Relative paleointensity (RPI) and age control in Quaternary sediment drifts off the Antarctic Peninsula
Relative paleointensity (RPI) and age control in Quaternary sediment drifts off the Antarctic Peninsula
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DOI：
10.1016/j.quascirev.2019.03.006
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发表时间：
2019-05
影响因子：
4
通讯作者：
J. Channell;C. Xuan;D. Hodell;S. Crowhurst;R. Larter
中科院分区：
文献类型：
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作者：
J. Channell;C. Xuan;D. Hodell;S. Crowhurst;R. Larter
高纬度海洋沉积物中缺乏有孔虫碳酸盐，导致传统的氧同位素地层学在全球大部分地区的第四纪年龄控制中不起核心作用。这一限制影响了对记录西南极冰盖(WAIS)和南极半岛冰盖(APIs)过去不稳定至关重要的南极半岛外第四纪沉积物漂移的解释。在这里，我们使用了2015年在RRSJR298号巡航期间从这些沉积物漂流中恢复的活塞岩芯，以测试由稀少的δ18O数据增强的相对古强度数据对年龄控制的有用性。热磁和磁滞数据以及等温剩余磁化(IRM)采集曲线表明，在取芯沉积物中存在普遍的磁铁矿和次要的氧化磁铁矿(“磁铁矿”)。磁铁矿很可能是碎屑岩。磁铁矿是一种自生矿物，与磁铁矿颗粒的表面氧化有关，主要赋存于最上层沉积物的氧化带和以前间冰期气候阶段沉积的埋藏氧化带。低浓度的活性有机质明显导致孔隙水硫酸盐还原受阻，解释了反应性磁铁矿涂层的氧化带埋藏和下部存活。在一些位置，磁化对RPI代理有削弱作用，而在其他位置，磁铁矿不那么明显，RPI代理可以与RPI参考模板充分匹配。位于漂移4的ODP1101站公布的RPI数据可以与当时的RPI模板充分关联，这可能是由于磁铁铁矿在沉积物深度&∼10 m消失(溶解)的结果。
Lack of foraminiferal carbonate in marine sediments deposited at high latitudes results in traditional oxygen isotope stratigraphy not playing a central role in Quaternary age control for a large portion of the globe. This limitation has affected the interpretation of Quaternary sediment drifts off the Antarctic Peninsula in a region critical for documenting past instability of the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). Here we use piston cores recovered from these sediment drifts in 2015 during cruise JR298 of the RRSJames Clark Rossto test the usefulness for age control of relative paleointensity (RPI) data augmented by scant δ18O data. Thermomagnetic and magnetic hysteresis data, as well as isothermal remanent magnetization (IRM) acquisition curves, indicate the presence of prevalent magnetite and subordinate oxidized magnetite (“maghemite”) in the cored sediments. The magnetite is likely detrital. Maghemite is an authigenic mineral, associated with surface oxidation of magnetite grains, which occurs preferentially in the oxic zone of the uppermost sediments, and buried oxic zones deposited during prior interglacial climate stages. Low concentrations of labile organic matter apparently led to arrested pore-water sulfate reduction explaining oxic zone burial and downcore survival of the reactive maghemite coatings. At some sites, maghemitization has a debilitating effect on RPI proxies whereas at other sites maghemite is less evident and RPI proxies can be adequately matched to the RPI reference template. Published RPI data at ODP Site 1101, located on Drift 4, can be adequately correlated to contemporary RPI templates, probably as a result of disappearance (dissolution) of maghemite at sediment depths >∼10 m.