🚀 go-pugleaf

In article <777@jc3b21.UUCP> larry@jc3b21.UUCP (Lawrence F. Strickland) writes:
>
>Now the show I saw contended that for North America, at least, the continent
>was built up from deposition on an originally smaller continent based in
>southern Canada.  They called it the Canadian shelf or something like that.
>They also noted that this rock PRE-DATED the formation of Pan-Gaea!

That's Canadian Shield. It is the core of the present North American continent.
Yes, it does predate Pangaea, by quite a bit. On the order of 1.5 billion
years old, while Pangaea was only about 2-400 million years ago. Plate
tectonics as a process is older than Pangaea. The Appalachians were formed
by the collision of Proto-North America and Proto-Europe about 4-500 million
years ago. Can't remember exact times, but that's about right.
The Atlantic reopened about 180 million years ago, splitting North America
and Europe along nearly the same boundry (but not quite).

Continents have been drifting around the world for about the last 1.5
billion years, sometimes joining, sometimes breaking up.

It is, however, real difficult to figure out the geography older than
200 million years ago. This is because we don't have any seafloor
records older than that. All the oceanic crust is less than 200 million
years old!

There have been some attempts at reconstruction, despite the difficulties.
Let's see, references....
Best I can do is geological journals for stuff that technical. Maybe
you can find some of these journals in a University Geology library.

Scotese, C. R., et al. 1979. Paleozoic base maps. Journal of Geology.
	    87: 217--277.
Smith, A.G., et al. 1973. Phanerozoic world maps. Special Papers in
	    Palaeontology. 12: 1-42.
Whittington, H. B., et al. 1972. Ordovician geography and faunal provinces
	    deduced from trilobite distribution. Philosophical
	    Transactions of the Royal Society of London, Series B.
	    263: 235--278.

These should provide a start. I don't know where to find much in the
way of popular material dealing with this subject, though.

New continental crust has been added, as well. Sometimes pieces
of oceanic crust get jammed onto the continents. The volcanism near
subduction zones will create island arcs that also often are
accreted onto the continents. The Shield areas are the continental
cores, generally the areas of low geologic activity older
than 1 billion years.

You should be able to find some relatively simple geology texts that
can explain these aspects of plate tectonics.
Example of one I like:

Press, Frank, and Siever, Raymond. 1982. Earth. W.H. Freeman and Company,
	San Francisco.

I just took a look at it and there is a Middle Ordovician (475-490 Million
years ago) world map in there, p. 457.

Have fun!

--------------------------------------------------------------

		 Don't Should on yourself.

Bob Myers                       myers@hobiecat.Caltech.Edu