Geoscience Reference
In-Depth Information
Fig. 11.5
A chronosequence of desert pavements derived from sandstone and dolerite drifts from
the Taylor Glacier in Arena Valley: (
a
) Taylor 2 drift (pedon 76-38); (
b
) Taylor 3 drift (pedon
86-23); (
c
) Taylor 4a drift (pedon 82-14); (
d
) Taylor 4b drift (pedon 76-29); (
e
) Altar drift (pedon
82-17); and (
f
) Arena drift (pedon 86-20) (Bockheim
2010a
)
and older age (B, C, D, E, and F). The proportion of clasts with ventifaction
increases progressively through time from 20 % on drifts of Holocene and late
Quaternary age (A) to 35 % on Miocene-aged drifts (E, F). Desert varnish forms
rapidly, especially on dolerite clasts, with nearly 100 % cover on surfaces of early
Quaternary and older age. Macropitting occurs only on clasts that have been
exposed since the Miocene (E, F).
The morphology of patterned ground changes through time as ice within polygon
fi ssures sublimates (Fig.
11.6
). In central Beacon Valley images obtained from a
digital elevation model show the increasingly diffuse expression of high-center,
sand-wedge polygons with time on three drift sheets on the valley fl oor, including
regular pentagonal and hexagonal polygons on Taylor II drift (A), poorly expressed
polygons on Taylor III drift (B), and diffuse polygons on Taylor IV drift (C). The
apparent lineations on Taylor III and IV surfaces may refl ect prevailing wind abla-
tion from the southwest to northeast (Bockheim et al.
2009
).
