The Proterozoic Eon, occupying nearly half of Earth history from 2.5 to 0.5 billionyears ago, is marked at its beginning and end by dramatic events in the tectonic,paleoclimatic, chemical, and biological evolution of the planet. The onset of theProterozoic Eon witnessed the emergence of continents and perhaps the introduction ofplate tectonics, Earth's first extensive ice ages, oxygenation of the hydro-atmosphere, anddevelopment of eukaryotes. The end of the Proterozoic Eon is characterized bysupercontinental turnover and very rapid continental drift rates, a series of glaciationswhich left their marks on every continent, the rise of atmospheric oxygen to sustainmulticelled organisms, and an evolutionary "explosion" of animal life.
Establishment of coherent paleogeographies of these important intervals is a crucialprerequisite for describing the events and understanding the underlying processes.Paleomagnetism is the most direct quantitative method for charting continental drift throughtime. The purpose of this dissertation is to use paleomagnetism to constrain tectonic andpaleoclimatic processes at the beginning and end of the Proterozoic Eon.
A paleomagnetic study of Early Cambrian rocks in western Mongolia finds somewhatambiguous results and addresses tectonic models of the Paleo-Asian Ocean. Review of themost reliable studies among the Proterozoic-Cambrian global paleomagnetic databasepermits the hypothesis that an episode of inertial interchange true polar wander (TPW)occurred in Early Cambrian time. The Cambrian TPW event and a previously hypothesizedOrdovician-Devonian TPW migration share a common axis and suggest the existence oflong-lived mantle mass anomalies inherited from the previous supercontinent, Rodinia.The breakup of Rodinia and subsequent amalgamation of Gondwanaland appear analogousin several ways to the Gondwanaland-Super-Asia supercontinental transition, suggesting a500-600-Myr cyclicity.
An exhaustive review of paleomagnetic and geochronological constraints uponNeoproterozoic glaciogenic deposits fails to find a convincing high-paleolatitudeoccurrence. Detailed study of one of these deposits in South China reveals a reliablepaleomagnetic pole implying a paleolatitude of 34±2°, with both paleoclimatic andpaleogeographic implications. A reliable estimation of 11±5° depositional paleolatitude for2.2-billion-year-old lavas directly overlying a glaciogenic formation in South Africa,extends the occurrence of low-latitude continental ice sheets further back into thePrecambrian.
