Approaches in rock magnetic analysis: Insights into remanence acquisition, sea-level reconstruction, and advancement of techniques

Abstract

Iron is ubiquitous in most systems and the magnetic properties of natural materials can provide insight into Earth and environmental processes. This dissertation includes two studies on using magnetic properties to enhance our understanding of Earth’s systems and one study to advancing techniques in rock magnetism. The first part of this dissertation examines the potential of speleothems as recorders of paleosecular variation of the Earth’s magnetic field. We precipitated ammonium dihydrogen phosphate speleothems analogs with different ratios of magnetite and kaolinite clay. Through these experiments and modelling, we find that sensitivity to field strength is non-linear and maximized for an intermediate ratio of magnetite to kaolinite. The mechanism of speleothem remanence acquisition can be described by a two-step process: flocculate moment alignment with the field and flocculate-substrate interactions. 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. The second study characterizes red layers that are relatively common in Bahamian speleothems, but the formation mechanism is not well agreed upon. Using electron microscopy and magnetic measurements, we find that the red layer is composed of iron-oxide framboids that likely initially precipitated as pyrite. We find that these psedomorphs can be used as an indicator of high sea-levels across carbonate speleothem records. The last study involves advancing techniques in rock magnetism. Measurements of susceptibility as a function of temperature are an important, standard method of quantifying a sample’s magnetic mineralogy and high temperature susceptibility bridges (HTSBs) are common in rock magnetism laboratories. Here, we argue that HTSBs can be used to simultaneously perform simple differential thermal analysis (DTA), a technique used to measure phase transitions and exo-/endothermic reactions. For standard samples of vivianite, goethite, and maghemite, we identify DTA-analogous information. In the case of goethite and vivianite, the reactions identified do not have a corresponding expression in susceptibility, demonstrating that this approach expands the utility of this common instrument.