History records that English naturalist James Hutton thought of it first: “The present is a key to the past.” That quote summarizes one of the most important basic principles of geology. When we want to understand the geological past of some rock unit we go out and try to find a modern equivalent. If we are studying a particular sandstone, we look at modern sands. They commonly accumulate at the bottoms of shallow seas. So, our sandstone may well have formed in just that sort of environment. That’s the way we think, that’s the way our science works.
We aren’t going to do sandstones today, let’s do what’s called a black shale. And let’s pick a special one that is located where Chestnut Street intersects Rte. 20 just west of Sharon Springs. See the upper half of our first photo. This is called the Chittenango Black Shale, and it quickly generates geological thoughts of an ancient, relatively quiet, even stagnant, deep-water seafloor. Black shales were once black muds and that tells us that there was very little oxygen on the floor of the ocean. That’s what happens on a stagnant sea floor. Microbes consume the oxygen until it is gone. With no oxygen there should have been few or no animals and few or no fossils.
But this one has something special in it. Here and there, if you are patient and look carefully, you will find concentrations of fossils, unusual fossils. See our second illustration. This is a hodge-podge of Devonian age invertebrate animals. What’s curious about this is that they are all very small, none being more than a quarter inch in size. There were plenty of large seafloor animals during the Devonian time period, so why are all the Chittenango fossils all so small?
There’s a mysterious pattern here and that begs to be explained. Paleontologists, long ago, came up with an attractive hypothesis – they thought that the ancient Chittenango Shale had once been something we call a Sargasso Sea. That’s a stretch of ocean with a floating mat of algae inhabited by a diverse assemblage of small lightweight, mostly invertebrate animals. The modern Sargasso Sea stretches off eastward from Puerto Rico. Geologists saw that today’s Sargasso served to explain the ancient Chittenango Sea – the present is a key to the past!
We stand along a busy Rte. 20 and look once more at the Chittenango Black Shale. We gaze into its past. Down at the sea floor it is cold and quiet. No animals are seen. Few if any fish swim in the waters above; there is just too little oxygen to keep them alive. But up at the surface there is plenty of oxygen, we see a jungle of large floating algae. Small invertebrate animals float or swim about through this maze of greenery. From time to time one of them dies and its skeleton, a shell, sinks slowly to the bottom. It joins a host of other small shells that have preceded it. All of them willl spend the next 390 million years right there.
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologists.” Read their blogs at “thecatskillgeologist.com.”
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