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Hi, Jon–
>> My text says that Gondwanaland was assembled from continents and
microcontinents very early in the Paleozoic, or even in the late Proterozoic,
and stayed pretty well in one piece until it broke up in the mid-Mesozoic.
In Dalziel's reconstruction in the Sci Am article, the pieces of Gondwana are
separated into three in the earlier supercontinent Rodinia; as Rodinia breaks
up, proto Antarctica+Australia+India rift away from Laurentia (today's W.
coast) and swing around to meet proto-Africa (today's E. African side), which
in turn seems to be pushed into proto-S.America. Gondwana is thus assembled
into its familiar configuration by the Cambrian.
I am a slightly puzzled at the dates; his "latest Neoproterozoic" map (with
Gondwana more or less complete) shows an age of 550 million years, but I had
thought of the Cambrian as beginning 570 million years ago. Is my date info a
bit obsolete here?
>> I'd be very interested in learning how the SE US could "scrape along" Peru,
on Gondwanaland's _west_ coast, then swing north around the northern coast of
Gondwanaland in time to suture to Baltica in the late Devonian or early
Pennsylvanian.
Soon after the assembly of Gondwana, Siberia, Baltica, and Laurentia all detach
from proto-S.America (today's W. coast) and each other to go their separate
ways. Laurentia is rather frisky, circling around Gondwana/S. America with
several brief collisions; Baltica does not have as far to go, but is generally
close to Greenland and hits and sticks halfway through Laurentia's end run.
Indeed, since Laurentia stays near the equator during much of the action, it
might be easier to think of Gondwana as swinging around Laurentia and Baltica,
which never get as far from each other as Gondwana gets from the pair of them.
–Doug