Day 4: Saturday, May 15th, 2004

Rocky I, II and III: The Geology of the Colorado Front Range with Paul Myrow (Colorado College)

By Heather Hoey

8:20am

We left late again today, but I think everyone’s getting used to it by now. We waved good-bye to the Taylors and continued on our journey south to Colorado Springs. At the beginning of the drive we had story time and Tim read us the section in our manuels entitled, “Interstate 25, Denver-Colorado Springs.” It was so full of interesting in formation that Tess was soon fast asleep. We again passed the huge dike and the Table Mountains we passed yesterday on our way to red Rocks and Dinosaur Ridge. Then the talking began to cease and Art Blakely grew louder, filling the van with soothing, high-spirited music. As the music consumed our ears, the incredible geologic topography consumed our eyes. We watched mountain after mountain rise one side and tried to distinguish sky from land on the other. We saw the Fountain Formation become the Dakota Hogback and wondered what lay ahead of us in Colorado Springs. Soon we saw the skyline of Denver disappear behind us and the snow capped mountains, including Pike's Peak, loom before us.

10:30am

As we rolled into Colorado Springswe were greeted by the view of parachutes from the Air force Acadamy and marveled at how these pilots in training, along with the rest of Colorado Springs, awoke every morning to the sight of Pike's Peak. What a drastic contrast these glorious mountains are to the Cretaceous limestone of Richmond.
Soon we arrived at Colorado College where we met Paul Myrow, one of Ron’s friends from undergrad and grad school. Paul has been a geology professor at CC for seventeen years, and Ron informed us that he was an important player in redefining the Cambrian/Precambrian boundary and just awesome all around. Before we made our first of eight stops, Paul told us that within the city limits of Colorado Springs there are outcrops representing every period except the Silurian, nearly all of which he proceeded to show us in the outcrops around Colorado Springs.
Our first stop was at an outcrop on the side of the road where we saw an angular unconformity between angled Cretaceous shale with fossils and horizontal quaternary gravel/conglomerate, presenting a gap of 60-something million years.

At the second stop on route 24 off an exit ramp, we tasted 500 million years old shrimp poop that partially made-up the upper Cambrian sandstone seen in this outcrop. The technical term for this shrimp poop is glauconite, a green mineral formed by the mineralogical change of mud as an inarticulate brachiopod digested the mud. This Cretaceous sandstone was located on top of 1.1 billion year old Precambrian Pikes Peak granite, presenting a nonconformity.
In the granite, we saw ancient weathering called core stones which appeared as rounded areas near the contact.
Around the corner from this unconforminty, Paul showed us where a transgression had occurred and told us about aquieous dune structures. We learned that you can tell the direction of dune migration and the velocities and direction of the currents from observing and interpreting crossbedding and minor crossbedding of the preserved sand dune structure. We saw all this in an example of Tidal Sand Dunes in the Sawatch Formation from the Cambrian. Above this we saw Manitou Formation from the Ordivician. After seeing all of this, we went to lunch.

After lunch we headed over to stop number three at the 96ft bridge section. Near the base of the bridge we saw on outcrop that showed an example of paleokarste topography, meaning a dolomite cave filled in with limestone. This was from the Ordovician. It was probably caused by the rise of the oceans which then receded and then came in again. From here we took a short little twenty minute hike to another outcrop where we saw trace fossils in a sandstone that were created from the burrowing of plant roots through soil. These plants were called lepidodendron and were big plants of the Pennsylvanian and that shallow roots and reproduced by way of seeds. These plants were able to grow from the recession of sea level leaving Colorado Springs in a swampy-like area. From the information up to this point, it was unclear if the sea was actually receding of if the land was rising. This Pennsylvanian unit is called the Glen Eyrie Shale Member.

Our fourth stop was the most incredible and the most beautiful. Paul took us to Garden of the Gods were we marveled at both the geologic beauty and the insanity of the rock climbers. In Garden of the Gods, we saw lots of the Fountain Formation which was formed in accordance with the ancestral rockies. Within the Fountain formation we saw lots of ripples, cross-bedding, and coarse deposition. We saw that in the sandstone there were layers of very fine, well sorted material and then there would be a layer of coarser material. This offset of fine and coarse grained material repeated over and over again, leading to the conclusion that this formation was created by flash floods. A few steps later, we found ourselves in front of a very similar rock except for one great difference; this sandstone was white, not red like the previous Fountain Formation. These two differed in color because they differ in oxidation. It is believed that petroleum leached through the white sandstone taking with it all the hematite. It is hematite that makes the red sandstone red. It takes only half of one percent of hematite to cause a red coloration. The white, fine grained sandstone is known as Lyons Sandstone. Around a corner and up a hill we came to Triassic apalan silica or chert in limestone. Here we also saw some stromatolights, which were created when microbes crawled up and trapped carbonites creating mound like structures. Finding these microbes ensures that during the Triassic this area had been a hyper salient, lagoon type environment. We know this because after the Cambrian microbes only lived in hostile environments. Up another little hill we found salt bushes and fibrous gypsum all over the place, representing the beginning of the Morrison Formation.

3:42pm

From here we left the Garden of the Gods and found ourselves at our fifth stop. It was located behind a Christian Publishing company of somesort and we were constantly looking over our shoulders afraid someone was going to come kick us off for talking about unbiblically correct science. Here we saw a normal monocline that just kept going. It was kind of confusing. We saw angled shale on top of horizontal Dakota sandstone and we learned about Walther’s Law while looking at the Barton Group. According to the Walther’s law as sea level come in and goes back out, the rocks will follow a specific pattern. The pattern is that as the sea level comes in the composition of the rocks in that area will reflect the different sea levels. So, at the shore there will be sandstone, then in shallow water there will be shale, in deep water limestone, and then as the sea level resides again it will reverse in order starting with limestone, then shale, and back to sandstone. In the outcrop we viewed at this site it follows this pattern until the Fort Hayes limestone follows sandstone showing the there was a drastic change in sea level. It is believed that this is due to a long term climatic change.

We moved on from the Christian area to another no trespassing area. We stayed long enough to get a good view of the Black shale known as the Pierre Formation turn into white Foxhill sandstone and noted that this change was a another recession.

At out seventh stop we saw coarse sand conglomerate with white K-spar which represented the Laramide Orogeny at the end of the Cretaceous. One of Paul’s colleagues thinks that major rivers removed so much sediment that it allowed the present Rocky Mountains to rebound half of its modern height.

Our last stop was at the Mesa overlook where we got an overview of everything we had looked at up close. We invited Paul to join us later that night at out camp ground outside Colorado Springs but he had spent the previous night movie hopping and decided it was best to be with his “better half.” We drove back to CC and waved goodbye after thoroughly thanking him for the incredible tour of the geology of his area. Thanks Paul!!! You rock!!! (Paul also has a cd out. If you’re interested contact him at CC.)