Painted Desert

Painted Desert

Thursday, June 26, 2008


First, the answer to the previous post's puzzler:
This is the piece of bone. Bone looks different depending where you are, but the pieces here often have a blue cast to them, and they definitely break differently than petrified wood or sandstone do. The best way to tell bone is to examine it closely and see if any of it looks spongy, as the inner part will. At least, that works with animals that don't have hollow bones. Also—I am not kidding—you can try licking it. Fossil bone will often stick slightly to your tongue. Try it by licking your computer monitor.
Last week we went out to try to locate a site excavated in the 40s by the late great paleontologist Edwin Colbert. He'd gotten a phytosaur skull there, and knowing exactly where it was would help us figure out the biostratigraphy of the area, or which life forms were present during which rock (and thus time) intervals. We had old color photos and a dot on a map. Unfortunately, nothing anywhere near the dot on the map looked anything like the rocks in the photos. Some scientists make careful notes about their location and activities in the field, but apparently Colbert was not one of them.
On the way home we drove around looking for rocks that looked anything like those in the picture. We passed a family of tourists who were jumping out of their minivan, their own old color photograph held out in front, everyone excitedly pointing into the distance. They were having more luck than we were.
The next day we went out to look for the lowest (and thus oldest) Late Triassic strata in the area. There was rumored to be some out west by the train tracks, so we went out a little adventure into unexplored territory.
We walked in a wash, or dry riverbed, until we came to some of the strangest rocks I've ever seen:
The rocks were white with splotches of blue, yellow and red, and they looked like a bad mosaic made by a five-year-old. It was sandstone cemented with calcite that had been colored by a rising and falling water table that no doubt changed the oxidation conditions of the iron in the sand.
After that we came to some brick-red sandstone that had split just so, making it look like bricks in more than color:
Later on I found a chert pebble with ancient Paleozoic fossils inside it (that's older than Triassic). These small fossils were probably some form of sea life, hundreds of millions of years ago when the ocean covered this part of the continent.
As we walked we came upon a game trail. There were deer and coyote prints in it. They'd all stayed right on this path, not stepping off it, unlike the cattle whose prints we could see all around.
A dust devil climbed the slope in front of us.
As we walked back in the river we could see fantastic forms in the river-bottom sediments. Here are layers of mud that were deposited by the river, then eroded:
Now, more on all these colors you can see in my pictures… two of the more important factors in controlling the color of the rocks are the reduction state of iron (whether the iron atoms have a +2 or a +3 charge) and the amount of organic matter. Rocks with high organic matter and reduced (+2) iron tend to be black, grey, blue, or green; rocks with low organic matter and oxidized (+3) iron tend to be yellow, orange, or red. And in this part of the geologic record at least, rocks with more sand (as opposed to mud or silt) tend to be whiter.
Here are some layers of red, white and blue. They record changing conditions or environments during the Triassic, from more to less sandy, and from wetter conditions or waterlogged environments (blue) to arid conditions or dry environments (red). In the blue layers can be found lots of fossils, especially of watergoing creatures like phytosaurs.
Here's a hillside with alternating bands of blue and white. This might have been a waterlogged area that experienced periodic influxes of sand. Maybe a swampy spot near a river, the edges of which were occasionally breached during floods. That's open to interpretations.
Here is a paleosol exposure—an exposed part of an ancient soil. It is red, so the iron in it is oxidized; it was exposed to lots of oxygen, meaning it probably formed in a dry area. But there are mottles in the paleosol. The white polka dots are areas of reduced iron that formed around those black dots, which are bits of organic material.
So I leave you with the pink polka-dotted paleosol.HH

Friday, June 20, 2008

Odds & ends

Okay, here's a picture in which you can find the bone. I found this group of junk on a hillside the other day. It has chert, petrified wood, concretions, probably some sandstone, and a piece of bone too. But which is the bone? Totally unfair, since with the quality of the picture and the washed-out noontime light I'm not even sure I could spot it just from this. But hey. I will tell which is the bone next time.
On our day off, Katie and I went to Holbrook. On the way we stopped at Stewart's Rock Shop, which is a creepy tourist trap off the highway. Just a taste:
The interior of the shop was dark, cluttered, and crammed with petrified wood and fossils. Some of which were blatantly mislabeled. I made some comment that prompted the employee at the counter to say, "Hey, you guys would be good paleontologists." This was reassuring.
After that we continued to Holbrook, where there are a variety of dinosaurs (most of which did not actually live in the Triassic). I fell in love with this one, but sadly human-dinosaur romance is not sanctioned in our society. Some day, we will be together. For now, all we can do is hug.
The fresh air and southwestern cooking have really been good for Katie, and she's grown since we came out here:
Most of the dinosaur sculptures out here have a distinctive, child-bearing-hips look. I have been told this is to ensure stability of the concrete model but I think it's ridiculous.
I will leave you with these great sites from our visit. I am not making these up.

Sunday, June 15, 2008

Phytosaurs and more

The phytosaur skull I found is slowly being worked on in the lab. Each day more of it is revealed from the rock by the fossil preparator. The skull still has some teeth in it, which is good… most of these skulls were rolling for a while along the bottom of a river until they came to rest, and the teeth usually snap off. Here is a picture of the skull now:
In case you can't tell, the end of the snout is toward the left, and the back of the head is toward the right. You can also see the ocular or eye-hole. I'm excessively proud of myself since it's one of the best-preserved skulls ever found here, and is the talk of the employees in the other departments, who have seen it and keep asking if I was part of the team that found it. I hear that someday it will go on display in the museum here. But it wasn't hard work to find it, I don't think.
I thought it was hard work digging it out though… my hands were all chewed up from contact with the rocks on the edge of the trench we dug around the skull… but the skull I found was in mudstone. Our supervisor found a skull the other day in sandstone, and it's been even tougher to remove. Here is our preparator using a rock saw to loosen some of the rock around the skull:
It's a big skull. You can totally see the outlines of it here:
The really crazy thing about this phytosaur is that parts of the skull are green. You can see an exposed section here:
We don't know why it's green. Perhaps it's radioactive. I happen to think "Radiactive Phytosaur" would be a great name for a band.
I mentioned that the second skull was harder to dig out because it was in sandstone. So what's up with sandstone and mudstone? They're two kinds of rock; the first is made out of sand that's been cemented, the second out of mud that's been cemented. (In between these two grades would be siltstone.) For a rock to be cemented, water has to trickle through carring some cement, such as silica. The spaces between grains of sand are bigger and so more water can come through with cement. Thus, sandstone tends to be a lot harder than mudstone.
In the beautiful badlands here, most of the hills are made of mudstone, which weathers softly. Occasionally there are bands of sandstone (marking where an ancient river channel was) and these can form cliffs.
The more pure mudstones here have what's called "popcorn weathering," a surface texture produced by the clay shrinking and swelling with the weather. It looks like this:
It forms nubbly hillsides everywhere. Here is Katie examining some mudstone; she's standing on sandstone.
When you dig a few inches into the mudstone, you get past the weathered surface, and can easily break off chunks of hardened clay that have very jagged edges and smooth sides. These are clods of ancient soils that formed on the floodplains of the Triassic. They have some fantastic colors. Here's a picture of a mottle in a clod of mudstone:
The black dot in the middle of the bullseye was probably a bit of organic matter than created "reducing" conditions in the surrounding soil; that is, it caused electrons to be donated to the iron in the soil. Iron happens to change color based on whether it's oxidized or reduced, and this causes a lot of the color changes in the beautiful badlands rocks. More on those colors later, as I promised.HHH

Wednesday, June 11, 2008

Ghost Ranch

Saturday afternoon, we began our drive to Ghost Ranch. We stopped in Gallup to pick up some mosquito nets at Wal-Mart, because we'd been told the gnats were particularly bad up there. The Gallup Wal-Mart turned out to be the Most Crowded Wal-Mart Ever, and this was one of the delays that contributed to it taking something like 8 hours to get to northern New Mexico. Another delay was the Best Mexican Food Ever in Cuba, NM.
We arrived in Ghost Ranch long after dark and were introduced to the world-famous paleontologists that we'd be working with for the weekend. I'll stick to my custom of not mentioning names here, but I will say that despite recently being featured in a movie about dinosaurs, the two movie stars were extremely nice and friendly and down-to-earth. That night we camped under the stars in the New Mexico mountains, and I saw two shooting stars before I fell asleep.
The next morning we went to work in one of the Ghost Ranch quarries. The density of bones is so great in these bone beds that we worked through the sediment systematically, choosing an area and taking half an inch at a time off the top, brushing away the loose dirt and taking care of any bones that appeared. These were mostly fragments, bits of somebody's long-lost rib or toe bone, but occasionally we would find whole bones, which would be carefully drizzled with consolidant before being lifted out with their surrounding sediment. Here is a metatarsal (long foot bone) of a dinosaur or one of its relatives, next to an unidentified bone:
Despite finding bone every few minutes, I found the process slightly frustrating. The bones were mostly very small (I found one complete vertebra no larger than the nail on my pinky finger) and I got tired of having to stop digging all the time to painstakingly piece something together and lift it out without breaking it more. Too many bones!
It was a beautiful place to work, though, with a blue resevoir filling a dammed river valley and high sandstone cliffs in the distance. Here's a picture of the men working in another section of the bone bed:
And the women, who all happened to be working in the upper section:
Here is our quarry from the distance:
And a picture of me, for people who want to see that sort of thing:
It was very gnatty. Long stretches would go by during which the sun beat down extremely hot, and I was wearing two shirts so the gnats couldn't bite me, but they would swarm noisily around my head and walk across my face, tickling me. Then every once in a while a breeze would come up and it would be blissfully cool and gnat-free for a few moments.
Here is a picture of us at work. I think this is a good depiction of what paleontologists actually do:
Lots of hunching over meticulously scraping at rock in the blazing sun.
At the end of the day, I checked out my gnat bites… they were mostly concentrated right where my socks ended.
There was a huge discrepancy in who was getting bitten and how it affected them. I might have had 20 or 30 bites and they didn't itch. Katie counted 215 bites on her (no, I am not kidding) and they've been driving her crazy with itchiness. The gnats bit her through her clothing everywhere. Right now she is covered in calamine lotion. Ironically, the major ingredient in the lotion is bentonite, which is the clay that forms the mudstone hills in the badlands we've been exploring. Perhaps we should have had her simply roll in the mud.
That evening we prepared the fossils we'd found, scraping the matrix (material they were imbedded in) off and gluing any broken bits together. Here are the fossils I found (note that the only significant part of this picture is the fossils themselves, just the fossils):
Then we played Mario Kart and Guitar Hero. But the last people to bed were a couple of our team who stayed up into the wee hours discussing the minutiae of an aetosaur specimen that the museum had in their collection there. Scientists!
The next morning we worked in the quarry a bit more. I finally found some larger bones, a humerus and some more metatarsals. See if you can spot all four bones in this picture:
And we had a quiet drive back to Arizona. I'm still trying to catch up on my sleep.HHH

Thursday, June 05, 2008

Mapping and more

I've been going mapping with Katie lately. Mapping is important for understanding the paleoenvironment an animal came from, but it hasn't always been treated as important. Many paleontologists used to (and some probably still do) remove bones from the rock without making much note of what kind of rock it was and what its relationship was to the rocks around it. They might have a nice dinosaur skeleton but be unable to say whether it lived in a desert or by a lake. Nowadays, mapping out and describing rock units is key to understanding an animal's life history.
We head out to the field with topographic maps, a GPS unit, and colored pencils. We use the colored pencils to color the different rock units in on the map wherever we find them. Here is Katie studying the map as it relates to the surrounding terrain.
Mapping requires a lot of guesswork, especially where fluvial (stream or river) systems are concerned. Streams migrate over time, so a sand deposit formed in a streambed might be thin, it might change position as you move up into younger rocks, it might disappear entirely for a while. Some questions we might try to answer with mapping include: are the blue mudstones in the south area the same as those in the north area? Do they connect? Could they have been formed at the same time? Take a look at this picture. Is the sandstone I was standing on the same as the sand in that white layer in the distance? The only way to be sure is to walk it out. What if erosion has cut away too much to allow you to follow the sandstone all that way? You will just have to make your best guess.
While walking around we've encountered many interesting things on a smaller scale. Here's a picture of what are likely some fossilized burrows in the sandstone:
If you look closely you can see the horizontal layers in the rock. These are layers of sand and silt deposited by different stream conditions over time. After they were deposited, some animal made burrows in the streambed, and sand filled them in. The burrows stand out slightly from the rock because the sand is more resistant to weathering than the silty layers are.
I've also done some more prospecting and excavating. Here's a picture of some "arm" bones from a Triassic reptile…
Below see outlines of the bones (black) and the part I first spotted sticking out of the sand (white):
It has taken me a few days to learn to spot bone. Some day I'll post a test for you all: I'll take a picture of a flat with bits of all kinds of stuff on it, and you can see if you can find the bone.
I also found the end of what turned out to be the top half of a phytosaur skull sticking out of the flat, and this was excavated over the past couple days. Here it is during excavation.
We had to uncover enough to find out basically where the bone was, but other than that we tried to leave a layer of mudstone around it to protect the bone, which was a bit crumbly. Then we put the plaster jacket on:
We were able to flip the jacket upside-down without all the mudstone and bones falling out, despite it weighing an estimated 300 pounds. Later the preparator will carefully dig in and remove the bone fragments, gluing them together. When he's done the skull should look like the top portion of this one:
One of the nicest things about working out here is just the beautiful scenery. Here's where I spent the last couple of days:
Not bad!

Monday, June 02, 2008

The excavation

As we drove out to the site on Saturday, our supervisor told stories of excavations past. Four-hundred-pound plaster casts of bones being hauled for miles out of the wilderness, workers rotating around the skeleton so no one had to spend too long in the heaviest corner. Researchers using the last of their water not to drink, but to prepare more plaster to cover the final bones. The crew in Mongolia who ran out of burlap and began using their clothes to cover the last finds. It's good to know where the priorities are in this field.
The hope that we'd dig in and find a full skeleton beneath the previously discovered armor plates was balanced by the hope that we wouldn't find a full skeleton. Something that complete would take two weeks to excavate. It would be an exciting and significant find, but it'd also take a chunk out of the time we had to do the work that'd already been planned for the summer.
As we approached the site, our supervisor stopped in his tracks. He thought the area looked like a good place to find fossils. And it was in fact where we had found the fossils. I asked, "What makes this look like a good site to you?" and he said, "I don't know," which made me laugh. In the end, we didn't find much more than the scutes. The bright spot was that one of the scutes was nearly complete and in good condition for a Triassic-age bone.
We dug around the bones with awls and coated them with clear glue to lessen the chance of their breaking up. A moat was dug around the bones to put them on little pedestals of rock. Then it was time for the plaster. Toilet paper was placed over the bone and wetted to make it stay, and then plaster bandages were soaked in water and layered over the toilet paper and the rock surrounding the fossil. No plaster was allowed to touch the fossil. The pedestal was also wrapped, including a little lip that was dug slightly underneath. When the plaster hardened, the pedestal was chiseled under and the whole plaster cast flipped, leaving a nice package that the preparators could dig into and remove the bone in the lab.
This took most of the day. It was good work for an intern because there was plenty of opportunity for conversation as we dug around the bones, and that leaves time for me to think up questions to ask. I wasn't given a great deal of detail on what I'd be doing this summer before I got here, but I didn't expect I'd be working side-by-side with my supervisor, who has something like ten years' exerperience in the field. The other paleontologist on the team is a new PhD and it's good for me to listen to their conversations.
Some of you haven't had the chance to ask me the inevitable question, so the answer is, no, I don't want to be a paleontologist. No, dinosaurs aren't what I'm into. I don't dislike them. But I haven't found an area I'd really want to go into yet, so why not spend a summer doing something interesting? In gorgeous country, I might add. And why not learn everything I can about it? I may never do anything with paleontology again. But there's no reason to hang back all summer as if I may never do anything with paleontology again. So I intend to do as much and learn as much as I can.
We carried the plaster jackets back to the car and later dropped them off at the prep lab. That evening I went for a little walk in the wilderness area here, hoping to see some wildlife, but the only thing I saw was a funny beetle.
Yesterday Katie and I went to Flagstaff for some shopping and sight-seeing. Flagstaff has an attractive downtown with as much bike as car traffic, the peacefulness of which is shattered only by a screaming cacophony of train whistles every five minutes or so. Katie says that every train that goes at west goes through Flagstaff and this is not entirely unbelievable. Great long trains of double-stacked container cars pulled by three or four engines. I love to see trains and I like to imagine all the things being shipped on them that are not being shipped by trucks. But my god, the noise.
Katie was determined to find an authentic Mexican restaurant, but with luck against us we ended up settling on Thai. For some reason there are four Thai restaurants in the downtown area. I am thinking Flagstaff has a Thai population of some kind. We were asked how hot we'd like our meals to be, on a scale of 1 to 5, and I chose 3, thinking, you know, medium, like medium salsa, which is usually a hair too mild for me. But the 3 I received was more like the 4 or 5 of my imagination. The terrible part was that the food was exceedingly good. I didn't want to stop eating. But my tongue and lips were in searing pain. O delicious food of death!
We went to the Museum of Northern Arizona, which was small but very classy. I would recommend it to anyone passing through Flagstaff. And then we headed back home.
This week I am doing mapping with Katie and will also be exploring some of the newly acquired land here. On the weekend I will be going to Ghost Ranch in New Mexico, site of one of the most famous death assemblages of the Triassic, with hundreds of dinosaur skeletons. And to sign off, here is a pic from my evening hike the other night.