"中布容事件"时南极底层流在马里亚纳海沟南部的沉积记录. (Chinese)

A Study of the Sediment Record for Antarctic Bottom Water in the Southern Mariana Trench During the Mid-Brunhes Event (MBE). (English)

A gravity core sample with 533 cm long obtained in the southern Marina Trench was analyzed by grain-size smear tests, XRF scanning, paleomagnetism and magnetic anisotropy. The paleomagnetic analysis revealed the Brunhes-Matuyama reversal event （B-M boundary） at 507 cm, near the bottom of the core, indicating that the sample contains the record of at least 0.78 million years of the depositional environment. The chronological framework was established by analyzing the relative paleomagnetic intensity （RPI） and long-term variation in paleomagnetic inclination. The grain-size analysis and XRF scans indicate that the sediment type in the core underwent a fundamental change from bottom to top: at the bottom it is dominated by pelagic clay with evidence of terrigenous input; at the top it is dominated by siliceous ooze consisting mainly of diatoms. Analysis indicated that this change was mainly because of the appearance of the Antarctic Bottom Water （AABW） during the Mid-Brunhes Event （MBE）. The paleomagnetism establishes the age model, and the magnetic anisotropy and sediment composition indicate that the MBE began to influence this area with the appearance of the AABW around 553 ka. The sediment type began to change from terrigenous input to biogenesis, at about 417 ka, by which time the main composition of the sediment was already biogenetic. The AABW enhanced the change until the sediment was almost completely composed of pure siliceous ooze from 336 ka until the present day, indicating the termination of the MBE in this area. [ABSTRACT FROM AUTHOR]

对马里亚纳海沟南部的柱状样品进行了涂片粒度、岩心扫描（XRF）、古地磁及磁化率各向异性分析。古地磁分析结果表明,该柱底部507 cm处发生了倒转事件（B/M界限）,表明该柱至少记录了78万年以来的沉积环境演变,通过对古地磁相对强度及倾角长期变化分析建立了该柱布容时期以来年代框架。涂片粒度分析及XRF扫描结果均显示,该柱样沉积物类型自底部到顶部发生了根本性转变,底部以代表陆源输入的远洋黏土为主,上部以代表生源作用的硅质软泥为主,分析认为造成这种变化的主要原因在于中布容事件（MBE）时南极底层水（AABW）对该区域的影响。结合沉积物类型、磁化率各向异性及古地磁年代学分析,认为中布容事件对该柱样所在区域的影响始于约553 ka,南极底层流开始影响该区域,沉积物类型由陆源向生源转变;到约417 ka时,沉积物类型主要成分已完成由陆源向生源转变,之后,南极底层流进一步增强;到约336 ka时,沉积物类型几乎全由硅质软泥主导,且之后不再发生较大变化,表明MBE对该区域影响的结束. [ABSTRACT FROM AUTHOR]

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