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The Middle Devonian
Martin Formation contains a moderately rich marine and brackish
water fauna, preserved at many localities as silicified external
casts. Our exploration of this formation is primarily from the
areas north of Payson up to around the Flagstaff area. In addition
to a varied invertebrate fauna, the lower Martin contains both
brackish and freshwater deposits, and this includes fossil arthrodires
such as Bothrioleipis and a Cooksonia like land plant foliage.
Here we are concentrating on the marine invertebrates.
Depositional Environment
The Martin marine
sedimentary deposits are an example of a Middle Devonian Off-reef
Community. This represents a shallow continental shelf sea, with
a rich assortment of corals and brachiopods. It is not a reef,
but a series of bioherms subject to storm damage and wave action
containing a large amount of damaged corals and bryozoans. In
such an environment, Stromotoporoids often encrust corals and
form large associations along with the rugose horn corals, tabulate
corals and a host of brachiopods. Nearly all invertebrates represented
here are filter feeders. Trilobites are very rare in that the
weak molts did not survive both the rough action of faster currents
and storm flows. In fact, we have so far, never found a single
trilobite part in the Martin formation in over 35 years of searching!
Devonian
Martin Formation Sea
Below is illustrated
a living diorama of all the fossils in life position that we
have found in the Martin Formation. (Click for full size). Ive
added a few Bothriolepis Arthrodire fish as well, from the underlying
Devonian dolomites from a fresh to brackish water estuary type
environment. The panel on the left is the original drawing, and
on the right with added letters for the identification key listed
below. Drawing by the Author.
Key: A
- Bothriolepis, B - Hexagonaria, C - Stromatoporoid, D - Rhynconellid,
E - Productid, F - Sponge, G - Zaphrentites, H - Chondrites,
I - Pachyphyllum, J - Thamnopora, K - Crinoids, L - Cyrtosprifer,
M - Stromatoporoid
Fossil Preparation
Nearly all invertebrate
fossils are silicified in a limestone matrix. Removal is with
dilluted Muriatic acid, which is available in gallon jugs at
ACE Hardware stores for cleaning brick. The amount of dillution
varies with the dolomitization of the limestone matrix. More
dolomite, more concentration. Typically for average limestones
we used a dillution of about 4 to 1. Fossils such as trace fossils
of course are not subjected to this treatment. Also to note,
if you suspect any fish bone material the acid will destroy it.
Typically, the layers with the bone material is not in the same
layers as the corals.
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Rhynconellid Brachiopods
Pachyphyllum Woodmanii Coral
