what is magnetostratigraphy?

Question

i understand what it is, but i need a definition

Answer 1

It is the technique of measuring the magnetic orientation recorded in rock in order to determine the age of the rock.

By correlating the paleomagnetic signal in the rock with the global paleomagnetic record of reversals and excursions of the earth’s magnetic field it is possible to establish the relative date of a stratigraphic interval within deposits of rock. Combined with isotopic dating of ash deposits it can resolve the age of a deposit of sedimentary or volcanic rock down to tens of thousands of years.

Because most ash deposits are periodic, but may be hundreds of thousands of years apart, the rock record between these cannot be further measured by isotopic methods. Because the earth's magnetic field has reversed itself many times, and also undergoes excursion events where the magnetic pole wanders and changes in strength, there is a higher resolution record preserved in rocks which are susceptible to magnetism. Many sedimentary rocks contain small amounts of iron, and most volcanic rocks also contain iron and this iron retains its original magnetic orientation. In igneous rocks such as basalt the magnetic orientation is preserved at the time it cools and becomes solid. In sedimentary rock the magnetic orientation is established as the sediment is deposited and lithifies. If any rock is heated above a few hundred degrees by burial processes, the signal is destroyed by the heat.

To measure paleomagnetic data, small samples are taken with a special core drill, or cut from softer sedimentary rocks with a knife. The exact orientation of the samples original position must be recorded and measured, typically using a special tool that holds a compass. These samples are then put in a very sensitive magnetometer that records the orientation of the magnetic field in the sample. Through multiple steps of heating the sample to higher and higher temperatures and remeasuring the magnetic field the various orientations of the magnetic fields within the sample can be separated and the original magnetic field determined.

Dr. Robert Butler wrote one of the best texts on paleomagnetism. The book is now out of print, but he has been generous enough to make his entire book downloadable at:
http://www.geo.arizona.edu/Paleomag/book/

Another place you can see the paleomagnetic record is in the time scale published by the Geological Society of America.
http://www.geosociety.org/science/timescale/timescl.htm
The black and white bar on this chart shows the periods of the many magnetic reversals that have been measured over the Cenozoic and Mesozoic periods. Earlier paleomagnetic measurements do exist and have been important in understanding past plate tectonic movements.

Answer 2

The comparison of the pattern of magnetic reversals in a sequence of strata, with a reference column showing the succession of reversals through time

Answer 3

Try Google then.................