Collaborative Research: Testing hypothese of late Cretaceous

合作研究：检验晚白垩世的假设

• 批准号: 1114011
• 负责人: Peter Ward
• 金额: $ 15.44万
• 依托单位: University of Washington
• 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=1114011&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; hypothese; 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.

就像飞盘一样，所有在太空中自由运动的行星都想绕着一个叫做“主惯性矩”的轴旋转。 地球上或地球内部的任何大的“疣”，如果引力不平衡，就会向赤道迁移，迫使自转轴（地球的“两极”）“漂移”？相对于其固体质量。 这被称为“真正的极地漫游”（TPW），是许多行星体的物理学的一部分。 行星的整个固体部分在同一时间相对于自转轴漂移，因此与地球上构造板块的正常运动完全不同。 在过去的十年里，地球物理学界一直在激烈地争论是否可能存在一个短暂的TPW爆发，这与大约8400万年前的一个长时期的地磁正常极性（称为白垩纪长正常时）的结束有关。 同样地，几乎在同一时间海底磁异常模式的微小摆动也被解释为异常微弱、波动的地磁场的结果。 最近，研究人员从意大利的经典Scaglia Rossa石灰岩中获得了更高分辨率的化石磁性（古地磁）数据，证实了Chron 33 R中存在主要（~20度）的倾斜变浅，而南达科他州的同时代数据显示了TPW假设所预测的持续下降和倾斜异常。 意大利的数据还提供了一个挑衅性的暗示，即可能有一系列短期的，~百万年规模的振荡叠加在这一长期趋势上。 PI称之为“真正的极地摆动”（TPw），以区别于更长的时间尺度的TPW运动，这是大多数以前的地球物理调查的重点。 根据PI的说法，整个固体地球可能一直在做类似于地质学“草裙舞”的事情。 然而，区分这些假设需要一套全球分布的高质量，高分辨率的磁测数据，可以准确地从一个地区到另一个地区进行比较。 该项目将支持实地和实验室工作，以便通过扩大取样地点的地理范围，增加这一重点区间的此类观测密度，并利用生物地层学和高分辨率锶同位素变化来完善地层对比。该计划是利用便携式（Winkie（TM））金刚石钻头取芯系统启动一项浅层科学钻探计划，以便从这些研究的关键部分收集连续定向岩心。如果这些TPW运动的任何一种形式存在，它们至少有两个重要的原因是非常重要的：首先，它们代表了一种以前未被认识的TPW类型，具有未知的驱动机制。 第二，它们似乎与地磁反转频率基本上下降到零的少数时间间隔之一的结束有关。这些异常方向的持续时间比地球外核正常发电机过程所能解释的要长。 另一方面，由数据暗示的运动和变化似乎太快，无法用地幔动力学解释，如果某种形式的TPW负责。 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~ 500万年的跨度中保持记忆方面存在类似的问题。 无论哪种情况，新的结果都应该增加我们对地球物理学的理解，并可能为白垩纪长正常年代结束的根本原因提供线索。 更广泛的影响。无论是异常场配置或TPW可以帮助划分地质时间和周围的白垩纪长正常年代，提供了一个基础，在一个时间的主要全球碳氢化合物封存的高分辨率磁性地层学。如果TPW是原因，它有额外的含义，第三级海平面变化将是全球异步的，在层序地层学领域的一个基本假设相矛盾。 TPW预测了海平面变化的正交模式，地理区域向赤道移动经历相对海侵，而那些移动，回归。 反过来，这意味着石油地质学家在过去30年中设计的全球层序地层框架将在地球的一半范围内出现180度的相位差。这项工作的结果也可能对伟大的“Baja-BC”辩论产生影响，因为需要在年龄上密切匹配的单位之间进行与流离失所者的比较。 这项研究将涉及本科生和研究生的培训和早期职业PI。