Multiple High-resolution Records of Geomagnetic Field Reversals from Plio-Pleistocene Sediments in Confidence Hills, Death Valley, California

Kirschvink 9419041最近对地磁逆转的高分辨率研究引起了激烈的争论，争论的焦点是它们的过渡虚地磁极位置(VGP)是否落在两个首选的纵向带上，一个以美洲为中心，另一个以澳大拉西亚为中心。如果这些优势带确实存在，则表明过渡场几何形状受核/地幔边界的地质构造控制。然而，对这些数据的另一种解释包括，条带是沉积物获得剩余磁化过程的人工产物，和/或采样点的非随机分布的人工产物。要解决这些问题，将需要详细研究额外的高分辨率地磁逆转记录，特别是在数据稀缺的首选纵向频带内的地点。以前在加利福尼亚州南部死亡谷的信心山中进行的上更新世湖泊沉积工作，提供了奥杜瓦伊事件顶部和底部反转的多个高分辨率记录。此外，地层的构造变形使现今磁场方向和特征方向易于区分，并允许在过渡方向上进行经典的古地磁‘褶皱测试’。这些结果表明，这两个反转是完全不同的--下Olduvai与中间VGP方向到澳大拉西亚地区的限制是一致的，而来自上Olduvai的VGP与这些带成90度角。PI将把这项详细的研究和比较扩展到与留尼汪岛和Jaramillo亚克伦有关的逆转。这是能够获得足够数量的完全可靠数据的唯一方法，并且应该提供对纵向约束假说的关键检验。****

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. ****