Cambrian
            Fossils in the Bright
            Angel Shale

            
of
            Northern Arizona - SW Locality

            
Trace
            Fossils Section

            
 
The Bright Angel Shale is loaded with a good variety
of trace fossils, and record lots of activity on the muddy
floor of this shallow continental shelf sea during the
Early Middle Cambrian.

Updated 7/30/17
 

            
The SW locality
            near Ashfork Arizona consists of three facies, a lower green
            shale member with body fossils of trilobites and other marine
            fauna, and two upper members within walking distance which has
            a base of a yellow crumbly shale loaded with only trace fossils
            of low diversity capped by the third member, the Muav Limestone
            which here was non fossiliferous. We scouted the middle member
            extensively, and found some well preserved trace fossils - Some
            being quite enigmatic! While the nearby Tapeats Sandstone consists
            of primarily the Skolithos and Cruziana ichnofacies, this deeper
            water shale seems to be a mix of Cruziana and Glossifungites
            ichnofacies components.

            
Here is a photo
            pictorial of some of the more interesting trace fossils we have
            found at the second yellow shale facies.


Trilobite Tracks, Resting places 
     Cruziana - Grazing traces as the trilobites plowed through the upper layers of sediment.
 

            

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A composite of both Cruziana and Diplichnites
Cruziana is the deep bulldozer like tracks from trilobites,
and Diplichnites is a surface scampering trace from 
trilobites as well.
(click to enlarge to full size)
 
 
 
 
Rusophycus - Resting place where the trilobite dug a pit and hid under the surface from predators. (Like Anomalocaris)
 

            

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Simple Tubular Feeding Traces
 

            

Paleophycus sp. (Worm like sub surface miner)
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Paleophycus sp. (Worm like sub surface miner)
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Bilobed Traces
 

            

Left side - Isopodichnus (Shrimp/Arthropod)
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Aulichnites (Gastropods grazing)
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Close up - Aulichnites (Gastropods grazing)
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Scattered bioturbation traces and tooling marks
  The sediments is so reworked here by so many organisms that it is a mash up of near surface grazers and current generated 
tooling marks, and broken up burrows that have aligned with the currents.
 

            

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Problematica
   We think these large "half burrow" like structures which are also found in great abundance in the southern extension of the Cambrian
 sea - the Abrigo formation are mud casts from bottom wave ripples (Sedimentary structures).  They do not appear to have a biogenic origin.
 

            

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A few Sedimentary structures
 

            

Cyano bacterial mat hard ground 
(AKA: Elephant skin)
When an algal or bacterial mat grows on the surface of
mud, it wrinkles the surface to form this type of pattern.
(click to enlarge to full size)


Locomotion Traces
   These two slabs are very unusual, we believe them to be a mollusk of some type pulling its way along the surface hard ground.
 

            

Protovirgularia sp.
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Protovirgularia sp.
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U Tube Domiciles Traces
   A worm like animal living permanently in the sediment in a narrow U tube with two holes at the surface for feeding and waste removal.
 

            

Arenicolites sp.  Also seen just below it is the 
"scampering" traces of trilobites Diplichnites.
(click to enlarge to full size)



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