Fossils from Lake Mary Road

Permian Kaibab Harrisburg Member

Expedition: 8/22/2009
Updated 8/29/09


Formerly known as the Kaibab Alpha, the Harrisburg member contains by far the most abundant fossil assemblage in the formation. Most fossils are found moderately well preserved in a tan dolomitic limestone which strongly resists any acid. By either examining road cuts or cracking open the tan dolomites, you can find abundant mollusks such as gastropods, bivalves, and scaphopods, and sometimes huge wheelbarrow tire sized nautiloids. ( ! ) Excellent exposures of both upper Harrisburg and lower Fossil Mountain members can be found all along Lake Mary road on the way to Flagstaff. This documents one such site we visited, which on a previous expedition seemed very promising for finding both trilobites and huge nautiloids. We were not disappointed....

 One of the road cuts we visited was rich in the tan dolomites. Since the cut was quite broken up, many fossils are exposed along the breakage planes. Additional cracking with a hammer of promising specimens usually revealed an occasional rare Permian trilobite.
 A large Pectin, covered with spines. The fossil is a negative mold of the mollusk.
 Long tapered scaphopod. Once identified in older texts as "Dentalium", we now believe that this is a new Kaibab specific species. Dentalium has an open end for water flow. These do not.
 The rock break shows a cross section of a large nautiloid. This is the outer whorl.
 The huge nautiloid I found, which had obvious septa on the ends.
 Dawn finds a superb Anisopege trilobite pygidum. It is probably "Anisopyge Mckeeii". In the Permian, trilobites were nearly all gone. It is very rare to find them in middle Permian sediments like these.
 Straparolus Gastropod internal cast. We found one area with many poorly preserved specimens and occasionally one very well preserved.
 Thallassenoides burrows. These are the in filled domiciles of callanassid shrimp, these were filled in with a high quartz gravelly in filling, indications of a near shore environment in the tidal zone.
 Classic Y branching in Thallassenoides.
 Another nice Straparolus cast...
 Close up of unknown mollusk.
 Mollusk internal casts. The fine details are missing making identifications nearly impossible, but Id venture that the one on the left is a pectin.
 Here is the large nautiloid I found, it is filled with tons of small shelly fossils!
 Close up on the end showing the partitions in the shell - the septa.
 Dawn found this magnificent 2 inch Straparolus (Kaibabensis?) gastropod, with excellent ornamentation on the whorls.
 Anisopyge McKeeii trilobite pygidium. This close up shows the unusual narrow tapered appearance of the pygidum which differs from the well rounded appearance of the Mississippian Phillipsia we find in the Redwall.
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