Paleomagnetism and Magnetostratigraphy of the James Ross Basin, Antarctica

南极洲詹姆斯罗斯盆地的古地磁学和磁性地层学

• 批准号: 1341729
• 负责人: Joseph Kirschvink
• 金额: $ 41.51万
• 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: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1341729&HistoricalAwards=false
• 关键词: Paleomagnetism; Magnetostratigraphy; James; Ross; Basin

Non-Technical Summary: About 80 million years ago, the tip of the Antarctic Peninsula in the vicinity of what is now James Ross Island experienced an episode of rapid subsidence, creating a broad depositional basin that collected sediments eroding from the high mountains to the West. This depression accumulated a thick sequence of fossil-rich, organic-rich sediments of the sort that are known to preserve hydrocarbons, and for which Argentina, Chile, and the United Kingdom have overlapping territorial claims. The rocks preserve one of the highest resolution records of the biological and climatic events that led to the eventual death of the dinosaurs at the Cretaceous-Tertiary boundary (about 66 million years ago). A previous collaboration between scientists from the Instituto Antártico Argentino (IAA) and NSF-supported teams from Caltech and the University of Washington were able to show that this mass extinction event started nearly 50,000 years before the sudden impact of an asteroid. The asteroid obviously hit the biosphere hard, but something else knocked it off balance well before the asteroid hit. A critical component of the previous work was the use of reversals in the polarity of the Earth?s magnetic field as a dating tool ? magnetostratigraphy. This allowed the teams to correlate the pattern of magnetic reversals from Antarctica with elsewhere on the planet. This includes data from a major volcanic eruption (a flood basalt province) that covered much of India 65 million years ago. The magnetic patterns indicate that the Antarctic extinction started with the first pulse of this massive eruption, which was also coincident with a rapid spike in polar temperature. The Argentinian and US collaborative teams will extend this magnetic polarity record back another ~ 20 million years in time, and expand it laterally to provide magnetic reversal time lines across the depositional basin. They hope to recover the end of the Cretaceous Long Normal interval, which is one of the most distinctive events in the history of Earth?s magnetic field. The new data should refine depositional models of the basin, allow better estimates of potential hydrocarbon reserves, and allow biotic events in the Southern hemisphere to be compared more precisely with those elsewhere on Earth. Other potential benefits of this work include exposing several US students and postdoctoral fellows to field based research in Antarctica, expanding the international aspects of this collaborative work via joint IAA/US field deployments, and follow-up laboratory investigations and personnel exchange of the Junior scientists. Technical Description of Project The proposed research will extend the stratigraphic record in the late Cretaceous and early Tertiary sediments (~ 83 to 65 Ma before present) of the James Ross Basin, Antarctica, using paleo-magnetic methods. Recent efforts provided new methods to analyze these rocks, yielding their primary magnetization, and producing both magnetic polarity patterns and paleomagnetic pole positions. This provided the first reliable age constraints for the younger sediments on Seymour Island, and quantified the sedimentation rate in this part of the basin. The new data will allow resolution of the stable, remnant magnetization of the sediments from the high deposition rate James Ross basin (Tobin et al., 2012), yielding precise chronology/stratigraphy. This approach will be extended to the re-maining portions of this sedimentary basin, and will allow quantitative estimates for tectonic and sedimentary processes between Cretaceous and Early Tertiary time. The proposed field work will refine the position of several geomagnetic reversals that occurred be-tween the end of the Cretaceous long normal period (Chron 34N, ~ 83 Ma), and the lower portion of Chron 31R (~ 71 Ma). Brandy Bay provides the best locality for calibrating the stratigraphic position of the top of the Cretaceous Long Normal Chron, C34N. Although the top of the Cretaceous long normal Chron is one of the most important correlation horizons in the entire geological timescale, it is not properly correlated to the southern hemisphere biostratigraphy. Locating this event, as well as the other reversals, will be a major addition to understanding of the geological history of the Antarctic Peninsula. These data will also help refine tectonic models for the evolution of the Southern continents, which will be of use across the board for workers in Cretaceous stratigraphy (including those involved in oil exploration).This research is a collaborative effort with Dr. Edward Olivero of the Centro Austral de Investigaciones Cientificas (CADIC/CONICET) and Prof. Augusto Rapalini of the University of Buenos Aires. The collaboration will include collection of samples on their future field excursions to important targets on and around James Ross Island, supported by the Argentinian Antarctic Program (IAA). Argentinian scientists and students will also be involved in the US Antarctic program deployments, proposed here for the R/V Laurence Gould, and will continue the pattern of joint international publication of the results.

非技术摘要：大约8000万年前，现在詹姆斯罗斯岛附近的南极半岛尖端经历了一次快速下沉，形成了一个广阔的沉积盆地，收集了从高山侵蚀到西部的沉积物。 这个洼地积累了一系列厚厚的富含化石、富含有机物的沉积物，这些沉积物已知可以保存碳氢化合物，阿根廷、智利和英国对此有重叠的领土主张。 这些岩石保存了最高分辨率的生物和气候事件记录之一，这些事件导致了白垩纪-第三纪边界（大约 6600 万年前）恐龙的最终死亡。 阿根廷南极研究所 (IAA) 的科学家与美国国家科学基金会支持的加州理工学院和华盛顿大学团队之前的合作表明，这场大规模灭绝事件在小行星突然撞击之前近 5 万年就开始了。 小行星显然对生物圈造成了沉重打击，但早在小行星撞击之前，就有其他东西使生物圈失去了平衡。 先前工作的一个关键组成部分是利用地球磁场极性的反转作为测年工具？磁性地层学。 这使得研究小组能够将南极洲的磁反转模式与地球其他地方的磁反转模式联系起来。 其中包括 6500 万年前覆盖印度大部分地区的一次大型火山喷发（洪水玄武岩省）的数据。 磁模式表明，南极洲的灭绝是从这次大规模喷发的第一个脉冲开始的，这也与极地温度的迅速上升同时发生。 阿根廷和美国的合作团队将把这一磁极性记录再往前推约 2000 万年，并横向扩展以提供整个沉积盆地的磁反转时间线。 他们希望恢复白垩纪长正常间隔的结束，这是地球磁场历史上最独特的事件之一。 新数据应该完善该盆地的沉积模型，更好地估计潜在的碳氢化合物储量，并允许更准确地比较南半球的生物事件与地球其他地方的生物事件。这项工作的其他潜在好处包括让几名美国学生和博士后研究员参与南极洲的实地研究，通过IAA/美国联合实地部署扩大这项合作工作的国际范围，以及后续实验室调查和初级科学家的人员交流。项目技术描述 拟议的研究将利用古地磁方法扩展南极洲詹姆斯罗斯盆地晚白垩世和早第三纪沉积物（距今约 83 至 65 Ma）的地层记录。 最近的努力提供了分析这些岩石的新方法，产生它们的初级磁化强度，并产生磁极性模式和古地磁极位置。 这为西摩岛较年轻的沉积物提供了第一个可靠的年龄限制，并量化了盆地这一部分的沉积速率。新数据将能够解析来自高沉积率 James Ross 盆地的沉积物的稳定残余磁化强度（Tobin 等，2012），从而产生精确的年代学/地层学。这种方法将扩展到该沉积盆地的剩余部分，并将允许定量估计白垩纪和早第三纪之间的构造和沉积过程。拟议的野外工作将完善白垩纪长正常时期（Chron 34N，~ 83 Ma）末期和 Chron 31R 下部（~ 71 Ma）之间发生的几次地磁反转的位置。布兰迪湾提供了校准白垩纪长正常年代（C34N）顶部地层位置的最佳地点。 尽管白垩纪长正时层顶部是整个地质时间尺度中最重要的相关层位之一，但它与南半球生物地层的相关性并不好。定位这一事件以及其他逆转将有助于了解南极半岛的地质历史。这些数据还将有助于完善南部大陆演化的构造模型，供白垩纪地层学工作者（包括参与石油勘探的工作者）全面使用。这项研究是与南方科学研究中心 (CADIC/CONICET) 的 Edward Olivero 博士和布宜诺斯艾利斯大学的 Augusto Rapalini 教授合作完成的。 此次合作将包括在阿根廷南极计划（IAA）的支持下，在未来前往詹姆斯罗斯岛及其周边重要目标的实地考察中收集样本。 阿根廷科学家和学生也将参与美国南极计划的部署，这里为劳伦斯·古尔德号 R/V 提出，并将继续国际联合发布结果的模式。