Magnitude 7.7 Earthquake in Chile

Holy cow, this one is HUGE. Here is a shot of a seismogram here in Arizona. This is how much shaking we have had!


Here is another seismogram reading about 2 hours later, its still going!


Let me give you some background so you know kinda what you are looking at. This is a seismogram readout from a seismometer located in Tucson. It records shaking in the earth. Most of the readouts on this machine are totally unfelt be humans, but the sensitivity of the machine is such that it picks up vibrational waves as they pass by. The earthquake was powerful enough in Chile to be very strongly noticed by the machines. There is resonant readings as the waves reflect within the earth. Kinda like when you splash in a pool of water. Although you might not be right next to someone who is splashing, you can see waves caused by it go by, and then as the waves reflect off the sides of the pool and go by again.

Here is an intensity map of the earthquake from the USGS:

Fossils

Due to an overwhelming response, here is my fossil collection:


This first photo is a collection of crinoid stems in a piece of weathered Redwall Limestone. The crinoid heads are missing, but the stems are nicely preserved because of their calcium carbonate pieces. those guys are about 335 million years old. The limestone that they are found in is one of the larger rock layers found at the Grand Canyon.

This next photo is a storm segment from the Naco formation. There are a least 3 different types of fossils in this piece. Can you find them? The twig looking ones are fossilized bryozoan, a moss-like creature. There are also crinoid stem segments, and a couple of clam-like shells






This picture shows an assortment of other fossils also from the Naco formation. There are (from left to right) a couple of clam-like fossils, crinoid stem segments, saved entirely in 3D (the little barrel shaped guys), a streched spiral gastropod (found in the Upper Iowa River neah Decorah, IA), and a few intact brachiopods. The difference between the brachiopods and the clam like ones is that the clam like ones (they have a technical name but i cant seem to remember what it is) are symmetrical through the suture, and the brachiopods' symmetry is perpendicular to the suture line. Here is a close up of the clam like ones...

Papago Park

I visited another local park here in Phoenix today. Its called Papago (pap-a-go) Park. It is located not far from ASU, but has some very interesting geology.

This perticular butte is fascinating to many people for mostly non-geological reasons. It has a hole in it that when standing in offers spectacular vistas of downtown. Anyway, the history of the rock. Formed at the same time as Hayden Butte, Hole-in-the-rock (thats actually its proper name) is formed from totally different processes. 17 million years ago, somewhere within 2 km or so, there once stood a mountain fromed from granite and quartzite. One very violent day there was a massive landslide that came off the mountain and headed toward an ancient river. The landslice eventually became lithofied (turned into stone) and formed the butte. Interesting enough, the mountain that formed the landslide had eroded completely and cannot be found anymore. The butte is composed out of a composite sedimentary rock called breccia (bretch-a) which is an amalgamation of mud, sand , and broken up parts of granite and quatrzite (all of which came from the parent mountain) some of the chunks of granite are as large as a house.

The holes in the rock were formed when these boulders fell out of the breccia, and then were exposed to what is called cavernous erosion. This erosion over the course of millions of years formed the caves that so many people enjoy today. On an even more interesting note, this butte has the Great Unconformity running right through it! Remember from my trip up to payson, how where was the section of 1.2 billion years missing. Well that same gap exists at the base of the butte. The base of the butte is made up of granite that is 1.8 billion years old (as old as the oldest rocks found at the bottom of the Grand Canyon). however i found a xenolith of some kinda ash metamorphic that is even older. I had to take a sample of that back for my collection (as oldest rock)

Payson

Yesterday we took a great field trip to see some cool rocks about 2.5 hours north east of Phoenix. These rocks are at the southwestern edge of what is called the Matzatzal Province. The Matzatzal province is the oldest rocks layer found in Arizona, ranging between 1.6-1.8 Ga, this layer is represented in the Grand Canyon as Vishnu Schist.

Here at stop #1, you can see the basement rock layer for our study, the Payson granite. The layer right above the granite is the Tapeats Sandstone (also represented at the GC). Whats amazing here is what is called the great unconformity. To the untrained eye, theese rock layers look like a normal transition, or juust like the same rock alltogether. But the bottom layer is 1.2 billion years older than the top layer (540 million years old.) What this means is that there is 1.2 billion years of rock history that is entirely gone.

Here is one of my professors (Dr. Stump) explaining some of the finer details of the strata (strata means column of rocks).
Here is another shot of the rocks:


A little farther up the section we came to the disconformity between the Redwall Limestone and the Naco Formation. The Naco is the layer on the top of the road-cut, whilst the Redwall is the bottom layers:

Here are some other views of the two groups. Can you see the division??


The Naco formation is LOADED with fossils! We took 60 minutes to sample and log some (which we also got to keep for our personal collections) I found about 30 or so in that time. Ranging from crinoids to brachiopods, there were some sweet samples! Ask me sometime and I'll post close-up's of the different ones. I also founs a cool sample that has criniods, brachiopods and fossilized bryozoans. These fossils are all form the Pennsylvanian period so they are about 300 million years old.
Here is a scenery shot of what the forests look like up there:

Here is a self portrait of me as I an taking notes:





There are more scenery shots. One of them is our group sitting at the top of the main section of Coconino Sandstone.
Here is one last shot of the group hiking to a remote locaton to look at a sample of the Apache Group formation, and then the Apache Group Formation itself.

Phoenix, a brief history.

Todays little jaunt was pretty fun. I took James along and so we both got to learn all sorts of cool geology stuff. I am taking notes from Emily's last comment and will be "dumbing down" my blogs so that they are easier to understand.

This morning's trip was down to a place called South Mountain. South Mountain is a prominent feature of the Phoenician skyline. In fact, it can be seen from just about anywhere in the valley. It is most easily identified as the mountain that has all of the antennas on it. Anyway, I have known about south mountain for about as long as I have lived here in phoenix. However, this trip was remarkably interesting because it really opened my eyes to the great geological history that I live on top of. Here is an aerial of where we met:


This location, as it turn out is quite unique. It is the juncture of 1700 million year old gneiss and 22 million year old granite.(geologists use the term Ga, an acronym for giga-annum, which is latin for "billion years". I will use the abbreviation Ga for billion years old, and Ma for million years old from this point on.) Anyway, what happened is a LONG time ago, more than seventeen hundred million years ago rocks were formed through various means. Over the millions of years, and at a depth of about 10km under the surface, these rocks were heated and deformed. This intense pressure and heat transformed, or more appropriately, metamorphosed these rocks into the gneiss that is now found at the surface. Fast forward to 22 million years ago, a large plume of hot magma from deep within the earth is ejected and intrudes the gneiss. When the rock cools, it becomes granite.

Here is another view of the boundry:


Up to this point things have been relatively dull. All of this activity takes place 10km underground. On the surface, life is flourishing. It is early in the Cenozoic era. Then something rather catastrophic happens. There is an series of earthquakes. Huge earthquakes! To give you an idea of just how big these quakes were think about this. The typical earthquake in california, for example the 1989 Loma Prieta quake (you know the one that happened during the world series that year?) made the earth move only a couple of meters. They call this movement displacement. Anyway, the series of quakes, which can be called rifting, displaced this mountain by more than 40Km. Here is another aerial image of how far that is:

Incredible, if you ask me. The south mountain range used to be homogeneous with the McDowell Range. The big gray area in between the ranges is metro Phoenix.

Well, next week will take me to Payson, AZ in the search of mississippian fossils.

Hayden Butte Revisited

Back to the butte. Tuesday took us back to Hayden butte, but this time to stratorgaph the lower sedimentation layers (notably from the base up to the ash layer from the superstition caldera eruptions. This lab took a bit longer than usual, however it was great to get up close and personal with various rock outcropping. Generally speaking, the bedding we looked at consisted of about 70 layers of alternating sandstone and shale. Only 3 of of the layers contained trace fossils. The oldest layer had trace fossils of worm burrows, which was again repeated in a layer about 10 meters above. The other trace was the mudcracks. Upon closer inspection it appears that the mud cracks formed on several sandstone layers in superpositioned horizons, in my estimations there were 4 distinct horizons that them. I'm gonna try and get a scan or two of the hand drawn stratographic sections that we did (about 6 pages in all). I'm looking forward to Oct 27, when we will be on a fieldtrip to south mountain to checkout some sweet synclinic action. ohh yeah.

In a lighter note, I really enjoy the names geologists come up with for things. For example gneiss (pronounced nice) is a common metamorphic rock. Schist is another common metamorphic rock. Anyway there are many others with strange and unusual names. But i couldn't leave these two alone. So i came up with an idea for a t-shirt:

Hayden Butte Lab

This is the first outdoor lab for the historical geology class. Located on ASU Campus, Hayden Butte (A Mountain) is a well known site for and ASU student. The butte holds the Sun Devil Stadium (Home of ASU Football and Super Bowl XXX) on a saddle on the south east side. The lab began by looking at the oldest rocks on the butte, located on the north side in a drainage canal parallel to Rio Salado Pky. The exposed sandstone layers here are estimated to be only 17 Ma. The oldest sandstone beds are perforated with trace worm burrow fossils.

Just up the rock strata we found:

This is the trace fossil of mud cracks. Cracks were formed into a layer of mud, that has since turned into shale. Sand filled the cracks and formed a layer of sandstone. Later, the underlying shale eroded and left the negative impression of the cracked mud.

A little farther up the strata we found:

This section of Sandstone / Shale Interbedding shows a fault. Although the age of the fault is unknown, is can be assumed that it was caused by the tilting event.

Now this was unusual:


This is a very perculeier formation. What this is is a 2m thick volcanic ash formation. However as you can see, the bedding has been convoluted into ball and pillow shapes. This can be caused by either seismic activity on the wet rock, or by being compressed from above (also while the rock was still wet. This formation was so cool that I had to grab a smaple for my collection.

Finally the youngest rocks on the butte were a nice andesite lava flow. A short ways down from the top I found some eroded chunks of the andesite:


and here is what I thought was really cool; this is where a lava flowed over sandstone, resulting in contact metamorphisim:


And here is a rip-up clast of sandstone that had been metamorphosed into quartzite: