Kirschvink 9419041 Recent high-resolution studies of geomagnetic reversals have generated heated debate concerning whether or not their transitional Virtual Geomagnetic Pole positions (VGPs) fall along two preferred longitudinal bands, one centered over the Americas and an antipodal one over Australasia. If these preferred bands are indeed real, it would suggest control of the transitional field geometry by geological structures at the core/mantle boundary. However, alternative interpretations of these data include the suggestion that the banding is an artifact of the process through which the sediments acquire their remanent magnetization, and/or an artifact of the non-random distribution of sampling sites. Resolution of these questions will require the detailed study of additional high-resolution records of geomagnetic reversals, particularly from sites located within the preferred longitudinal bands where data are scarce. Work conducted previously on the Plio-Pleistocene lake sediments in the Confidence Hills of southern Death Valley, California, has provided multiple, high-resolution records of the top and bottom reversals of the Olduvai event. In addition, tectonic deformation of the strata make it easy to distinguish the present field direction form the characteristic directions, and allow a classic paleomagnetic 'fold test' to be conducted on the transitional directions. These results demonstrate that the two reversals are quite different -- the lower Olduvai is consistent with confinement of the intermediate VGP directions to the Australasian regions whereas VGPs from the upper Olduvai lie 90 degrees away from these bands. The PI will extend this detailed study and comparison to reversals associated with the Reunion and Jaramillo subchrons. This is the only way in which a sufficient quantity of fully reliable data can be acquired, and should provide a critical test of the longitudinal confinement hypothesis. ****
