Exploring the rich Pennsylvanian Naco Formation in Winkelman

[Arizona Chris]

ARIZONA FOSSIL ADVENTURES By Chris Schur

Exploring the Winkelman Red Brachiopod Site.

On Highway 77, one mile north from the turnoff to Winkleman is one of the most awe
inspiring scenes to be found in Arizona. Here, the road cuts through a vaulted
limestone canyon hundreds of feet deep, with the multihued layers clearly visible.
At this location lies an old quarry on the north side of the road which cuts right
into the Paleozoic Naco limestone cliffs.
This February, we visited this site with some paleo friends to examine the fauna
present and determine the suitability for future outings. We found that large
boulders of limestone littered the bottom of the old abandoned quarry, which were
once part of the surrounding cliffs. A hundred feet or so into the man made canyon,
the limestone boulders contain bright red chertized fossil casts of several types
of brachiopods, crinoids and bryozoans. Also present everywhere are worm burrow
trace fossils, found in a spectacular violet hued limestone matrix.

Description of fauna present:

Brachiopods.
Two types of marine brachiopods are abundantly preserved in red chert. The first
type, a small Spirifer ranges in size from less than a quarter of an inch upwards
to over an inch. This is by far the most desirable, but less common of the two
brachs seen here and are usually preserved as complete three dimensional casts with
limestone filled centers.
The second and far more common is an unidentified rounder heart shaped brachiopod.
With sizes ranging from one half to two inches in diameter, including many large
and fragmented shell pieces. The wall is thin, and the center also filled with
limestone, so one must be careful in using acid to extract the delicate red or pink
chert specimens, or they will fall apart.

Crinoids.
This site contains some of the largest crinoid stems I've ever seen. While most are
3/8 of an inch in diameter, we found many much larger. The really big ones were
nearly an inch in diameter, with a small rounded five point star shaped central
canal. Countless smaller stems are seen as well, forming much of the grey colored
limestone matrix itself, often referred to as "crinoidal limestone". Some of the
largest ones however were preserved in red chert, and several one to three inch
long specimens were retrived.

Bryozoans.
Two types of "moss animals" were found here. The common net like Fenestrellina
types were abundant, filling in the spaces in the limestone matrix with mostly
small fragments. The second, and much more common type was a small branched animal,
usually preserved as a black film on many of the loose limestone boulders in the
bottom of the canyon.

Trace Fossils.
On the visible surfaces of many of the large boulders in the bottom of the canyon
are the trace remains of hundreds of channels and tunnels in the fossilized ocean
bottom from burrowing invertebrates typical of mid to late Paleozoic time periods.
On many of the exposed surfaces of the limestone, we can see one to two inch
diameter trails where the animal tunneled through the muddy bottom crossing and
passing through the tunnels of others as well. Often we see and entire block of
violet hued limestone with burrows passing through the stone, filled in with white
limey sediment, layer upon layer as the sea bottom slowly filled in with more mud.
Cross sections of the burrows are oval in shape, and typically an inch tall, and 1
1/2 inches wide. As for a possible animal that formed the burrows, the fossil
record here does not preserve any mollusk or crustacean large enough to have made
them, indicating that either it was a soft bodied animal that did not fossilize or
a crustacean whose chitinous outer exoskeleton that dissolved or fell apart soon
after death and prevented fossilization as well. A useful observation is that
within the violet limestone matrix containing the burrows, we find many of the red
chertized brachiopods intermixed. This indicates that the red brachs coexisted with
the burrowing animals and shared a common ecosystem.

Extraction of the Fossils.
When you visit this site, be prepared to do a bit of hard rock quarrying to remove
the good specimens. Because this site has been known for years, don't expect to
pick up small pieces of limestone matrix and have them filled with choice
specimens! The best specimens will have to be removed with hammer and chisel from
the large limestone blocks. We have found that a standard geological pick is not
enough to extract the material. The best tool is a heavy duty 1/2 to 1 inch
diameter masonry cold chisel and a heavy hand sledge. Also mandatory will be a good
pair of safety glasses to deflect flying shards of matrix, and a pair of work
gloves to protect your hands.
Remove the prospective fossil by chiseling a deep channel around it, keeping at
least an inch away from the delicate red chert. When the channel is at least an
inch deep, you can pop it off with one swift blow, or work around the base with a
smaller chisel.

Once the specimen and surrounding matrix is removed, the fossil can either be
displayed as is, or removed from the matrix. While mechanical preparation works
well here, some success with smaller specimens can be had by dissolving the
limestone with acid. For most small pieces, vinegar works well, remove only the
outside material but do not leave in too long because many of the larger
brachiopods are filled in the center with limestone which helps support the fragile
shell material. Muriatic acid that has been diluted with water works faster, but
should only be used under adult supervision. The large crinoid stems come out
particularly well with the acid treatment, leaving a hollow center in the stems.
Further explorations.

We have not been further up the canyon, however there is no doubt that the best and
freshest specimens will lie in the rugged cliffs beyond the collection site. While
such a hike should not be attempted by the inexperienced, prepared fossil hunters
may uncover a rich bounty of more red chertized fossils in the walls beyond. The
Pennsylvanian Naco limestone contains in other parts of the state some of the best
brachiopod fossils to be had, along with plentiful bryozoans and other interesting
marine invertebrates. Other layers of limestone contain no apparent fossils at all.
But it is the lure of the ancient sediments that push the fossil hunter onward,
always hopeful that next discovery could be just around the corner!
For furthur reading on this spectacular area, refer to USGS Bullitin 176 highway
road log by Wess Pierce. I wish to thank Tom McGarvin of the Geological Survey
office in Tucson for helping with the identification of the sites age.

 

[DPS Ammonite]

The Winkelman Quarry has been hit real hard by many paleontology classes. The main quarry is nearly an ex site. I suspect that there are many better fossils nearby away from the road. 
 

See this MS thesis about the site. It lists and shows many species not officially described by peer reviewed literature like the papers from the Kohl’s Ranch locality East of Payson.

 

I look forward to hiking away from the quarry to find better fossils. Like many Naco sites, the further away from the road you go the better the fossils.

 

Reid, A.M. (1966). Stratigraphy and Paleontology of the Naco Formation in the Southern Dripping Springs Mountains, Near Winkelman, Gila County, Arizona. Masters Thesis - The University of Arizona.   link https://repository.arizona.edu/bitstream/handle/10150/551821/AZU_TD_BOX253_E9791_1966_101.pdf?sequence=1     One of best papers on Naco fossils. Lists many species and has so so photos.