Second field day in SW Utah Jurassic: Wooster geologists begin their projects

During another beautiful day in southwestern Utah, Team Utah 2022 began to collect field data and specimens. We started in Manganese Wash with Lucie’s project, which involves the stratigraphy and paleoenvironments associated with the transition from the lower Co-Op Creek Limestone Member of the Carmel Formation (Middle Jurassic) into the upper. Lucie is pictured here at the start of her column: a thick unit of micritic limestone (N 37.281936°, W 113.803458°). Nick and Shelley provided the stratigraphic measurements using a Brunton compass and Jacob’s Staff while Lucie and I did the lithological descriptions and sampling.

A Google Maps image of our field area today.

The lower part of the Carmel has beautiful stromatolites and other microbial mat units.

This is the enigmatic sandstone near the base of the upper part of our member we mentioned in the last post. Note the marly unit below the sandstone. Vicky mined out many trace fossils from this unit as we did our measuring, sampling and describing.

Here is one of Vicky’s trace fossils — a good specimen of Chondrites. (The specimen is held upside-down to show the ichnofossils.) She also found Gyrochorte, Planolites, and several unknown traces.

The top of our Manganese Wash section consists of thick biooosparite/grainstone beds with current ripples, low-angle cross-stratification, and lots of crinoid debris (N 37.283125°, W 113.803696). These are the classic ooid shoal deposits we’ve seen in this part of the Carmel many times. Lucie’s section thus goes from restricted lagoonal and intertidal carbonate sediments at the base to normal marine subtidal carbonates at the top.

In the afternoon we went to the nearby “Oyster Ball Valley” (C/W-157) to find specimens of the trace fossil Gyrochorte (shown above) in the upper part of the Co-Op Creek Limestone Member of the Carmel Formation. Vicky is testing the hypothesis that these trace fossils and others are smaller in size than elsewhere because of the restricted nature of their environments. We didn’t collect specimens today but instead measured the dimensions of over a hundred examples.Shelley is here measuring Gyrochorte traces with calipers.

Vicky is doing the same. Note Vicky had the best sun protection of us all!

Finally, this is the Santa Clara River as it passes under the earthen bridge at the junction of Gunlock Road and Manganese Wash Road. This river has caused us many inconveniences over the years of our work here. Sometimes it washed out the bridge and was uncrossable. This year it, alas, shows the effect of the great western drought. We could jump across it now.