Paleomagnetism and Magnetostratigraphy of the James Ross Basin, Antarctica

非技术摘要：大约8000万年前，南极半岛尖端在现在的詹姆斯罗斯岛附近经历了一段快速下沉的时期，形成了一个广泛的沉积盆地，收集了从高山向西侵蚀的沉积物。这个凹陷积累了厚厚的一系列化石丰富、有机丰富的沉积物，这种沉积物已知可以保存碳氢化合物，阿根廷、智利和英国对这些沉积物有重叠的领土主张。这些岩石保存了生物和气候事件的最高分辨率记录之一，这些事件导致了白垩纪-第三纪界线(约6600万年前)恐龙的最终死亡。阿根廷南极洲研究所(IAA)的科学家与美国国家科学基金会(NSF)支持的加州理工学院和华盛顿大学的研究小组之前的合作表明，这种大灭绝事件始于小行星突然撞击前近5万年。这颗小行星显然猛烈地撞击了生物圈，但在小行星撞上之前，另有什么东西让它失去了平衡。之前工作的一个关键组成部分是使用地球极性的反转？S磁场作为测年工具？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上其他地方的磁反转模式联系起来。这包括6500万年前覆盖印度大部分地区的一次大型火山喷发(一个洪水玄武岩省)的数据。磁场模式表明，南极的灭绝始于这次大规模喷发的第一次脉冲，这也与极地温度的快速上升相吻合。阿根廷和美国的合作团队将把这一磁极记录再向前延伸约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漫长的正常间隔的结束，这是地球历史上最具特色的事件之一-S磁场。新的数据应该会完善盆地的沉积模型，更好地估计潜在的碳氢化合物储量，并允许更准确地将南半球的生物事件与地球其他地方的生物事件进行比较。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接触到南极洲的实地研究，通过IAA/美国联合实地部署扩大这一合作工作的国际层面，以及后续实验室调查和初级科学家的人员交流。本研究将利用古地磁方法扩展南极詹姆斯罗斯盆地晚白垩世和早第三纪沉积(距今约83 Ma至65 Ma)的地层记录。最近的努力为分析这些岩石提供了新的方法，产生了它们的初级磁化，并产生了磁极模式和古地磁极位置。这为西摩岛上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。新的数据将能够解析高沉积速率的James Ross盆地(Tobin等人，2012年)沉积物的稳定剩余磁化作用，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，并将允许对白垩纪至早第三纪之间的构造和沉积过程进行定量估计。拟议的野外工作将完善在白垩纪长正常时期(Chron 34N，~83 Ma)结束和Chron 31R下部(~71 Ma)之间发生的几次地磁反转的位置。白兰地海湾为标定白垩纪C34N长标准时序顶部的地层位置提供了最佳位置。尽管白垩纪长标准时序的顶部是整个地质时间尺度中最重要的对比层位之一，但它与南半球生物地层学的对比并不是很好。定位这一事件以及其他逆转事件，将大大增加对南极半岛地质历史的了解。这些数据还将有助于完善南部大陆演化的构造模型，这将对白垩纪地层研究人员(包括参与石油勘探的人员)全面使用。这项研究是与澳大利亚科学调查中心(CADIC/CONICET)的爱德华·奥利维罗博士和布宜诺斯艾利斯大学的奥古斯托·拉帕里尼教授共同努力的。这项合作将包括在阿根廷南极计划(IAA)的支持下，为他们未来前往詹姆斯罗斯岛及其周围的重要目标进行实地考察时收集样本。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·古尔德提出了建议，并将继续国际联合发布结果的模式。

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.