Sedimentation, Stratigraphy, and Paleoenvironments
of the Lower Members of the Carmel Formation
(Middle Jurassic, southwestern Utah)

Kirsten Bannister

The Middle Jurassic Carmel Formation in southwestern Utah is composed of shallow-marine to peritidal sedimentary rocks, including complexly interbedded limestones, siltstones, sandstones, and evaporites that accumulated during two major transgressive cycles. The Carmel is composed of seven, second-order shallowing-upward cycles and is believed to have been deposited in off shore and shoreline environments near the southern margin of the Middle Jurassic Western Interior seaway (Carmel seaway) that extended into southern Utah from Canada.

Previous interpretations separated the Carmel into six members (A-F), each of which represents a portion of the shallow marine peritidal system. Members A through C were studied for this report. Member A, an oolitic shoal assemblage, represents the highest energy environment preserved in the Carmel Formation, and contains fossil fragments of gastropods and bivalves; the fossils of this member are most likely transported and reworked remains derived from elsewhere in the system by storms.

Members B and C are indicative of a restricted lagoonal environment grading into an intertidal sequence. Member B represents a hyper saline lagoon and represents an arid laggon with little or no water circulation occurred. It lacks fossils, although a variety of sedimentary structures are present, including small scale ripple marks, laminated siltstone and mudstone coated with gypsum hopper crystals. Member C includes sedimentary structures and fossils representing an intertidal onshore zone. Structures include crossbedding on small and large scale, ripple marks, desiccation cracks. An array of fossils including bryozoans, crinoids, and bivalves are found within a variety of lithologies.

Overall, the Carmel Formation represents the margins of a much larger, intra-cratonic marine basin and records periods of high to low energy conditions and normal to hypersaline marine to peritidal environments.