An Integrated Paleomagnetic, Isotopic, and Stratigraphic Test of the Inertial Interchange True Polar Wander Hypothesis, Bitter Springs Stage, Australia

惯性互换真实极地漂移假说的综合古地磁、同位素和地层测试，澳大利亚比特斯普林斯舞台

• 批准号: 0514657
• 负责人: Adam Maloof
• 金额: --
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0514657&HistoricalAwards=false
• 关键词: Integrated; Paleomagnetic; Isotopic; Stratigraphic; Test

Since the 1950s, inertial interchange true polar wander (IITPW) has been recognized as a phys-ically viable process in which the entire solid Earth may shift as much as 90. with respect to thespin axis in 106-107 years. Nevertheless, IITPW events have not been demonstrated convincinglyin the geologic record for two main reasons: (1) studies have been plagued by uncertainties inthe age, quality, and correlation of paleomagnetic poles collected from various types of rocks ondifferent continents, and (2) no serious effort has been made to link the effects IITPW may haveon the stratigraphic record due to changes in global climate structure, ocean circulation, sea level,nutrient cycling, organic carbon burial, methane storage, and continental weathering.The IITPW hypothesis provides a series of testable predictions because an IITPW event willaffect every continent differently, but predictably, depending on the continent's changing positionrelative to Earth's spin axis. For example, the further a craton is from the inertial interchangeaxis (Imin), the greater the changes in sea level and paleomagnetic inclination will be. Maloofet al. [70] identified an interval of relatively light carbon isotopes in *800 million year old (Ma)carbonate rocks of East Svalbard (Norway) that is bracketed by large shifts in relative sea leveland paleomagnetic orientation. They argue that the coincidence of these isotopic, magnetic, andeustatic changes can be explained by rapid shifts in global paleogeography associated with a pairof inertial interchange true polar wander IITPW events. The same isotopic interval has also beenidentified in Bitter Springs Formation equivalents in Australia. Australia is an ideal locality totest the IITPW hypothesis because most models of middle Neoproterozoic paleogeography placeAustralia further away and in a different direction from Imin than East Svalbard. Therefore, thestratigraphy spanning this interval in Australia should show unique paleomagnetic and sea levelshifts that are both larger in amplitude and different in shape than those documented in Svalbard.This proposal will test the IITPW hypothesis through an integrated investigation of the physical,geochemical, and magnetic stratigraphy of the Bitter Springs Stage in Australia.Intellectual Merit. All paleogeographic reconstructions to date rely on two fundamental as-sumptions: (1) the motion of continents is dominated by plate tectonics, and (2) Earth's magneticfield is geocentric and dipolar on time scales *104 yrs. Documenting IITPW in the geologic recordwould have profound implications for interpreting plate motions over the last 2 billion years. Fur-thermore, documenting the sedimentological and biogeochemical consequences of an IITPW eventat *800 would shed light on the equilibrium Earth System prior to the first of at least three majorNeoproterozoic glaciations. A falsification of the IITPW hypothesis would lead to an equally im-portant suite of results documenting ancient secular variation of the geomagnetic field or perhapsan unexpected Neoproterozoic paleogeography.Broader Impacts. (1) The distribution of continents is crucial to any first order understandingof general fluid circulation on the Earth. Therefore, the science of developing geologically andpaleomagnetically realistic paleogeographies is necessary for generating models of ancient climatesand for understanding the limits of global change. (2) This proposal will be the start of a researchproject led by the PI and involving laboratory collaborations with MIT (S.A. Bowring, B.P. Weiss),Yale (D.A.D. Evans), and Caltech (J.L. Kirschvink). These collaborations not only will produceimportant science, but also will begin a technology transfer to Princeton, where the PI will setup a paleomagnetics laboratory in 2006. (3) Study of the Bitter Springs Stage is an ideal studentproject because it requires the knowledge of a suite of complementary subjects, from basic fieldmapping and sequence stratigraphy to paleomagnetism, stable and radiogenic isotope systems, andwhole-Earth geophysics. The PI will recruit underrepresented students to receive extensive trainingin field and analytical methods, and to play active roles in discovery-based research science.

自20世纪50年代以来，惯性交换真极移(IITPW)被认为是一个物理上可行的过程，在这个过程中，整个固体地球可能会移动多达90次。相对于针轴，在106-107年之间。然而，IITPW事件在地质记录中并没有被证明是令人信服的，主要原因有两个：(1)从不同大陆不同类型的岩石中收集的古地磁极的年龄、质量和相关性的不确定性一直困扰着研究，(2)由于全球气候结构、海洋环流、海平面、营养循环、有机碳埋藏、甲烷储存和大陆风化的变化，IITPW事件对地层记录的影响没有认真努力联系起来。IITPW假说提供了一系列稳定的预测，因为IITPW事件对每个大陆的影响是不同的，但是可预测的，取决于大陆相对于地球自转轴的位置变化。例如，克拉通距离惯性交换轴(伊明)越远，海平面和古地磁倾角的变化就越大。Maloofet等人。[70]在挪威东斯瓦尔巴群岛*8亿年前的碳酸盐岩中发现了一个相对较轻的碳同位素区间，该区间被相对海平面和古地磁方向的巨大变化所包围。他们认为，这些同位素、磁性和海平面变化的重合可以用全球古地理的快速变化来解释，这些变化与一对惯性交换真极移IITPW事件有关。在澳大利亚的苦泉组中也发现了相同的同位素间隔。澳大利亚是检验IITPW假说的理想地点，因为大多数中新元古代古地理模型都位于距离伊明更远、方向与东斯瓦尔巴群岛不同的澳大利亚。因此，澳大利亚跨越这一时期的地层学应该显示出独特的古地磁和海平面变化，其幅度和形状都比斯瓦尔巴记录的大而不同。这一提议将通过对澳大利亚苦泉期的物理、地球化学和磁性地层学的综合研究来检验IITPW假说。到目前为止，所有的古地理重建都依赖于两个基本假设：(1)大陆的运动由板块构造主导，(2)地球磁场在时间尺度上是地心和偶极的*104年。将IITPW记录在地质记录中将对解释过去20亿年来的板块运动具有深远的影响。此外，记录IITPW事件的沉积学和生物地球化学后果将有助于揭示至少三次主要的新元古代冰川中的第一次之前的平衡地球系统。IITPW假说的证伪将导致一套同样重要的结果，记录古代地磁场的长期变化，或者可能是一种意想不到的新元古代古地理。(1)大陆的分布对于对地球上一般流体循环的任何一级了解都是至关重要的。因此，发展地质学和古地磁学上真实的古地理对于建立古代气候模型和理解全球变化的极限是必要的。(2)这项建议将是由国际和平研究所领导的一个研究项目的开始，该项目涉及与麻省理工学院(S.A.Bowring，B.P.Weiss)、耶鲁(D.A.D.Evans)和加州理工大学(J.L.Kirschvink)的实验室合作。这些合作不仅将产生重要的科学成果，还将开始向普林斯顿转移技术，国际和平研究所将于2006年在那里建立一个古地磁学实验室。(3)苦泉阶段的研究是一个理想的学生项目，因为它需要一系列互补学科的知识，从基础野外填图和层序地层学到古地磁学、稳定和放射性同位素系统以及全球地球物理。国际学生联合会将招收代表性不足的学生，接受实地和分析方法方面的广泛培训，并在以发现为基础的研究科学中发挥积极作用。