Portal mountain was our first destination to explore new
sites where Permian-Triassic rocks may be preserved in Southern
Victoria Land. The Permian rocks in Antarctica are characterized
by the Weller Coal Measures (see
photo journal) that are exposed as a narrow belt along
the edge of the Polar plateau from the Mawson Glacier to the
Mulock Glacier in and around the Portal Mtn. and Mt. Crean
sites (Isbell and Cuneo, 1996). The Portal Mtn. (~220 m) Weller
section consists of interstratified fine to course-grained
quartz/feldspar sandstones, laminated siltstone, mudstone
and coal. We quickly recognized several depositional environments
including braided and meandering streams and lucustrine environments.
The distribution of plants fossils and coal appear to be lithofacies
dependent with the most abundant plants and coal found within
the meandering streams with significant scarcity of both in
the lacustine and braided stream environments. While we were
successful at constraining these facies through the middle
Permian and into what appeared to be late Permian fauna (evidenced
by the change in size of the glossopteris leaves) it was not
clear that the early Triassic (e.g. no Feather-Weller contact)
was present as suggested by Isbell and Cuneo (1996). In addition,
there was no obvious boundary breccia as seen previously at
Mt. Crean and Graphite peak (Retallack et al., 1998; Retallack
and Krull, 1999). Samples were collected for carbon isotope
analyses to determine if a Permian-Triassic d13C excursion
is present at or near the last coal at the top of the section
(see photo journal for
Portal Mtn.).
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