| 四川冕宁昔格达组磁性地层学初步研究及意义* |
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| 引用本文： | 姚海涛,赵志中,乔彦松,李朝柱,王书兵,王燕,陈永生,蒋复初.四川冕宁昔格达组磁性地层学初步研究及意义*[J].第四纪研究,2007,27(1):74-84. |
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| 作者姓名： | 姚海涛 赵志中 乔彦松 李朝柱 王书兵 王燕 陈永生 蒋复初 |
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| 作者单位： | 中国地质科学院地质力学研究所,北京,100081 |
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| 基金项目： | 中国地质调查局地质调查项目 |
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| 摘 要： | 文章首次对川西安宁河流域冕宁昔格达组河湖相沉积物进行岩石磁学和磁性地层学初步研究。结果表明沉积物具有正常的沉积组构,适合磁性地层学研究;赤铁矿和磁铁矿是主要载磁矿物;沉积物记录的古地磁场方向基本都为正极性,主要形成于高斯正极性时,约4.18~2.58Ma。综合对比表明,分布在大渡河、安宁河和金沙江干流的昔格达组以典型黄灰色岩性组合为特征,具有基本相同的沉积序列和磁极性序列,主要形成于高斯正极性时。
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| 关 键 词： | 攀西地区 昔格达组 岩石地层学 磁性地层学 岩石磁学 |
| 文章编号： | 1001-7410（2007）01-74-11 |
| 收稿时间： | 2006-03-09 |
| 修稿时间： | 2006-05-09 |
MAGNETOSTRATIGRAPHIC DATING OF THE XIGEDA FORMATION IN MIANNING, SICHUAN AND ITS SIGNIFICANCE |
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| Yao Haitao,Zhao Zhizhong,Qiao Yansong,Li Chaozhu,Wang Shubing,Wang Yan,Chen Yongsheng,Jiang Fuchu.MAGNETOSTRATIGRAPHIC DATING OF THE XIGEDA FORMATION IN MIANNING, SICHUAN AND ITS SIGNIFICANCE[J].Quaternary Sciences,2007,27(1):74-84. |
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| Authors: | Yao Haitao Zhao Zhizhong Qiao Yansong Li Chaozhu Wang Shubing Wang Yan Chen Yongsheng Jiang Fuchu |
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| Institution: | Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081 |
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| Abstract: | The Xigeda Formation is renown for its well-developed Late Cenozoic fluvial-lacustrine sequence, which is distributed discontinuously in valleys of the Dadu River, the Anning River, the Jinsha River, and the Yalong River in the Panzhihua-Xichang region, Southwestern Sichuan. The sediments provide great potentials for understanding the formation process of the East-West geomorphological boundary zone of China between the Tibetan Plateau and the Yangtze Block. However, its lithostratigraphic and chronologic views in different areas remain contentious topics in the past 70 years. Here we contribute to this debate with detailed magnetostratigraphic result from the Mianning Section with a thickness of 300.7m at Zhoujiadagou in Mianning County. The 300.7-m section can be divided into two parts from top to bottom: the yellow coarse sand and thin silty clay alternating beddings (0~112.6m) and the grey leading silty clay layers (112.6~300.7m). Preliminary rock magentic and magnetostratigraphical studies on this new discovered section have been carried out. Anisotropy of magnetic susceptibility shows that the sediments have normal deposition fabrics with horizontal foliation planes and have not been subjected to physical disturbance since deposition, indicating a high potential for magnetostratigraphic research. Temperature-dependent susceptibility curves of representative samples illustrate that hematite and magnetite are the dominant magnetic carrier minerals. Stepwise thermal demagnetization successfully isolated 342(96 ％ ) well-defined characteristic magnetization (ChRM) after removing one or two soft components of magnetization. Six magnetozones are recognized in the Mianning Section: three normal, N1 (0~97.5m), N2 (102.5~166m), and N3 (168~297.2m); and three reversed, R1 (97.5~102.5m), R2 (166~168m), and R3 (297.2~300.2m). According to Electron Spin Resonance age of river terrace (1.29Ma) on the topmost of the Xigeda Formation and the Cande and Kents polarity time scale, magnetostratigraphy of the Mianning Section can be correlated to Gauss normal chron and Gilbert reverse chron, roughly ranging from 4.18Ma to 2.58Ma. Lithostratigraphy and magnetostratigraphy correlations have been carried out for several typical Xigeda sediment sections, e.g. the Haiziping Section at Luding, the Fulin Section at Hanyuan, the Xigeda Section at Panzhihua from the north to the south along the Anning River Valley. All these sections have basically similar sedimentary sequences consisting of the upper yellow layer and the lower grey layer and polarity sequences mostly corresponding to the Gauss chron as Mianning Section. It is believed that the Xigeda Formation distributed in the valleys of the Dadu River, the Anning River, and the Jinsha River in the Panzhihua-Xichang region means the "yellow and grey layer complex", and has basically synchronously evolved, mostly corresponding to the Gauss chron. |
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| Keywords: | magnetism Panzhihua-Xichang region Xigeda Formation magnetostratigraphy lithostratigrphy rock |
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