华南中-晚二叠世之交碳酸盐岩磁学特征及环境意义
Magnetic Properties of Middle-Late Permian Carbonates in South China and Their Environmental Significances

磁学参数作为可靠的古气候和古环境指标,能为全球环境变化、气候过程研究提供有价值的资料.对广西来宾铁桥剖面瓜 德鲁普-乐平统界线地层进行详细岩石磁学研究,结果表明,铁桥剖面样品中主要磁性矿物是顺磁性矿物以及少量磁铁矿、赤铁 矿.在瓜德鲁普-乐平统界线附近,岩石磁学特征发生显著变化,磁化率先增大再减小,携磁矿物成分呈硬磁性矿物(赤铁矿)→ 软磁性矿物(磁铁矿)→硬磁性矿物(赤铁矿)的变化趋势,这些转变仅在界线上下大约4m 的岩层内完成,与中二叠世晚期的海 平面变化、古海水温度变化同步.中-晚二叠世之交碳酸盐岩磁学参数的变化显著,反映磁性矿物在各圈层之间的运移和转换发 生了转变,这一转变起因于当时的气候环境变化.瓜德鲁普世晚期和乐平世早期,海平面较高,来宾地区物源少,铁桥剖面的携磁 矿物主要来自粉尘赤铁矿;中-晚二叠世之交短暂的大规模海退作用使华南古陆面积大幅度增加,同时陆生植物大规模灭绝,地 表侵蚀加剧,来宾地区物源增多,此时,铁桥剖面的携磁矿物主要来源于河流输入的磁铁矿.
As a reliable proxy for paleoclimate and paleoenvironment, magnetic parameter could provide valuable data for the re- search of g1oba1 environmenta1 changes and climatic processes. A detailed study has been carried out on rock magnetisrn in order to revea1 the change of climate and environment and its reasons across Guadalupian-Lopingian(G-L) boundary at Tieqiao sec- tion in Laibin area, (Juangxi, China. The results show that the dominant magnetic minerals from Tieqiao section are paramag- netic minerals with a sma11 amount of magnetite and hematite as we11. There is a remarkable change in the properties of rock magnetism near the G-I boundary. Magnetic susceptibility increases first and then decreases. Magnetic carriers show the trend of being transformed from hard magnetic minerals(hematite) to soft magnetic minera1 (magnetite) and then turning to hard magnetic minerals(hematite). A11 of these changes occur within4 m-thick strata interva1 above and be1ow the G-L boundary, and synchronize with the fluctuation of sea-1eve1 and ancient seawater temperature duringlate Middle Permian. The significant changes in magnetic parameters for Middle-Late Permian carbonates suggest that the migration and conversion of magnetic minerals between different spheres in earth system has shifted, which resulted from the climatic and environmenta1 changes. High sea-1evelduring Late Guadalupian and Early Lopingian resulted in the decrease in terrigenous supply in South China. Therefore, the magnetic carriers in Tieqiao section mainly are hematite through aeolian transportation during this period. How- ever, pronounced regression during the Middle-Late Permian transitionled to the expansion of exposedland area. Meanwhile, 1and plants experienced widespread extinction, whichled to increased sediment source. The magnetic carriers in contemporane- ous sediments of Tieqiao section are mainly fluvia1 magnetite