柳林地區(qū)新近紀紅粘土的巖石磁學研究及古環(huán)境意義
發(fā)布時間：2018-11-08 14:52
【摘要】：中國黃土高原紅粘土作為中國北方新近紀最典型的沉積產(chǎn)物,蘊含著豐富的古氣候與古環(huán)境變化信息,詳細地記錄了黃土高原新近紀以來的發(fā)展演化歷程。黃土高原東緣在地理位置上處于呂梁山西側(cè),呂梁山的隆升造就了山前砂礫石層堆積,砂礫石層之上以厚層的紅粘土為特征,紅粘土堆積直接不整合覆蓋于中生代砂巖之上,紅粘土堆積中常夾雜有砂礫石、化石等典型的水成物質(zhì),這些成分良好地指示了新近紀以來呂梁山隆升、黃土高原粉塵堆積的演變記錄。中國黃土高原東部、呂梁山西麓的柳林地區(qū)正是在這種環(huán)境下形成了一套巨厚的紅粘土沉積序列。在前人對新近紀紅粘土研究的基礎(chǔ)上,選擇了呂梁山西麓、黃土高原東緣的柳林縣衛(wèi)家洼村紅粘土剖面進行詳細的巖石磁學研究,通過環(huán)境磁學、古地磁學以及磁化率各向異性相結(jié)合的方法對該區(qū)域加以評估,并進一步探討新近紀以來呂梁山西麓、黃土高原東緣紅粘土粉塵堆積的古環(huán)境演變過程。衛(wèi)家洼紅粘土剖面東側(cè)為呂梁山,西側(cè)為黃河,現(xiàn)代地貌屬于黃土丘陵溝壑區(qū)。該區(qū)域經(jīng)歷了強烈的剝蝕作用,地形以中生代基底之上的黃土、紅粘土沖溝和山谷為特征,紅粘土地層出露較好。衛(wèi)家洼紅粘土剖面厚度約為112m,上覆為黃土-古土壤序列,下未見底。該新近紀地層根據(jù)野外巖性特征可分為三段:上段,Om～30m,由深紅棕色的紅粘土與鈣質(zhì)結(jié)核互層為主,表現(xiàn)出比第四紀黃土-古土壤更強的風化作用;下段,81m～112m,為紅粘土或砂質(zhì)粘土夾雜灰白色砂層、砂礫石層,紅粘土為淺紅棕色,主要由兩個從上至下變粗的沖積扇相沉積序列組成;中部過渡段,30m～81m,兼有上下段的巖性特征,部分層位巖性復雜。首先通過K-T曲線、磁滯回線研究表明剖面紅粘土的磁性礦物與黃土基本相同,這保證了后面環(huán)節(jié)的古地磁實驗、磁化率各向異性等研究方案實施的可行性和數(shù)據(jù)結(jié)果的準確性;然后通過古地磁學實驗得出柳林紅粘土剖面記錄的地磁極性柱與地磁極性年代表的C3n.1n～C4n.2r相對應,衛(wèi)家洼紅粘土的起始時間可以追溯到8.1Ma左右,并對剖面的三個段位進行年齡區(qū)間劃分和沉積速率計算,分析不同沉積速率所代表的沉積物源搬運距離、搬運介質(zhì)以及動力能量的穩(wěn)定性;最后利用磁化率各向異性研究推斷出柳林地區(qū)紅粘土磁性顆粒的優(yōu)勢取向以及沉積動力方向在不同深度上的表現(xiàn)形式有所差異。結(jié)合磁極性地層結(jié)果表明,柳林剖面受到呂梁山隆升的影響,沉積古環(huán)境分為3個階段,8.1Ma～7.3Ma紅粘土處于水下沉積的階段,受到由東向西的水流搬運堆積;7.3Ma～5.5Ma主要為西北方向風成粉塵沉積,階段內(nèi)部分時期參雜來自東側(cè)呂梁山水流作用的過渡帶;5.5Ma以來,磁化率各向異性開始顯示完整的風成沉積特征。
[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.
【學位授予單位】：西北大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P318.41;P532
，
本文編號：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.
【學位授予單位】：西北大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P318.41;P532
，
本文編號：2318810
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