Sequence Stratigraphy, Chemostratigraphy, and Biostratigraphy of Lower Ordovician Units in Northeastern and Western Central Utah: Regional Implications

• Main Author: Davis, Colter R.
• Format: Text
• Language: unknown
• Published: DigitalCommons@USU 2017
• Subjects: sequence stratigraphy; chemostratigraphy; biostratigraphy; lower ordovician; northeast utah; western utah; central utah; regional implications; Geology; Argentine; Newfoundland
• Online Access: https://digitalcommons.usu.edu/etd/5879; https://doi.org/10.26076/2532-4bce; https://digitalcommons.usu.edu/context/etd/article/6943/viewcontent/2017_Davis_Colter.pdf

The Lower to Middle Ordovician Garden City Formation and Pogonip Group are mixed carbonate and sandy marine rocks deposited on the western margin of ancestral North America. The Garden City Formation was deposited in the Northern Utah Basin and the Pogonip Group was deposited in the Ibex Basin. These two basins experienced different rates of subsidence that resulting in significant thickness differences between rock units and different rock types related to sea level change. This study provides a unique opportunity to examine changes in rock types, rock chemistry, and fossil types as sea level changed within two separate basins in Utah. Nine cycles of sea level rise and fall have been identified within rocks of the Pogonip Group. Similar sea level cycles were located within the rocks of the Garden City Formation using fossils and rock chemistry trends that occur within both rock units. The bases of these sea level cycles often contain high concentrations of sandy and silty materials. Sea level cycles are expressed as rock packages with silty/sandy shallow water rock types at the base that transition into deeper water rock types at the top of the package. Sand and silt increase within rock types over time which may indicate a gradual overall drop in sea level. New carbon isotope data from the Garden City Formation and the Pogonip Group range from -2.9 to 1.2 per mil and -2.2 to 0.6 per mil, respectively. Four distinct carbon isotope trends are recognized in both sections indicating a correlation between the two areas. This new carbon isotope data likely represent Ordovician global primary seawater chemistry based on the correlation of similar carbon isotope data from the Argentine Precordillera and western Newfoundland.