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Re: The Final Days
Andrew A. Farke wrote:
>Mountain habitats have very poor preservational potential--usually there is
>much more erosion than deposition going on. Are there really *any* mountainous
>habitats preserved? I guess you might get the occasional terrace or cave, but
>that's about it. <
Like with many generally accepted "truths" things are not quite that simple.
High-altitude fossil sites from the Pleistocene and Pliocene are fairly common,
particularily in Western North America and Central Asia. Indeed in the Western
US it is absolutely necessary to factor in the altitude of Pleistocene sites to
make sense of distributional or ecological data (for a good example of this see
Harris, A. H. 1985. Late Pleistocene vertebrate paleoecology of the west.
University of Texas Press, Austin, 293 pp.).
Older high-altitude sites are rare but not unknown. Florissant for example is
usually stated to have been at approximately the same altitude as today when
the fossil beds were formed. While the youngest sites (say <5 Ma old) are often
in true high-mountain terrain older ones are typically found on high plateaus,
often with interior drainage where large-scale deposition can occur even at
quite high altitudes.
Whether any Mesozoic high-altitude sites are preserved is more uncertain. It
seems unlikely that any would have survived if they had remained att high
altitude ever since then. However what comes up can also come down. There are
plenty of evidence for large scale vertical motion of large continental areas.
Again some of the most striking examples are in the Western US where the
Colorado Plateau and the Basin and Range Province have been elevated by several
thousand feet since the Neogene. The same is true for much of eastern and
southern Africa ("High Africa"). In the case of the Western US this is due to
the continent overriding part of an ocean ridge while the African "bulge" is
centered on the Great Rift, an incipient ocean.
Such areas might preserve fragments of high altitude deposits when they return
to lower altitudes, as they presumably ultimately will do. That such processes
were active in the Mesozoic too is clear from e. g. Australia. Much of
Australia was flooded by the sea during early/middle Cretaceous but then the
sea *receded* during the Campanian transgression when sealevels elsewhere in
the world reached record levels. Most of the Australian continent must have
risen for at least a several hundred meters to accomplish this.
The best places to search for Mesozoic highland sites might be in ex-rift
marginal areas which were presumably also high "bulges" at one time. To judge
from Tertiary fossil sites in High Africa, deposits protected from erosion by
volcanics have the best chance for long-term survival. The Inter-Trappan beds
of India come to mind. Since India was right on top of the Reunion hotspot at
the time they were formed they were quite possibly at a higher altitude then
than they are now.