High‐resolution analysis of early diagenetic effects on magnetic minerals in post‐middle‐Holocene continental shelf sediments from the Korea Strait
High‐resolution analysis of early diagenetic effects on magnetic minerals in post‐middle‐Holocene continental shelf sediments from the Korea Strait
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DOI：
10.1029/2003jb002813
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发表时间：
2004-03
影响因子：
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通讯作者：
Jian Liu;R. Zhu;A. Roberts;Shaoquan Li;J. Chang
中科院分区：
文献类型：
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作者：
Jian Liu;R. Zhu;A. Roberts;Shaoquan Li;J. Chang
[1]研究的两个来自朝鲜海峡的沉积物岩心包含了近6000年沉积的泥层（厚度分别为14 m和32.62 m）。沉积物具有均匀的岩性和地球化学性质，但磁性质的显著下核变化表明成岩作用对其磁性有显著影响。与深海沉积物相比，在这些快速沉积的大陆架沉积物中，对影响磁性矿物组合的早期成岩反应的扩展观点是显而易见的。根据地磁性质的变化，将沉积物划分为4个下降段。段1受成岩作用影响最小，碎屑磁铁矿和赤铁矿含量最高，固相硫含量最低。段2以顺磁性黄铁矿为主，磁铁矿和赤铁矿含量急剧下降，表明碎屑磁性矿物具有活性还原溶蚀作用。第3段赤铁矿随深度逐渐消失，与磁铁矿的最低浓度一致。层段4自生灰长岩在岩心下增强，明显形成于沉积物-水界面以下3 ~ 30 m深度，黄铁矿化反应受阻。这些结果表明，获得由灰长岩携带的磁化的时间延迟了数千年，这表明对含灰长岩的大陆架沉积物的地磁场行为的研究应谨慎进行。此外，深部磁性矿物碎屑的几乎完全破坏表明，对快速沉积的陆架沉积物的磁性研究不太可能提供与同沉积环境过程有关的有意义的特征。
[1] Two studied sediment cores from the Korea Strait contain mud sequences (14 m and 32.62 m in thickness) that were deposited during the last 6,000 years. The sediments have uniform lithology and geochemical properties, however, marked down-core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties. An expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep-sea sediments. The studied sediments are divided into four descending intervals, based on magnetic property variations. Interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite, and the lowest solid-phase sulfur contents. Interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations, which suggest active reductive dissolution of detrital magnetic minerals. Interval 3 is marked by a progressive loss of hematite with depth, and coincides with the minimum magnetite concentration. Interval 4 has an increasing down-core enhancement of authigenic greigite, which apparently formed at depths of 3–30 m below the sediment-water interface due to arrested pyritization reactions. These results indicate delays of thousands of years for acquisition of magnetizations carried by greigite, which suggests that studies of geomagnetic field behavior from greigite-bearing continental shelf sediments should be conducted with care. Also, virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn-depositional environmental processes.