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Geological > Geology of Long Island Sound
Figure 2:  160,000,000 - 30,000,000 Years Ago
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A View of the North Atlantic Margin, in the Vicinity of Connecticut, During the Jurassic Period of the Mesozoic Era, About 180,000,000 Years Ago

As tension worked to stretch the region, the position and orientation of fractures, faults, and rifts was influenced by the existing fabric of the bedrock. A north-south rift basin (red arrows top right), now known as the Connecticut Valley, nearly split Connecticut and Massachusetts in two. Further to the east, a more successful rift tore Avalonia apart, and initiated the opening of the Atlantic Ocean. A portion of Avalonia remained attached to Africa, and is found in Morocco today. Another portion now lies along the Atlantic coast from southeastern Connecticut northward into Canada.

Streams preferentially created valleys where bedrock units and fault/fracture zones were most easily eroded. A distinct north-south grain, controlled by the shape of the stream-sculpted bedrock surface, developed on the landscape as stream valleys coalesced to form a drainage system that flowed southward across north-central New England, western Massachusetts and Connecticut. As it matured, this drainage system, and others up and down the east coast of North America, began to efficiently carry sediment from the eroding mountains to the western margin of the emerging Atlantic Ocean. This initiated the development of the Atlantic Coastal Plain and continental shelf.

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