Abstract
Quantum diamond microscope (QDM) magnetic field imaging is a recently developed technique capable of mapping magnetic field sources in geologic samples at 1 micrometer resolution. Applying QDM imaging to speleothems can provide high‐resolution time series of detrital input into the cave environment, which, in turn, can yield useful paleoenvironmental information. Here we map the magnetic field over a speleothem from midwest Brazil over a 174 year timespan with annual to sub-annual resolution and perform backfield remanence acquisition experiments to quantify changes in the magnetic grain population through time. We find that magnetic particles occur in highly enriched layers of 10–100 µm thickness that sample the same detrital source population. Combined with petrographic observations and electron microprobe mapping of Mg and Ca, we conclude that detrital enrichment in our sample is caused by drier conditions leading to slow or halted speleothem growth. This interpretation is compatible with oxygen isotopic data and implies that speleothem magnetism can be used to infer the past occurrence of drought and potentially quantify their duration. Future high-resolution magnetic imaging of speleothems may provide additional insight into the mechanism of detrital enrichment and establish their role as a proxy for local moisture and infiltration.
Highlights
Environmental magnetism studies seek to extract information about past Earth surface conditions using rock magnetic techniques, which can quantify properties of Fe-bearing mineral populations in sediments
We find that the distribution of ferromagnetic content within the speleothem is highly non-uniform, with virtually all resolvable signal occurring in 10–100 μm scale horizons of high magnetic field intensity (Figure 5)
If the association between magnetization and aridity is correct, the presence of multiple thin (∼20 μm) magnetized horizons pre- and post-dating the main magnetized laminae suggests that the arid intervals occurred with gradual onset and resolution
Summary
Environmental magnetism studies seek to extract information about past Earth surface conditions using rock magnetic techniques, which can quantify properties of Fe-bearing mineral populations in sediments. Environmental magnetism studies provide unique insight into past climates and environments. Full applications of environmental magnetism are reviewed elsewhere (Verosub and Roberts, 1995; Liu et al, 2012), prominent examples include quantifying climatic and chemical conditions during deposition [e.g. Most environmental magnetism studies are based on measurements of magnetic properties in millimeter to centimeter scale specimens, hereafter referred to as bulk specimens. In the case of sedimentary samples deposited over time, analyses of bulk specimens at a range of stratigraphic heights can be compiled to construct a time series of magnetic properties, which can in turn be interpreted to record paleoenvironmental change. The temporal resolution of such studies is limited by the minimum volume of sample that retains sufficient magnetic content to be detectable using available instrumentation
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call