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Geo of Ct. Beginning 500 mya 250 mya Today. The beginning. To understand how the various rocks of Connecticut came to be assembled, we need to take a global view.

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geo of ct

Geo of Ct


500 mya

250 mya


the beginning
The beginning

To understand how the various rocks of Connecticut came to be assembled, we need to take a global view.


The outer, rigid shell of the earth is broken into large, irregular plates, which move around only slightly faster than your fingernails grow.  This where they are today -- note that Connecticut is in the eastern North American plate and west of the Eurasian and African plates. In various places, the plates move apart, together, or side-by-side.


500 million years ago, the plates were arranged something like this.  Instead of the modern Atlantic Ocean, we had the Iapetus Ocean to the east of what is now Connecticut.  In Greek mythology, Iapetus was the father of Atlantis, thus the name. The bar connects similar points in this and the following slides.


The plates slowly collided one by one, finally forming a super-continent called Pangaea (meaning "all one Earth") not long before the beginning of Mesozoic time.  The collision between proto-North America and Proto-Africa (possibly with a couple of smaller plates as well) wrinkled the earth to form the Appalachian Mountains.  Most of New England is within this mountain chain.


Again, here is the arrangement of the continents today.  Connecticut was involved in the events that rifted Pangaea apart to open the Atlantic Ocean and create this modern pattern, starting 200 million years ago.


New England today shows regions that had different geological origins, which are pieces of the ancient plates that collided and fused together.  Several un-labeled pieces, called terranes, actually constitute the Iapetus group, much of which was in the ancient ocean. Avalonia was left behind when Africa separated from eastern North America, which opened the present Atlantic Ocean.  The "Newark" terranewas also created by that event; it and others like it are named for a similar piece in New Jersey.

  • Rift zone of Pangaea. As Africa separated from North America, a series of rift valleys formed (including the Hartford basin labeled by H
  • Folding
  • Sediments and lava flows
  • Faulting tilted the rocks downward to the east
  • lava flow (basalt) ridges from the south. The central Connecticut Valley, Proto-North America,
  • Sedimentary rocks, and the eastern and western terrain uplands flanking the central valley.
  • Glaciers shape, pluck and deposit

This series of slides illustrates the plate tectonic assembly of Connecticut. By Ralph Lewis accessed by Laurie Haddock May 1 2011