Speleothem magnetism

The magnetic recordings preserved in calcite speleothems and the nature of their constituent magnetic minerals hold enormous potential for paleomagnetic and paleoenvironmental reconstructions. Speleothems lock magnetization in instantly, are not affected by post-depositional effects, and can be dated with high precision. The natural remanence in speleothems is carried mainly by magnetite, and the main remanence acquisition mechanism is depositional, through physical alignment of detrital magnetic grains parallel to the Earth’s magnetic field. Detrital particles are deposited on speleothem surfaces either from receding flood waters, or directly from drip water percolating through overlying rock and soil. Chemical remanence, acquired in situ by particles growing through a critical volume, is of secondary importance. Previous studies of speleothem magnetism have shown that geomagnetic features are successfully recorded by speleothems, and can be reproduced at a local and regional scale. Future studies that benefit from increasingly sensitive magnetometers, operating at high spatial resolution, should be able to resolve short-term geomagnetic variability, and characterize events such as geomagnetic excursions at an unprecedented scale. The environmental magnetism of speleothems is still an untapped reservoir, but holds the promise of bridging the gap between mineral-magnetic records from other sedimentary archives and established speleothem environmental proxies (e.g., oxygen and carbon isotopes).

► Speleothems are ideal tools for paleomagnetic and environmental magnetic studies.
► Remanence in speleothems is mainly depositional, and is acquired almost instantly.
► Magnetic minerals are deposited from flood and drip waters, or precipitated in situ.
► Recent instrumental advances allow magnetic investigation at sub-mm resolution.
► Speleothems can grow continuously and be dated isotopically with high precision.