Magnetic fabric of stalagmites and its formation mechanism

Abstract

Speleothems have been regarded as ideal archives for recording variations of the Earth's magnetic field because they crystallize rapidly and are seldom modified by post-depositional processes, and because they can be precisely dated. Magnetic fabric research on speleothems has potential to reveal details of their interior structure and the distribution of ferrimagnetic minerals, which would benefit investigations of geomagnetic field behavior. Two stalagmites (HS4 and WD1) from caves in the middle reaches of the Yangtze River were collected for magnetic fabric study. The anisotropy of magnetic susceptibility (AMS) of the stalagmites is mainly controlled by calcite crystals and the directions of the minimum axes of AMS ellipsoids indicate that their crystallographic orientations are roughly perpendicular to the growth laminae. Anisotropy of the isothermal remanent magnetization (AIRM) indicates that the distributions of ferrimagnetic minerals in the stalagmites are not correlated with stalagmite growth laminae. Mean directions of the maximum principal axes of AIRM (R 1 axes) for WD1 are close to that of the natural remanent magnetization, which suggests that the orientation of ferrimagnetic minerals in this stalagmite are likely to have been controlled by the geomagnetic field. © 2012 American Geophysical Union. All Rights Reserved.