Variations of the Magnetic Susceptibility across the PT Boundary at Xinmin Section in Anshun, Guizhou and Their Paleoclimatic Implications
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摘要: 贵州安顺新民二叠系—三叠系界线剖面磁化率测试结果表明，该剖面二叠系磁化率整体偏低（平均6.4×10-8 m3/kg），界线之上磁化率快速增加并相对稳定在1.3×10-7 m3/kg附近，与华南其他二叠系—三叠系剖面磁化率变化趋势相同；与陆源孢粉丰度、TiO2曲线的同步变化趋势表明，新民剖面磁化率主要来自陆源物质。结合磁化率、地球化学指标的变化特征，将源区P—T之交古气候划分为3个阶段：阶段Ⅰ（12层中部）为化学风化作用较强的温暖潮湿的气候条件；阶段Ⅱ（2层上部P—T界线）整体处于较强化学风化作用条件下温热潮湿的气候环境，变化较为频繁，表现为温润/湿热交替；阶段Ⅲ（P—T界线之上）物理风化加强，化学风化明显减弱，经短暂“过渡段”，气候总体转变为干热的条件。Abstract: Magnetic susceptibility results from Xinmin section in Anshun, Guizhou indicate that the Permian Dalong Formation is with low values(6.4×108 m3/kg in average) and that their values increase significantly across the PT boundary and are high, about 1.3×107 m3/kg, in the Triassic Luolou Formation, which shows the same variation trend with that across other PT boundary sections in South China. A good positive correlation with both terrestrial sporopollen abundance and TiO2 variations proves that terrestrial influx attributes most of the magnetic susceptibility at Xinmin section. 3 paleoclimatic stages in the source area were figured out based on the variations of magnetic susceptibility and geochemical climatic proxies: StageⅠ(bed 1 to the middle of bed 2) is characterized by a warm/humid climate with strong chemical weathering; while a hot/humid climate with stronger chemical weathering dominates stageⅡ(top of bed 2 to the PT boundary), the climate condition change rapidly between much milder climate and humid climate; after a short transitional period, the climate in stageⅢ(above the PT boundary) turns into a relatively hot/dry climate with obvious much stronger physical weathering and weaker chemical weathering.
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Key words:
- magnetic susceptibility /
- geochemistry /
- palynology /
- paleoclimate /
- PermianTriassic boundary /
- South China /
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