Marine Fossils at the Fire Break Road

[Arizona Chris]

Permian Marine Fossils at the
Fire Break Road on the Rim
Permian Kaibab Formation,
Fossil Mountain (Gamma) member 

The Fossil Mountain member of the Permian Kaibab formation (285 million years age) outcrops on the top of the Mogollon Rim (Southern end of the Colorado Plateau) as you top out after a steep climb on Highway 87 north of Payson. As is most of the Kaibab Limestone, it is highly dolomitized and very hard and brittle. Fossils do not survive well the process of dolomitization of limestone, however the larger more robust brachs, mollusks and bryozoans do fairly well. This locality is one of the first fossil sites we ever located over 25 years ago, and we continue to return to explore its riches. Its also a great place to go in the summer, when its hot in Payson and broiling in the Valley.
This trip which was on July 14th this year had great weather in the morning, and the Monsoon did not rain until later that afternoon. We came back with a nice batch of Productids, Brachs, Sponges, Bryozoans, Stromotoporoids, trace fossils and raspberries! The location of this site is no secret - Go north on Highway 87 and about half a mile on the left before Highway 260 is the fire break dirt road. Drive 1/4 mile to end and park. Fossils are everywhere.

 

Images of the Site and Fossil in Situ:

Up on the Mogollon Rim, at 7200 feet elevation consisted mainly of Ponderosa Pines.  There had been a large fire years before, and the
ground was mostly barren still.

 

Dawn searches the slopes where the lithology suddenly changed from Productid to Urchin bearing layers:

 

The ground is covered with cherts, and dolomite pieces.  This magnesian limestone will not dissolve in acids.

 

Images of Fossils cleaned up

 - Leucon Hexactanellid Glass Sponges (Actinocoelia Meandrina)
   - Sponge images are photographed under water for best photographic appearance.

 

Surface texture of a sponge

 

Inside, the patterns in the cherts record the sponges internal details in startling color!

 

Many Productid Brachiopods (Productus sp.) were found at this site, but preservation varied considerably. They ranged in size from
an inch up ward to around 4 inches for the monster ones.

 

The most gigantic one Dawn found was base ball sized!  She always finds the coolest fossils...

 

Nearly 100% of all productids found had both valves intact.  This is the bottom of the brach, which is very flat compared to the top:

 

This was the first time I had ever found these productids with the flat valve missing!  You can see the insides of the pedicle valve has muscle
 attachments scars:

 

Meekella Brachiopod, large and poorly preserved.  This was the only one we found:

 

Urchin Material Found at Site:
Here is one of the two types of spines found, the tuberculated spines here:

 

The other type of spine found was ribbed on its exterior and were easily degraded by the taphonomy of preservation:

 

Microscope close ups of Fossils - 10x.

 

 

Rhynoconellid and some bryozoans:

 

Stromotoporoids (A type of flat sponge)
  - plentiful in the dolomites, and here is a cross section, about 1/4" thick showing internal pillar details:

 

Dawn found that right next to where we parked was filled with wild raspberries.  Harvest time!

 

The Author - waiting for Dawn to finish collecting raspberries...
While waiting, I wandered down the road and found the BEST urchin material of the day!

 

After washing and scrubbing with nylon brushes to remove dirt and moss, they are laid out to dry:

 

We had a fantastic fossil hunt this last weekend, hope you can get to Arizona some day and check out this site!

[jewelonly]

A very nice report!! I especially love the preservation of the sponges. Lovely colors! And, you found a way to improve on fossil collecting...hunt while picking wild raspberries! Looks like a wonderful day!  

 

Leah

[FossilDAWG]

I wish I had known about this site when I lived in Arizona (Tucson).  Permian formations are present in the mountains around southern Arizona but they are massive limestone beds and it is very difficult to actually get much out of them, as the rock is diamond-hard and tends to break through the fossils when you try to chisel them out.

 

Don

[Auspex]

Thank you for this outstanding report! It is beautifully crafted, and highly informative on both the site, and the fossils. Great images, too

[Monica]

AMAZING!!!  I love those productid braciopods - they're massive!!!

 

Thanks for sharing!

 

Monica

[doushantuo]

What the others said!

[Arizona Chris]

Thanks Everyone!  there are many fossil sites in Arizona that you will all enjoy visiting.  And anytime any of you are in Arizona, be prepared for some fossiliferous fun!