Characteristics and Paleoclimatic Significance of Magnetic Susceptibility and Stable Organic Carbon Isotopes from a Bore in Zhoulao Town, Jianghan Plain
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摘要: 江汉平原地处我国东西、南北自然环境的过渡地带, 该地带距今30ka (大约相当于MIS3阶段) 以来的气候变化是研究过去全球气候变化的重要时段之一, 已越来越引起人们的关注.在精确测年的基础上, 对采自江汉平原湖区周老镇钻孔(ZL01) 沉积物柱样的磁化率和有机碳稳定同位素进行了处理和分析, 其结果表明: (1) 该区磁化率和有机碳稳定同位素值的变化特点具有较好的一致性和可对比性, 它们与古气候的关系为: 磁化率的高值、有机碳稳定同位素的偏正值与偏冷、偏干的气候环境相对应; 反之与偏温暖湿润的气候环境相对应. (2) 根据磁化率和有机碳稳定同位素值的变化特点将本区30 kaB. P.以来的古气候分为3个大的气候演化阶段, 在每一个大的气候演化阶段中又可分为若干次小的气候演变阶段.这3个大的气候演化阶段分别为阶段Ⅰ : 其年龄约为30 000~ 14 100 aB. P., 磁化率和δ13C的平均值分别为655.69 × 10-6 SI和-23.15 × 10-3, 均为本区最高值并且曲线波动较大; 阶段Ⅱ : 相应时段为14 100 ~ 3 540 aB. P., 磁化率平均值为较低值369.38 × 10-6SI和δ13C为偏负值(- 27.29 × 10-3), 相对较稳定; 阶段Ⅲ : 年代相当于3 540 ~ 650 aB. P., 平均磁化率为本区最低值311.0 × 10-6 SI, δ13C平均值为- 24.49 × 10-3, 且曲线波动较大. (3) 磁化率与有机碳稳定同位素值发生突变处可能是突发性温度事件的反映.Abstract: Jianghan plain lies in Chinaese east-west and south-north natural transition area. The study of climate change in this area from 30 ka plays an important part in understanding global paleoclimatic events and has been given increasing attention. In this paper, based on 14C dating, an analysis is made of magnetic susceptibility and stable organic carbon isotopes from the bored core in Zhoulao town, Jianghan plain. The results indicate that (1) magnetic susceptibility and stable organic carbon isotopes in this area have good coherence and relativity in the patterns of their evolution. Their relation to paleoclimate is that the higher values of magnetic susceptibility and the stable organic carbon isotope correspond to a colder and drier environment, while the lower values correspond to a warmer, wet environment. (2) According to the pattern of change of magnetic susceptibility and stable organic carbon isotopes, the sequence of climate change from 30 kaB.P. can be divided into 3 main stages: the age of the first stage varies from 30 000-14 100 aB.P., and the average value of magnetic susceptibility and δ13C is 655.69 ×10-6SI and -23.15×10-3 respectively, with a relatively high vibration curve, which is the highest of the three stages; the age of the second stage is from 14 100-3 540 aB.P., and the magnetic susceptibility and δ13C have a low vibration curve with average values of 369.38 ×10-6SI and -27.29×10-3; the age of the third stage is between (3 540-) 650 aB.P. and the average value of magnetic susceptibility is 311.0 ×10-6SI, the lowest of the three stages, and that of δ13C is -24.49×10-3, also with a high vibration curve. Each stage can be further subdivided into several climatic events. (3) The sudden change of magnetic susceptibility and organic carbon isotopes may indicate a sudden temperature change.
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图 1 江汉平原湖区周老镇ZL01孔有机碳总量(TOC)、碳氮比值(C/N)和氢碳比值(H/C) 随深度变化
Fig. 1. Variation curve of organic carbon (TOC), (N/C) and (H/C) along with depth in Zhoulao town of the Jianghan plain
图 2 江汉湖区周老镇(ZL01) 孔磁化率和有机碳稳定同位素随深度变化曲线
Fig. 2. Variation curve of magnetic susceptibility and organic carbon stable isotope (δ13C) along with depth in Zhoulao town of the Jianghan plain
表 1 14C测年数据
Table 1. Data of the radiocarbon age
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