Paleointensity file format and SPD criteria
This page describes the TDT input expected by the LAPOD paleointensity tool and the selection parameters used in the current Class A/B criteria. Parameter definitions follow the Standard Paleointensity Definitions (SPD).
TDT input file structure
LAPOD reads plain-text ThellierTool-style TDT files. A file contains a header followed by one measurement per line.
Thellier-tdt
35.0 0.0 0.0 0.0 0.0
CUA20 20.00 5698.6577 196.03 -61.54
CUA20 100.00 5552.3418 193.71 -62.39
CUA20 100.11 5671.0669 194.44 -60.79
CUA20 200.11 5753.5120 194.68 -63.08
CUA20 200.00 5340.1873 194.84 -63.04
CUA20 100.12 5116.0336 196.94 -63.29
Header
| Entry | Meaning in LAPOD |
|---|---|
Thellier-tdt |
File identifier. |
35.0 0.0 0.0 0.0 0.0 |
The first value is interpreted as the laboratory field B_lab in µT. The remaining header values are preserved by the format but are not required by the current LAPOD calculations. |
Measurement rows
| # | Field | Description |
|---|---|---|
| 1 | Specimen | Specimen identifier, e.g. CUA20. |
| 2 | Treatment | Temperature plus treatment code, e.g. 300.00, 300.11 or 300.12. |
| 3 | Moment | Magnetic moment/intensity value used by the TDT file. Values must use one consistent unit throughout the specimen. |
| 4 | Declination | Declination in degrees. |
| 5 | Inclination | Inclination in degrees. |
Treatment codes used by LAPOD
| Code | Interpretation |
|---|---|
.00 | Zero-field heating step (Z). |
.11 | In-field heating step (I). |
.12 | pTRM check. |
Method and step order.
LAPOD uses the chronological order of the .00 and .11 measurements to identify ZI and IZ
steps. The user-selected experimental method should therefore agree with the sequence
encoded in the file. Auto detect is provided as a consistency check, not as a replacement
for the experimental record.
Selection parameters used by LAPOD
The definitions below follow SPD terminology. The numerical Class A and Class B thresholds displayed in the analysis page are LAPOD selection settings and can be edited by the user; SPD standardizes parameter definitions, not a single mandatory acceptance-threshold set.
| Parameter | SPD-based definition | Interpretive use |
|---|---|---|
| n (N) | Number of Arai-plot points included in the selected best-fit segment: n = end − start + 1. | Controls whether the estimate is supported by enough experimental steps. |
| β | Relative scatter of the selected Arai segment. β is the standard error of the slope divided by the absolute slope. | Lower values indicate a more tightly defined linear segment. |
| f | NRM fraction used for the best fit, following Coe et al. (1978): f = Δy′ / |Y_int|. | Measures how much of the original remanence is represented by the selected interval. |
| q | Quality factor combining NRM fraction, gap factor and relative scatter: q = f g / β. | Higher values indicate a better combination of remanence fraction, point distribution and linearity. |
| MADanc | Maximum Angular Deviation of the anchored PCA fit to the paleomagnetic vector for the selected demagnetization steps. | Quantifies directional scatter around the anchored principal component. |
| α | Angular difference between the anchored and free-floating best-fit directions on the vector component diagram. | Tests the directional consistency of the selected demagnetization component. |
| δCK | Maximum absolute pTRM-check difference normalized by the total TRM represented by the x-intercept of the selected Arai best-fit line. | Measures the largest alteration signal detected by an individual pTRM check. |
| δpal | Cumulative alteration parameter: the absolute difference between the uncorrected Arai slope b and the alteration-corrected slope b*, normalized by b. | Evaluates the cumulative effect of alteration recorded by the sequence of pTRM checks. |
Key SPD expressions
β = σb / |b|
f = Δy′ / |Yint|
q = f g / β
MAD = arctan[ ((τ2 + τ3) / τ1)1/2 ]
δCK = max(|δpTRMi,j|) / |Xint| × 100
δpal = |(b − b*) / b| × 100
Important:
SPD provides standardized definitions and calculation procedures for paleointensity statistics.
It does not prescribe the Class A/B limits used by this LAPOD interface. Those limits are a
user-editable selection scheme and should be reported explicitly in any study that uses them.
Supporting quantities
| b | Slope of the selected Arai segment. Under SPD, the slope is determined using standardized major-axis fitting. Paleointensity is B_anc = |b| × B_lab. |
|---|---|
| σb | Standard error of the Arai best-fit slope. |
| g | Gap factor describing the spacing of selected Arai points along the fitted segment. |
| pTRM check | Repeat TRM acquisition used to test whether the specimen's ability to acquire TRM has changed during the experiment. |
SPD references and resources
LAPOD uses the terminology of the Standard Paleointensity Definitions (SPD). For complete derivations, indexing conventions and additional paleointensity statistics, consult the official SPD resources.