On improving the selection of Thellier-type paleointensity data

Abstract

The selection of paleointensity data is a challenging, but essential step for establishing data reliability. There is, however, no consensus as to how best to quantify paleointensity data and which data selection processes are most effective. To address these issues, we begin to lay the foundations for a more unified and theoretically justified approach to the selection of paleointensity data. We present a new compilation of standard definitions for paleointensity statistics to help remove ambiguities in their calculation. We also compile the largest-to-date data set of raw paleointensity data from historical locations and laboratory control experiments with which to test the effectiveness of commonly used sets of selection criteria. Although most currently used criteria are capable of increasing the proportion of accurate results accepted, criteria that are better at excluding inaccurate results tend to perform poorly at including accurate results and vice versa. In the extreme case, one widely used set of criteria, which is used by default in the ThellierTool software (v4.22), excludes so many accurate results that it is often statistically indistinguishable from randomly selecting data. We demonstrate that, when modified according to recent single domain paleointensity predictions, criteria sets that are no better than a random selector can produce statistically significant increases in the acceptance of accurate results and represent effective selection criteria. The use of such theoretically derived modifications places the selection of paleointensity data on a more justifiable theoretical foundation and we encourage the use of the modified criteria over their original forms.

Paleomagnetic directional groups and paleointensity from the flood basalt in the Tarim large igneous province: implications for eruption frequency

“…We have to emphasize that the quality of these data and the number of specimens are not sufficient to establish reliable absolute paleointensity estimates (e.g., Patterson et al 2014). Nonetheless, a relatively similar lithology studied here may allow discussion about the relative differences among the flows.…”

The multimethod palaeointensity approach applied to volcanics from Terceira: full-vector geomagnetic data for the past 50 kyr

“…Heating, both in-field and in zero fields, was done in an ASC-48TD thermal demagnetizer. The IZZI-Thellier data were interpreted using the ThellierTool 4.2 software (Leonhardt et al 2004), which implies that some parameters (such as DRAT tail ) must be derived from the ThellierTool output using the Standard Palaeointensity Definitions (Paterson et al 2014), since they are not provided by the program. To assess the quality of our results we used four sets of criteria: TTA, TTB (Leonhardt et al 2004) and SELCRIT-01 (Selkin & Tauxe 2000) as modified by Paterson et al (2014); and CLASS-A (de Groot et al 2014).…”

“…The performance of those selection criteria was recently tested by Paterson et al (2014) and some refinements were proposed. Other methods to obtain reliable estimates of the palaeofield were also put forward: the usage of microwaves to directly excite the samples' magnetic system was found to be useful in reducing the thermally induced alteration that many volcanic samples exhibit during classical Thellier experiments (Hill & Shaw 1999.…”

The HISTMAG database: combining historical, archaeomagnetic and volcanic data

“…Since then, a variety of different palaeointensity protocols as well as quality checks and corrections (for anisotropy, alteration, cooling rate dependence) have emerged. The reader is referred to, for example, Brown et al (2015a) or Paterson et al (2014), and references therein for a detailed discussion.…”