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Sequence Stratigraphy of the Middle Cambrian Marjum Formation: Response of Sedimentary Facies and Biota to Sea Level Changes

Douglas Smith

Utah State University Geology Department

Logan, Utah

[email protected]

The Marjum Formation provides an insight into the transition from a carbonate ramp to platform in an embayment that existed in southwestern Utah during the Middle Cambrian. Lithologic and faunal characteristics will provide information on the sequence stratigraphy of the Marjum Formation. Sections of the Marjum Formation and its equivalent have been measured in shallow platform (Drum Mountains), intermediate (Wheeler Amphitheatre), and deep ramp (Marjum Pass) environments. At these locations, the Marjum Formation consists mainly of calcisiltites, shales, limestone-rhythmites, bioherms, and some intraclastic, oolitic and oncolitic wacke-packstones. A significant number of horizons were found to contain prolific amounts of polymerid and agnostid trilobites. Identification of specific species within these horizons will aid in constraining times of deposition. Facies patterns, lithology, and fossil content will facilitate identification of bounding surfaces, parasequences, and systems tracts. These features will be correlated across the embayment and used to identify responses of different sedimentary environments to fluctuations in sea level. Rates and magnitudes of sea level changes will be determined using lithology, body and trace fossils, TOC, and stable carbon isotopes. Understanding the controls on facies distribution and biostratigraphy within the Marjum Formation will result in the development of improved hydrocarbon exploration models.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid