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Ryan Anderson • Mar 22, 2009

Planetary Surface Processes Field Trip: Day 7

The Painted Desert and Petrified Forest

This article originally appeared on Ryan Anderson's "The Martian Chronicles" blog and is reposted here with permission.

(This is the final day of a week-long field trip in Arizona. Get caught up with days 1, 2, 3, 4, 5, 6.)

The Painted Desert
The Painted Desert The colorful layers of the Painted Desert formed in the Triassic period when meandering tropical rivers deposited layers of mud and clay. Some of these layers are due to volcanic ash choking up the rivers and altering to clay.Image: Ryan Anderson

Friday was the last day of the field trip, and we spent it at the Petrified Forest National Park. We were there to study the colorful clays and river deposits, but we began the day with an unexpected bonus: our guide, Bill Parker, is a paleontologist at the park, and he took us to see some of the skeletons that have been found there, and the people who work on them. I spent much of my childhood wanting to be a paleontologist, so to actually see it in action was a special treat. We learned that there is recent evidence that almost all dinosaurs had feathers! We also got to see the reconstruction of what one of the animals may have looked like based on the skull, which was something that I didn’t realize that paleontologists did.

Matt Brown, fossil preparer
Matt Brown, fossil preparer Matt Brown, a fossil preparer at Petrified Forest National Park chips away at the protective plaster around the skull of an alligator-like dinosaur.Image: Ryan Anderson
Dinosaur reconstruction
Dinosaur reconstruction A reconstruction of what one of the dinosaurs being studied at the park may have looked like, based on its skull.Image: Ryan Anderson
The badlands terrain of the Painted Desert
The badlands terrain of the Painted Desert The clays in the rocks expand when wet and contract when dry, creating an unstable surface where plants can't get a foothold. The bright colors are from different types of clay, different types of deposits, and different degrees of oxidation.Image: Ryan Anderson
Clay-bearing river or delta deposits
Clay-bearing river or delta deposits These may have been deposited extremely rapidly, since there was the fossil of an 8-foot-tall horsetail in the outcrop, still standing upright and crossing several layers!Image: Ryan Anderson
Giant horsetail fossils
Giant horsetail fossils Jeff Martz, one of our paleontologist guides, pointing at the two giant horsetail fossils. Click for full-resolution to see the fossils more clearly.Image: Ryan Anderson
A close-up of one of the horsetail fossils
A close-up of one of the horsetail fossils The green part is a couple of inches across.Image: Ryan Anderson
Petrified logs
Petrified logs Petrified logs, formed when silica replaced the organic material of the wood, are more resistant to erosion than the sandstone in which they formed, and end up lying on the surface.Image: Ryan Anderson

That concludes our geologic tour of Arizona! I went the first version of this trip two years ago, and then as now I was humbled by how complex and difficult to interpret our planet is, even when we can reach out and touch the rocks and analyze them at our leisure. On the other hand, there were many things that we saw from the ground that were much easier to interpret from aerial and satellite data. When you’re on the ground, it is much harder to get an feeling for the overall shape of what you are looking at. A combination of both orbital and ground-based studies is very important to really begin to understand the geology in detail, and even then there is a lot that we can’t figure out!

This trip has also impressed upon me how much more geology I need to learn. I need to know sedimentology and stratigraphy if I’m going to be attempting to read the story hidden in the layered pages of rock on Mars. But for now, I at least know what it is that I don’t know, and that’s a good start.

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