September, 28th 2008
On September 28th a fair number of E,L&T freshmen students and a few sophomores, including me, went to Brownie Beach and Jug Bay Wetlands Sanctuary. Our first stop was Brownie Beach which lies on the western shore of Chesapeake Bay. It is located on the north top of the Calvert Cliffs which are world-famous for their sediments, strata and the fossils you can find there.
The Calvert Cliffs formed about 12 million years ago during the early to middle Miocene Epoch. The sediments that constitute the cliffs were once part of the Appalachian Mountains. While today Brownie Beach is a Mid-Atlantic costal environment, the area used to be completely under water. So, if we had been standing at the same spot on Brownie Beach 15 million years ago, we would have been tens of meters underwater (!). As the water level slowly decreased, the cliffs formed and fossils were encased in it. Today one can find hundreds of different fossils from the fauna and flora of the Miocene epoch and the time after that. Some of these include shell fish fossils, mollusk shells, ray plates, bones from terrestrial vertebrates, various fish vertebrate, whale teeth and Maryland’s state fossil, the shell Ecphora gardnerae gardnerae. The most abundant fossil, and the one I mainly found, was shark teeth. I only found smaller examples of shark teeth, the biggest being about one centimeter long. The teeth can be identified by carefully looking at their shape, especially their crown, and looking at whether or not they have serrations or notches. I identified (kind of) two of the teeth I found to be from Alopias grandis, the tresher shark and from Sphryna zyguena, the hammerhead shark. The reason that only the teeth and not the shark skeleton remained as fossils is that the skeleton is made out of cartilage which is not solid enough to be preserved in this environment. The easiest and most direct way to distinguish fossils from the Miocene Epoch from remains from recently decayed organism is to look at the color of the object in question. Because minerals like phosphate and calcium would deposit in the teeth and bones with time, the fossils have a black color while recent remnants are brownish white.
After we finished collecting fossils and studying the cliffs we visited Jug Bay Wetlands Sanctuary alongside the Patuxent River. The area we visited mainly consisted of freshwater wetlands, marsch and forests. One of the things we noticed as we walked through the forest is that the ground is made out of sand, which pointed out that we were in an aquatic environment. We stopped by one of the stream systems which go through the forest and noticed how over millions of years the stream formed its immediate environment, including the valley and the overhangs around it. Streams have the power of erosion and play an important role in shaping the surface of the earth.
Like most environments on our planet Jug Bay was not spared human impact. In the 1890’s a railroad track was build traversing the area. The railway slowed the flow of water because it acted as a dam. The consequence is that today Patuxent River no longer floats as broadly as it once used to. The positive human impact includes the conservation work being done like protecting the wildlife and making sure no invasive species enter the environment. Lastly we visited the Refuge center of the sanctuary and looked at their various exhibits. One exhibit that caught my eye demonstrated the relationship of the particle size of sediments and the time it needs to settle down in the water. There were four glass tubes filled with water, an artificial plant and a different kind of sediment each: gravel, sand, silt and clay. Upon turning the tubes upside down, one can observe which sediment would settle down first and which would cloud the water. The gravel being the biggest sank down first and silt and clay were the last and thereby clouded the water. Because Jug Bay sediment mainly comprises silt and clay, the water is clouded and sunlight is blocked. I found this exhibit to be a simple and effective way to teach interested people why the water at the sanctuary is foggy.
Overall I would recommend this field trip to next years E,L&T students, not only because of the interesting geology and biology one can learn, but also because of the beautiful scenery. I would also recommend taking an umbrella with you……
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