Jurassic bivalves in a shallow epicontinental seaway: Evan Shadbolt’s Independent Study thesis

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or labwork to collect data, and then spend their senior years finishing extensive Senior I.S. theses. This year we have the COVID-19 pandemic to deal with in the spring, so our students have not had a chance to publicly present their hard work and scientific ideas. Some, then, will be writing blog posts like this. The text and images below are from Evan Shadbolt (’20) who worked with me on Team Utah 2019. The picture above shows Anna Cooke (’20), Evan Shadbolt (’20) and me at an outcrop of the Carmel Formation (Middle Jurassic) near Gunlock, Utah, in March 2019. And now Evan takes over —

The Jurassic bivalves Plagiostoma ziona (right) and Camptonectes stygius (left).

The Carmel Formation of the Middle Jurassic has many mysteries. One of these enigmas is its bivalves. The formation contains the famous oyster balls called ostreoliths. Despite bivalves making up 80 percent of the fossils found in the Carmel Formation, it is not understood how the bivalves lived in this community. The formation is located in southwestern and central Utah. It was deposited when an epicontinental seaway covered most of Utah. The paleoclimate of Utah was hot and dry, which meant that the environment was evaporite heavy. This also meant that the seawater at the southernmost extent of the seaway in Utah was hypersaline. The bivalves lived in normal marine conditions, but there was little biological diversity. During the Jurassic, there was a calcite sea, and aragonite shells were dissolved away.

In mid-March 2019, I went with a College of Wooster group to southwestern Utah. There we collected bivalves from the Carmel Formation and identified them. Then we researched them and constructed a systematic paleontological overview of the known bivalves. We have possibly identified ten different types of bivalves, and three distinct communities in the Co-op Creek Limestone Member of the Carmel Formation. The communities were the Plagiostoma community, Camptonectes community, and the Liostrea Community. Each of these communities was dominated by a unique bivalve. The Liostrea community was associated with hardgrounds, while the Camptonectes and Plagiostoma communities lived in the same type of environment. We also hypothesize that the area was frequently hit by storms, which caused damage to these communities. The communities were possibly ephemeral, but the bivalves themselves could be considered opportunists. The communities in the Carmel Formation were also small and patchy throughout the area. The bivalve genera that appeared in the Carmel Formation were common in other Jurassic bivalve communities around the world.

My IS experience was fun and unique. Getting to travel to Utah and collect fossils with Team Utah 2019 was a rewarding experience. We spent a week there exploring the Utah environment. Luckily, I was able to collect my fossils over the spring break of my Junior year, so I could start my research early. I felt I was well prepared to start my IS, thanks to the help of the Team Utah 2018 and my advisor, Dr. Wilson. The IS writing experience was not as stressful as I thought it would be. The deadlines were all reasonable and even if I felt I did not do enough work that week, Dr. Wilson was always fine with the amount of work. I feel that the Earth Sciences department at The College of Wooster properly prepare you for writing your IS.

A reconstruction of the bivalve community sampled at Water Tank.

A reconstruction of the bivalve community sampled at Eagle Mountain Ranch.