Magnetostratigraphy and provenance of the Qingzhou loess in Shandong province
Magnetostratigraphy and provenance of the Qingzhou loess in Shandong province
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山东青州黄土磁性地层学及物源
DOI：
10.3724/sp.j.1227.2011.00184
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发表时间：
2011-09
影响因子：
3
通讯作者：
Chen DongDong
中科院分区：
文献类型：
--
作者：
Peng ShuZhen;Zhu LiJun;Xiao GuoQiao;Qiao YanSong;Gao ZhiDong;Chen DongDong
鲁中山区北侧的山间谷地和山前地带广泛分布着不同厚度的黄土沉积。然而，黄土沉积的基本年龄和物质来源尚不清楚。利用磁性地层学和光学受激发光(OSL)方法对山东青州黄土剖面进行了研究，并用矿物学方法进一步探讨了其主要物源。磁性地层学结果表明，未识别出Brunhes/Matuyama(B/M)反转边界，其基本年龄小于0.78 Ma。根据沉积速率外推，根据上部沉积速率由OSL年龄推算出青州黄土的基本年龄约为0.5 Ma。到目前为止，鲁中山区北侧还没有更古老的黄土沉积的报道。研究结果表明，本区黄土沉积时代可能为中更新世。青州黄土的基本年龄与长江中下游下蜀黄土基本同步。青州剖面粘土矿物主要成分为伊利石。其他粘土矿物组成主要为蒙皂石、绿泥石和高岭石，与黄土高原西峰黄土相似。而青州黄土样品中蒙皂石含量和伊利石/高岭石比值均高于黄土高原西峰黄土样品，说明鲁中北部山区黄土与黄土高原黄土沉积物具有不同的物源。粘土矿物分析进一步印证了早先的结论，即冰期出露在莱州湾和黄河下游河流平原的海相地层是青州黄土沉积的主要物质来源，这是黄河下游局部干旱化的标志。鲁中山区的黄土沉积始于0.5 Ma左右。青州黄土的形成时代与中更新世以来持续的高纬度寒潮基本同步，表明东亚冬季风的加强使大量暴露在莱州湾和黄河下游河流平原海相地层中的物质进入鲁中山区。结果表明，中更新世以来青州黄土的形成是区域地质作用和全球变化共同作用的结果。
Loess deposits with varying thickness are widely distributed on the intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous regions. However, the basal ages and material resources of the loess deposits are not clear. The paper studied the Qingzhou loess profile in Shandong with magnetostratigraphic and optical stimulated luminescence (OSL) methods and further investigated its main provenances with the mineralogical methods. The magnetostratigraphic results showed that the Brun- hes/Matuyama (B/M) reversal boundary was not recognized, suggesting a basal age younger than 0.78 Ma. Ex- trapolations by sedimentation rates, based on the upper part depositional rate from the OSL age, the basal age of the Qingzhou loess is about 0.5 Ma. Until now, older loess deposits have not been reported on the northern side of the central Shandong mountainous regions. The results of the paper indicate that the loess deposits in this area might have strated from the Middle Pleistocene. The basal age of Qingzhou loess is approximately synchronous with the Xiashu loess in the middle-lower reaches of Yangtze River. Major components of clay minerals in the Qingzhou profile are dominated by illite. Other clay mineral compositions are mainly smectite, chlorite and kaolinite, which are similar with the Xifeng loess in the Loess Plateau. However, the contents of smectite and the ratios of illite and kaolinte in the Qingzhou loess samples are higher than those in the Xifeng loess samples of the Loess Plateau, indicating that the loess in the northern side of the central Shandong mountainous regions has different sources from that of the loess deposits in the Loess Plateau. The clay mineral analysis further reinforces the earlier conclu- sion that the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of Yellow River during the glacier periods are the main material sources for the Qingzhou loess deposits, which is an indicator to the local aridification of the lower reaches of the Yellow River. Loess deposition in the central Shandong mountainous regions started at around 0.5 Ma. The age of Qingzhou loess is approximately synchronous with the ongoing high-latitude cold since the Middle Pleistocene, which indicates that strengthened East Asian winter monsoon was sufficiently energetic to bring substantial quantities of material from the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of the Yellow River to the central Shandong mountainous regions. The results therefore suggest that both regional geological process and global changes were responsible for the forma- tion of Qingzhou loess since Middle Pleistocene.
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DOI：
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