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

最近对地磁倒转的高分辨率研究引起了激烈的争论，即它们的过渡虚拟地磁极位置（VGPs）是否沿着两个首选的纵向带，一个以美洲为中心，一个对跖点在澳大利亚。如果这些优先带确实存在，则表明过渡场几何形状受核幔边界地质构造的控制。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，需要对地磁倒转的额外高分辨率记录进行详细研究，特别是在数据稀缺的优选纵向带内的地点。先前在加利福尼亚死亡谷南部信心山的上新世-更新世湖泊沉积物上进行的工作，已经提供了Olduvai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当前磁场方向和特征方向，并可对过渡方向进行经典的古地磁“褶皱试验”。这些结果表明，这两次反转是完全不同的——Olduvai下部与中间VGP方向限制在澳大拉西亚地区一致，而Olduvai上部的VGP则与这些带相距90度。PI将把这项详细的研究和比较扩展到与留尼旺和哈拉米洛亚时相关的逆转。这是能够获得足够数量的完全可靠的数据的唯一方法，并且应该为纵向约束假设提供一个关键的检验。* * * *

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. ****