Figure 1. Stereographic projection showing the mean paleopole position
and its A95 from this study and the published paleopole
position and its A95 for Mongolia, Norway, Turkey, and
Antarctica.
4 Results
4.1 Effect of a k-cutoff
A widely used filter to establish site-mean directions that represent
spot readings of the paleomagnetic field is to check for high
within-site scatter by means of a k-cutoff. Sites with low kvalues are interpreted as either remagnetized or not representative of a
spot reading and are therefore discarded (Figure S1). We analyze the
effect of the k-cutoff size on between-site scatter using the mean
paleopole of a dataset (Figure 2) and its N, A95, K, and
S (Figure 3). The pole positions do not significantly change when
applying a k-cutoff (Figure 2). When a low k \(\mathbf{\geq}\)10
cutoff is applied, the number of sites remaining in the dataset
decreases by approximately 15-30% (Figure 3a), omitting sites with
near-random direction distributions. Increasing the cutoff size beyond
20, the decay in sites decreases. The A95 increases with
increasing k-cutoff due to a decrease in N (Figure 3b). As expected,
discarding sites with high within-site scatter leads to a higher K and
lower S, although the effects are small (Figure 3c, d), except in the
dataset from Norway where K rises from 30 to 70. No major improvement
becomes apparent in any of the variables at the commonly used cutoff
sizes of 50 and 100. Importantly, although the application of a k-cutoff
may subtly decrease S and increase K, the decrease in N leads to an
increase of the A95, and thus to a decrease in precision
of the paleopole when a k-cutoff is applied, whereas the pole position
remains approximately the same.