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.


Wilson, Mark




Geology | Paleontology | Sedimentology


Utah, Bajocian, Bivalve, Communities, Carmel Formation, Jurassic

Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis Exemplar



© Copyright 2020 Evan L. Shadbolt