Figure 10: (A and B) Plots showing how deep (A) or how many
seismic cycles (B) pit crater centroids are beneath the Base Cretaceous
unconformity along dyke-strike (Supporting Table 1). Inset into (B):
schematic depicting what constitutes a seismic cycle. (C) Plot of cone
height along dyke strike (Supporting Table 1). See Figure 3B for
explanation of measured parameters.
For each pit crater chain situated within dyke-induced graben, the depth
of their pit crater centroids beneath the Base Cretaceous unconformity
varies by ≲60 m along their length (Fig. 10A). Several pit crater chains
(A, D, F, G, and I) show a broad northwards increase in centroid depth
(Fig. 10A). Above some dykes, pit crater centroids all occur along the
same stratigraphic reflection (i.e. D and G), even though the number of
cycles between their level and the Base Cretaceous unconformity may vary
(i.e., the post-overburden varies in thickness over a length-scale
longer than that of an individual crater or chain of craters Figs 6D,
7B, and 10B). For other chains, pit crater centroids coincide with
different (deeper or shallower) reflections along their length (i.e. A,
B, C, E, F, H, and I; Figs 6, 7, and 10B). The pit craters associated
with tectonic normal faults have centroids that occur at the same
stratigraphic reflection above the Top Athol Formation, except forX3 which is the only pit crater to terminate below the Top Athol
Formation (Fig. 8).
The total height of the pit craters varies across the data, with most
extending down into the Mungaroo Formation (Figs 4A and 6-8); pit
craters G5, G11, and G12 appear to terminate at or above the Top
Mungaroo Formation (Fig. 7C). Our measurements show pit crater total
height ranges from 114–868 m (Supporting Table 1). In places, mapped
bases of pit crater pipes coincide with the upper tips of underlying
dykes (G2, G4, G6, G10a, G12, and H2) or dyke-induced fault planes
(B/C2, C2, C3, F9, F13, I2, and I3) (Figs 6-7). The X1 -X5pit crater pipes all extend down to tectonic faults (e.g., Fig. 8).
Where the base of pit crater pipes intersect dyke-induced or tectonic
faults, they typically do so where the fault planes are relatively steep
or sub-vertical (e.g., Figs 6C, 7B, F, 8B, and C). Other pit craters
appear to terminate within strata overlying dyke upper tips or fault
planes (Figs 4A and 6-8).
Where pit craters display a funnel-like morphology, we measure the
height of their inverted cone section and occasionally the deflection of
the uppermost stratigraphic reflection within them (i.e. the deflection
height) (Fig. 3B). We show inverted cone heights are
~18–245 m, with slopes of 7–51°, and that these values
vary across the study area and along individual pit crater chains (Figs
10C, 11A, and B; Supporting Table 1). The corresponding pipe height of
these funnel-like pit craters are 27–789 m (Fig. 11A; Supporting Table
1); the heights of pipe-like pit craters are 107–254 m (Table 2). There
is no correlation between cone height and total height or pipe height
for pit craters within dyke-induced graben (either those above dykes or
dyke-induced faults), or for those associated with tectonic normal
faults (Figs 11A and B; Supporting Table 1). Deflection heights are
~4–21 m, with slopes <12°, and do not
correlate with either total height or cone height (Figs 11C and D;
Supporting Table 1).