Tonto Creek Fossils

An Survey of Some new Areas

Expedition: 1/3/2009
Updated 1/23/09


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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