Ten Sleep Canyon is a dramatic entry to the Bighorn Mountains:
But I was befuddled by the geology signs as I ascended: The first said: Pennsylvanian, 290-330 Million Years Ago (MYA). Then came Mississippian, 330-360 MYA, which is older; and finally came Cambrian, which is older yet (500-530 MYA) !! That seemed topsy-turvy to me. When you build a layer cake, the first layer down is the oldest, and the second layer is younger. It was as if someone carrying a cake had tripped and flipped it upside down on the floor.
Googling around the internet didn’t clarify my conundrum. But days later I came across a sign at Shell Canyon Falls that gave me the clue. In the diagram, the brown is the Cambrian rock that has buckled up because of tectonic pressures. Let’s say the white layer is the Mississippian that was laid down next. Then the gray we’ll call the Pennsylvanian. Imagine the earth above my red line eroded away.
So if you’re driving up the red line, you come first to the gray layer (the youngest), then the white, (the middle-aged), then the brown (the eldest, on top). It moves from the youngest rock at the bottom to the oldest at the top. Interesting!!
In the meantime, I began thinking about all that limestone; in places it’s 9000 feet thick. Words like foraminifera and coccolithophores floated up from my memory banks. These tiny sea organisms are types of plankton that die and their exoskeletons drift to the bottom, accumulating really really slowly. Think about the time it would take to accumulate 9000’!! ...Especially considering it all gets compressed by sediments on top then cooked to a perfect hardness. Overcook it and it becomes marble.
Foraminifera & Coccolithophores
(Oops, only one photo of the canyon and lots of these...cuz they're cool!)
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