Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin
Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin
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DOI：
10.1016/j.epsl.2013.06.026
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发表时间：
2013-08-15
影响因子：
5.3
通讯作者：
Kesler, M. S.
中科院分区：
文献类型：
--
作者：
Channell, J. E. T.;Hodell, D. A.;Kesler, M. S.
透射电镜观察伊比利亚西南边缘晚第四纪沉积物的磁性以细菌磁铁矿为主，碎屑钛磁铁矿和赤铁矿也有贡献。活性赤铁矿，加上低有机质浓度和缺乏硫酸盐还原，导致异化铁还原和铁（II）的可用性丰富的趋磁细菌。磁铁矿粒度指标（kappa(ARM)/kappa和ARM/IRM）和s -比（对赤铁矿敏感）在标准/标准间时间尺度上变化，包含轨道功率，模拟浮游三角洲O-18。在冰期和冰川同位素阶段，碎屑/生物磁铁矿比值和赤铁矿浓度较大，反映了海平面下降时期碎屑（磁铁矿）输入增加，与有利于赤铁矿粉尘供应的大气条件相一致。另一方面，磁化率对与浮冰碎屑（IRD）相关的粗碎屑多畴（MD）磁铁矿具有非常不同的响应。高磁化率和/或磁性粒度粗化，标志着海因里希岩（HS），特别是HS2、HS3、HS4、HS5、HS6和HS7，以及更古老的海因里希样碎屑层，表明该地区对极锋位置波动的敏感性。相对古强度（RPI）记录具有基于浮游三角洲O-18与冰芯年代学相关性的良好约束的年龄模型，然而，它们与参考记录（如PISO）不同，特别是在冰川极大期附近，主要是由于在赤铁矿输入增强的间隔内，RPI记录的标准化效率不高。(C) 2013 Elsevier B.V.版权所有
Magnetic properties of late Quaternary sediments on the SW Iberian Margin are dominated by bacterial magnetite, observed by transmission electron microscopy (TEM), with contributions from detrital titanomagnetite and hematite. Reactive hematite, together with low organic matter concentrations and the lack of sulfate reduction, lead to dissimilatory iron reduction and availability of Fe(II) for abundant magnetotactic bacteria. Magnetite grain-size proxies (kappa(ARM)/kappa and ARM/IRM) and S-ratios (sensitive to hematite) vary on stadial/interstadial timescales, contain orbital power, and mimic planktic delta O-18. The detrital/biogenic magnetite ratio and hematite concentration are greater during stadials and glacial isotopic stages, reflecting increased detrital (magnetite) input during times of lowered sea level, coinciding with atmospheric conditions favoring hematitic dust supply. Magnetic susceptibility, on the other hand, has a very different response being sensitive to coarse detrital multidomain (MD) magnetite associated with ice-rafted debris (IRD). High susceptibility and/or magnetic grain-size coarsening, mark Heinrich stadials (HS), particularly HS2, HS3, HS4, HS5, HS6 and HS7, as well as older Heinrich-like detrital layers, indicating the sensitivity of this region to fluctuations in the position of the polar front. Relative paleointensity (RPI) records have well-constrained age models based on planktic delta O-18 correlation to ice-core chronologies, however, they differ from reference records (e.g. PISO) particularly in the vicinity of glacial maxima, mainly due to inefficient normalization of RPI records in intervals of enhanced hematite input. (C) 2013 Elsevier B.V. All rights reserved.