Precambrian-Cambrian Sedimentology, Stratigraphy, and Paleontology in the Great Basin (Western United States)
- Author(s): Sappenfield, Aaron Dale
- Advisor(s): Droser, Mary L.
- et al.
Thick accumulations of Neoproterozoic and early Phanerozoic strata are distributed throughout much of the arid continental interior of western North America, providing an expansive and well-exposed archive of this important time in Earth’s history. The information presented herein supplements evaluations regarding the utility and limitations of this archive by providing an integrated sedimentological, paleontological, and geochronological description for Precambrian-Cambrian strata exposed in the area and by reporting the discovery of new trace and body fossils housed there.
The first chapter of this dissertation describes the sedimentology and stratigraphy of Precambrian-Cambrian conglomeratic and sandstone-dominated units exposed in the central Great Basin. Seven localities distributed along a 600 km north-south transect are described using existing data supplemented by information compiled from more than 5 kilometers of newly measured stratigraphic section. These data collectively facilitate development of a unified framework regarding the nature and timing of deposition in the area while also providing a series of stratigraphic tie points applicable to both regional and global correlation schemes. The second chapter reports the discovery of Zoophycos burrows from early Cambrian sediments exposed in eastern California. The Zoophycos ichnogenus is a well-known and considerably-studied deposit feeding trace fossil that, like other deposit feeding burrows, had not previously been reported in pre-Ordovician strata, making these the oldest examples of this celebrated burrow. Most importantly, Zoophycos burrows reported herein provide the earliest definitive evidence of deposit feeding to date, pushing back the advent of this feeding strategy to near the Precambrian-Cambrian boundary. This dissertation’s final chapter reports medusozoan macrofossils from the early Cambrian Zabriskie Quartzite as the earliest fossil evidence of cnidarian medusae and the oldest example of a metazoan mass stranding event currently on record. Given that these are fossils of nonmineralized forms, the Zabriskie fossils also advance reconstruction of the taphonomic dynamics responsible for the preservation of soft-bodied macrofauna in nearshore facies through the Precambrian-Cambrian transition. The features of this comparison imply that a preservational bias may have been introduced near the onset of the Phanerozoic, shifting the predominant environment for soft-bodied preservation in sandstone facies from subtidal environments to the supralittoral zone.