Re: Pangaea

[gator@mail.utexas.edu (c. brochu)]

it seems inconceivable
>for the above-sea-level land masses to remain largely unchanged.

Indeed, plate tectonic theory does not rely on continents retaining their
current configurations over time.  Remember, it's the plates that are
drifting, not the continents by themselves.  Plate configurations are
immune to sea-level changes - the margin may be above or below sea level,
but the margin itself will be there regardless.  As the plates move, the
continents attached to them move as well.  These continents may or may not
be right on a plate margin.

>
>3) What is the theory for the creation of Pangaea?  What would
>cause a planet to form with all its higher land mass to form on
>one side?  Was it on the side or was it formed at one of the poles?
>Is a planet stable with this deformity?  Is that the reasoning
>for the breakup of Pangaea?  These are questions I have never
>seen discussed when I have read about Pangaea.

It depends on which "Pangaea" you're talking about.  There have been at
least two times since the Proterozoic (late Precambrian) in which the known
continental masses were united.  They broke up at the beginning of the
Cambrian, came together again during the Permian, and broke up again at the
beginning of the Jurassic.  No one seems to know if there was any special
"process" involved or if this was just "one of those things" - all the
continents happened to collide at once because of pre-existing plate
movements.
>
>4) About the breakup, this has been blamed/credited for dividing
>the dinosaur families according to the area of Pangaea.  Is this
>an over-generalization?  Now that dinosaurs are being found in
>areas thought to be out of reach due to the breakup, suddenly
>we have a "land-bridge".  Forgive me for being sacrilegious, but
>this *sounds* like someone's pet theory was being disproved and
>everyone rushed to save it.  It seems that only the surface of
>dinosaur fossils has been touched.  What will happen if more
>out-of-bounds dinosaurs are found?  Will Pangaea start to look
>like a quilt with "land-bridges" and other patches criss-
>crossing the dinosaur map?  ( This is the list's area of
>expertise.  Feel free to be offended and refute my assertions. )
>

Plate tectonics is still the best explainer of dinosaurian diversity.
Dinosaurs are found in areas "out of reach" only because they were there
before the breakup.  No land bridge is required.  Current work in
Antarctica is elegantly confirming this hypothesis.  The pattern shows
similar dinosaurian faunas around the world in the Triassic and divergent
faunas in the Late Cretaceous; this coincides with contiguous land masses
in the Triassic (Pangaea) and separated land masses in the Cretaceous.
Incedentally, dinosaurs are similar between western North America and Asia,
between eastern North America and Europe, and more or less unique in South
America and India because of a complex interplay between tectonics and sea
level fluctuation.


regards, chris



__________________
Christopher Brochu
Department of Geological Sciences
University of Texas at Austin
Austin, TX 78712
512-471-6088

gator@mail.utexas.edu


You know how it feels when you're leaning over on a barstool and almost
fall over, but not quite?  I feel like that all the time.