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Cross Section M
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The Mesozoic and Cenozoic Divergent Continental Margin
Upper Jurassic, Cretaceous, and Cenozoic; 175 my - present
Under ConstructionThe Atlantic continental margin record of Virginia (and the entire Atlantic sea board) is preserved in the coastal plain province, and under water along the continental shelf. Simplistically, the record is of a gently east-dipping, seaward-thickening wedge of sediments. The edge of the coastal plain sediments is the farthest western extent of the continental margin sediments and they cover both igneous and metamorphic basement rock and part or all of some Triassic rift basins. North of the Richmond and Taylorsville basins, for example, completely buried basins have been recently discovered.
Some stratigraphic units of the margin thin to a feather edge at the western edge of the coastal plain province, but other units originally extended farther west and have been since truncated by erosion. We don't know how far west the truncated stratigraphic units originally extended. It is possible that during the Cretaceous all of Virginia was under water, but during most of this time Virginia was a coastal region as it now is.
The coastal plain sediments have a complex history caused both by subsidence of the continental margin, and fluctuations in sea level. These are too complex to pursue, but having raced through vast amounts of geologic history in this story it seems now that we come screeching to a near crawl as we approach the present, and events begin to take on more of a human time scale. For example, sea level has been slowly rising over the past few hundred years, almost imperceptibly inundating the exposed coastal plain. The process is so slow we do not notice it. But the large storms which lash the modern coast, and which cause erosion of the beaches and barrier islands is the work of these storms haltingly but steadily pushing these beaches and barrier islands farther and farther inland as the sea transgresses again across eastern Virginia. It is becoming more and more obvious that the coastal regions belong to nature and not us and nature will eventually take the beaches and barrier islands back.