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Magnetic records of Core MD77-181 in the Bay of Bengal and their paleoenvironmental implications

机译：孟加拉湾MD77-181岩心的磁记录及其古环境意义

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High-resolution environmental magnetic measurements were carried out on Core MD77-181 in the Bay of Bengal, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization of all samples, and temperature-dependence of magnetic susceptibilities and magnetic hysteresis parameters of representative samples. The results suggest that (1) the magnetic mineral assemblage of the upper 9.82 m sediments (corresponding to the last 160 ka) is dominated by pseudo-single domain magnetite, with more abundant coarse grains in glacial periods than in in-terglacial periods; (2) the uppermost 6.50 m of sediments (corresponding to the last 70 ka) shows significant temporal variations in grain sizes of magnetic minerals, possibly reflecting the teleconnection between variations of the Indian summer monsoon and rapid cold events of the North Atlantic (Heinrich events); (3) the sediments below 9.82 m are dominated by paramagnetic minerals (probably including pyrites), suggesting reductive diagenesis. The magnetic records of Core MD77-181 are comparable to those of Core MD77-180 in the Bay of Bengal, and ODP Hole 722B in the Arabian Sea. This study suggests that the paleoceanographic event at ~160 ka significantly changed the redox state of the northern Indian Ocean, from a reductive environment before the event to an oxic or suboxic environment after the event.
机译：在孟加拉湾的MD77-181岩心上进行了高分辨率的环境磁测量，包括磁化率，所有样品的磁滞剩磁，等温剩磁以及代表性样品的磁化率和磁滞参数随温度的变化。结果表明：（1）上部9.82 m沉积物（对应于最后160 ka）的磁性矿物组合以拟单畴磁铁矿为主，冰川期的粗粒含量比冰川期的丰富。 （2）最高的6.50 m沉积物（对应于最后70 ka）显示出磁性矿物的粒径有明显的时间变化，这可能反映了印度夏季风的变化与北大西洋快速寒冷事件（Heinrich事件）之间的遥相关）; （3）9.82 m以下的沉积物以顺磁性矿物（可能包括黄铁矿）为主，表明还原成岩作用。 MD77-181岩心的磁记录可与孟加拉湾的MD77-180磁记录和阿拉伯海的ODP 722B磁记录相媲美。这项研究表明，约160 ka的古海洋事件大大改变了北印度洋的氧化还原状态，从事件发生前的还原性环境变为事件发生后的有氧或亚缺氧环境。

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