How can you tell the difference between a dinosaur bone and a piece of petrified wood?

I have learned the value of being able to properly distinguish dinosaur bone from petrified wood. While on our field trip I happened across what I thought was a large round piece of petrified wood. So thinking that it was just another chunk of cretaceous wood, I decided to see just how big it was. Before doing this however I conducted the “lick test” to make sure it was not bone. The reason the “lick test usually works is because bone is porous, this allows the moisture from your tongue to be absorbed into the bone. This causes your tongue to stick to the bone. Wood is not porous so it does not have the same affect. After doing this test I determined that's what we had found was wood. I soon learned that this test is not always accurate. It turns out what I thought was a large piece of tree was actually a Hadrosaur femur. The most sure fire way to find out if something is bone or wood is to ask a paleontologist. If you have any hunch that you have found a bone the best thing to do is take its GPS location and leave it exactly how you found it.    

The Kaibab Monocline

Our class was able to meet with Dr. Alan Titus in the Grand Staircase National Monument. We helped dig up some real dinosaur bones. It's not every day you find yourself digging up something you've seen only in the movies and natural history museums. 

We were asked to give a brief explanation of something we learned on the field trip. I have chosen a geological feature known as the East Kaibab monocline.  A monocline is a single bend (mono) of rock strata. (picture below)

The East Kaibab monocline dips from west to east and runs north to south. The formation of the monocline is due to a west dipping reverse fault. This fault lays in the Precambrian rock beneath the newer folded Mesozoic and Paleozoic Rock. The hanging wall of the reverse fault moved up and pushed up overlaying rock with it. The foot wall moved down allowing the rock above to settle. Over millions of years the Mesozoic and Paleozoic rocks has slowly been eroded down into jagged hogbacks and deep slot canyons. The weather resistant sandstone forms most of the protruding hogback features. East (picture looking south) of the Navajo and Dakota sandstone the less erosion resistant Tropic Shale (Caleb Franks is standing in) forms a valley that parallels the monocline. (picture below)

 

Crevasse Splays

I can think of few events in my life that can compare to digging up dinosaurs with Alan Titus. Not that there haven't been fantastic moments in my life, but digging up dinosaurs with a busy paleontologist is just kind of unique experience that not a lot of things compare to. That just goes to show how incredible geology really is.

While working with Alan, digging up what we think to be a Hadrosaur, in the Grand Staircase National Monument, I was told about an interesting event that happens along rivers called a crevasse splay. Some of the dinosaurs were found in crevasse splay deposits. My interest was peaked and so I will attempt to paint a picture for you.

Imagine that it is the rainy season of the year. The river's banks are filling and soon the water will overcome the levees. It isn't anything new to the area seeing as this is a well established meandering river. As you are overlooking the river, you see a weak point in the levee begin to give to the weight of water against it. All of the sudden the river breaks through at that point. It starts out small but rapidly grows into a side channel. The swift moving water from the river cuts a ravine in the soft levee sediment. As you look past that point where the levee broke, you see a Hadrosaur grazing in the flood plain. You call out to it to move out of danger but it is too late. The water overtakes the dinosaur and it disappears from view. Soon you can see the sediment carried from the river, through the crevasse, and out into the flood plain settling into a fan shape. You, however, don't see the unfortunate Hadrosaur.

This is an aerial  view of a crevasse splay. One much like an unsuspecting Hadrosaur could get caught up in. Turns out that crevasse splays are fantastic places to find well preserved dinosaurs. However, sometimes the river's cut bank will erode far enough into the flood plain to scour out buried dinosaurs and other fossils. Pretty cool stuff, right?

On are wonderful trip to Moab we spent a lot of time in Arches National Park. I would like to tell you about the difference between a natural arch and a natural bridge. Natural arches most often form when there is a narrow section of sandstone that is permeable that sits on top of shale which is impermeable. When water seeping through the sandstone meets the shale it is forced out forming springs.   The water will begin to erode the shale and weaken the sandstone by dissolving its cement. When this happens the sandstone begins to be undercut and rock fall will occur until a hole is formed creating an arch.  The arch then grows upward through successive rock falls.  Natural bridges form where a stream once ran.    One type of natural bridge is created by potholes in a streambed. The stream may undercut the lip of a pothole to form a natural bridge much like in the photo of Skull Arch.    This is called a pothole arch. Everyone should go on these field trips. You learn so much about the cool things the earth does and see some of the most amazing sites mother nature has to offer.

Delicate Arch

On the spring 2012 field trip we went to Arches National Park.  We saw a ton of beautiful arches and a lot of other cool geology.  My favorite arch of the trip was Delicate Arch.  It is the same arch you can see on many of the Utah State license plates.  I had no idea that the arch was so big.  The arch is pretty high up there.  You can sit and watch birds flying beneath you.  Through the arch you can see the La Sal Mountains.  We got to stand underneath the arch and touch it.  It was amazing!  

Fault to the side of trail -Slickrock Member
on left, Morrison Fm on right.

However, the arch wasn’t the only cool part of the Delicate Arch Trail.  The small hike up to the arch was pretty cool in and of its self.  There was a smaller picturesque arch on the way up there.  Also, when we were hiking up the Entrada formation we stopped and looked at some ripple marks formed by the wind during the Jurassic.  Because of ripple marks you can even tell what direction the wind was blowing almost 200 million years ago.   On the start of the hike we saw a fault to the side of the trail.  This fault formed from the collapse of the Salt Valley anticline.  It's really cool to actually be able to see faults.  Next to that fault We saw a lot of little white lines in the Slickrock Member of the Entrada Formation.  They were joints and mini faults in which fluids has precipitated calcite  I had come across lines like that before I took geology, but I didn't know why they had formed.  Because of geology class I now know how arches formed and a whole host of


other things I have always wondered about.  During the field


trip, it was great to actually see the things we had learned 


about in class.

Calcite filled faults

Groundwater Bleaching

To be entirely truthful, (as compared to partially truthful), few things in the world are as cool as the study of rocks.  Particularly Sedimentary rocks.  Like Judy from "What's Up Doc?" I share the sentiment that "I can take your igneous rocks or leave 'em. I relate primarily to micas, quartz, feldspar. You can keep your Pyroxenes, magnetites and coarse grained plutonics as far as I'm concerned."
As such, the field trip we took to Arches National Park was most exceptionally engaging.  The different formations we saw tell of the history of the Earth, and within Arches, of the Mesozoic period of time.  It's like the ultimate time machine, but without having to wear the bulky safety suit!  Off to dino Land!!!

One of my favorite parts of the whole trip was our journeying through the Fiery Furnace (which was aptly named btw.)  Within the Fiery Furnace we saw that in the Entrada layer of Sandstone, there were streaks of white sandstone within the red.  This was like, seriously cool, because for my research paper I had written on groundwater bleaching that had taken place within the Navajo Sandstone, and I realized that the same general processes that had taken place within the Navajo had also taken place within the Slickrock Member of the Entrada. As acidic groundwater (pH 4.8 or less)  had travelled through the sandstone, it removed the iron oxide coating that coated the individual quartz grains.

In this picture we can see bleaching that has taken place from groundwater.  In the front is the Navajo Sandstone, which is bleached.  In the back is the Entrada Sandstone, and on the right side you can see a layer of white stone within that layer.  Cool huh?  Fact.

In sum, Geology is boss.  You should all major in it.  The trip was fantastic, and I learned a whole lot!  But aside from the academic aspect of it, we also had so much fun!  We went to Rock shops, and somersaulted down sand dunes. Good times.

Salt Valley Anticline Graben

On our way to Arches National Park for our awesome field studies spring 2012 course, we stopped at a little pagoda to learn about the Salt Valley Anticline just before the turnoff on Rte 163 towards Moab.  The most exciting feature of this anticline is the huge graben that has formed over time.  First, it started out with the formation of the anticline: in the Paradox formation, salt well below the earth's surface began to rise as it flowed upward.  As it rises, it pushes the rock and sediment on top up with it, forming an n-shaped hill or a dome.  This deformation is what created the anticline.  Because of this uplift, the rock starts to form cracks called joints that allow water to pass through all the way down to the salt, where it begins to dissolve.  Where the salt is dissolved, there is weak rock or gaps that, with the help of gravity, cause the rock layers to collapse and form this spectacular graben. (Picture above: The collapsed Salt Valley anticline in the center of Arches National Park)

And our field trip only got better from here!  We got to see lots of arches, fins, toured Fiery Furnace, saw amazing faults, huge large-scale cross beds, hogbacks, dinosaur tracks, petroglyphs, balancing rocks, tons of fossils, poured acid on plenty of calcite, and ended it off chillin at Dead Horse Point. We saw the coolest stuff!