Since the 1950s, inertial interchange true polar wander (IITPW) has been recognized as a phys- ically viable process in which the entire solid Earth may shift as much as 90. with respect to the spin axis in 106-107 years. Nevertheless, IITPW events have not been demonstrated convincingly in the geologic record for two main reasons: (1) studies have been plagued by uncertainties in the age, quality, and correlation of paleomagnetic poles collected from various types of rocks on different continents, and (2) no serious effort has been made to link the effects IITPW may have on the stratigraphic record due to changes in global climate structure, ocean circulation, sea level, nutrient cycling, organic carbon burial, methane storage, and continental weathering. The IITPW hypothesis provides a series of testable predictions because an IITPW event will affect every continent differently, but predictably, depending on the continent's changing position relative to Earth's spin axis. For example, the further a craton is from the inertial interchange axis (Imin), the greater the changes in sea level and paleomagnetic inclination will be. Maloof et al. [70] identified an interval of relatively light carbon isotopes in *800 million year old (Ma) carbonate rocks of East Svalbard (Norway) that is bracketed by large shifts in relative sea level and paleomagnetic orientation. They argue that the coincidence of these isotopic, magnetic, and eustatic changes can be explained by rapid shifts in global paleogeography associated with a pair of inertial interchange true polar wander IITPW events. The same isotopic interval has also been identified in Bitter Springs Formation equivalents in Australia. Australia is an ideal locality to test the IITPW hypothesis because most models of middle Neoproterozoic paleogeography place Australia further away and in a different direction from Imin than East Svalbard. Therefore, the stratigraphy spanning this interval in Australia should show unique paleomagnetic and sea level shifts that are both larger in amplitude and different in shape than those documented in Svalbard. This proposal will test the IITPW hypothesis through an integrated investigation of the physical, geochemical, and magnetic stratigraphy of the Bitter Springs Stage in Australia. Intellectual Merit. All paleogeographic reconstructions to date rely on two fundamental as- sumptions: (1) the motion of continents is dominated by plate tectonics, and (2) Earth's magnetic field is geocentric and dipolar on time scales *104 yrs. Documenting IITPW in the geologic record would have profound implications for interpreting plate motions over the last 2 billion years. Fur- thermore, documenting the sedimentological and biogeochemical consequences of an IITPW event at *800 would shed light on the equilibrium Earth System prior to the first of at least three major Neoproterozoic glaciations. A falsification of the IITPW hypothesis would lead to an equally im- portant suite of results documenting ancient secular variation of the geomagnetic field or perhaps an unexpected Neoproterozoic paleogeography. Broader Impacts. (1) The distribution of continents is crucial to any first order understanding of general fluid circulation on the Earth. Therefore, the science of developing geologically and paleomagnetically realistic paleogeographies is necessary for generating models of ancient climates and for understanding the limits of global change. (2) This proposal will be the start of a research project led by the PI and involving laboratory collaborations with MIT (S.A. Bowring, B.P. Weiss), Yale (D.A.D. Evans), and Caltech (J.L. Kirschvink). These collaborations not only will produce important science, but also will begin a technology transfer to Princeton, where the PI will set up a paleomagnetics laboratory in 2006. (3) Study of the Bitter Springs Stage is an ideal student project because it requires the knowledge of a suite of complementary subjects, from basic field mapping and sequence stratigraphy to paleomagnetism, stable and radiogenic isotope systems, and whole-Earth geophysics. The PI will recruit underrepresented students to receive extensive training in field and analytical methods, and to play active roles in discovery-based research science.
