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Geological > Geology of Long Island Sound
Figure 1:  300,000,000 - 200,000,000 Years Ago
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A View of Southern New England's Place in the World 300,000,000 - 200,000,000 Years Ago

By around 300 million years ago, plates of continental crust, including ancient versions of the landmasses that we now know as Africa, Avalonia, North America, South America, Europe and Asia, had converged to form a supercontinent called Pangaea. The closing of the oceans that had once separated Africa and North America occurred in a sequence of events that assembled, heated, folded and deformed the bedrock of New England, as described in Connecticut Geology. This happened in an environment of east-west compression that culminated in Avalonia being crunched in a continental-scale "fender bender" between Africa and North America (green box on the globe, upper left of figure). The Appalachian Mountains formed as the margins of the colliding continents were crumpled. In central and southern New England, this crumpling further enhanced an overall north-south alignment of rock units and structural features.

The green shaded area, to the lower right of the figure, approximates where our region would have fit into the scheme of things about 200 million years ago. By that time, Pangaea had started to break apart and the North Atlantic Ocean had just begun to open. The majestic peaks of the eroding Appalachian Mountains formed the western margin of the expanding Atlantic Ocean basin, and the rocks of New England were in a fairly cool state, so they tended to break when stressed. As the large red arrows indicate, compression during convergence was replaced by tension in the opposite direction as Pangaea was rifted apart. The north-south fabric that had developed in the bedrock as Pangaea was assembled incorporated less competent rock units and structural features that became susceptible to extensional faulting and fracturing as Africa separated from North America.

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