Kentucky River Fault Zone Geologic Base Map
Georgia | Kentucky | Nevada | Washington |
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Kentucky River Fault Zone Geologic Base Map
Georgia | Kentucky | Nevada | Washington |
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All of the rocks you will be observing on this field trip are limestones and shales of Ordovician age (510 to 440 million years old). For a reference point, the first dinosaurs appeared only about 245 million years ago. These rocks contain various features that can be separated into two groups based on when they occurred. The fossils, mud cracks, and fine laminations you will be observing are just as old as the rocks. They were either deposited or formed in the sediments that were eventually lithified into the rocks you see today. On the other hand any faults, folds, veins, sinkholes, or groundwater dissolution features you see formed some time after the rocks did (they cross-cut the earlier features, like limestone beds). It's not important for you to understand all of the terms you just read yet, but if you remember which features formed along with the rocks and which came afterward everything will be much clearer for your trip.
The fact that limestone is all you seem to find around Lexington has some meaning. Why can't we find a layer of conglomerates, or a large granite pluton around here? Why are we able to collect marine fossils so far from the nearest beach? In order to answer these questions we must look at what the world was like when the rocks you will see formed. Because of plate tectonic movements, the continents of today were in greatly different places. In the Ordovician North America was near the equator, a much warmer climate. Also during this time Baltica (northern Europe) is moving toward ancient North America. As you might have guessed the ocean floor between the two continents was being subducted under North America. This subduction and the subsequent continental collision produced the first mountain building event of the Appalachians. Behind this line of new mountains was a large inland sea. Calm shallow warm water is where carbonate typically forms, and limestone is made of carbonate.
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