Ichnology of the Bright Angel shale formation, Grand Canyon, Arizona: indicators for Middle Cambrian paleoecology

Miller, Anne Elizabeth (2019) Ichnology of the Bright Angel shale formation, Grand Canyon, Arizona: indicators for Middle Cambrian paleoecology. Masters thesis, Northern Arizona University.

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Abstract

The Cambrian Explosion represents a major diversification event for early life that ultimately led to the evolution of modern organisms. Most studies have focused on the remarkable examples of soft-bodied preservation in localities such as the Burgess Shale, Chengjiang, and Sirius Passet. However, studies on the Cambrian ichnological record are lacking. The Bright Angel Shale in Grand Canyon, AZ provides an extensive Middle Cambrian trace fossil record that has been poorly studied. This project aims to redress that gap by studying the trace fossil record of the Bright Angel Shale and relating it to the known record of body fossils in order to add to the understanding of Middle Cambrian shallow marine paleoecology. Fifteen stratigraphic sections, with their corresponding bioturbation index, were measured in the Bright Angel Shale at eleven localities in eastern and western Grand Canyon. Three lithofacies were identified comprising the heterolithic facies, cross-stratified to massive sandstone facies, and maroon sandstone facies. Bioturbation is generally high and ranges significantly throughout the Bright Angel Shale stratigraphic sections showing some cyclicity in eastern Grand Canyon and abrupt changes in western Grand Canyon. Fifteen ichnogenera were identified throughout these sections including three ichnospecies. Ichnogenera were semi-quantified by counting their occurrence in horizons vertically at each stratigraphic section with their corresponding lithofacies and bioturbation index. The trace fossils were also systematically described, each with a discussion on their potential trace makers of known fossils from other Cambrian strata. The eastern Grand Canyon contains higher ichnodiversity, while the west has low ichnodiversity. In both regions of Grand Canyon, Palaeophycus and Teichichnus are the most common ichnogenera. All ichnotaxa from the Bright Angel Shale represent the Skolithos and Cruziana ichnofacies. The depositional environment of the Bright Angel Shale most likely consisted of a tide- and wave-dominated, shallow marine shelf with estuaries, tidal channels, and tidal flats that were often influenced by storm and tidal energy. Potential trace fossil producers of the Bright Angel Shale reveal the prevalence of vermiform organisms such as annelid and priapulid worms. These worms have been identified in the Burgess Shale and Chengjiang lagerstätten, but their record is very small compared to the preponderance of arthropods. The Bright Angel Shale also contains a record relatively high in arthropods, but lacks any record on worms. Overall, the preponderance of vermiform trace makers in the Bright Angel Shale based on the trace fossil record adds to the Cambrian story that worms may have been much more abundant than previously thought.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Bright Angel Shale; Cambrian; Grand Canyon; Ichnology; Paleoecology; Trace Fossils
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	28 Jan 2022 23:16
Last Modified:	28 Jan 2022 23:16
URI:	https://openknowledge.nau.edu/id/eprint/5596

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