Geoscience Reference
In-Depth Information
Table 11.1
Commonly used equipment, main use and examples.
Instrument
Main uses
Examples
Gravity meter
Large-scale surveys of subsurface
bodies of different density or of
bodies that are changing mass or
volume
Boundaries of sedimentary basins, detecting
granite plutons and, in conjunction with elevation
surveys (such as differential GPS), studies of the
infl ation and defl ation of volcanic regions
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Magnetometer
Medium- to small-scale surveys of
bodies with a magnetic character
that is distinctly different from that
of the surrounding rock
Dykes, sills, ore bodies and other buried
geological contacts
Seismic surveys
Survey of features with an acoustic
impedance contrast (related to
density) on a wide range of scales
from tens of metres to thousands of
kilometres
Extensively used method for surveying stratigraphy
within sedimentary basins. Can also be used to
examine deep crustal structure or to locate
magma chambers
Portable XRF
Small-scale variation (decimetres to
metres) in the major and minor
element concentrations of rocks
exposed at the surface
Provenance of derived rocks through chemical
characterization. General characterization to
determine position of high-resolution surveys.
Generation of data for time-series analysis to
determine if there are regular cycles relating to
the time of deposition recorded in the rocks
Gamma-ray
spectrometer
Small-scale spatial variation in the
Th, K and U concentration in rocks
exposed at the surface. 30 cm to
tens of metres
Variation in clay mineralogy and/or organic
carbon content (U can be used as a proxy for
organic carbon). Characterization of the U, Th
and K composition of granites
Magnetic
susceptibility
meter
Very small-scale spatial variation in
the response of rocks to an
imposed magnetic fi eld; this relates
not only to the composition of
rocks containing magnetic minerals
but also paramagnetic minerals
such as clay minerals
Variation in the clay, carbonate and silica content
of mudstone successions. Detection of variation in
interbedded salt and mudstone/carbonate
deposits. Generation of data for time-series
analysis to determine if there are regular cycles in
the rocks
make a separate record of where each datum point was
collected and any other constraints or observations. If the
measurements are taken over a large- to medium-scale lateral
grid, GPS or differential GPS can be used, but notes will be
necessary for vertical grids and those of small spatial scale. The
most easily accessible way to display a large amount of data
and ensure that you do not miss anything is to construct a
table with cells for each of the datum entries that you need
(Figure 11.1).
