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

Kirschvink 9419041 最近对地磁反转的高分辨率研究引发了激烈的争论，即它们的过渡虚拟地磁极位置 (VGP) 是否落在两个首选的纵向带上，一个以美洲为中心，另一个以澳大利亚为中心。 如果这些优选带确实是真实的，则表明过渡场几何形状是由核/地幔边界处的地质结构控制的。 然而，对这些数据的另一种解释包括这样的建议：条带是沉积物获得其剩余磁化强度的过程的伪影，和/或采样点非随机分布的伪影。 要解决这些问题，需要对地磁反转的额外高分辨率记录进行详细研究，特别是来自数据稀缺的首选纵向带内的地点。 之前对加利福尼亚州死亡谷南部信心山的普里奥-更新世湖沉积物进行的研究，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，地层的构造变形使得很容易区分当前磁场方向和特征方向，并允许对过渡方向进行经典的古地磁“褶皱测试”。 这些结果表明，这两个反转有很大不同——下奥杜瓦伊与中间 VGP 方向对澳大利亚地区的限制是一致的，而上奥杜瓦伊的 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旺亚时间和哈拉米略亚时间相关的逆转。 这是获得足够数量的完全可靠数据的唯一方法，并且应该为纵向约束假设提供关键检验。 ****

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. ****