Cambrian Trace fossils from SE Arizona - Latest expedition!

[Arizona Chris]

Hi all,

 

Once again we are back from a weekend of fossil sleuthing in south eastern Arizona south of Tucson.  The Upper middle cambrian Abrigo formation is mostly limestones, but the lowermost member is either a dark grey shale, or green glauconitic micaceous shale.  Gorgeous stuff!  Three main localities were visited - the 80/90 Roadcut (mostly trilobits and brachs), Ajax Hill near Tombstone (trilobits), and and area near Colossal Cave just south of Tucson.  (tons of trace fossils).  Trace fossils are very abundant in both the Abrigo Formation and the slightly older Bright Angel Shale in northern Arizona. Nearly all trace fossils found were in a micaceous glauconitic green shale, in isolated beds found throughout the Abrigo, especially in its lowest beds. The most commonly found types were from sediment ingesting worms, with a number of disks and rings from stemmed Echinoderms where they attached to the sediments. Also found were the attachment depressions of solitary and colonial cnidarians. Years of searching did not however reveal any trilobite tracks or traces. This was surprising since there are so many trilobite fossils in the Abrigo.

Most fossils are in a single bed or plane and represent variations on Planolites, or Paleophycus. Another surprise was that no Skolithos was found either. This seems to indicate we are in a deeper water environment rather than near shore like the Tapeats or Bolsa sandstones.  

 

Collecting of the shales was pretty easy.  Most were in big piles at the bottom of small cliffs, and often did not have to be split.  Nearly all were on the bottom of the slabs (positive hyporelief) and you had to flip over the slab to see what was on the bottom.  Here is a representative selection of fossils we have found at the three sites.

 

Paleophycus

 

 

 

Hold fast traces of a stemmed echinoderm, possibly Gogia.

 

Bergauaria - A prize find. dozens of Cnidarian (sea anemome) suction cup marks can be seen clustered in a group on this former hardground.

 

Thanks for looking.  we put together a far more extensive write up if your interested on our paleo web site, please visit for more exciting specimens:

 

http://www.schursastrophotography.com/paleo/Abrigo-6.html

 

Chris