Petrified Forest National Park
Here are some enrichment items from the CAUSE class visiting the Petrified Forest, a truly wonderful place.
Virtual Field Trip: Hardwoods—CAUSE and Park Paleontologist William Parker Explore the Petrified Forest
The fossil record includes some amazing things. If there were trees and insects far back in time, wouldn't you expect that the insects would have burrowed into the trees then as they do now? And wouldn't you expect that a tree with some of those burrows would be fossilized? Well, here is one example. Park Paleontologist William Parker of the Petrified Forest National Park explains fossil burrows to the CAUSE team.
Video: Ancient Bee's Nests, Petrified Forest National Park (1:56 minutes)
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Male Park Ranger of Petrified Forest National Park: What you'll find in here, too, is you'll actually find insect traces, where they were underneath the bark, burrowing in just like modern ones do. This log, they call it the discovery log. This is actually a pretty important discovery.
What you're looking at here are insect traces and actual nest-- like little capsules here. You can see they're lined up. Little capsules of some nests of some kind of insect that actually lived in this log. You can see them here and here, coming out.
Now, these have been interpreted to be bees' nests. And if that's true, these would be the earliest record of bees by about 130 million years. Some entomologists disagree and say that this is very similar to some of the traces that modern beetles make, rather than bees.
But what they did is, some of these capsules in here, they went in and they found some preserved resins. And they actually tested them for geochemically, and they found the chemical that bees secrete. So some more work needs to be done on these to verify these results. But they were definitely made by some kind of insect. And it's a great example of how insects lived in these logs and used them as a food source and as a home.
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Petrified Forest National Park is best known for trees turned to stone, but also has an immense wealth of fossils of various types from the late Triassic (in the Mesozoic, about 210 million years ago). Here, Park Paleontologist William Parker and assistant Randall Irmis explain to the CAUSE class the paleontological excavation of plates of the armored amphibian known either as Koskinonodon or Buettneria.
Video: Uncovering Fossils - Petrified Forest National Park (2:58 minutes)
Male Park Ranger of Petrified Forest National Park: We're heading into one of the famous locality areas at for paleontology at the Park.
Female CAUSE Student #1: Volcanic ash? Is that what you just said?
Female CAUSE Student #2: Yeah.
Male Park Ranger: There is volcanic ash here.
Female CAUSE Student #2: It is. It's volcanic ash.
Male Park Ranger: There's a big hole. See, so a lot of times when we find the bones, this is what you'll find. There's an accumulation, and it's rolled down the hill. And this is what happens to the bones when they sit on the surface for a long period of time. They basically break apart into smaller and smaller fragments, and at a point in time, it becomes impossible to put them back together. So all the bones at the bottom of the hill have basically come from these bones here.
So what we do is we dig in, and we see if we can uncover them. These little tools, like dental picks, and things like that, and brushes, and we slowly expose the bone. It's kind of hard to see at first, but once we get it cleaned off, you'll be able to see it a lot better. Yeah, everything you're seeing here that's dark colored is bone, and the gray is the rock that's surrounding it.
So what we would do next is we would come here and we'd excavate around this. And we kind of leave this suspended on a pedestal. And then we cover the bone and the surrounding rock and the pedestal with plaster. Generally, we take strips of burlap and plaster, and we'd cover it with a little separator in between, usually toilet paper or tissue paper, to keep the plaster from sticking to the actual bones.
And then, after we have it all pedestaled, and a plaster cap on top, we'd undercut it, flip it over, put plaster on the other side, and then that's basically a handy carrying case to bringing it back to the lab. And then once we had it in the lab, we'd open it up and remove all the rock, glue together all these broken cracks and stuff. And pretty much you'd end up with the whole element, just like you see in the museum.
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Video: Agate Chunks in Sand, Petrified Forest National Park (4:24 minutes)
Optional Enrichment (no, this won't be on the quiz!). The formation of fossils is both rare and normal—most dead things are eaten, burned, or otherwise recycled before they are turned to stone, but over the diverse environments of the planet, conditions favoring fossilization are bound to occur in some places at some times. Here, Irene Meglis and Dr. Alley use a little geological sleuthing to understand why the fossil trees of Petrified Forest National Park were preserved.
Dr. Richard B. Alley, Instructor/Geologist: All right, so what do you make of this, Irene?
Irene, CAUSE Student: I don't know. We see some different rocks here in the sandstone.
Dr. Richard B. Alley: Yeah.
Irene: I was wondering what they were.
Dr. Richard B. Alley: Well, they're beautiful, aren't they? Look at those nice shiny ones. Those are agates. If those were sitting out here in the open, you could take them, cut them, and polish them. You could make little earrings or pins or something out of them. They're made of the same material as petrified wood. That's cool.
Irene: What kind of material is that exactly?
Dr. Richard B. Alley: It's little crystals of quartz. You get these big crystals that people like to go "oom" about, but these are just lots of little tiny crystals of quartz—silica. And they're sitting here in a sandbar from a river. This is a sandstone, as you correctly identified, and we can see there's little cross-bedding in it. But these cross beds are not the giant ones of a wind-blown sand dune; these are the little curving ones of a river. And it’s a river that can carry rocks like this. So we're sitting in a river. Now, what do you make of them? Here, somebody has broken this one, but what do you make of the sides like this?
Irene: You can sort of see that they're rounded.
Dr. Richard B. Alley: They're rounded. And where do you suppose they got that?
Irene: Water flowing over them, and particles hitting them.
Dr. Richard B. Alley: Bouncing along in the river. But are they really rounded?
Irene: No, some of the edges are sharp. We see a sharp edge here.
Dr. Richard B. Alley: Some of the edges are sharper. So they've been transported a little distance in a river. If you take one of these and go a long ways in a river, it gets really round. So these things have gone a little ways in a river, but not too far. Now do you remember, the rivers are coming from the south pretty much along here, a little bit from the south and east, sort of going this way. Do you remember what's behind this? What rocks are we going to see when we drive 20 miles south of here?
Irene: We see some more sandstones.
Dr. Richard B. Alley: It's the same stuff. We're in the Chinle, from way north to here, and all the way south of here. These haven't been carried very far, so they must have come out of the Chinle. Then they were washed along and put back into the Chinle. So these are things that weren't really old when the river picked them up because they're coming out of basically the same beds. They must have formed right in these rocks around us. Probably very near the surface, very quickly after muds were put down, and then they were picked up again, moved a little ways, and put back down here. They're coming from slightly older rocks, but not much, because there's a little of this, but not too much difference. So now, what can we say? This is the same stuff as the petrified wood. And we can see just by looking at this and what we know about the rocks, that this had to be forming right in the muds where the petrified wood formed. What does that tell us?
Irene: I think it tells us that there was a lot of silica.
Dr. Richard B. Alley: Where is it getting silica?
Irene: Well, this area was once in a tropical area. Volcanoes?
Dr. Richard B. Alley: Yes, volcanoes. Down south of us, there are big volcanoes, and they're putting out glass. Volcanic glasses are often really full of silica. A glass is something that didn't have time to make a crystal, so the atoms in there are messed up, and they really want to dissolve and re-precipitate as crystals—the little crystals that make this up. So there's lots of volcanic glass, and it's dissolving in the groundwater. Then the groundwater takes that and puts it back down. And when it can, it puts it in a tree and makes a petrified log. If there's no tree to put it into, it will take a little spot, like a worm burrow or even dung. It will take whatever it can find and make agates and other things. So this is telling us that the hard water deposits here were going to be silica. They're going to be little crystals of pretty agate, and they'll go wherever they can go. And so the petrified wood—it's an accident, but it's an accident that was waiting to happen. There's a reason why it's here.