Reinterpretation of the glacial chronology of South Westland, New Zealand
Reinterpretation of the glacial chronology of South Westland, New Zealand
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新西兰南韦斯特兰冰川年代学的重新解释
DOI：
10.1080/00288306.2001.9514917
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发表时间：
2001
影响因子：
2.2
通讯作者：
Olav B. Lian
中科院分区：
文献类型：
--
作者：
P. Almond;N. Moar;Olav B. Lian
Almond于1996年建立的西南地区冰川年代地层学是基于咸水森林及其周围冰川地貌上黄土覆盖层的土壤地层学。黄土片和形态确定的土壤特征与海洋氧同位素记录建立的全球气候事件。花粉分析和少量的放射性碳年龄支持年代地层学。在这项研究中，我们已经使用了全元素，矿物和植硅体分析，和发光测年的黄土/土壤地层单位与气候事件的相关性进行测试。已纳入Okarito森林新地段的数据。发光测年法的价值有限。热释光测年法得出的年龄不可接受且精度低，年代非常古老，且在地层学上顺序相反。光学测年法（IRSL）消除了其中一些异常，但准确性的不确定性仍然是一个问题。一些光学年龄明显比相关的放射性碳年龄年轻。我们怀疑沉积物的高度风化性质与沉积物的来源相结合可能是造成这些影响的原因。针对钾长石或石英的常规光学测年法不能在韦斯特兰应用。黄土层Lla、Llb、L2、L3和L4现在被认为是末次（Otira）冰期。L1 a在16 ka前的海洋氧同位素阶段（OIS 2）积累，但在24 ka后才积累; Lib在OIS 2阶段也积累，但在24 ~ c之间。36 ka。L2在OIS 3期间从45到c累积。五万黄土层L3和L4现在与OIS 4对比。黄土片L5的土壤蚀变表明，在最后一次间冰期之前，可能在OIS 6的沉积相一致的显着的风化。根据修正的黄土地层学，冰川推进M5和M6，以及相关的地貌，没有黄土覆盖，都发生在OIS 2。两个冰川推进，M4a和M4 b，都被分配到OIS 3，并被认为发生在45和50 ka之间。24和36 ka。与推进M2和M3相关的冰碛整合覆盖于L4之上，并与OIS 4相关。覆盖在L1-L5黄土层上的Ml冰碛被认为是怀梅阿冰期（OIS 6）。我们目前的工作是一致的，最近的研究在峡湾，这表明一个更复杂的冰川地层的Otiran比在西北地区的认可。
Abstract The glacial chronostratigraphy for South Westland established by Almond in 1996 was based on the soil stratigraphy of loess coverbeds on glacial landforms in and around Saltwater Forest. Loess sheets and morphologically identified soil features were correlated with global climatic events established by the marine oxygen isotope record. Pollen analysis and few radiocarbon ages supported the chronostratigraphy. In this study, we have used total element, mineral and phytolith analysis, and luminescence dating of loess to test the current correlation of loess/soil stratigraphic units with climatic events. Data from new sections in Okarito Forest have been incorporated. Luminescence dating was found to be of limited value. Thermoluminescence dating yielded unacceptable and low‐precision ages that were anomalously old, and in strati‐graphically reversed sequence. Optical (IRSL) dating removed some of these anomalies but uncertainty about accuracy remained a problem. Some optical ages were significantly younger than associated radiocarbon ages. We suspect the highly weathered nature of the sediments being dated in combination with sediment provenance may be the cause of these effects. Routine optical dating which targets potassium feldspars or quartz cannot be applied in Westland. Loess sheets Lla, Lib, L2, L3, and L4 are now thought to be of Last (Otira) Glacial age. L 1a accumulated in marine oxygen isotope stage (OIS) 2 before 16 ka, but after 24 ka, and Lib also accumulated in OIS 2 but between 24 and c. 36 ka. L2 accumulated during OIS 3 from 45 to c. 50 ka. Loess sheets L3 and L4 are now correlated with OIS 4. Soil alteration in loess sheet L5 indicates significant weathering consistent with deposition before the last interglacial, probably during OIS 6. On the basis of the revised loess stratigraphy, glacial advances M5 and M6, and associated landforms, which have no loess cover, both occurred during OIS 2. Two glacial advances, M4a and M4b, are both assigned to OIS 3, and are thought to have occurred between 45 and 50 ka and c. 24 and 36 ka, respectively. Moraines associated with advances M2 and M3 are conformably overlain by L4 and are correlated to OIS 4. Moraine Ml, which is draped by loess sheets L1‐L5, is thought to be of Waimea Glaciation age (OIS 6). Our present work is consistent with recent studies in Fiordland, which suggest a more complex glacial stratigraphy for the Otiran than is recognised in North Westland.