Geology Reference
In-Depth Information
Glossary
Aliasing
Low-frequency spectral peaks that do not represent real periodic
behavior in a time series, but rather are an artifact of under-sampling the
highest frequency cycles in the time series. Aliasing occurs when the sam-
pling interval is greater than the interval necessary to sample the shortest
period cycle twice per cycle.
Anhysteretic remanent magnetization (ARM)
A laboratory remanence
that results from applying a small DC magnetic field (~50-100 μT) to a
sample in the presence of an alternating magnetic field that is decreased
from some peak value to 0. In most laboratories, the peak field is about
100 mT. A partial ARM can be applied by only switching on the DC field
over a limited range of alternating field during the decrease from a peak
alternating field value.
ARM susceptibility (χ
ARM
)
In this case, it is not the susceptibility that
causes an induced magnetization, but the ARM acquired as a function of
the DC magnetic field used for the application of the ARM. Usually it is cal-
culated by dividing the ARM by the strength of the DC field used during
application of the ARM.
Astrochronology
The astronomical calibration of cyclostratigraphy.
Band-pass filter
A filter that passes a range of frequencies and suppresses
or attenuates frequencies outside that range.
B
c
The coercivity of a sample that results from a hysteresis loop measurement.
It is the field that is required to reduce the magnetization of a sample to 0
while the field is being applied.
B
cr
The coercivity of remanence of a sample that results from a hysteresis
loop measurement. It is the field required to reduce the magnetization of a
sample to 0 after the field has been turned off, i.e., the sample is measured
in 0 field.
Chemical or crystallization remanent magnetization (CRM)
The
remanent, or spontaneous, magnetization acquired when a ferromag-
netic mineral grows chemically, or crystallizes, in the presence of a
magnetic field. When new crystal grains grow through a certain
volume, typically submicron in size, the spontaneous magnetization
becomes stable.
Chron
A period of one dominant geomagnetic polarity, although shorter
periods of opposite polarity (subchrons) can exist within a chron. The
