Barrier Islands and the Outer BanksĮxtending from the eastern Shore of Virginia along the coasts of North and South Carolina, Georgia, and portions of Florida is an extensive barrier island complex. Several theories have been proposed for the Bays' formation, including sea currents, groundwater seepage, aeolian processes, and even extraterrestrial impact. They are visible on maps and photographs from space, especially where lakes, boggy swamps, or savannahs occupy the bays. They can be as large as thousands of acres, and nearly 500,000 of them occupy the Atlantic Coastal Plain. The bays are often difficult to visualize from land, as their rims can be only a few centimeters in height. This formation of broad flat ridges and rolling hills formed from a combination of fluvial Cretaceous sediments deposited around 90 million years ago by meandering streams, and marine sediments deposited about 45 million years ago during a sea level highstand. The Sandhills, a strip of ancient beach dunes, are a distinctive feature of the Upper Coastal Plain and stretch from North Carolina into Georgia along the Fall Line. For example, the Orangeburg Scarp, extending from central North Carolina to northeast Florida, formed from wave erosion during an interval of high sea level during the mid- to late Pliocene (3.5–2.5 million years ago). These seven sea level shifts are traceable along the Atlantic seaboard and include two that occurred during the Pliocene epoch, followed by four during the Pleistocene epoch and the current Holocene shift. In South Carolina, seven terrace-scarp pairs stairstep the topography of the lower Coastal Plain, representing seven cycles of the receding ocean levels.
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