Rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the California continental borderland
Rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the California continental borderland
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DOI：
10.1029/jb095ib04p04437
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发表时间：
1990-04
影响因子：
--
通讯作者：
B. Leslie;S. Lund;D. Hammond
中科院分区：
文献类型：
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作者：
B. Leslie;S. Lund;D. Hammond
为了定量评价沉积物成岩作用对磁性矿物的影响，对加州大陆边缘地区(圣佩德罗盆地、圣卡塔利纳盆地和圣尼古拉斯盆地)海洋沉积物的岩石磁性进行了研究。以前的研究已经注意到，这些沉积物中的自然剩余磁化强度主要由碎屑磁铁矿携带，在沉积后不久就衰减到其表面价值的10%或更少。这种下降是由与沉积物成岩作用有关的磁铁矿溶解作用引起的，与古气候变化或碎屑磁性物质区域流入的变化无关。详细的岩石磁性测量表明，向较软的剩馀矫正力移动，以及磁场强度损失的速度和程度随深度的差异可能与溶解过程有关。向较软的剩余矫顽力的转变与磁性矿物颗粒尺寸随深度的粗化有关，这是由于最细颗粒磁性材料的优先溶解。强度的减小与磁铁矿浓度的减小成线性关系，表明溶解发生的速率常数在0.3KYR~1.6KYR−1之间。来自边界的速率常数、硫化物浓度和磁铁矿粒度估算与前人对磁铁矿溶解的研究一致。我们的结果证明了硫化物和磁铁矿表面积在溶解过程中的重要性。沉积物中粘性剩磁的异常峰表明云母自生生长，并随后转化为黄铁矿。
The rock magnetic properties of marine sediments from the California continental borderland (San Pedro, Santa Catalina, and San Nicolas basins) have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals. Previous studies have noted that the natural remanent magnetization in these sediments, primarily carried by detrital magnetite, decays to 10% or less of its surface value soon after deposition. This decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material. Detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process. The shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest-grained magnetic material. The intensity decreases, which are linearly proportional to magnetite concentration decreases, indicate that dissolution occurs with rate constants ranging from 0.3 to 1.6 kyr−1. The rate constants, sulfide concentrations, and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution. Our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process. Anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite.