Forum
Buying gear? Please use these links to help 14ers.com:

More info...

Other ways to help...

Fossils in the Crestones

Have an interesting or epic climbing story? Post it here.
User avatar
Posts: 319
Joined: Sat Aug 19, 2006 2:51 pm
Location: Tempe, AZ

Postby Hiking Mike » Sun Sep 17, 2006 11:30 am

Yup, I live right by a highway cut that exposed upturned layers from the Cambrian Era (maybe even Pre-Cambrian) into the Mezozoic, so I've see some of that carboniferous rock. Also, the Pensylvainan left the Fountain Formation, so we have big red rocks sticking up out of the ground nearby too. They even made one into a concert venue. :D

Are there any other possible explanations for the "fossil" if the rock is too high-energy for preservation?

User avatar
Posts: 319
Joined: Sat Aug 19, 2006 2:51 pm
Location: Tempe, AZ

Postby Hiking Mike » Sun Sep 17, 2006 11:37 am

Stevevets689
I think that you're talking about the Pierre Shale, which is a dispropotionately huge formation made by that inland sea. It seems kind of unlikely that it would make up the Crestones, but interesting theory. :) :-k

User avatar
Posts: 205
Joined: Fri Aug 18, 2006 9:25 pm
Location: Northwest Arkansas

Postby Joe Miner » Sun Sep 17, 2006 11:45 am

You are correct about the Fountain, it is a high-energy conglomerate dumped off of the Front Range and is responsible for "Red Rocks". while I have found some fossils in conglomeratic sandstones in the Mid-Continent, they are usually more marine in origin and seldom terrestrial. The Pierre is fossiliferous, but is Cretaceous in age and is a fairly monotonous fine-grained shale scattered throughout the west.

User avatar
Posts: 980
Joined: Thu May 18, 2006 4:57 pm
Location: Broomfield, CO

Postby jfox » Sun Sep 17, 2006 3:47 pm

The geologic units/formations in the Crestone area are mainly the 'Sagre de Cristo' formation which is comprised of arkosic conglomerate, sandstone and siltstone. Also in the area is the 'Minturn' and 'Belden' formations.

The 'Minturn' is comprised of arkosic sandstone, conglomerate, shale and limestone. The 'Belden' consists of shales, limestones and sandstone. All of these formations are Pennsylvanian in age (290 - 323 million years old).

The conglomerates are what is left of the ancestral Rocky Mountains. However, even though the rocks comprising the Sangre de Cristo range are 290 - 323 million years old, the mountain range has only recently formed (geologically speaking). It is Neogene in age, ~23 million years old. The range is the footwall block of a normal fault and is the result of the opening of the Rio Grande Rift. The current San Luis valley is the basin of the rift.

Most all other mountain ranges in CO are Late Cretaceous in age, 70 - 65 million years old, and were created during the Laramide orogeny.

So yes, it would not be uncommon to find fossils up there. A few could have survived such a high energy depostional environment intact!
Last edited by jfox on Fri Sep 22, 2006 7:28 am, edited 1 time in total.

Posts: 5
Joined: Sat Sep 16, 2006 1:08 pm

Postby Faureout » Sun Sep 17, 2006 6:52 pm

The Crestone Conglomerate contains fragments of many types of rocks, so it certainly is possible to find fossils in it.

User avatar
Posts: 1061
Joined: Sun Jul 30, 2006 5:20 pm
Location: Woodland Park

Postby guitmo223 » Sun Sep 17, 2006 9:19 pm

Since it seems that there are many geologists here, I have a related question:

When I climbed Crestone Needle, it seemed almost as if the rocks were held together with concrete, or a substance very similar to concrete. I thought at the time that naturally occuring concrete could actually occur, with the right combinations of volcanic ash and pulverized limestone. Any thoughts on this?
"Although prepared for martyrdom, I preferred it be postponed" - Sir Winston Churchill

User avatar
Posts: 980
Joined: Thu May 18, 2006 4:57 pm
Location: Broomfield, CO

Postby jfox » Thu Sep 21, 2006 2:36 pm

guitmo223 wrote:Since it seems that there are many geologists here, I have a related question:

When I climbed Crestone Needle, it seemed almost as if the rocks were held together with concrete, or a substance very similar to concrete. I thought at the time that naturally occuring concrete could actually occur, with the right combinations of volcanic ash and pulverized limestone. Any thoughts on this?


Hmmm....interesting thought. However, concrete/cement hardens due to a chemical process, of which I am not very familiar. Rock, such as you're talking about, 'welds' together via heat and pressure. i.e.- welded tuffs from volcanic pyroclastic flows and deposits etc. Now in some rock, 'cementing' is chemically driven for instance. What holds sandstone together is typically a calcium-carbonate mineral which bonds the grains in the pore spaces.

Since the Sangres are an arkosic sandstone and conglomerate, it is most likely that it is this sort of CaCO3 precipitate which has infiltrated the pore spaces of the sand to bond them into sandstone. Sort of like the cement you make a sidewalk out of.

User avatar
Posts: 5145
Joined: Wed May 04, 2005 11:46 am
Location: Craig

Postby Scott P » Thu Sep 21, 2006 3:43 pm

When I climbed Crestone Needle, it seemed almost as if the rocks were held together with concrete, or a substance very similar to concrete. I thought at the time that naturally occuring concrete could actually occur, with the right combinations of volcanic ash and pulverized limestone. Any thoughts on this?


Congomerate is a mix of sand and pebbles cemented by lime.

Sandstone is sand cemented by lime.

Mudstone is mud (usually) cemented by lime.

Shale is, well you get the picture.

The common theme is cemented by lime. Usually the main difference between conglomerate, sandstone, mudstone and shale, is just the grain size. Chemically they are all fairly close to each other in most places in the same area.

Yes, naturally occuring cement is very common.

User avatar
Posts: 1122
Joined: Sun Jul 16, 2006 7:11 pm
Location: Centennial, CO

Postby Floyd » Thu Sep 21, 2006 4:07 pm

Well I have to say, this is probably one of the most intelligent sounding forum discussions I have read. I'm going back to the Posting Hotties thread.

User avatar
Posts: 435
Joined: Sun Jul 16, 2006 5:50 pm
Location: Colorado Springs

Postby Dan the Mountain Man » Thu Sep 21, 2006 4:40 pm

Being a paleontology major, I feel I could shed a little light on the situation. First off, finding bit and peices of organic material in a tuff or ash flow is not out of the question, that is true. However this is extremely rare as the temperature of ash flows is so high that will burn away all organic material. For the most part, only molds are left over, and even these are hard to see in rocks past 30Ma since these areas are most prone to weathering. The fern fossil that complete would not be in an ingeous rock, ever.

Second off, basing rock type textures from a photo is risky stuff. While fine grained sedimentary rocks might appear to be igneous, it is near impossible to tell as both have similar structure, and only mineralogy and petrology will determine which catagory the rock will fall into. Bedding is also very common in sedimentary rocks and the clasts are much different morphologically than an ingnous sample.

On a few other notes, not all sandstones and mudstones are cemented by lime, there are quite a few silicious cements that will do the same job. Also, the Carbiniferous generally only includes the Mississippian and Pennsylvanian and not the Permian, this terminology is namely used in Europe and not so common for the states.

J fox is absolutely right. The conlomerates are arkosic in nature and the Minture and Maroon formation exemplify the ancestral rockies, before the Laramide Orogeny. Even though we mostly see the large conglomerates in the crestones, there are many different depositional environements as well, and even very large high energy streams will have slower areas in which deposition of finer material can occur and preserve fossils. You have to remember that the paleo-ecology varies as much as a current stream system, so you cannot over-generalize.

Dan
Bis zur Grenze gefordet, koennen wir alle mehr, als wir wollen -Reinhold Messner

One does not climb to attain enlightenment, rather one climbs because he is enlightened- Zen Master Futomaki

User avatar
Posts: 5145
Joined: Wed May 04, 2005 11:46 am
Location: Craig

Postby Scott P » Thu Sep 21, 2006 4:57 pm

not all sandstones and mudstones are cemented by lime


You are right and it was a generalization. Not all, but most (hence my usually under mudstone). This is especially true in CO and UT (I've actually written a book on it). :wink: Never been to the Crestones though.

User avatar
Posts: 435
Joined: Sun Jul 16, 2006 5:50 pm
Location: Colorado Springs

Postby Dan the Mountain Man » Thu Sep 21, 2006 6:33 pm

No offense Scott, I just wanted to make sure to point it out. I understand when generalizations need to be made to help understand a point, I just wanted to throw out the possibility. I myself have never looked at the rocks in the Crestons in detail, or tried to test and see how calcareous they are.

Dan
Bis zur Grenze gefordet, koennen wir alle mehr, als wir wollen -Reinhold Messner

One does not climb to attain enlightenment, rather one climbs because he is enlightened- Zen Master Futomaki

PreviousNext

Who is online

Users browsing this forum: No registered users and 4 guests