Team Jurassic Utah sets to work

May 16th, 2018

Santa Clara, Utah — Team Jurassic Utah had its first day in the field, and it was excellent. As you might recall from this blog, last month I visited southwestern Utah alone to scout out locations for this crew, and today we began work. On the left is Galen Schwartzberg (’19), in the middle is Ethan Killian (’19), and on the right is our geological technician Nick Wiesenberg. They are at Gunlock Reservoir with the delicious Middle Jurassic Carmel Formation exposed in the background. Note the beautiful blue sky. Perfect geology weather.

Classic professorial pointing at Gunlock Reservoir. Photo by Nick.

This is the familiar southwestern Utah stratigraphic column, modified after the column on the Zion National Park website.

We spent the morning exploring the Carmel exposures around Gunlock. At this point we’re doing orientation and working on observation skills. The students proved to be quick studies with the stratigraphy and paleontology, adding already new ideas and information about the Carmel fossils. No one can resist the fascinating oyster balls of the Carmel (officially they are ostreoliths), so Nick, Ethan and Galen found new horizons and worked out a rough stratigraphy of their occurrence. In some places they are so common they’re stacked up. We noted a pattern of shape distribution (spherical vs. flattened), and that the large ostreoliths (up to 75 cm in diameter) seem quite different in origin from the more numerous small ones like those shown above.

Here we were able to determine that the large ostreoliths are consistently stratigraphically below the small ones, and there are subtle changes in sediment color enabling us to predict their distribution. It is 12.6 meters from the large to the small ostreoliths, stratigraphically, and 16.9 meters from the small ostreoliths to the base of the Iron Springs Formation.

The team tramping through the Gunlock region. Note the landmark conical Veyo cinder cone in the background. Photo by Nick.

The Gunlock area we examined in the morning is #1 on the above image. We then drove north through Gunlock to Veyo (top of the image) and turned south on Utah Hwy 18 past the extending Carmel outcrops in Dammeron Valley (#2) to work in the Carmel in suburban Diamond Valley (#3). There we found many shelly fossils, mostly bivalves and crinoids, and numerous tiny encrusters and borings.

I ended the day by giving a presentation to the SW Chapter of the Utah Friends of Paleontology at Dixie State University. I talked about the origin of oyster balls, oddly enough, and what they tell us about the paleoenvironments of the Middle Jurassic in southwestern Utah. It was a fun and inquisitive group with excellent questions and ideas about some of the remaining oyster ball puzzles.


Wooster Geologist in Southwestern Utah (April 2018)

April 21st, 2018

St. George, Utah — I visited southwestern Utah for a week to prepare for an Independent Study expedition next month to study the Carmel Formation (Middle Jurassic). I wanted to update locality information I had collected in the 1990s (ancient times!), find different sections, and meet new people. It was much fun and very productive. The daily blog entries are linked below —

April 16: A Wooster Geologist returns to the Jurassic of southwestern Utah
April 17: Another geological scouting day in southwestern Utah
April 18: Another day in the shallow Jurassic seas of southwestern Utah
April 19: Delightful fossils in the Middle Jurassic Carmel Formation on my last field day

Next month we will have posts from the project!

Delightful fossils in the Middle Jurassic Carmel Formation on my last field day

April 19th, 2018

St. George, Utah — Today I met Jerry Harris, Professor of Geology at Dixie State University in St. George. He was very friendly, generous and knowledgeable, guiding me to two fantastic Carmel outcrops I would not have approached on my own. Shown above is one complete section of the Carmel Formation in the Dammeron Valley. The reddish rocks in the lower right are the underlying Temple Cap Formation; the top of the ridge is the end of the Carmel here — it is unconformably overlain by the Iron Springs Formation (Upper Cretaceous). This is an extensive exposure perfect for exploring.

The red unit here in the Dammeron section is the top of the Temple Cap Formation. I’m not sure if the Carmel commences with the green marls, but classic Carmel limestone is found immediately above.

A curious unit within the lower few meters of the Carmel is this bedded gypsum deposit. It represents a significant accumulation of evaporite minerals, and thus the evaporation of a lot of seawater in an enclosed basin.

The Carmel limestones show normal (but restricted) seawater and lots of evidence of high energy. These carbonate crossbeds are almost herringbone.

This is a view west from the top of the Dammeron Valley section. In the distant left you can see the familiar Square Top Mountain and pointy Jackson Peak. On the right is the majestic Veyo Volcano. The Gunlock exposures are just a few kilometers away, but no outcrops connect them to the Dammeron Valley.

Jerry Harris also showed me large exposures of the Carmel Formation in Diamond Valley, a few kilometers south of the Dammeron Valley location. It is not picturesque, but there is plenty of Carmel under that sagebrush. The excavation for that water tower turned out to be especially good for shelly fossils, so Jerry took me there right way.

The most common fossil is the pectenid bivalve Camptonectes. It has calcitic valves, so they are well preserved, unlike the numerous aragonite-shelled mollusks in the Carmel that are seen only as ghostly molds.

To my delight, some of the bivalves at this locality are encrusted by small cyclostome bryozoan colonies. Jurassic bryozoans are very rare in North America. In fact, Paul Taylor and I have described most of them from the Carmel! (Taylor, P.D. and Wilson, M.A. 1999. Middle Jurassic bryozoans from the Carmel Formation of southwestern Utah. Journal of Paleontology 73: 816-830.) The exquisite bryozoan colonies above are as good as any we’ve found before. A thorough study of all the Carmel sclerobionts is worth pursuing.

There are also nice wedge-shaped limid bivalves at the water tank exposure in Diamond Valley.

These fossiliferous slabs have lots of treasures. I only wish they were more common in the Carmel.

Here’s a simple Google Maps image of my three main areas of study north of St. George. 1 = Gunlock, 2 = Dammeron Valley, 3 = Diamond Valley. Curiously, the most fossiliferous part of the Carmel Formation (the upper unit of the Co-op Creek Limestone Member) differs significantly between Gunlock on the west and the two valleys on the east, even though they are only a few kilometers apart. The Gunlock area has oyster balls and hardgrounds, which are absent in the east. The trace fossils are also more abundant and diverse in Gunlock than in the other two sections. Shelly fossils, though, appear to be more common in the east. It will be fun to sort out these facies differences in more detail.

Finally, I wanted to include an image of the cinder cone and lava flows at the entrance to Diamond Valley. They are within Snow Canyon State Park and have been dated at an astonishingly young age of 32,000 years.

Great day, great scouting trip. Thanks again to Jerry Harris and Andrew Milner!

Another day in the shallow Jurassic seas of southwestern Utah

April 18th, 2018

St. George, Utah — Back to the Gunlock region for me to revisit old Carmel Formation research sites to check for access issues and new exposures. This trip has also given me a chance to update my images of the unit. Most of my previous images are shockingly on film. I’ve been in this business a long time.

Above is one of my favorite Carmel outcrops, the cliff at Eagle Mountain. The white and buff layers are the Co-op Creek Limestone Member of the Carmel Formation (Middle Jurassic). They are topped by a thick, well-cemented conglomeratic sandstone, The Iron Springs Formation (Upper Cretaceous). This is a nice example of an erosional disconformity between the units with an interval of time unrecorded (a hiatus). The cliff is on private land, so I’m in the process of finding the owners. The image was taken looking northeast from: 37°18.428’N, 113°44.408’W.

Today I looked at some smaller details in the Carmel sections. I found these exquisite mudcracks near the Eagle Mountain locality. This is solid rock, even though the cracks look modern. This shows, of course, that this patch of muddy seafloor dried out, producing the cracks by desiccation of clay minerals.

On top of the mudcracked layer is a thin carbonate bed with vugs and cracks filled with gypsum. This represents a hypersaline environment where gypsum and/or anhydrite was precipitated as evaporite minerals. We thus went in time from a dry seabed to one covered by shallow briny water.

Within the gypsum-rich layers are intraclasts of carbonate mud derived from the mudcracked layer below. When the seawater returned it had enough energy at times to rip up pieces of the hardened mud below.

Finally, on top of the gypsiferous layer is a limestone rich in star-shaped crinoid debris (ossicles of Isocrinus nicoletti). This represents the influx of normal marine water, albeit in a restricted context. As far as I can tell, there are multiple triplet layer sets like this near the middle of the Carmel in the Gunlock area. What was controlling these changes in sealevel and chemistry?

I would be neglecting my duties as a geologist if I didn’t mention that there is much more to the geology here than the Carmel Formation. Above we see the underlying Navajo Sandstone with its massive cross-bedded eolian dune features. The Navajo is topped here by thick basaltic lava flows of Pleistocene-Holocene age (the Santa Clara Volcanic Field).

Lovely place for a geologist!

Another geological scouting day in southwestern Utah

April 17th, 2018

Kanab, Utah — My day began with a visit to the St. George Dinosaur Discovery Site at Johnson Farm, where I met Andrew R.C. Milner, the Site Paleontologist and Curator. This museum is built over an extraordinary set of dinosaur trackways. These tracks were not even discovered when I started working in the area, and now this building houses a busy and productive center for vertebrate paleontology in the region.

Andrew is a dinosaur paleontologist and an expert on vertebrate trace fossils, and he also knows a lot about the Carmel Formation and its outcrops in Utah. He gave me local contacts, and will join us in the field when we start the official Utah Jurassic expedition next month. He has been very helpful.

I then drove to Mt. Carmel Junction on the eastern side of Zion National Park, about two hours from St. George. It is a small place with a surprisingly long Wikipedia page. It sits in the center of several extensive exposures of the Carmel Formation, including this cross-bedded unit made almost entirely of crinoid ossicles. These rocks are called encrinites. This particular Middle Jurassic encrinite is one of the youngest known. This exposure is at Stop #5 of Tang (1997). It is still easily accessible at the northwest corner of the junction.

Alas, this great expanse of Carmel Formation, known as Stop #6 in Tang (1997) is no longer accessible, at least not easily. If you look carefully you can see a barbed-wire fence at the base of the outcrop. I could find no evidence of who owns this land, and jumping a fence out here can have serious consequences! Unfortunately there are far more such fences here than were present in the easy-going 1990’s. This makes taking students here harder for casual examinations of the rocks.

I spent the night in nearby Kanab, Utah, where I got to spend excellent time with my Father, who was in the area hiking with two friends. I then drove back to St. George the next morning, passing through a long stretch of northern Arizona. This included driving by the storied Colorado City of FLDS fame. Follow those links if you don’t know the story!

A Wooster Geologist returns to the Jurassic of southwestern Utah

April 16th, 2018

St. George, Utah — This week I’m exploring the wonderful Middle Jurassic Carmel Formation exposed in southwestern Utah. It is a rare bit of solo fieldwork I’m doing to prepare for a Wooster Independent Study expedition here with students and Nick Wiesenberg in about a month. My colleagues, students and I last did research here almost two decades ago, so I wanted to make sure I knew how access and exposures have changed. Better to explore early than be surprised while leading a team! (One new thing in the above image: a lake where I used to wade across the Santa Clara River to get to the Carmel outcrops.)

The Carmel Formation is 100 to 300 meters thick, more or less, through parts of southern Utah. It is relatively thin by Utah Jurassic standards. It is a mostly marine unit, having been deposited in a narrow restricted seaway. I’ve long been fascinated by its fossils, which are almost entirely mollusks and traces of arthropods. It is time to revisit these exposures with new eyes and ideas.

This is a view looking north across typical Carmel Formation outcrops about a half-hour northwest of St. George. The rocks are exposed in strike valleys, which are great for finding bedding plane slabs with fossils and sedimentary features, but miserable for constructing stratigraphic columns. Luckily most of that tedious work is done. In the background are two iconic mountains for the area: Square Top and Jackson Peak. In April 1983, a B-52 bomber tragically crashed into Square Top.

The Carmel Formation is capped unconformably in this region by the Upper Cretaceous Iron Springs Formation, a conglomeratic sanadstone here. It is cemented well, capping the less resistant Carmel limestones and claystones below. This is a typical strike valley exposure of the top of the Carmel.

This is a Google Maps view of today’s field area, which is in the middle of the image stretching diagonally from the reservoir in the southeast (right) to where the dirt road bifurcates in the northwest.

One of the interesting features of the Carmel is a widespread carbonate hardground. Tim Palmer and I published on it a long time ago, but there are still many questions about its formation and the variety of borings on its surface. Above are two fragments found loose in a wadi.

The Carmel has beautiful sedimentary structures, like the ripples on the left, and cool trace fossils like the arthropod trackway (Gyrochorte) on the right.

I’m intrigued with the dominant oysters in the Carmel: Liostrea strigilecula. They formed “oyster balls” (ostreoliths) almost unique to the Carmel, and these large masses of unknown origin and significance. They seem to be small reef-like forms, but also show signs of occasional overturning. They hosted encrusting bryozoans and boring bivalves.

An early morning view of my field area. The reddish unit below is the Temple Cap Formation, with the base of the Carmel white turning into, shall we say, carmel-colored. The water is part of the Gunlock Reservoir.

Today I sorted out access to a few old localities, and found some new ones. Much has changed here in the last 20 years. There are new roads in and around the growing cities of St. George and Santa Clara, the Santa Clara river has been further managed with massive earthen works (in response to frequent flash floods, no doubt), and there seem to be new barbed-wire fences across some Carmel exposures. Nevertheless it felt like old times as I tramped across the gravelly hillsides scanning the ground for geological treasures.

I must add as a footnote an image of this ugly-but-simple bridge over the Santa Clara River at Miner’s Canyon. For years my students, colleagues and I waded through the river here because the water was too deep for our rental vehicles. This meant we had lots of walking to do once we were on the other side, including walking back loaded with rock samples. Now we can just drive across. I have a feeling, though, that this bridge will not survive the next flash flood!

Wooster’s Fossil of the Week: A Middle Jurassic trace fossil from southwestern Utah

November 10th, 2017

1 Gyrochorte 2 CarmelTime for a trace fossil! This is one of my favorite ichnogenera (the trace fossil equivalent of a biological genus). It is Gyrochorte Heer, 1865, from the Middle Jurassic (Bathonian) Carmel Formation of southwestern Utah (near Gunlock; locality C/W-142). It was collected on an Independent Study field trip a long, long time ago with Steve Smail. We are looking at a convex epirelief, meaning the trace is convex to our view (positive) on the top bedding plane. This is how Gyrochorte is usually recognized.
2 Gyroxhorte hyporelief 585A quick confirmation that we are looking at Gyrochorte is provided by turning the specimen over and looking at the bottom of the bed, the hyporelief. We see above a simple double track in concave (negative) hyporelief. Gyrochorte typically penetrates deep in the sediment, generating a trace that penetrates through several layers.
3 Gyrochorte Carmel 040515Gyrochorte is bilobed (two rows of impressions). When the burrowing animal took a hard turn, as above, the impressions separate and show feathery distal ends.
4 Gyrochorte 585Gyrochorte traces can become complex intertwined, and their detailed features can change along the same trace.
5 Gibert Benner fig 1This is a model of Gyrochorte presented by Gibert and Benner (2002, fig. 1). A is a three-dimensional view of the trace, with the top of the bed at the top; B is the morphology of an individual layer; C is the typical preservation of Gyrochorte.

Our Gyrochorte is common in the oobiosparites and grainstones of the Carmel Formation (mostly in Member D). The paleoenvironment here appears to have been shallow ramp shoal and lagoonal. Other trace fossils in these units include Nereites, Asteriacites, Chondrites, Palaeophycus, Monocraterion and Teichichnus. (I also ran into Gyrochorte in the beautiful Triassic of southern Israel.)

So what kind of animal produced Gyrochorte? There is no simple answer. The animal burrowed obliquely in a series of small steps. Most researchers attribute this to a deposit-feeder searching through sediments rather poor in organic material. It may have been some kind of annelid worm (always the easiest answer!) or an amphipod-like arthropod. There is no trace like it being produced today.

We have renewed interest in Gyrochorte because a team of Wooster Geologists is going to southern Utah this summer to work in these wonderful Jurassic sections.
6 Heer from ScienceOswald Heer (1809-1883) named Gyrochorte in 1865. He was a Swiss naturalist with very diverse interests, from insects to plants to the developing science of trace fossils. Heer was a very productive professor of botany at the University of Zürich. In paleobotany alone he described over 1600 new species. One of his contributions was the observation that the Arctic was not always as cold as it is now and was likely an evolutionary center for the radiation of many European organisms.


Gibert, J.M. de and Benner, J.S. 2002. The trace fossil Gyrochorte: ethology and paleoecology. Revista Espanola de paleontologia 17: 1-12.

Heer, O. 1864-1865. Die Urwelt der Schweiz. 1st edition, Zurich. 622 pp.

Heinberg, C. 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6: 227-238.

Karaszewski, W. 1974. Rhizocorallium, Gyrochorte and other trace fossils from the Middle Jurassic of the Inowlódz Region, Middle Poland. Bulletin of the Polish Academy of Sciences 21: 199-204.

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 40: 151–172.

Tang, C.M., and Bottjer, D.J., 1996, Long-term faunal stasis without evolutionary coordination: Jurassic benthic marine paleocommunities, Western Interior, United States: Geology 24: 815–818.

Wilson. M.A. 1997. Trace fossils, hardgrounds and ostreoliths in the Carmel Formation (Middle Jurassic) of southwestern Utah. In: Link, P.K. and Kowallis, B.J. (eds.), Mesozoic to Recent Geology of Utah. Brigham Young University Geology Studies 42, part II, p. 6-9.

[An earlier version of this article was posted on April 17, 2015.]

Wooster’s Fossils of the Week: The tiniest of brachiopods (Middle Jurassic of Utah)

November 3rd, 2017

While preparing for this summer’s expedition to the Middle Jurassic of southwestern Utah, I found this specimen in our collection from the 1990s. You may be able to just make out the wedge-shaped outline of a mytilid-like bivalve with several cup-like oysters (Liostrea strigilecula of oyster reef and oyster ball fame) encrusting the shell exterior. This specimen, labeled EM-1, is from our Eagle Mountain exposure of Member D, Carmel Formation, near Gunlock, Utah.

If you look very closely near the middle of the clam, you will see some super-small encrusting shells the size of sand grains. Two are shown above, photographed with all the extension tubes on my camera. Believe it or not, these are shells of thecideide brachiopods, among the smallest known. They are, as far as I can tell, the only brachiopods thus far recorded from the Carmel Formation. They are abundant in this unit, encrusting carbonate hardgrounds as well as shells.

We know who these minuscule critters are from the careful analysis of their interiors by my colleague Peter Baker at the University of Derby. They are, in fact, the first thecideide brachiopods to be described from the Jurassic of North America. We published a description of them in 1999, naming them as the new genus and species Stentorina sagittata. The etymology of the genus name: “From the Greek Stentor (herald, of the Trojan War) in recognition of the first discovery of thecideoid brachiopods in the Jurassic of North America.” How’s that for classical drama about an itty-bitty brachiopod? We said of the new species name: “From the way the edges of the hemispondylium converge on the median ridge to form a characteristic arrowhead-shaped structure on the floor of the ventral valve.” Sagittate means arrowhead-shaped.

I’m looking forward to more paleontological treasures from the Carmel Formation of southern Utah.


Baker, P G. and Wilson, M A. 1999. The first thecideide brachiopod from the Jurassic of North America. Palaeontology 42: 887-895.

Carlson, S.J. 2016. The evolution of Brachiopoda. Annual Review of Earth and Planetary Sciences 44: 409-438.

Wooster’s Fossils of the Week: An oyster reef from the Middle Jurassic of southwestern Utah

September 29th, 2017

It was a pleasure to pull this massive specimen out of the cabinets, where it had been sitting for more than 20 years. It is a small reef of the oyster Liostrea strigilecula (White, 1877) from the Carmel Formation (Middle Jurassic) near Gunlock, southwestern Utah. It is out of storage because I’m returning to this section in Utah with students this summer to begin fieldwork again. The rocks and fossils are fascinating, and it is time someone looked seriously at them again.

A closer look at these little oysters shows how they could construct such a tight, nearly seamless structure. Each oyster grew in a cup-like fashion (first pointed out by Tim Palmer) so that they nestled together rather than overgrowing each other. These same oysters in this same locality also formed the famous oyster balls (ostreoliths). These reefal equivalents grew on carbonate hardgrounds, which are abundant in the Carmel Formation.

Liostrea strigilecula was named by Charles Abiathar White (1826-1910) as Ostrea strigilecula in 1877. White was an American paleontologist and geologist who did considerable work on midwestern and western North America. He was born in Massachusetts and worked in Iowa as the state geologist from 1866 to 1870. He returned east to teach at Bowdoin College for a couple of years, and then he joined the United States Geological Survey from 1874 into 1892. In 1895 he became an associate in paleontology at the United States National Museum. White was one of the first fellows of the American Association for the Advancement of Science, one of the first members of the Geological Society of America, and he was elected a member of the National Academy of Sciences in 1889. Abiathar Peak in Yellowstone National Park was named after him. A more thorough biography can be found at the link.

I’m looking forward to seeing these beautiful oysters in the field again!


Bennett, K. 2017. White, Charles Abiathar. The Biographical Dictionary of Iowa. University of Iowa Press, 2009. Web. 19 September 2017

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.

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.

Wooster’s Fossils of the Week: Belemnites (Jurassic of Wyoming)

May 12th, 2017

This week’s fossils are among the most recognizable. They certainly are popular in my paleontology courses because no one has ever misidentified one. Belemnites (from the Greek belemnon, meaning javelin or dart) were squid-like cephalopods that lived in the Jurassic and Cretaceous Periods. You would never guess their original appearance from the fossils above. These are guards or rostra, internal hard parts that look nothing like the external animal. They are often found in large accumulations called “belemnite battlefields” (Doyle and MacDonald, 1993).
The above image shows a remarkable fossil belemnite in the State Museum of Natural History, Stuttgart, Germany (courtesy of User Rai’ke on Wikimedia). It shows their squidy form and ten equal-sized arms studded with little hooks for holding prey. They probably ate small fish and invertebrates.
The guard or rostrum is solid calcite at its distal end with a phragmocone (chambered shell) at the other. This phragmocone is only rarely preserved. The rostrum above is from the Zohar Formation (Jurassic) of the Golan in northern Israel near Neve Atif.

Belemnites have played an important role recently in sorting out Mesozoic climate change. Their solid calcitic rostra are ideal for examining stable isotopes that fluctuated with water temperature. Dera et al. (2011) showed that the Jurassic had significant climate variations based on the isotopes in belemnite fossils.

Belemnites have a long history in folklore. The English called them “thunderbolts” because they thought they were formed by lightning strikes. The Scottish knew them as “botstones” that cured horses of various ailments. The Swedish thought they were “gnome candles”. The Chinese called them “sword stones”. Much more prosaically, the belemnite is the state fossil of Delaware.
An engraving of belemnite rostra by Captain Thomas Brown (1889).


Brown, Captain T. 1889. An atlas of fossil conchology of Great Britain and Ireland. With descriptions of all the species. Swan Sonnenschein & Co.

Dera, G., Brigaud, B., Monna, F., Laffont, R., Pucéat, E., Deconinck, J-F., Pellenard, P., Joachimski, M.M., and Durlet, C. 2011. Climatic ups and downs in a disturbed Jurassic world. Geology 39: 215–218.

Doyle, P. and MacDonald, D.I.M. 1993. Belemnite battlefields. Lethaia 26: 65-80.

[Originally published on November 20, 2011.]

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