Bivalves of the Fort Apache Limestone

[Arizona Chris]

Greetings all,

 

After about 200 pounds of limestone have been hauled out on our backs, we have used countless gallons of muriatic acid to dissolve out the clams and other bivalves from the limestone.  Here is a short report on what we have found so far.  The locality is the same - The HIgh Line Trail east of Payson.  They are all Leonardian in age, and Permian Marine exclusively.

 

 Identifying bivalves is always challenging since there are so many similar looking types, and many of them are internal casts which present no outward identifying features as well. Fortunately for us, Stephen Winters of Florida State University in 1963 wrote a landmark memoir for the GSA - Memoir 89 in which he spent years identifying many of the tiny mollusks we were finding in the same formation from 2000 pounds of material he collected at the best localities on the Fort Apache Indian reservation. Recall that off the reservation where the formation starts to thin out considerably, there are virtually no fossils to be found anywhere! This new locality off of the High line Trail we have discovered has many of the same faunal elements as what Winters found, and appears to be nearly as rich as his typical localities.

Preparation

Limestones were collected on the basis of visible silicified fossils eroding out of the limestones on the surface along the trail. Complete specimens were almost never seen in the field, and many times you had to collect blindly any promising rock. Hauling this out on your backpack was quite unpleasant, however one must keep in mind that THIS locality is one of the rarest in all of Arizona because the Fort Apache Limestone here contains visible fossils. 10% muriatic acid was used to free the specimens, and three sets of sieves were used to separate out the large amount of terrigenous material (find sand) from the silicified fossils. The fines were dried and examined under a binocular microscope for specimens.

 

Palaeonucula levatiformis. The number one most common clam, they ranged in size from extremely tiny - less than 1mm size up to 5mm.

 

 Astartella subquadrata. Another common find, many had excellent detail in the ribbing as seen here.

 

Parallelodon anaklassium. Rare but stunning with the wing on an elongate trapezoidal shaped shell. Many fragments of this one were found before this magnificent complete specimen was found.

 

 Permophorus sp. ? Many of these are internal molds making a definite identification impossible.

 

Bakevellia sulcata. We found a half dozen of this species, after dissolving about 200 pounds of limestone. They are VERY peculiar!

 

Palaeonucula levatiformis. These are some of the smallest found.

 

Aviculopecten sp. More pieces showed up later in the acid fines. this one is several inches long. Think of this as the outer rim of a large pectin like shell.

 

 

Aviculopecten sp. More of a wing from one side.

 

Thanks for looking, I have more images and details on my web page:

 

http://www.schursastrophotography.com/paleo/Fortapache-3.html

 

[ynot]

Nice finds!

Thanks for sharing here.

[Macrophyseter]

Dayumn noice shells!

[JUAN EMMANUEL]

Those wings are very nice. It's hard to believe they are intact when they are that fragile. 

[Arizona Chris]

We can always hope to find that intact aviculopecten some day!