Monday, November 15, 2010

Fossil Fish and Dino Tracks

Although I would prefer having a permanent year-round park service job, being a summer seasonal and underemployed during the winter definitely has its positive side.   How else would I be able to volunteer to do cool geological stuff?

 St. George, UT is rapidly becoming known world-wide for its fossilized dinosaur trackways,   and opportunities abound to work (for free, of course) either in our museum ( or at the sites where these trackways can be found.  There are fossils galore brought to the museum from fieldwork around the state.

Last winter I began prep work in the lab on a fist-sized piece of fine-grained mudstone.  This unobtrusive little sample would eventually be found to contain the proximal portion of a 210-million year old fish fossil, a semionotid, from the Owl Rock member of the Chinle Formation of AZ-UT-NV-CO.  The Owl Rock tells of an extensive inland lake system that periodically evaporated.  This particular fossil was found not in the St. George area but in eastern Utah.  

After returning in late September from my summer in Katmai, I went back to the museum where I tenderly and lovingly extracted my fossil from the cabinet drawer in which it had been tenderly and lovingly placed the previous April.   I situate the specimen under a microscope and meticulously pick away at the barely discernible grains of lithified mud matrix, slowly uncovering the delicately fragile scales and fins.   I am constantly amazed at the fact that I am the first person in the history of the universe to observe this fossilized fish, buried these past millions of years deep within the rock.

Eubrontes tracks in Lower Kayenta mudstone
In the field there is always more exhilarating action to be found.   East of town in Warner Valley is a shallow sandy wash in which a dinosaur trackway was discovered in 1982 in the mudstone bedrock.   These tracks are not the dinosaur fossils themselves but are trace fossils; they are geologic records of biological activity, impressions made by some kind of dinosaur.  Most trace fossils reflect the behavior of the organism - footprints showing that something walked here.   
Grallator and Eubrontes are not the names of the dinosaur but are the names of the footprints, belonging to some specific (and often unknown) type of dinosaur.  They are found here in the Lower Kayenta Formation of the Early Jurassic Period – it is thought that 195 million years ago this part of what would one day become southwestern Utah was covered by many small, shallow lakes.  The dinosaurs left their footprints as evidence of their passage along the muddy shores of these lakes.
Grallator track in Lower Kayenta mudstone

This past Saturday a crew of 18 dedicated volunteers was hard at work in Warner Valley, delineating the edges of the wash with shovels, brooms, and brushes in preparation for further photographing, mapping, and measuring of the tracks and trackways. 

Cleaning a Eubrontes track

There is certainly enough lab and field work available to keep  any interested volunteers busy for years to come!

Lunch break

Eubrontes trackway from near dustpan trending  past white bucket

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