Characterization of the Cretaceous Normal Superchron

数值模拟表明，一个稳定的（不可逆的）地球发电机可能会更有效地产生更强的偶极场，这种情况可能会出现在一个有利的模式横向变化的热通量的核幔边界。因此，无论是为了了解地球发电机是如何工作的，还是为了推断过去的下地幔条件，找出白垩纪正常超时（CNS）期间的平均场强是否真的异常高都很重要，在此期间，地球发电机停止逆转的时间跨度约为121至83 Ma。研究人员提出了一个主要的努力，以表征古磁场强度和定向分散在CNS。他们计划在马达加斯加、韩国、哥斯达黎加、新西兰和新西兰等地进行野外工作，收集熔岩样本。格陵兰岛和斯瓦尔巴特群岛在CNS爆发期间，就在CNS爆发之前，就在CNS爆发之后。他们还将从哥伦比亚河高原收集中新世中期（一个高逆转率的时期）的玄武岩。本研究旨在回答以下重要的问题，仍然没有解决：（一）是否在CNS的平均强度异常高，低或不寻常的，（二）是否有长期的强度趋势的CNS内，和（三）是否波动的强度在时间尺度上的顺序104年类似于最近的字段或明显不同。另一种关于CNS发生的推测是，地磁场可以突然地进入和脱离不可逆状态，这仅仅是由于在地核中运行的高度非线性地球发电机过程。研究人员将检验这一假设，看看是否有一个可识别的时间趋势，在古强度或分散导致的开始或结束的中枢神经系统。这个国际合作项目包括将资深科学家，博士后和学生聚集在一起，分享他们的知识和想法。科学结果将在目前正在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。白垩纪正常超时期间地磁场的特征也具有社会相关性，并引起广泛的科学界的兴趣，试图了解地幔行为并确定羽流，大火成岩省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.