Collaborative Research: Testing the Hypothesis of Late Cretaceous True Polar Wobble (TPw)

合作研究：检验晚白垩世真极摆（TPw）假说

• 批准号: 1114432
• 负责人: Joseph Kirschvink
• 金额: $ 25.74万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114432&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Hypothesis; Late

Like a Frisbee, all planets moving freely in space want to spin around an axis called their 'principal moment of inertia'. Any large 'wart' on the planet, or inside it, that is not balanced gravitationally will migrate towards the Equator, forcing the spin axis (the 'poles' of the planet) to 'wander?' relative to its solid mass. This is called 'True Polar Wander' (TPW), and is part of the well-understood physics of many planetary bodies. The entire solid part of the planet wanders at the same time relative to the spin axis, and as such is quite different from the normal motion of tectonic plates here on Earth. A vigorous debate has been raging within the geophysical community for the past decade about the possible existence of a short burst of TPW associated with the end of a long period of geomagnetic Normal polarity, called the Cretaceous Long Nomal Chron, around 84 million years ago. Similarly, small wiggles in the pattern of sea-floor magnetic anomalies at about the same time have been interpreted as a result of an anomalously weak, fluctuating geomagnetic field. Recently, the investigators have obtained higher-resolution fossil magnetic (paleomagnetic) data from the classic Scaglia Rossa lime-stones in Italy which confirm the presence of a major (~20 degree) shallowing of inclination in Chron 33R, whereas coeval data from South Dakota display both persistent declination and inclination anomalies as predicted by the TPW hypothesis. The Italian data also provide provocative hints that there might be a series of short, ~million-year scale oscillations superimposed on this long-term trend. The PIs call these 'True Polar wobbles' (TPw) to distinguish them from longer time-scale TPW motions which have been the focus of most previous geophysical investigations. The entire solid Earth may have been doing something akin to a geological 'Hula dance', according to the PIs. However, distinguishing these hypotheses requires a globally distributed set of high-quality, high-resolution magnetic data that can be compared accurately from area to area. This project will support field and laboratory work aimed at increasing the density of such observations in this focused interval by expanding the geographic extent of the sampling sites, and to refine the stratigraphic correlation using biostratigraphy and high-resolution Sr isotope variations. Ths plan is to launch a shallow scientific drilling program with portable (Winkie(TM)) diamond-bit coring systems to collect continuous oriented core from critical sections for these studies.Intellectual Merit. If either form of these TPW motions exist, they would be fundamentally important for at least two important reasons: First, they would represent a previously-unrecognized class of TPW, with an as-yet unknown driving mechanism. Second, they seem to be associated with the end of one of the few time intervals in which the frequency of geomagnetic reversals drops essentially to zero. These anomalous directions have longer durations than can be explained plausibly by the normal dynamo processes thought to operate in Earth's outer core. On the other hand, the motions and changes implied by the data seem too rapid to be explained by mantle dynamics if some form of TPW is responsible. For the counter-hypothesis, there are similar problems in understanding how an anomalous state of the geodynamo would have a memory persisting for the ~5 Myr span of the Italian data set. In either case the new results should increase our understanding of terrestrial geophysics, and could possibly yield clues to the underlying cause of the end of the Cretaceous Long Normal Chron. Broader Impacts. Either anomalous field configurations or TPW could help sub-divide geological time in and around the Cretaceous Long Normal Chron, providing a basis for higher-resolution magnetostratigraphy at a time of major global hydrocarbon sequestration. If TPW is the cause, it has the additional implication that the 3rd order sea-level variations would be globally asynchronous, contradicting a fundamental assumption in the field of sequence stratigraphy. TPW predicts a quadrature pattern of sea-level variation, with geographic areas moving towards the Equator experiencing relative transgressions, and those moving away, regressions. In turn, this implies that the global sequence stratigraphic framework that petroleum geologists have devised over the past 30 years would be 180 degrees out of phase over half of the planet. Results of this work could also have bearing on the great 'Baja-BC' debate, as comparisons with displaced terranes would need to be made between units closely matched in age. This research will involve the training of under graduate and graduate students and an early career PI.

像飞盘一样，所有在太空中自由移动的行星都希望绕着一个称为“主要惯性时刻”的轴线旋转。 在地球上或内部的任何大“疣”上没有平衡的重力将朝向赤道迁移，迫使旋转轴（地球的“杆”）到“徘徊？”相对于其固体质量。 这被称为“真正的极地徘徊”（TPW），是许多行星机构众所周知的物理学的一部分。 相对于自旋轴，行星的整个固体部分同时徘徊，因此与地球上构造板的正常运动完全不同。 在过去的十年中，地球物理界的一场激烈的辩论一直在激烈，即可能存在与长期的地磁正常极性结束相关的短暂爆发的TPW，大约是8400万年前，称为白垩纪长期的名称纪录。 同样，大约同一时间的海底磁异常模式的小摆动已被解释是由于异常弱的，波动的地磁场的结果。 最近，研究人员从意大利经典的Scaglia rossa lime-stones获得了高分辨率的化石磁性（古磁）数据，该数据证实了Chron 33R中的主要倾斜度（约20度）的存在，而南达科他州的同时数据如TPW假设所预测的那样，显示持续的偏斜和倾斜异常。 意大利数据还提供了挑衅性的暗示，即可能存在一系列短期左右的尺度振荡，叠加在这一长期趋势上。 PI称这些“真正的极性摇摆”（TPW）将它们与较长的时间尺度TPW运动区分开，这是大多数先前的地球物理研究的重点。 根据PI的说法，整个固体地球可能在做类似地质“呼啦舞”的事情。 但是，区分这些假设需要一组全球分布的高质量，高分辨率磁数据，可以从面积到区域进行准确的比较。 该项目将通过扩大采样位点的地理范围，并使用生物地层学和高分辨率SR同位素变化来改善地层相关性，以支持在此重点间隔中提高此类观察值密度的现场和实验室工作。该计划是通过便携式（Winkie（TM））钻石芯系统启动浅层科学钻探计划，以收集这些研究的关键部分的连续方向核心。如果存在这些TPW动作的任何一种形式，则至少有两个重要原因在根本上将在根本上很重要：首先，它们将代表先前未认可的TPW类，并具有尚未知道的驾驶机制。 其次，它们似乎与少数时间间隔之一的结束相关联，在该时间间隔中，地磁逆转的频率基本上降至零。这些异常的方向的持续时间比正常的发电机过程可以在地球外核中运行的持续时间更长。 另一方面，如果某种形式的TPW负责，数据所隐含的动作和变化似乎太快而无法用地幔动态来解释。 对于反假设，理解地geodynamo的异常状态如何在意大利数据集的〜5 MYR跨度中持续存在类似的问题。 无论哪种情况，新的结果都应提高我们对陆地地球物理学的理解，并可能为白垩纪长正常成年终结的根本原因提供线索。 更广泛的影响。异常的场构型或TPW可以帮助白垩纪长正常成年及周围的地质时间分区，这为在主要全球碳氢化合物隔离时提供了高分辨率磁层学的基础。如果TPW是原因，则具有额外的暗示，即第三阶海平面变化将是全球异步的，这与序列地层领域的基本假设相矛盾。 TPW预测了海平面变化的正交模式，地理区域朝着赤道经历相对侵犯的赤道，而那些移走的人会回归。 反过来，这意味着石油地质学家在过去30年中设计的全球序列地层框架将是地球一半以上的180度。这项工作的结果也可能与巨大的“ Baja-BC”辩论有关，因为与流离失所者的比较需要在年龄紧密匹配的单位之间进行比较。 这项研究将涉及对研究生和研究生的培训以及早期职业PI的培训。