Palaeosols across the Permian-Triassic boundary at Graphite
Peak are strikingly similar to those across the boundary in
the Sydney Basin (Retallack 1999b). The suite of tuffaceous
and coaly paleosols in the Late Permian upper Buckley Formation
are very similar to those in the Newcastle Coal Measures of
New South Wales. Green and red paleosols of the Early Triassic
Fremouw Formation are similar to those of the Narrabeen Group
of New South Wales (Retallack 1976, 1977a, 1977b). At Graphite
Peak there is also claystone breccia, pale green in color,
but otherwise similar to claystone breccias at the Permian-Triassic
boundary in Victoria Land and southeastern Australia (Retallack
et al. 1998a). At Graphite Peak, the breccia includes claystone
clasts with birefingence fabrics and weathering like those
of associated paleosols, as well as numerous altered volcanic
rock fragments and much quartz. These boundary beds have yielded
rare (0.8 grains.cm-2), small (152 mm) grains of shocked quartz
(Retallack et al. 1998b). Becker and Poreda have also recently
found fullerenes in the boundary breccia (Becker and Poreda,
2001). A statistically significant but faint iridium anomaly
(up to 59 pg.g-1 over background of 20 pg.g-1) also has been
detected, but it is from the base of the coal underlying the
claystone breccia (Kyte for Retallack et al. 1998a).
Stable isotope analyses of organic carbon in our samples
from Graphite Peak (Fig. 3) show that the global Permian-Triassic
boundary d13C excursion (Holser et al. 1989, 1991; Morante
1996) is at the contact of the Buckley and Fremouw Formations
(Krull & Retallack, 2000). This contact is 1 m above the
last Vertebraria root and directly above the last coal in
the section. The region around Graphite Peak has been shown
to have both Late Permian (stage 5) palynofloras (Farabee
et al. 1991) and glossopterid fructifications (Retallack et
al. 1998b, Retallack & Krull 1999) and earliest Triassic
(Lystrosaurus zone) vertebrates (Elliot et al. 1970; Cosgriff
et al. 1982; Hammer 1990a, 1990b; Lucas 1998). Graphite Peak
was the initial discovery site for earliest Triassic vertebrates
in Antarctica (Barrett et al. 1968), and has yielded bones
of Lystrosaurus murrayi, Thrinaxodon liorhinus, Austrobrachyops
jenseni and Prolacerta broomi (Colbert 1974; Colbert &
Kitching 1977; Hammer 1989, 1990a; Retallack & Hammer
1998) 24-83 m above the base of the Fremouw Formation (280-339).
This assemblage is also found about 40 m above the Permian-Triassic
boundary in South Africa (Smith & Ward, 2002). The Fremouw
Formation also yielded fossil plants including Voltziopsis
africana (55 m above base of Fremouw Formation or 301 m )
and Dicroidium zuberi (110 m above base or 366 m), which are
Early Triassic species (Retallack 1977a, 1977b, 1995). Permian-Triassic
boundary at the Buckley-Fremouw contact is the same as mapped
by Collinson & Elliot (1984a), Barrett et al. (1986) and
Collinson et al. (1994).
We have preliminary analyses at Graphite Peak sediment samples
provided by Retallack from a previous field season at Antarctica
for fullerenes and bulk noble gases. A fullerene component
was successfully isolated from the acid resistant residue
(100 mg) of the Graphite Peak boundary breccia. The helium
isotopic ratio of this fullerene component is (30-80x106)
and the sub-atmospheric 40Ar/36Ar ratio are consistent with
other Permian-Triassic sites (Becker et al., 2001). Interestingly,
this ET fullerene signal occurs only at the “upper”
boundary layer (see Fig. photo gallery) (~65cm.), coincident
with the shocked quartz and not with the Ir that occurs below
the coal (~145 cm.) (Retallack et al., 1998). Thus our data
support the notion that the boundary is present at Graphite
Peak and is coincident with the biostratgraphy, chemostratigraphy
and shocked
|
