Wooster Geologists

This morning the Wooster Geologists visited the westernmost exposure of the lower Carmel Formation at Nielson’s (1990) Jackson Peak section. Nick and Vicky are shown above on the road towards the conical Jackson Peak in the background. The site was as buggy as any other on this trip, with not a breath of wind to relieve us.

Nick took this image of our team hiking up a wadi in search of a good place to make a stratigraphic column. Jackson Peak looms in the background.

We established the base of the section in a wadi at N 37.327356°, W 113.858144°. Because of the rough terrain, the gnats, and the mostly-covered nature of the stratigraphy here, we decided to use Nielson’s (1990) original measurements and then sample along his column. Note that burned trees give very little shade.

Another image by Nick of Wooster Geologists at work. In the background is Square Top Mountain, which is most notable as the site of a B-52G crash in 1983.

This is the highest in-place outcropping of the typical lower Carmel Formation stromatolitic micrite beds. You can see the fine microbial layering on the weathered surfaces of the rock. Sampled as JP-1.

Like an old friend, the distinctive sandstone we saw in the Manganese Wash section showed up here at Jackson Peak. It has the same weathering appearance and, at the handlens level, the same lithological composition. Sampled as JP-2.

Unlike at the Manganese Wash section, the sandstone at Jackson Peak has an ooid shoal biosparite/grainstone directly above it, our sample JP-3.

This ooid shoal deposit as the same low-angle cross-bedding and current ripple marks as we’ve seen in all our Carmel Formation sections.

At the top of the ridge we were studying, Lucie and Vicky came across our second rattlesnake of the trip. It buzzed immediately, so Lucie and Vicky moved away quickly. Nick got this great image.

On our way back from the Jackson Peak section we met two Bureau of Land Management officers on horseback. Now there’s a cool job. (Photo by Nick.)

As is our tradition on these southwestern Utah expeditions, after we finished our work at Jackson Peak, we visited the 1857 Mountain Meadows Massacre site a few miles to the north.

This is the cairn marking the mass grave of 34 of the victims buried on the massacre site. It is a sad and enraging story we encourage you to read at the link above.

Today Team Utah 2022 climbed the outcrops in Dammeron Valley, north of St. George, to collect trace fossils from the Co-op Creek Limestone Member of the Carmel Formation (Middle Jurassic). It was a bit of a slog up the rubbly talus cones that provided passage over the cliffs, but the trace fossils up there were worth it. Beautiful day, but our friends the gnats lurked in the shadows. Thanks to Nick for the image.

The very base of the section is the gypsum-bearing red claystone and siltstone Temple Cap Formation, shown here with Lucie for scale.

About midway up the slope, just above the highest stromatolitic unit, abundant trace fossils appear. Vicky is ready to collect!

The trace-bearing outcrop is not very photogenic, but those brown slabs on the surface have numerous ichnofossils. Location: N 37.276667°, W 113.640350°.

The red marker shows our study site in Dammeron Valley. Note it is just above the boundary between the whitish lower part and brown upper part of the member.

I was particularly interested in these funnel-shaped traces (the circular pits), which were abundant, along with the familiar Gyrochorte. We haven’t seen these elsewhere in the Carmel Formation in SW Utah.

This slab shows a thick mass of Planolites trace fossils. Each stripe on the Jacob’s Staff is 10 cm.

And that was it for the day. Later we’ll report here on what we found after our lab analyses back in Wooster.

Many veterans of the Wooster Geology expeditions to southwestern Utah will remember the insatiable, abundant, nearly overwhelming biting gnats that occasionally proliferated during our fieldwork. We’ve suffered them each day, but this was the worst experience thus far, mainly because we were collecting data in a nearly windless wadi at their mercy. (Image by Nick.)

But first, our day began with another section for Lucie’s Independent Study project, this one on the Eagle Mountain Ranch at N 37.307688°, W 113.739697°. Above is a ghostly, pensive Lucie in the shadows waiting to scramble up from the base of her section. It is again a stromatolitic sequence, this time with desiccation cracks and a top layer of calcitized gypsum nodules. Above this we eventually reached the lower oolitic shoal deposits of the upper unit. It all went as planned, with critical stratigraphic measurements (and structural observations) from Nick and Shlley.

After lunch was our descent into Buggy Gulch, otherwise known as the Manganese Wash section we measured, sampled and described on Sunday (N 37.283125°; W 113.803696). Beautiful day for us and, unfortunately, the clouds of gnats. We were stuck in place measuring current ripples and cross-bedding in the main oolitic shoal deposits. Shelley showed us how to do the work with her mad structural geology skills. We collected a boatload of data at the expense of our sanity. I’m scratching bites as I write this.

Bug complaints aside, the sedimentary structures here are well developed. Here is a set of current ripples with easily-measured crests and clear directional indicators.

The cross-sections through the shoals display complex cross-bedding, the product of multiple changes in current directions and velocities. This is important data for our paleoenvironmental reconstructions.

Finally, we’ll end the day with a gorgeous prickly pear cactus flower, suitably crawling with insects.

One of my favorite Jurassic outcrops in all the world is found on the Eagle Mountain Ranch north of Gunlock, Utah (locality C/W-142; EMR). It has an exposure of the Carmel Formation with the perfect orientation to produce fossils weathered out of the matrix, yet not dissolved. We met the new owners of the ranch, Layne and Betsy Bangerter, who could not have been more friendly and accommodating. It was also a beautiful, cool day. Nick took the above image during lunch.

The main task we had today was collect trace fossil data and specimens for Vicky’s Senior Independent Study project. The star was the common Gyrochorte, of course.

This large trace fossil, with its two lobes of curved spreiten (essentially internal laminae) confuses me. I’ll have to spend some time thinking about it before hazarding an identification.

We found a couple of these odd gouges along bedding planes. I like to think they represent ichthyosaurs running their snouts through the sediment. (I have zero evidence for this interpretation.)

We found many other fossils as well, including a rare coral (good work, Lucie) and nicely-bored bivalves.

Tomorrow we return and dig (literally) into the lower part of the member for Lucie’s project. Here we see it nicely exposed along a cutbank of the Santa Clara River. (The water level is so low we can’t see it from here.)

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.

Washington, Utah — In March 2020 a team of Wooster Geologists was in beautiful southwestern Utah sampling, measuring and analyzing rocks and fossils from the Middle Jurassic Carmel Formation north of St. George. The Covid-19 pandemic forced us to end that trip and retreat to Wooster. Surely, we thought, at the very least we will be able to return in the summer, but you know that story. Finally, after 26 months, a new team is back on those fascinating rocks.

Pictured above in the now-classic scene is Team Jurassic Utah 2022 posing in front of the Carmel Formation exposed on the northern shore of Gunlock Reservoir. On the left is Nick Wiesenberg, our indispensable geological technician. To the right are then Shipei (Vicky) Wang (’23), Lucie Fiala (’23), and Professor Shelley Judge. It is a beautiful May day as we begin our geological orientation. The primary goal of this expedition is to collect specimens, measurements and observations to support the Senior Independent Study projects of Vicky and Lucie.

We are fortunate geologists indeed to be able to stay in an Air BnB house in Washington, Utah, during our fieldwork. This morning we started with a briefing about the day’s activities. (Lucie on the left, Vicky on the right.) Note the geological map and stratigraphic sections supplemented by an iPad. (Photo by Nick.)

Our first field task was to find an outcrop for Lucie’s Senior IS project. She is looking at the Co-Op Creek Limestone Member of the Carmel Formation, concentrating on the transition between the informal “lower” portion and the informal “upper” part. This corresponds with the boundary between the (again informal) C and D members of Nielson (1990). The lower member is a distinctive set of supratidal and intertidal facies dominated by stromatolites, some of which were examined by Will Santella (’21) in his Senior IS. We found a nice exposure of these stromatolites just northeast of the Gunlock Reservoir.

Some of these stromatolitic and microbial mat deposits have remarkable burrows filled by a well-sorted calacreous sand that appears to be made mostly of crinoid debris.

Lucie and Vicky examine one of the stromatolite beds.

These lower Carmel Formation units also include well-preserved current ripple marks.

Here we are having lunch at one of our most interesting outcrops so far. These almost white rocks weather very differently than the usual limestones and shales above and below them. Turns out this is an exposure of the lowest rocks of the upper part of the Co-Op Creek Limestone Member. (Photo by Nick.)

This white unit is a sandstone at N 37.282454°, W 113.803273°. We have a hypothesis that the lower-upper transition here marks a Middle Jurassic transgression (when sea level rises relative to the land). Sandstone is very rare in the Carmel Formation, so it is telling us something significant about the transition from intertidal to subtidal environments. Score one important find for our first day.

Lucie demonstrates above how unconsolidated this sand is in places. We can run this sand through our venerable Ro-Tap!

The units immediately above the white sandstone include the familiar ooid shoal deposits of the upper part of the Co-Op Creek Limestone Member. These were studied by Anna Cooke (’20) in her Senior IS project.

A closer view of the ooid shoal deposits and underlying shales.

We will return to these outcrops tomorrow for full measurement, description and sampling.

Nick photographed this blooming prickly pear cactus near our study site today.

And Nick encountered our first rattlesnake of the season! This scary beauty is a Western Diamondback Rattlesnake. I hope it is the last one we see!

The head of this snake with its creepy tongue deserves a close-up!

References: (Which will be useful later.)

Nielson, D.R. 1990. Stratigraphy and sedimentology of the Middle Jurassic Carmel Formation in the Gunlock area, Washington County, Utah. Brigham Young University Geology Studies 36: 153-192.

Sprinkel, D.A., Doelling, H.H., Kowallis, B.J., Waanders, G., and Kuehne, P.A., 2011, Early results of a study of Middle Jurassic strata in the Sevier fold and thrust belt, Utah, in Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr., eds., Sevier thrust belt: northern and central Utah and adjacent areas: Utah Geological Association Publication 40, p. 151-172.   

Taylor, P.D. and Wilson, M.A. 1999. Middle Jurassic bryozoans from the Carmel Formation of southwestern Utah. Journal of Paleontology 73: 816–830.

Wilson, M.A. 1998. Succession in a Jurassic marine cavity community and the evolution of cryptic marine faunas. Geology 26: 379–381.

Wilson, M.A. 1997. Trace fossils, hardgrounds and ostreoliths in the Carmel Formation (Middle Jurassic) of southwestern Utah, in Link, P. and Kowallis, B., eds., Mesozoic to recent geology of Utah, Brigham Young University, v. 42, p. 6–9.

Wilson, M.A., Ozanne, C.R. and Palmer, T.J. 1998. Origin and paleoecology of free-rolling oyster accumulations (ostreoliths) in the Middle Jurassic of southwestern Utah, USA. Palaios 13: 70–78.