The importance of clays in speleothem magnetic remanence acquisition

Speleothems are promising recorders of paleosecular variation of the Earth's magnetic field, but ambiguities remain about the physical processes active during remanence acquisition. Speleothems have been used to determine relative paleointensity using classical methods for sedimentary materials. We created artificial speleothems by precipitating a solution of ammonium dihydrogen phosphate mixed with varying ratios of magnetite and kaolinite clay. These experiments were carried out over a range of Earth-like field intensities ranging from 15 to 70 [Formula: see text], allowing us to determine the conditions that maximize field sensitivity. We find that our artificial speleothems are good recorders of direction except for samples grown at low applied field strengths ([Formula: see text]) with a high magnetite to clay ratios (1:4). At any given field strength, more clay resulted in lower alignment efficiencies. Field sensitivity, or the amount of variation in the alignment efficiencies over the range of applied field strengths, was maximized for an intermediate ratio of magnetite to clay and nonlinear for the range of experimental and model parameters tested. The mechanism of speleothem remanence acquisition can be described by a two-step process: flocculate moment alignment with the field and flocculate-substrate interactions (FSIs). These findings have important implications for speleothem relative paleointensity studies since the delivery of detrital material within drip waters varies over time, causing a speleothem's alignment efficiency to fluctuate.