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Geological > Geology of Long Island Sound
Figure 4:  30,000,0000 - 26,000 Years Ago
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A View of Connecticut and a Portion of the Atlantic Coastal Plain in the Latter Part of Pliocene Time, About 2,000,000 Years Ago

Throughout the rest of Cretaceous time, and up until about 10,000,000 years ago (the first half of the Miocene), sea level was higher than it is today. Deposition of sediment from interior New England and Connecticut continued to build a seaward-thickening wedge of Coastal Plain strata along the continental margin in the vicinity of today's Long Island. The thin landward edge of the Coastal Plain wedge may have extended over and buried the bedrock of what is now coastal Connecticut by the middle of Miocene time. The protection afforded by this cover may explain why the bedrock surface along Connecticut's "coastal slope" is less eroded, and has a steeper slope than the bedrock surface that lies to the north.

Periods when sea level was much lower than it is today punctuated the latter half of the Miocene and persisted throughout the Pliocene. Whenever sea levels dropped sufficiently to expose the surface of the Coastal Plain wedge, stream erosion was active. The thin landward edge of the Coastal Plain wedge was eroded sufficiently to expose the bedrock of Connecticut's coastal slope, and only Upper Cretaceous (and older) strata remained in the vicinity of Long Island. The interior lowland that was to become Long Island Sound was carved out by streams that flowed eastward and westward from the divide south of Branford, Connecticut.

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