Structural and Geochronological Investigations of Neoproterozoic Rifting in Southwestern Laurentia

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AbstractThe Cambrian explosion and its Neoproterozoic precursors occurred in a context of extraordinary environmental perturbations, including extreme fluctuations between warm and cold climate, possible True Polar Wander, and the reorganization and eventual breakup of a supercontinent. The tectonic events may have been primary causes of both climatic and polar wander events. Despite significant progress over the last decade, the lack of absolute age control on most of these successions has severely limited testing new ideas owing to a lack of reliable global correlations and a chronology of rifting and continental plate motions on a par with the Phanerozoic. The PI proposes to continue a program of geological mapping, stratigraphic studies, and U/Pb dating of the relatively complete Neoproterozoic succession in southwestern Laurentia. Thus far, he has established a rudimentary structural and stratigraphic framework in a key area where the section records two major glacial intervals and their cap carbonate sequences (presumably correlative with the Sturtian and Marinoan events in Australia), as well as tectonism that led to the development of the southwest Laurentian passive margin. In addition, he has discovered three new ash horizons within this sequence, and found abundant authigenic xenotime in some ten major sand bodies spanning the Neoproterozoic. He will attempt to date these units with conventional TIMS analysis and microbeam analytical techniques on both zircon and xenotime.The broader impacts of this project include: i) graduate training of a doctoral student in geology at Caltech; ii) involvement of multiple institutions, including St. Andrews University, UCLA, MIT and the University of Arizona in the research effort, including improvement of national infrastructure for dating authigenic minerals in sandstones; in particular, development of a xenotime analytical standard in the course of this research, if we are successful, will be of immediate benefit to many researchers around the world; iii) presentations to the public in Death Valley National Park, which will contribute to greater public understanding of the significance of the natural resources in the park; and iv) the research may contribute to understanding how the biosphere responds to the extremes of global change, and therefore contribute to evolving international debate regarding global warming and related issues.