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

摘要

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 die supercontinent in association with the ～800 Ma Bitter Springs carbon isotope event. To further constrain early Neoproterozoic paleogeogra phy and to test proposed rapid rotations, we have developed sequence- and chemo-stratigraphically 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 superconti nent 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 authigeni-cally 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 pyrrho-tite in carbonates of die 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.