Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from the Tsailiao-chi section, southwestern Taiwan
Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from the Tsailiao-chi section, southwestern Taiwan
复制标题
DOI：
10.1016/s0012-821x(98)00239-8
复制
发表时间：
1998-12
影响因子：
5.3
通讯作者：
C. Horng;M. Torii;K. Shea;S. Kao
中科院分区：
文献类型：
--
作者：
C. Horng;M. Torii;K. Shea;S. Kao
为了建立台湾西南部蔡寮溪剖面古亭坑组下段620 m厚的中晚更新世泥岩序列的磁性生物地层学，我们进行了古地磁和矿物磁性测量，以及沉积物粒度测定和钙质超微化石鉴定。来自65个地点的古地磁样品揭示了两种类型的热退磁（25-400°C）行为：（1）在磁铁矿和磁黄铁矿为主的样品中的单组分稳定特征剩磁（S型），以及（2）当具有显着云英岩浓度的样品被加热到320-340°C以上时极性的突然变化（C型）。从S型样品和磁铁矿为主的C型样品（在340°C以上获得）得出的特征极性与超微化石生物地层学确定的特征极性一致。这表明磁铁矿和磁黄铁矿携带的NRM是可靠的。C型样品在340°C以下的剩磁分量基本上是反平行的，归因于云英岩。几乎反平行的方向可能是由于延迟形成的云英岩，但在这种情况下，该组件的不同方向必须是由于可变的剩磁锁定时间。或者，相反的极性可能是由于自反转，这需要进一步的研究。磁黄铁矿和云英岩可能都是自生形成的，但对所观察到的方向差异没有明确的解释。
To establish a magnetobiostratigraphy for a 620-m-thick middle to late Pleistocene mudstone sequence in the Lower Gutingkeng Formation of the Tsailiao-chi (TLC) section in southwestern Taiwan, we conducted paleomagnetic and mineral magnetic measurements, together with sediment granulometry and calcareous nannofossil identification. Paleomagnetic samples from 65 sites revealed two types of thermal demagnetization (25–400°C) behavior: (1) single-component stable characteristic remanence in magnetite- and pyrrhotite-dominated samples (Type S), and (2) abrupt changes in polarity when samples with significant greigite concentrations were heated above 320–340°C (Type C). The characteristic polarities derived from Type S samples and from magnetite-dominated Type C samples (obtained above 340°C) are consistent with those determined from nannofossil biostratigraphy. This implies that the NRM carried by magnetite and pyrrhotite is reliable. The essentially antiparallel remanence components in Type C samples below 340°C are attributed to greigite. The almost antiparallel direction could have resulted from delayed formation of greigite, but in this case, the different direction of this component must have resulted from variable remanence lock-in times. Alternatively, the opposite polarities may result from self-reversal, which warrants further investigation. Pyrrhotite and greigite may have both formed authigenically, but there is no clear explanation for the observed differences in direction.