Permian Crinoids and Corals in the Fort Apache Limestone

[Arizona Chris]

HI all,

 

A new Sunday upload for you, we just finished our evaluation on two more types of fossils we have found hidden in the limestones of the Fort Apache formation.  Now crinoid material and corals are very rare in this deposit - the blowing sands and silt from the nearby Schnebly Hill formation sand dune complex made life nearly impossible for any filter feeding organisms, and the constant rain of mud from above would clog their filter feeding apparatus.  So its not surprising that crinoids and corals are almost never found in the acid fines we obtained from just over 240 pounds in limestones.  In fact, only a few dozen echinoderm ossicles from a variety of unknown types which might include crinoids, cystoids or blastoids were found at all.  No calyx or plates were found.  As far as corals, ONE rugose coral was found, and its a tiny one at that!  That at least was identifiable from Winters Memoir 89 as it was the same coral.  So lets start with the crinoid stem pictorial:

 

 Sections of stems from stalked echinoderms are rare in the Fort Apache Limestone at all three of our sites east of Payson. This could include Crinoids, blastoids, and cystoids. There is really no way to identify the exact genus and species from scattered stem ossicles, so here I present to you anything that even remotely resembles a stem piece. The most common shapes are the small ovals with a round central axial hole, followed by more conventional round crinoid stem ossicles which are the larger sizes here. The extreme mud present on the bottom and raining down on the benthic community most likely prevented a large population of filter feeding crinoids from taking hold in this formation.

 

This represents a low power view of nearly every recognizable stem fragment we ever found in over 200 pounds of limestone. Some are round, some are star shaped. Many are ovals. A few ring shaped pieces are questionably stems, however they are included here for completeness. 7x

 

 A three stack of crinoid ossicles, we can almost can call this one a stem!

 

Very strange piece, a crinoid stem ossicle covered with an encrusting bryozoan. Few hard grounds existed in the Fort Apache, and we find quite a few shells, urchin parts and gastropods covered with such an encrustation.

 

Next we show off our rarest fossil found in the entire formation, the rugose coral.

 

 

Ten times rarer than trilobites, rugose corals are a very small part of the Fort Apache Sea benthic community. We only found one specimen in over 230 pounds of limestones that went into the acid bath. And its a small one - not even 1 centimeter in length. But its cnidarian features are unmistakable. Winters in his monumental monograph on the Fort Apache Fossils (GSA Memoir 89) found a very similar coral, in fact it appears to be identical to his photos - Lophamplexus sp. In addition to this rare coral find, just inside the calice was a coiled microconchid tube, which cemented itself to the coral after it had expired and was an empty husk lying on the sea bottom.

Why corals are so rare goes along with the missing crinoids, blastoids, sponges and brachs. The bottom of the Fort Apache Sea was filled with gooey muck from settled silt and sand from the nearby Schnebly Aeolian dune field. With a constant rain of such fine material, the filter feeding mechanisms of such animals would not function properly and get clogged. So only silt tolerant organisms are found here.

All images with an AmScope Trinocular microscope, 10mp camera and stacked with focus stacking software - Picolay. (free!)

 

 Lophamplexus sp. - 7x. Side view showing detail in the crenelations and bands on the exterior.

 

 Lophamplexus sp. with the microconchid tube on the left edge inside. 7x. You can see the septa defining the corals calice as ridges on the inside wall.

 

 Lophamplexus sp. This Close up at 20x shows the interior is filled with essentially sand that has been cemented together along with the coiled microconchid with its open tube on the lower left inside. The tube worm lived by cementing itself to a flat hard surface for an anchor. We have found plenty of them attached to urchin spines, shells and bryozoans. (Think similar to modern feather duster marine worms).

 

Well thats it this week, hope you enjoyed my presentation as much as we did writing it. 

 

[TqB]

Wonderful! Good to see such a special rugose coral.

[ynot]

Nice! I did enjoy it.

[Arizona Chris]

Thanks guys!  Not nearly as exciting as teleoconchs, but all part of the big picture.