Figure 4: (A) Interpreted composite section capturing the
tectono-stratigraphy of the area, intersecting all dykes (A-I) and
revealing the structure some dyke-induced normal faults and pit craters.
The line also intersects the Yellowglen-1 and Chandon-3 boreholes. The
time-migrated data is shown in the top panel, and in the lower panels we
show selected depth-converted, reflectivity data overlain by a variance
attribute. See Figure 4B for line location. (B-C) Time-structure maps of
the three major horizons (Base Cretaceous unconformity, Top Athol
Formation, and Top Mungaroo Formation) interpreted in Figure 4A.
Uninterpreted and interpreted versions of the maps are shown,
highlighting underlying dyke traces, faults, and boreholes. The
boreholes shown are: 1 = Chandon-1; 2 = Chandon-2; 3 = Chandon-3; 4 =
Yellowglen-1; and 5 = Mercury-1. (E) Uninterpreted and interpreted RMS
(root-mean squared) amplitude time-slice at 4.5 seconds two-way time
(TWT) showing the seismic expression of dykes A-I. For part of their
length, dykes B and C merge and we cannot determine if both dykes are
continuous, or if one cross-cuts and displaces the other.
Pit crater morphology
Pit craters occur across the dataset, primarily arranged in chains
aligned parallel to and occurring within dyke-induced graben (Fig. 5).
Five pit craters (X1 –X5 ) are located outside these graben
and are instead situated in the hanging wall of tectonic normal faults
(Fig. 5). Of the 54 pit craters within dyke-induced graben, 50 have a
funnel-like morphology in cross-section, as do four of the pit craters
associated with tectonic normal faults (Figs 5-8). The remaining four
pit craters within dyke-induced graben (A4, F5, G7, and H1), as well asX3 , have a pipe-like geometry and no inverted cone section (Figs
5-8).
At the Top Athol Formation, we mapped 61 pit craters (Fig. 5); three pit
craters observed at this structural level merge (e.g., E1a and b, F10a
and b, G10a and b; Figs 6E, 7A, and B) and one splits (G2/3; Fig. 8B) at
shallower depths. Of the 57 pit craters within dyke-induced graben at
the Top Athol Formation, 30 occur directly above dyke traces and 27 have
centroids situated ~75–653 m orthogonally from the
associated dyke trace (Fig. 5C). The only pipe-like pit crater located
directly above a dyke trace is A4 (Fig. 5).