All of the geomations/geoclips except these two were moved to content pages. Is there a place in the Module 9 content where you would recommend we place these two? I noticed we don't mention Capital Reef National Park in this Module.
Oysters! - Capitol Reef National Park
Rocks reveal how and where they were formed. Clues to the history of rock come from how it is put together, whether the pieces are big or little, sorted or mixed, angular or rounded, and so much more. Fossils also provide clues. Here, Dr. Alley and the CAUSE class are out in the desert at Capitol Reef National Park, but they are also in a shallow seaway from long ago. See why.
So we've been driving around the West, pointing at rocks-- there's a rock-- and saying, this is a sand dune. This is a lake. This is an ocean. But we haven't spent a lot of effort on, why do we say one is a sand dune, and one is a lake, and one is an ocean? Now in the case of the sand dune, when we looked at it, it was all sand. There were no little pieces, there were no big pieces, it was all intermediate size sand pieces. They had these structures that one sees in modern sand dunes. If you found anything that looked like a fossil, it was little reptile tracks. And so they had all the characteristics that you see in a modern sand dune.
Now here, we're in rocks that are very different. The rocks behind us are sort of washing away and they're making mud that washes down around our feet. And there's a number of characteristics of these, the layers are different, how big the grains are in them is different, sort of everything about them is different. And we can say these were rocks that were underwater. And we can go through the whole list of reasons why we can say they're underwater, but there's one very easy one. If we look down at our feet, and we look around at what's washing out of these rocks, what we find is oysters. And one can be very confident that if you find rocks full of oysters, you're not in the middle of the desert.
Mud Cracks - Capitol Reef National Park
Rocks occasionally are turned upside-down, but nature tells us when that happens. Mud cracks can show us that; they are wide at the top, narrow, and then end at the bottom. Fill mud cracks with another layer of sand or mud, and the cracks are "fossilized," to tell us which way was up when the rocks were deposited. Here, visit Capitol Reef with Dr. Anandakrishnan to see mud cracks, with a brief look at some right-side-up ones from the Grand Canyon.
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Look at this picture. You've got all these cracks developed over here. Imagine a second flood coming through here, a relatively gentle flood, water slowly flowing in here, a new layer of silt and sand and shales and clays. What's going to happen? All of that new material is going to filter down into these cracks and it's going to solidify in there as the water evaporates out of it.
So now 100 million years goes by. And we come along and we cut this open and we look at this layer and we look at these, and you'll see mud cracks. And we'll be able to tell that that layer of rock was oriented this way, because these mud cracks all start wide at the top and get narrow going downwards. And it quite often happens that these strata of rock, because of the incredible forces of nature of plates coming together, will take these layers and just flap them over upside-down. And we come along and we look at them, and you can't tell which way is up, which way is down until you find one of these mud cracks.
And then, even if the layer's upside-down, then you'll have these mud cracks teepeeing upwards. And you'll say, whoa-ho, this thing must've been flopped over and turned over upside-down. And it's the same processes-- I'm doing a Richard here. It's the same processes that produce these mud cracks, will fill them in, and then maybe after 100 million years, they'll get fossilized, turned into a hard clay layer, and then turned upside-down. But we'll still be able to tell what we call the stratigraphic relationship, the time relationship, which is older, which is younger, because clearly this is older than whatever would lay on top of it.
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