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paleomagnetic vector (Figure 3.2). When both sets of points trend into the
origin of the plot, a stable remanence direction has been isolated from the
sample at the highest alternating fields or temperatures needed to totally
remove the remanence. Although this remanence direction needs to be
checked to see if it is primary or secondary, it does show that the rema-
nence is in all likelihood ancient due to its high stability. The age of the
remanence is checked with tests that have become common in paleomag-
netic studies and are covered in the following section.
(a)
(b)
(c)
Up, N
Up, N
Up, N
NRM
100 °C
NRM
E
100
125 °C
150 °C
200 °C
125 °C
175 °C
225 °C
150
200
250
300
400 °C
250
275
325
375
400
375 °C
275 °C
300 °C
325
350 °C
350 °C
350 °C
375 °C
400 °C
E
E
300
325 °C
275 °C
250 °C
100 °C
125
200 °C
NRM
150 °C
RS33C-2
Stratigraphic position: 16 m
Tick marks: 0.1 mA/m
RS15B-1
Stratigraphic position: 31m
Tick marks: 0.1 mA/m
RS52B-1
Stratigraphic position: 40 m
Tick marks: 0.1 mA/m
Figure 3.2
Examples of orthogonal demagnetization diagrams (Zijderveld 1967) for thermal demagnetization from a
magnetostratigraphic study in Rio Sacuz, Italy. Most of the remanence was removed by thermal demagnetization up to
400°C. Subsequent rock magnetic measurements indicate that the magnetic mineralogy is predominately magnetite. Open
symbols are the vertical components and solid symbols are the horizontal components. Data plotted in stratigraphic
coordinates. Source: Spahn, Kodama & Preto 2013. Reproduced with permission of John Wiley & Sons, Inc.
