| Code |
Method Type |
IAGA7 |
URL |
Description |
|
| ST-BC |
Stability Tests |
C |
LINK |
Baked contact test. The baked contact test compares the NRM direction of an igneous intrusion to that of the country rock surrounding it. One expects a changing NRM vector across the heat affected zone of the country rock. When an igneous rock intrudes an older rock formation, the intrusion heats a region of the surrounding country rock and the baked region of the country rock will then cool in the same magnetic field as the intrusion, and so will acquire a direction of magnetization the same as that of the intrusion. Agreement between the direction of magnetization of the intrusion and that of the country rock provides strong evidence for the stability of the magnetization of the intrusion. Wilson 1962, McElhinny & McFadden 2000. |
| ST-BC-Q1 |
Stability Tests |
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Besse and Courtillot Quality Factor 1. Age uncertainties of < ± 15 Myr.. Besse & Courtillot, 2002. |
| ST-BC-Q2 |
Stability Tests |
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Besse and Courtillot Quality Factor 2. There must be a sufficient number of individually oriented samples from enough sites. At least six sites and 36 samples, each site having a 95% confidence interval less than 10° in the Cenozoic and 15° in the Mesozoic.. Besse & Courtillot, 2002. |
| ST-BC-Q3 |
Stability Tests |
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Besse and Courtillot Quality Factor 3. It must be demonstrated that a coherent characteristic remanence component has been isolated by the demagnetization procedure. McElhinny and McFadden (2000) attempted to standardize the description of the demagnetization status of a dataset using a demagnetization code (DC). Besse and Couttillot 2002 recommend using only poles with a DC of at least 2.. Besse & Courtillot, 2002. |
| ST-BC-Q4 |
Stability Tests |
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Besse and Courtillot Quality Factor 4. The age of the magnetization relative to the age of the rock should be constrained using field tests (fold test, conglomerate test, baked contact test. Reject poles that fail a fold test or a reversals test.. Besse & Courtillot, 2002. |
| ST-BC-Q5 |
Stability Tests |
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Besse and Courtillot Quality Factor 5. There should be agreement in the pole positions from units of similar age from a broad region and adequate knowledge of any structural corrections necessary. Reject poles from “mobile regions”, but incorporate data that are azimuthally unconstrained by using inclination only data as a constraint on paleolatitude.. Besse & Courtillot, 2002. |
| ST-CT |
Stability Tests |
G |
LINK |
Conglomerate test. The conglomerate test compares the NRM direction of conglomerate clasts to the matrix (host particles) NRM direction. This results in directions that are random relative to the matrix, or directions clustering around the matrix particle's vector mean. If the directions of the magnetization of the conglomerate cobbles are random then this suggests that the magnetization of the parent formation has been stable since the deposition of the conglomerate. Cox & Doell 1960, McElhinny & McFadden 2000, Graham 1949. |
| ST-F |
Stability Tests |
|
|
Fold test. |
| ST-F-1 |
Stability Tests |
F |
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Fold test 1: Compares Kappa before and after tilt correction. This fold test compares the precision parameter (kappa) of the NRM directions across a fold before and after fold correction (unfolding). The positive result signifies an improved precision (kappa) about the vector mean, resulting in less dispersion. Samples are taken from different limbs of a fold. If the in situ directions of magnetization on the separate limbs differ, but agree after unfolding the limbs towards the horizontal, then the magnetization must predate the folding and must have been stable since that time. McElhinny 1964, Watson 1956a, McElhinny & McFadden 2000. |
| ST-F-2 |
Stability Tests |
F* |
|
Fold test 2: Compares distributions of directions from various limbs of folds before and after tilt correction. This fold test is a comparison of precisions (kappa) between different fold limbs (groups) to determine if they could have been drawn from a common group. An estimated ratio of k1/k2 far from unity is interpreted to imply significantly different distributions, where the critical value is being determined by F-test distributions. If the observed value of exceeds the critical value of the F distribution at the required level of significance, then the hypothesis of a common true mean may be rejected. In other words, the sites on each limb may be considered as a separate group with each group having it's own common tilt correction. McFadden & Lowes 1981, McFadden & Jones 1981, McElhinny & McFadden 2000. |
| ST-F-3 |
Stability Tests |
F* |
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Fold test 3: Uses Watson's V to test for common mean after tilt correction. This fold test is used to determine if there is no common precision (kappa) between groups by using Watson's V statistic compared to a simulated random distribution. If there is not a common kappa and there are multiple sites on each limb, then it is still possible to make use of this V-test. If the null hypothesis of a common mean direction can be rejected in the in situ position, but not in the unfolded position, then this is evidence that the magnetization was acquired before the folding occurred. McFadden 1990, Watson 1983. |
| ST-F-4 |
Stability Tests |
F* |
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Fold test 4: Estimates confidence on Kappa as a function of tilt correction. Watson & Enkin 1993, Jackson 1986. |
| ST-F-5 |
Stability Tests |
F* |
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Fold test 5: Estimates confidence on maximum eigenvalue as a function of tilt correction. In this fold test the behavior of the eigenvalue t1 is examined during unfolding to find the point at which the tightest grouping is achieved. Because in the orientation matrix the polarity does not play a role and because the tightness of groupings is reflected in the relative magnitudes of the eigenvalues(t), we can predict that the variance along the principal axis grows and those along the other axis shrinks, as the data become more tightly grouped. Tauxe & Watson 1994, Tauxe 1998. |
| ST-IC |
Stability Tests |
C* |
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Inverse contact test. This is the inverse of the baked contact test. If stable magnetizations are observed in unbaked rocks that provide positive evidence for a baked contact test, then this also provides evidence that the unbaked sediments have retained their magnetization, at least since the time of baking. McElhinny & McFadden 2000. |
| ST-IFC |
Stability Tests |
G* |
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Intraformational conglomerate test. This is a variation on the conglomerate test, where the conglomerate lies within the formation and was deposited not long after the parent beds were deposited. Cox & Doell 1960, McElhinny 2000. |
| ST-R |
Stability Tests |
|
|
Reversals test. |
| ST-R-1 |
Stability Tests |
R |
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Reversals test 1: Compares N and antipodes of R directions by testing for common mean. This reversal test compares the normal and reverse directions, that are flipped 180 degrees, for a common mean. Originally the simple procedure was to invert one of the directions by 180 degrees and then test if the resulting two directions of magnetization were discernibly different, by testing for common kappa. However, this method is taken to be flawed, because the larger the circles of confidence the harder it would be to show the two directions were discernibly different from one another. McFadden & Lowes 1981, McElhinny & McFadden 2000. |
| ST-R-2 |
Stability Tests |
R |
|
Reversals test 2: Compares Watson's V statistic for normal and reverse modes with monte carlo simulation. This reversal test compares the means of the normal and reversed data, and assesses the quality using Watson's V-statistic to test whether the two samples could have been drawn from distributions sharing a common mean direction, depend on the number of observations in each sample and whether the two distributions share a common precision. Results can be classified as 'A' if ?c <= 5¿, 'B' if 5¿ <= ?c <= 10¿, or ¿C' if 10¿ <= ?c <= 20¿, and indeterminate if ?c > 20¿. McFadden & McElhinny 1990. |
| ST-R-3 |
Stability Tests |
R |
|
Reversals test 3: Compares bootstrapped means for N and R antipodes by testing for common mean. This reversal test compares the overlap of confidence intervals for bootstrapped means of reversed antipodal data. If the confidence intervals for the normal and reversed data overlap, then this suggests that the two means cannot be distinguished at the 95% level of confidence. Tauxe 1998. |
| ST-R-4 |
Stability Tests |
R |
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Reversals test 4: Defines degree of Alpha95 overlap for N and R antipodes. McFadden & McElhinny 1990. |
| ST-U |
Stability Tests |
U |
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Unconformity test. This unconformity test is applied in special cases when successive zones of normal and reverse magnetization are truncated by an unconformity in the sequence. If the polarity zones of the upper/younger sequence do not match those of the lower/older sequence, then the magnetization of the lower beds is older than the episode of erosion that created the unconformity. Kirschvink 1978. |
| ST-VV-Q1 |
Stability Tests |
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Van der Voo Quality Factor 1. The age of the formation must be known rather accurately. The age should be known to within a half of a geological period or within a numerical age of ± 4% for Phanerozoic data. For Precambrian rocks, the age should be known to within ± 4% or 40 Myr, whichever is smaller.. Van der Voo 1990. |
| ST-VV-Q2 |
Stability Tests |
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Van der Voo Quality Factor 2. There must be a sufficient number of individually oriented samples from enough sites. A minimum of 24 discrete samples of the geomagnetic field each having a ¿ > 10.. Van der Voo 1990. |
| ST-VV-Q3 |
Stability Tests |
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Van der Voo Quality Factor 3. It must be demonstrated that a coherent characteristic remanence component has been isolated by the demagnetization procedure.. Van der Voo 1990. |
| ST-VV-Q4 |
Stability Tests |
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Van der Voo Quality Factor 4. The age of the magnetization relative to the age of the rock should be constrained using field tests (fold test, conglomerate test, baked contact test).. Van der Voo 1990. |
| ST-VV-Q5 |
Stability Tests |
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Van der Voo Quality Factor 5. There should be agreement in the pole positions from units of similar age from a broad region and adequate knowledge of any structural corrections necessary.. Van der Voo 1990. |
| ST-VV-Q6 |
Stability Tests |
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Van der Voo Quality Factor 6. Both polarities should be represented and the two data sets should be antipodal.. Van der Voo 1990. |
| ST-VV-Q7 |
Stability Tests |
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Van der Voo Quality Factor 7. Pole positions should not fall on a younger part of the pole path or on the present field direction.. Van der Voo 1990. |
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