The Accomack Spit grew southward, forming the northern portion of today's Delmarva Peninsula.
When sea level dropped again roughly 150,000 years ago, in one of the Ice Age stages, the Exmore Channel was filled with sediment and the old path was blocked by the Accomack Spit.
a 7-9 million-year-old whale skeleton was excavated at Naval Weapons Station Yorktown in 2013 Source: US Navy (130409-N-XJ695-007) For at least several million years, the rivers we currently call the Susquehanna and Delaware have flowed from the uplands of New York and Pennsylvania to the Atlantic Ocean, while the Potomac River has eroded the remains of the Appalachian Mountains further south. They carved new channels across the Piedmont and Coastal Plain through soft sediments and hard bedrock, carrying dissolved and suspended particles downstream to be deposited on the ocean floor.
deposition from the north in Pliocene Epoch, prior to southern extension of Delmarva Peninsula in last 500,000 years Source: US Geological Survey, Professional Paper 1067-A: Upper Cenozoic Deposits of the Central Delmarva Peninsula, Maryland and Delaware (Figure 2) The rivers flowed down to the low spots on the edge of the continent formed by the Salisbury Embayment and Baltimore Canyon Trough.
The Exmore Channel, the oldest paleochannel dating back to 300,000-500,000 years ago, was the path of the combined Susquehanna and Potomac rivers east across the Continental Shelf.
After sea level rose and covered the Continental Shelf, an estuary formed at the ancient mouth of the Susquehanna River.
The Chesapeake Bay fills the drowned valleys of the Susquehanna and James rivers, plus tributaries that intersected the Susquehanna.
The sediments on the Coastal Plain include sharks teeth and whale fossils, documenting the different times when sea levels were higher and the Virginia shoreline located further west.The mouths of each river have migrated in discrete "jumps," shifting to new channels after sea levels rose/fell during glacial periods in the last 2 million years.When sea levels rose, sand and gravel was deposited at the mouth of the rivers, blocking the old channel.a fjord created by a glacier Source: National Park Service, Those Fabulous Fjords!The shape of the modern Chesapeake Bay was formed through a combination of both erosion by the Susquehanna River and deposition by ocean currents.The channel of the Susquehanna River has been pushed south, past the former deltas of the Potomac/Rappahannock/York rivers and down to the channel of the James River.