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

Kirschvink 9419041 最近的高分辨率地磁反转研究引起了激烈的争论，是否他们的过渡虚拟地磁极位置（VGPs）下降沿着两个首选的纵向带，一个集中在美洲和澳大拉西亚的对映之一。 如果这些优选带确实是真实的，则表明过渡场的几何形状受地核/地幔边界的地质构造的控制。 然而，这些数据的替代解释包括建议，条带是一个人工制品的过程中，通过沉积物获得其reversible磁化，和/或人为的非随机分布的采样点。 要解决这些问题，就需要详细研究更多的高分辨率地磁反转记录，特别是位于数据稀缺的优选纵向带内的地点的记录。 先前在加州南部死亡谷的Confidence Hills的上新世-更新世湖泊沉积物上进行的工作提供了奥杜威事件顶部和底部反转的多个高分辨率记录。 此外，地层的构造变形使其易于区分现今磁场方向和特征方向，并允许在过渡方向上进行经典的古地磁“褶皱试验”。 这些结果表明，这两个反转是完全不同的-低奥杜威是一致的限制的中间VGP方向的澳大拉西亚地区，而VGP从上奥杜威谎言90度远离这些频带。 PI将扩展此详细研究，并将其与Reunion和Jaramillo亚时相相关的逆转进行比较。 这是获得足够数量的完全可靠的数据的唯一方法，并应提供纵向约束假设的关键检验。 ****

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. ****