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Sea Over North America
An epicontinental sea is an ocean that
sits on top of continental lithosphere. Continental lithosphere is thick but light, riding
high on the semi-fluid asthenosphere. Most oceans are on top of oceanic lithosphere, which
is thin but heavy and thus sits lower than continental lithosphere. When sea
level is particularly high and a large area of continental lithosphere is at a
low elevation, the ocean water spreads over the continent and creates an
epicontinental sea.
In the past, the Pittsburgh area was often
covered by an epicontinental sea. For much of the time before the Pennsylvanian
Period, the Pittsburgh area was at a lower elevation than it is today. Sea level began to
rise during the Early Cambrian and remained high all the way through the
Ordovician, Silurian, and Devonian Periods. During the Pennsylvanian Period,
the Pittsburgh area was raised to its current elevation when Africa collided
with North America
LINKS:
A SENSE OF
TIME
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