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!

Hogbacks

San Rafael Swell and Hogbacks

On the Field Studies Fall 2011 class we went to explore the geology of the San Rafael Swell in Eastern Utah. The "swell" in this geological feature refers to dome which is pictured on the right- and on the San Rafael the west side of the dome  is at a gentler slope then the eastern side. As you drive through it you pass through a lot of time, because the closer to the center of the dome you get the older the layers get - it's like traveling through time in just a few short hours!

My favorite part about the trip was seeing the hogbacks on the eastern side of the dome. Many people believe that this geological formation is from the rock layers being pushed violently into the air from forces below (like earthquakes or the like) but those who know and understand more about geology understand that hogbacks don't have such a violent and sudden past.

Rather, this is from the dome itself and it's steeper eastern side.

As shown well in the picture to the left, you can see the angle of the rocks as they slop away from the anticline. These layers, like any other exposed formation, are then subjected to weathering. This lead to softer

shape, which leads to spectacular looking triangles that we call "flat irons". layers being eroded away and the more resist layers (like sandstone, etc) sticking around a little longer. As they erode away, little streams and rivers cut them into an ^ shape.

These are one of my favorite things in geology, I think they look so impressive and striking. And then knowing just how they were formed makes them even cooler - who needs dramatic and tragic earthquakes to make these things with you have geology to back you up?

~Tauni Sutherland

The Green River is very strange. Unlike most rivers, the Green goes straight though the Uinta Mountains instead of going around this enormous obstacle. The process that created this phenomenon began about thirty million years ago. At the time there was a Northern Green River that flowed east from the Uinta Mountains, and a Southern Green River that flowed south. Over the course of a few million years the Uinta Mountains were eroded creating what is called the Gilbert Peak Erosional Surface. On this erosional surface layers of sediment were deposited that are today called the Bishop Conglomerate and the Brown’s Park Formation. At the same time the southern Green River drainage was eroding faster than the northern Green River. The flat surface of the eroded and covered Uintas and the steeper gradient of the Southern Green river made it possible for the southern Green River to capture the northern Green River. The two rivers combined and began to flow over the eroded Uintas. Then about 10 million years ago a geological phenomenon called uplift raised the Uinta Mountains. This renewed uplift in the Rocky Mountains caused the Green River to cut right into the folds of the Uinta Mountains, thus creating the present landscape. This is called superimposed drainage. Without our knowledge of geological history it would have seemed impossible for the Green River to have its current course. The diagram below shows the changes in the Green River’s drainage north and south of the Uintas over this period of time: