Teaching Earth Sciences - Earth Science Teachers' Association

Figure 1 Wales is a classic example of an area mapped in terms of planation surfaces interpreted as Davisian peneplains (Brown, 1960) with successive incision events related
to eustatic sea level fall. This view is of the Black Mountains near Abergavenny.
geological history of lowland Amazonia. They describe a
major peneplain, an isochronous, Pan-Amazonian feature
that formed following the early to mid-Miocene phase of
Andean tectonic uplift. Peneplanation may have begun
about 15 Ma and ended about 9.5–9.0 Ma. A thin cover
of sediments was then laid down over most of lowland
Amazonia, burying the peneplain, which is readily observed
in riverbank exposures as an angular unconformity. The
authors correlate this unconformity with surfaces elsewhere
in South America, linking the erosional phase to ‘a common
cause, which is interpreted to be the still on-going collision
between the South American and Nazca tectonic plates’.
The Appalachian region of eastern North America was a
classic location for identifying peneplains. Stanford et al
(2001) correlate late Cenozoic fluvial deposits and erosional
landforms and Coastal Plain marine deposits to identify
periods of valley incision and planation, with incision
related to glacioeustatic lowering of sea level during
growth of the Antarctic ice sheet in the Middle to Late
Miocene and initiation of Northern Hemisphere ice sheets
in the Late Pliocene. The authors make the bold claim
that planation in coastal regions of low relief on passive
margins can be achieved in less than 20 million years, with
dissection in less than 5 million years.
As can be seen from the above, Earth scientists are still
continuing to identify peneplains, and these are sometimes
interpreted in the original sense of an erosional lowland
reduced to near base level at the end of an extended
period (cycle?) of erosion. However, it is preferable to
use the meaning of the term adopted by Fairbridge
(above). He believed that the complex history of subdued
cratonic surfaces, with their occasional pedological
evidence, veneers of marine deposits, and periodic
tectonic disturbances, needed a multidisciplinary
approach: which called for a ‘meeting of the minds’
between geomorphology, soil science, stratigraphy,
palaeoclimatology and plate tectonics (Fairbridge, 1988).
Battiau-Queney (1996) reviews a number of weathering
indicators that can be used to study past surfaces, but
stresses that weathering alone is unlikely to be able to
produce extensive lowlands, and that there may have been
geomorphological systems in the past with no modern
analogues. Fluvially-based erosional explanations, she
claims, are likely to be inadequate as well.
Peneplains and tectonic activity
Erosion surfaces have been observed in alpine locations.
Babault et al (2005) produced a very interesting paper on
the Pyrenees, where high elevation peneplains had been
44 Teaching Earth Sciences Vol 35 No 1 2010 www.esta-uk.net