Field Sampling andLaboratory Analysis To determine the magnetic polarity a rock, sampling begins in the field, either by drilling small cores out of well-indurated rocks or by cutting sm
Trang 1Field Sampling and
Laboratory Analysis
To determine the magnetic polarity a rock, sampling
begins in the field, either by drilling small cores out of
well-indurated rocks or by cutting small blocks (cubes)
out of less resistant rocks The orientations of these
samples with respect to the current magnetic field and their precise geographical locations are recorded Orientated samples are taken to the laboratory to have their magnetization analysed.
The intensity of the magnetic field is measured using a unit called a gauss (named after the German
Figure 3 An example of how rock sections can be correlated with each other based on their magnetic polarity zonation.The three columns on the left show the magnetostratigraphy of three stratigraphical sections in Utah, with black indicating normal polarity magnetozones and white indicating reversed polarity magnetozones.The short interval of normal polarity between two long intervals
of reversed polarity allows the three Utah columns to be correlated with each other.On the right, an attempt is made to correlate the Utah magnetostratigraphies with magnetozones in New Mexico and New Jersey (Newark).The match between the Utah and New Mexico magnetostratigraphies is fairly straightforward, but matching these with New Jersey data is more complex, because the Newark column has many more magnetic reversals.Molin Garza RS, Geissman JW and Lucas SG (2003) Paleomagnetism and magnetostratigraphy of the lower Glen Canyon and upper Chinle groups, Jurassic Triassic of northern Arizona and northeast Utah
Journal of Geophysical Research, v.108, no.B4, 2181
MAGNETOSTRATIGRAPHY 333