Sequence Stratigraphy of the Middle Cambrian Marjum Formation: Response of Sedimentary Facies and Biota to Sea-Level Changes
Date of Award:
Master of Science (MS)
W. David Liddell
W. David Liddell
Research on the Marjum Formation provides insight into facies transitions in the House Range embayment of southwestern Utah during the Middle Cambrian. Sections of the Marjum Formation and equivalents were measured in strata representing shallow- (Drum Mountains), intermediate- (Wheeler Amphitheater), and deep-ramp (Marjum Pass) environments. This traverse across the embayment reveals strong litho- and biofacies changes. The Drum Mountains strata (343 m thick) are dominated by thick-bedded shallow-water limestone facies containing polymerid trilobites and stromatolites. The Wheeler Amphitheater locality (392 m thick) provides an example of intermediate deposits between deep-water and shallow-water environments and is characterized by limestone and subordinate shale facies containing polymerid and agnostid trilobites, brachiopods, and sponge spicules. The Marjum Pass locality (424 m thick) contains equal parts shale and limestone facies with abundant fossils that include polymerid and agnostid trilobites, sponge spicules and soft bodied algae, representing deep-water environments.
Migration of litho- and biofacies observed within Marjum Formation sections across the embayment shows carbonate ramp build-up and progradation from the Drum Mountains to the Swasey Peak, Wheeler Amphitheater area. Lateral migration of deepwater shale and rhythmite-producing turbidite facies can also be observed on a larger timescale from the Drum Mountains, during the early Bolaspidella time (Wheeler Formation deposits), to the Marjum Pass area (Marjum Formation deposits) by late Bolaspidella time.
The Marjum Formation records two, third order shoaling-upward sequences. Fourth, fifth, and higher-frequency (rhythmite) cycles superimposed on these third order sequences can also be identified within the formation and are best preserved within the relatively deep-water deposits at Marjum Pass.
Identification of sampled trilobites allowed correlation of known faunal turnovers found by Robison and Vorwald with observed strata and systems tracts from this study. Stratigraphic locations of trilobite faunal turnovers were found to be associated with transgressive systems tracts in the Drum Mountains and Marjum Pass localities. Faunal turnover associated with significant sea-level events within these systems tracts suggests change in water depth altered the local environment forcing extinction and/or migration of organisms. Peak values of total organic carbon (TOC) at each measured section were also found to have a close relationship with maximum flooding zones. Associations of peak TOC values and faunal turnovers with significant sea-level events demonstrate the value of these tools for correlation across the embayment.
Smith, Douglas D., "Sequence Stratigraphy of the Middle Cambrian Marjum Formation: Response of Sedimentary Facies and Biota to Sea-Level Changes" (2007). All Graduate Theses and Dissertations. 6744.
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