American Journal of Science CONSTRAINTS ON NEOPROTEROZOIC PALEOGEOGRAPHY AND PALEOZOIC OROGENESIS FROM PALEOMAGNETIC RECORDS OF THE BITTER SPRINGS FORMATION, AMADEUS BASIN, CENTRAL AUSTRALIA

The supercontinent Rodinia is hypothesized to have been assembled and positioned in tropical latitudes by the early Neoproterozoic Era. Paleomagnetic data from limestones of Svalbard and basaltic dikes of South China have been interpreted to record rapid changes in paleogeography driven by true polar wander that may have rotated the supercontinent in association with the 800 Ma Bitter Springs carbon isotope event. To further constrain early Neoproterozoic paleogeography and to test proposed rapid rotations, we have developed sequenceand chemostratigraphically constrained paleomagnetic data from the Bitter Springs Formation of the Amadeus Basin of central Australia. A new paleomagnetic pole for the post–Bitter Springs stage 770 Ma Johnny’s Creek Member (Bitter Springs Formation) provides a positive test for a long-lived history of Australia and Laurentia in a single supercontinent as its similar position to late Mesoproterozoic north Australia poles reproduces the closure of the Laurentian “Grenville Loop.” This new pole also provides support for the hypothesis that there was significant rotation between north and south west Australia at the end of the Neoproterozoic as this rotation brings the south west Australia 755 Ma Mundine Well pole into much closer proximity to the north Australia Johnny’s Creek pole. Syn–Bitter Springs stage carbonates of the Love’s Creek Member of the formation contain a well-behaved remanence held by magnetite. The direction of this remanent magnetization falls on the Cambrian portion of Australia’s apparent polar wander path suggesting that the magnetite may have formed authigenically at that time. If primary, the Love’s Creek direction is consistent with the true polar wander hypothesis for the Bitter Springs stage, is internally consistent with the relative sea level changes inferred from the formation, and can constrain Australia to a SouthWest North America East AnTarctica (SWEAT) fit. A remanence held by pyrrhotite in carbonates of the Bitter Springs Formation corresponds to the apparent polar wander path of Australia at 350 Ma. This component can be used to constrain the history of the Devonian-Carboniferous Alice Springs Orogeny as it demonstrates that regional folding of basinal sediments occurred prior to 350 Ma, but that the latest stages of tectonism in the hinterland drove fluids through the sediments that altered redox conditions to favor pyrrhotite precipitation. * Department of Geosciences, Princeton University, Guyot Hall, Washington Road, Princeton, New Jersey 08544, USA ** Division of Geological & Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA *** Department of Geology & Geophysics, Yale University, New Haven, Connecticut 06520, USA § Department of Earth & Planetary Sciences, McGill University, Montreal, Quebec H3A 2A7, Canada §§ Department of Earth & Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, Illinois, 60208 USA † Corresponding author’s present addresses: Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, California 94720-4767 and Winchell School of Earth Sciences, 100 Union Street SE, University of Minnesota, Minneapolis, Minnesota 55455; Email address: [email protected] [American Journal of Science, Vol. 312, October, 2012, P. 817–884, DOI 10.2475/08.2012.01]