Abstract

The Lower Co-op Creek Limestone Member of the Carmel Formation is a sedimentary unit that formed at the southernmost tip of the epicontinental Sundance Seaway during the Bajocian stage of the Jurassic period. This member contains two distinct microbial structures: a laterally-linked hemispheroid stromatolite, and a unique mesoscopic thrombolite. There is a lack of information regarding the microbial structures of the Carmel Formation; this thesis seeks to remedy that by providing a more in-depth analysis of both the morphology and formational environment of stromatolites and thrombolites in the Carmel Formation, and by conducting a cyclical analysis on the laminae present in the laterally-linked hemispheroid stromatolites. The goal of this thesis is to determine whether or not stromatolite laminae can be used to create a chronology of weather and tidal events in the Sundance Seaway. Stromatolite laminae in the Lower Co-op Creek Limestone Member record tidal change; the distinct composition of stromatolite laminae is the result of a period of either high or low tide. Low tide, micrite-rich laminae are typically thinner by an average of 30 µm than high tide, grain-rich laminae. However, there is no statistically significant model which predicts changes in stromatolite lamination over time. Additionally, the presence of weather events cannot be determined from the data collected in this thesis. The lack of applicable statistically significant harmonic models is attributed to noise in the stromatolite laminae dataset due to unknown variables, a lack of data, and human error. Microbial mats of the Lower Co-op Creek Limestone Member likely obtained magnesium ions from hypersaline seawaters, instigating microbial growth and allowing for the formation of diagenetic dolomite crystals in stromatolite laminae. While associated with a biologically isolated environment and unique to the Bajocian, the thrombolite morphology present in the Carmel Formation likely formed in a shallow marine, slightly turbulent thrombolitic reef facies due to inherent similarities with earlier thrombolite specimens. The hypothesis that stromatolite laminae can be used to create a chronology of weather and tidal events in the Sundance Seaway is not fully supported by statistical cyclical analysis conducted on thin section data from 5 stromatolite outcrops, containing a total of 616 laminae across 7 thin sections.

Advisor

Wilson, Mark

Department

Geology

Disciplines

Geology | Paleontology | Sedimentology

Keywords

Stromatolites, Thrombolites, Utah, Carmel Formation, Bajocian, Middle Jurassic, Laminae

Publication Date

2021

Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis

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© Copyright 2021 William M. Santella