plateau since the Neogene. The Liulin area in the western foot of Luliang Mountain in the eastern part of the Loess Plateau in China formed a set of extremely thick red clay sedimentary sequences in this environment. Based on the previous studies of the Neogene red clay, the red clay profile of Weijiawa village, Liulin County, on the western foot of Luliangshan, the eastern edge of the Loess Plateau, was selected for detailed petromagnetic study, and environmental magnetics was adopted. Paleomagnetism and magnetic susceptibility anisotropy are combined to evaluate the area and to further explore the paleoenvironmental evolution of red clay dust accumulation in the western foot of Luliangshan and the eastern edge of the Loess Plateau since the Neogene. The red clay profile of Weijiawa is Luliangshan to the east and the Yellow River to the west. The modern geomorphology belongs to the loess hilly and gully region. The area experienced strong denudation and the topography was characterized by loess red clay gullies and valleys above the Mesozoic basement. The red clay strata were well exposed. The thickness of Weijiawa red clay section is about 112 m, the upper layer is loess-paleosol sequence, but the bottom is not seen below. According to the characteristics of field lithology, the Neogene strata can be divided into three sections: in the upper section, Om~30m, is mainly composed of crimson brown red clay and calcareous nodules, showing stronger weathering than Quaternary loess paleosol; In the lower section, 81mU 112m, red clay or sandy clay mixed with grayish-white sand layer, sand gravel layer, red clay is light red-brown, mainly composed of two alluvial fan facies sedimentary sequence from top to bottom. There are lithologic characteristics of upper and lower member in the middle transitional section, which is 30 m or 81 m, and some of the strata are complicated. First of all, through K-T curve, hysteresis loop study shows that the magnetic minerals of red clay in section are basically the same as loess, which ensures the paleomagnetic experiment in the latter part. Feasibility of implementation of magnetic susceptibility anisotropy and accuracy of data results; Then through paleomagnetic experiments, the geomagnetic polarity column recorded in the Liulin red clay profile corresponds to the C3n.1n~C4n.2r represented by the geomagnetic polarity year, and the onset time of Weijiawa red clay can be traced back to about 8.1Ma. At the same time, the three sections of the section are divided by age interval and the sedimentation rate is calculated, and the stability of sediment source transport distance, transport medium and dynamic energy represented by different deposition rates is analyzed. Finally, based on the magnetic susceptibility anisotropy, the dominant orientation of the red clay magnetic particles in Liulin area and the different forms of the sedimentary dynamic direction at different depths are inferred. The results of magnetic polar strata show that the Liulin profile is affected by the uplift of Luliangshan and the sedimentary paleoenvironment is divided into three stages. The 8.1Ma~7.3Ma red clay is in the underwater sedimentary stage and is transported and accumulated by the flow from east to west. The 7.3Ma~5.5Ma is mainly eolian dust deposition in the northwest direction, and in some periods it comes from the transitional zone of the eastern Luliangshan flow. Since 5.5Ma, the magnetic susceptibility anisotropy has begun to show the complete characteristics of the aeolian deposition.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P318.41;P532
，
本文编号：2318810
本文链接：https://www.wllwen.com/kejilunwen/diqiudizhi/2318810.html
