Collaborative Research: Testing hypothese of late Cretaceous

就像飞盘一样，所有在太空中自由运动的行星都想围绕一个被称为“主转动惯量”的轴旋转。行星上或行星内部的任何大型“疣”，如果引力不平衡，就会向赤道移动，迫使自转轴（行星的“两极”）“徘徊”。相对于它的固体质量。这被称为“真极漫游”（TPW），是许多行星体的众所周知的物理学的一部分。地球的整个固体部分同时相对于自转轴移动，因此与地球上构造板块的正常运动大不相同。在过去的十年里，地球物理学界一直在激烈地争论，是否存在与8400万年前一段长时间的地磁正极性结束有关的短暂的TPW爆发，这段时间被称为白垩纪长正常时间。类似地，大约在同一时间，海底磁异常模式中的微小摆动被解释为异常微弱、波动的地磁场的结果。最近，研究人员从意大利Scaglia Rossa的经典石灰石中获得了更高分辨率的化石磁（古地磁）数据，证实了Chron 33R中存在一个主要的（~20度）倾斜变浅，而来自南达科他州的同期数据显示了持续的赤纬和倾斜异常，正如TPW假说所预测的那样。意大利的数据也提供了一些具有挑衅性的暗示，即在这种长期趋势上可能叠加了一系列短的、大约100万年尺度的振荡。pi称之为“真极摆动”（TPw），以区别于更长的时间尺度的TPw运动，后者一直是之前大多数地球物理研究的重点。根据pi的说法，整个固体地球可能一直在做类似于地质“草裙舞”的事情。然而，区分这些假设需要一组全球分布的高质量、高分辨率的磁数据，这些数据可以在不同地区之间进行准确的比较。该项目将支持实地和实验室工作，旨在通过扩大采样点的地理范围来增加这一集中区间内此类观测的密度，并利用生物地层学和高分辨率Sr同位素变化来完善地层对比。该计划是启动一个浅层科学钻井项目，使用便携式（Winkie(TM)）金刚石钻头取心系统，从关键区域收集连续定向岩心，用于这些研究。知识价值。如果存在这些TPW运动的任何一种形式，它们将具有重要的根本意义，至少有两个重要原因：首先，它们将代表一种以前未被识别的TPW类别，其驱动机制尚不清楚。其次，它们似乎与地磁倒转频率基本降至零的少数时间间隔中的一个时间间隔的结束有关。这些异常方向的持续时间比在地球外核运行的正常发电机过程所能合理解释的时间要长。另一方面，数据暗示的运动和变化似乎太快了，如果某种形式的TPW是负责的，那么用地幔动力学来解释。对于反假设，在理解地球发电机的异常状态如何在意大利数据集的~5 Myr范围内保持记忆方面存在类似的问题。无论是哪种情况，新的结果都应该增加我们对陆地地球物理学的理解，并可能为白垩纪长正常时结束的潜在原因提供线索。更广泛的影响。无论是异常场构型还是TPW，都可以帮助细分白垩纪长正时及其周围的地质时代，为全球主要的油气封存时期提供更高分辨率的磁地层学基础。如果TPW是原因，它还意味着三级海平面变化将是全球异步的，这与层序地层学领域的基本假设相矛盾。TPW预测了海平面变化的正交模式，向赤道移动的地理区域经历相对海侵，而远离赤道的地理区域则经历回归。反过来，这意味着石油地质学家在过去30年里设计的全球层序地层格架将在地球的一半以上出现180度的相位偏差。这项工作的结果也可能对伟大的“Baja-BC”争论产生影响，因为需要在年龄密切匹配的单位之间与流离失所的地形进行比较。这项研究将包括本科生和研究生的培训以及早期职业PI。

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.