Tonto
            Creek Fossils


            
An
            Survey of Some new Areas


            
Expedition:
            1/3/2009

Updated 1/23/09
 

            
Introduction

            
The Devonian Martin
            Formation outcrops
            across the Mogollon Rim in central and northern Arizona. Our
            expedition this trip was to see if any new silicified coral material
            had weathered out since our last visit, several years ago. We
            were not disappointed. This locality near Tonto Creek is one
            of the few we have found in the state that contains Disphyllum
            tabulate corals. These organ pipe like assemblages can be found
            in large silicified chunks eroding out at the top of a hill along
            with a smaller rugose coral Pachyphyllum woodmani and some trace
            fossils and a few brachiopods. With us was our long time friend
            Vince Mele, and the three of us traversed from Devonian, through
            the Redwall limestone up to finally the Pennsylvanian Naco formation
            as we hiked the ridge line. Here are more details of the adventure.


 Dawn searches the Devonian
            outcrops in between patches of snow
 
 Vince
            took this shot of us at the Disphyllum locality with the Mogollon
            Rim in the background
 
 The
            ground at the Disphyllum locality is primarily dolomitic limestones
            with silicified fossils eroding out. The problem with dolomite
            is that it does not dissolve in muriatic acid very well if at
            all, making the extraction of the corals a hit and miss process.
 
 The sandy dolomitic limestones
            at the locality formed robust cross beds indications of a near
            shore more energetic condition, in between the more limey dolomitic
            limestones.
 
 Collection of the Disphyllum
            raw material. While it doesn't look like much here, the acid
            bath will free up much of the beautifully preserved corals.
 
 After the acid bath, one
            specimen was nearly falling apart from internal fractures. I
            left some of the limestone in the center of the coral head to
            keep it together.
 
 Another Disphyllum coral
            head with more silicification thus it was relatively intact.
 
 This Disphyllum was too
            diagenetially modified to preserve well and came out a mass of
            silica.
 
 Side view of the tabulate
            coralite in the Disphyllum
 
 We
            also found a few Pachyphyllum corals at this locality.
 
 

            
 The Pennsylvanian
            Naco Formation

            
We next moved on
            to another site near Christopher Creek at the Uranium mine. A
            low ridge of Pennsylvanian Naco formation eroded out to reveal
            massive brachiopods, and plenty of crinoid material. This is
            one of the few sites we have ever found complete crinoid calyxes
            with arms attached in the Naco preserved in limestone. We were
            not so lucky this time, but still found some great stuff!
 
 The ground at the site
            consisted of a fine grained limey shale which upon weathering
            released a huge amount of small fossils.
 
 Dawn
            gets down to work examining the very small fossils present all
            over the ground here.
 
 Close
            up of the ground, showing a few brachs mixed in the fragments.
 
 Back home after cleaning
            the specimens up I photographed a few lined up. The left end
            is crinoid stems, and on the right various plates which were
            originally part of a large crinoid calyx.
 
 In
            addition, we found a number of spiriferid brachs, and Composita
            Subtilitas.
 
 Here is some material from
            the Naco at the Tonto Creek site. Left is a red chertized shrimp
            burrow, middle a rugose solitary coral.
 
 Close
            up under my stereo microscope of one of the crinoid basal plates.


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