Episode 40
Copyright © John Page Williams, Jr. all rights reserved.
This is John Page Williams with another reading from Chesapeake Almanac. The month is December and the title is "Miocine Fossils: Putting Bay Time Into Perspective."
Brent Heath climbed out of his canoe, bent over, and felt around on the bottom like a big raccoon. Grinning, he straightened up with a huge scallop shell and a chunk of coral in his hands. We were on Dragon Run at the headwaters of the Piankatank River near the Route 17 bridge over the Dragon at Saluda.
The Dragon is fresh, a dark-water stream winding through a long, narrow cypress swamp. nothing like that scallop or the coral lives there today, for these creatures predate the Chesapeake Bay. The two fossils hark back to a very different time perhaps, 10 million years ago, when this part of the world was covered by warm, shallow, coastal seas. That was the Miocene Epoch in geologic time, a period that began about 25 million years ago and ended about 10 million years ago.
The present Chesapeake Bay seems to us as if it's been here forever. Yet we know that it is only about 15,000 years old, formed when the Atlantic Ocean flooded the mouth of the Susquehanna River system at the end of the last ice age. Several other bays preceded the present one, as earlier glaciers came and went, causing sea level to drop and rise over the past million years, known as the Pleistocene Epoch.
The Miocene Epoch predates even the glaciers by many, many years, but certain features of the region were already recognizable even then. The coastal plain had already formed, as the snows and the rains and the sunshine gradually weathered the Blue Ridge and Appalachian mountains, sending huge quantities of sand, gravel, and mud down the ancestors of our modern rivers. Thus, the eastern margin of the continent was already made up of these loose sediment, beginning around the present sites of Richmond, Fredericksburg, Washington, Baltimore, and Havre de Grace.
At times, sea level was low, and the coastal plain was exposed all the way to the edge of the continental shelf. At other times, like during the Miocene Epoch, the ocean covered virtually all of it. We can only imagine that the area was much like today's Atlantic Coast of Florida, Georgia, and South Carolina, with barrier beaches, shallow bays, and a relatively warm climate.
It's amazing to find out what lived in these warm seas. There were Brent Heath's big scallops and corals, plus porpoises, whales, oysters, sea turtles, rays, sharks, and other assorted fish, as well as crustaceans and mollusks both large and small. Their fossils are littered along beaches near Miocine outcrops on the Bayshore and the tributaries.
For over 10 million years, these creatures lived and died by the millions, and plankton lived and died by the trillions. It is difficult to comprehend those numbers in any but an intellectual sense. The upshot, though, was that they died and sank, they were buried in layers of seabed sediment several hundred feet deep. The estuaries that have developed in the past million years, including the present Chesapeake, have covered them over with more sediments, so the fossils of these Miocene creatures lie under much of our Bay region.
As noted, the Pleistocene Epoch has seen several ice ages come and go, with glaciers advancing and retreating and attended seafall and rise. When the sea level has been low in the periods during ice ages, the rivers in this area have run rapidly, down to the edge of the continental shelf and out into the Atlantic, cutting deeply through the soft sediments of the coastal plain.
This downcutting is the mechanism that has produced the high bluffs that occur in spots along the Bay's main stem and rivers. Not all of these bluffs contain Miocine deposits, but many of them do. The most famous are the Calvert Cliffs and the nearby Scientists Cliffs along the Bayshore in southern Maryland, which may be the largest exposed deposit of Miocene fossils in the world. Large deposits also exist on the Potomac below Colonial Beach around Westmoreland State Park in Stratford Hall. There are interesting smaller deposits on most of the Bay's rivers, including Brent Heath's vein on Dragon Run; scouted outcrops on Wilton Creek, about 10 miles downstream on the Piankatank; and the Boston Cliffs, which are less than 30 feet high, on the Choptank River above Cambridge.
These spots offer an intriguing look into a time which is otherwise very different to imagine. They are good points of interest for cruising people and small boat explorers who learn to recognize them in the Bay's creeks and rivers. However, wave action erodes the bases of the cliffs, both large and small, and chunks fall off from time to time. Climbing them is extremely dangerous.
There are several excellent resources from which to learn about the bay region's Miocene deposits and how to study them. The best is the Calvert Marine Museum in Solomon's at the mouth of the Patuxent. It has superb exhibits of Miocene fossils and can provide information on some ways to explore the Calvert Cliffs safely. A trip to the museum makes a good winter timeweekend outing. Both Westmoreland State Park in Virginia and Calvert Cliffs State Park in Maryland have good seasonal programs. Finally, A.J. and Robert L. Lipson's Life in the Chesapeake Bay has a good chapter on Miocene fossils. Make use of these resources, and they will give you a whole new perspective on the Chesapeake.
For more happenings around the Bay in December see our other Chesapeake Almanac podcasts and read our blog posts "Buffleheads and a Winter Miracle" and "Getting Outside in December."
