Characterization of the Cretaceous Normal Superchron

数值模拟表明，稳定的（非反转的）地球发电机可能更有效地产生更强的偶极子场，这种情况可能来自于穿过核-地幔边界的有利的横向变化的热通量模式。因此，了解地球发电机是如何工作的，以及推断过去的下地幔条件，以找出白垩纪正常超时（CNS）期间的平均场强是否真的异常高，这对了解地球发电机如何工作和推断过去的下地幔条件都很重要。研究人员提出了一项重要的工作，以表征古磁场强度和方向色散在中枢神经系统。他们计划在马达加斯加、韩国、哥斯达黎加、北格陵兰岛和斯瓦尔巴群岛进行实地工作，收集在CNS期间、之前和之后爆发的熔岩样本。他们还将收集哥伦比亚河高原中新世中期（高反转率时期）的玄武岩。本研究试图回答以下仍未解决的重要问题：(i)中枢神经系统期间的平均强度是异常高、低还是无异常；（ii）中枢神经系统内部是否存在长期强度趋势；（iii） 104年数量级的强度波动与近期野外的强度波动相似还是明显不同。关于CNS发生的另一种猜想是，地磁场可以突然切换到非反转状态，仅仅是由于在地核中运行的高度非线性地球动力过程。研究人员将通过观察在中枢神经系统的开始或结束之前是否存在可识别的古强度或分散的时间趋势来验证这一假设。这个国际合作项目包括让资深科学家、博士后和学生一起工作，分享他们的知识和想法。科学结果将在目前正在美国国家科学基金会支持下开发的综合古地磁数据库中提供，并将在期刊文章中传播。白垩纪正常超时纪的地磁场特征也具有社会意义和广泛的科学界的兴趣，他们试图了解地幔的行为，并确定羽流、大火成岩省的形成和气候变化之间的潜在因果关系。

Numerical simulations have suggested that a stable (non-reversing) geodynamo may be more efficient at generating stronger dipole fields, and that this condition can arise from a favorable pattern of laterally varying heat flux across the core-mantle boundary. Thus it is important both for understanding how the geodynamo works and for inferring past lower-mantle conditions to find out whether or not the average field strength really was unusually high during the Cretaceous Normal Superchron (CNS), the span of time from around 121 to 83 Ma during which the geodynamo stopped reversing. The investigators propose a major effort to characterize the paleomagnetic field intensity and directional dispersion during CNS. They plan field work to collect lava samples in Madagascar, Korea, Costa Rica, N. Greenland, and Svalbard erupted during, just before, and just after the CNS. They will also collect basalt of mid-Miocene age (a time of high reversal rate) from the Columbia River Plateau. This research seeks answers to the following important questions that are still unresolved: (i) whether the average intensity during the CNS was unusually high, low or unexceptional, (ii) whether there were long-term intensity trends within the CNS, and (iii) whether the fluctuation of intensity on time scales of order 104 yr resembled that of the recent field or was distinctly different. An alternative conjecture for the occurrence of the CNS is that the geomagnetic field can switch abruptly into and out of a non-reversing state, simply by virtue of the highly nonlinear geodynamo processes operating in the core. The investigators will test this hypothesis by seeing whether there is an identifiable temporal trend in paleointensity or dispersion leading up to the beginning or end of the CNS. This international collaborative project includes bringing senior scientists, postdocs and students to work together and share their knowledge and ideas. The scientific results will be made available in the comprehensive paleomagnetic database currently under development with NSF support and will be disseminated in journal articles. The character of the geomagnetic field during the Cretaceous Normal Superchron also has societal relevance and interests a broad scientific community trying to understand mantle behavior and determine potential causal relationships between plumes, large igneous provinces formation and climatic changes.