网纹化对皖南红土特征剩磁的影响

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南京大学学报(自然科学版) ›› 2014, Vol. 50 ›› Issue (2) : 192.

网纹化对皖南红土特征剩磁的影响

叶晓雯1，韩志勇1*，李徐生1，房迎三2，王晓勇1

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The influence of reticulating process on characteristic remanence of red soil in southern Anhui Province

Ye Xiaowen1, Han Zhiyong1, Li Xusheng1, Fang Yingsan2, Wang Xiaoyong1

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摘要

皖南的红土是形成于亚热带的风尘沉积，建立红土的年代框架主要依据磁性地层，但红土磁性地层的可靠性却存在争议。为查明风化作用对古地磁特征剩磁的影响，我们选择了安徽宣城官塘的红土剖面进行了高分辨率的磁性地层研究。结果显示，均质红土层的特征剩磁比较稳定，而网纹红土层的特征剩磁方向不稳定，极性变化频繁，难以准确划分出极性界线。岩石磁学的研究表明，均质红土与网纹红土的载磁矿物种类与含量不完全相同，原因在于沉积后强烈的网纹化作用，一方面使得原生碎屑磁性矿物发生转变，含量明显下降，另一方面形成了较多的次生磁性矿物，碎屑剩磁因此受到化学剩磁的严重干扰，导致常规方法获得的网纹红土的特征剩磁方向不可靠。据此我们认为在皖南网纹红土层内确定的B/M界线需要慎重对待。这一发现对其它南方网纹红土的古地磁测年也有参考意义。

Abstract

The red soil distributed in southern Anhui Province is?formed from the?subtropical aeolian deposits. Magnetostratigraphic correlation is the main method to establish the temporal sequence of the red soil. However, the reliability is still controversial. In order to identify the influence of reticulating processes on the characteristic remanence, we carried out high-resolution magnetostratigraphic measurements on the Guantang section in Xuancheng. The results show the characteristic remanence in the homogeneous red soil layer is relatively stable, but unstable in the reticulated red soil layer. This finding indicates it is difficult to?precisely draw?the?B/M boundary. The rock magnetism study illustrates that both type and content of magnetic?minerals in the homogeneous red soil layer are not identical with that in reticulated red soil layer. On one hand, intense reticulating processes altered the primary magnetic minerals and resulted in quantitative decrease，on the other hand, many secondary magnetic minerals formed. Therefore, the detrital remanence is so severely interfered by the chemical remanence that the directions of characteristic remanence obtained in reticulated red soil using conventional methods are unreliable. The B/M boundary in reticulated red soil layer in southern Anhui Province needs to be?reevaluated. This finding is significant for paleomagnetic dating?of other?reticulated red soil in South China

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叶晓雯1，韩志勇1*，李徐生1，房迎三2，王晓勇1. 网纹化对皖南红土特征剩磁的影响[J]. 南京大学学报(自然科学版), 2014, 50(2): 192

Ye Xiaowen1, Han Zhiyong1, Li Xusheng1, Fang Yingsan2, Wang Xiaoyong1. The influence of reticulating process on characteristic remanence of red soil in southern Anhui Province[J]. Journal of Nanjing University(Natural Sciences), 2014, 50(2): 192

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