Late Cretaceous Osmium Isotope Stratigraphy

晚白垩世锇同位素地层学

• 批准号: 0309264
• 负责人: Gregory Ravizza
• 金额: $ 20.95万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-15 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309264&HistoricalAwards=false
• 关键词: Late; Cretaceous; Osmium; Isotope; Stratigraphy

ABSTRACTOsmium isotope analyses will be performed on a suite of marine sediment samples in order to reconstruct seawater 187Os/188Os variations during the Maastrichtian and late Campanian. This sample suite will provide the global coverage required to determine empirically whether the resulting composite Os isotope record is representative of whole-ocean changes in 187Os/188Os. The specific study sites will include both outcrop samples collected from classic Scaglia Rossa sections in the Italian Apennines, and samples from archived ODP/DSDP material recovered from the Western Pacific, South Atlantic and Southern Ocean. Os isotope analyses will be performed by single collector magnetic sector ICP-MS at the University of Hawaii. This high through-put method is essential for this study in order to achieve the high temporal resolution required to resolve the influence of specific geologic events. Preliminary results reported in the text of the proposal demonstrate the viability of this approach, and indicate that there is a step-wise decline of approximately 50% in sediment 187Os/188Os ratios during the last 3 million years of Maastrichtian time, prior to the K-T boundary event. The specific phenomena this study focuses on are (1) emplacement of the Deccan Traps in the latest Maastrichtian and (2) a putative eustatic sea-level fall in the early Maastrichtian. Numerous stable isotope studies of benthic and planktic forams reveal evidence of a brief episode of global warming 200-300 thousand years prior to the K-T boundary. Several investigators suggest that this warming is caused by Deccan volcanism. The marine 187Os/188Os ratio is expected to decline as a result of unradiogenic, mantle-derived Os (low 187Os/188Os) associated with Deccan volcanism. By directly comparing Os isotope and oxygen isotope data from the same cores it will be possible to test the hypothesis that Deccan volcanism played a causative role in global warming.Published sequence stratigraphic data from the New Jersey continental margin documents a significant regression near the base of magnetochron C31R. This sea-level low stand is coincident with a shift to heavier oxygen isotope ratios in several published planktic and benthic foram records, an association that is suggestive of continental glaciation. Previous Os isotope work across the Eocene-Oligocene transition, and in recent glacial moraines, indicate that glacial cycles enhance the delivery of radiogenic continental Os (high 187Os/188Os) to the ocean. This study will seek evidence of high seawater 187Os/188Os coincident with the putative early Maastrichtian glaciation. If such evidence is found this will strengthen the case for Cretaceous glaciation, a controversial claim with broad implications for our understanding of Earth's climate evolution. It will also lay a foundation for seeking Os isotope evidence for older Cretaceous glacial events.The broader impacts of this research effort include heavy emphasis of graduate education and an opportunity for undergraduate participation in research at the University of Hawaii, a culturally and ethnically diverse university.

摘要通过对一系列海洋沉积物样品的锇同位素分析，重建了马斯特里赫特期和晚坎帕尼亚期海水187 Os/188 Os的变化。该样本套件将提供所需的全球覆盖范围，以凭经验确定由此产生的复合Os同位素记录是否代表整个海洋的187 Os/188 Os变化。具体的研究地点将包括从意大利亚平宁山脉的经典Scaglia Rossa剖面收集的露头样品，以及从西太平洋、南大西洋和南大洋回收的ODP/DSDP存档材料的样品。Os同位素分析将在夏威夷大学采用单收集器磁扇区ICP-MS进行。这种高通量的方法是必不可少的，这项研究，以达到高的时间分辨率所需的解决特定的地质事件的影响。初步结果报告的文本中的建议证明了这种方法的可行性，并表明，有一个逐步下降约50%的沉积物187 Os/188 Os的比例在过去的300万年的马斯特里赫特时间，之前的K-T边界事件。本研究所关注的具体现象是：（1）德干圈闭在马斯特里赫特晚期的就位和（2）马斯特里赫特早期假定的海平面下降。对底栖有孔虫和浮游有孔虫的大量稳定同位素研究揭示了在K-T边界之前20 - 30万年全球变暖的短暂事件的证据。一些研究人员认为，这种变暖是由德干火山活动造成的。海洋187 Os/188 Os比值预计将下降，这是由于与德干火山活动有关的非放射成因的地幔来源的Os（低187 Os/188 Os）。通过直接比较来自相同岩心的Os同位素和氧同位素数据，将有可能检验德干火山活动在全球变暖中发挥了因果作用的假设。已发表的来自新泽西大陆边缘的层序地层数据记录了磁时线C31 R基底附近的显著回归。这个海平面低的立场是一致的转变，以较重的氧同位素比在几个已发表的南极和底栖有孔虫记录，一个协会，这是暗示大陆冰川。以前的Os同位素工作在始新世-渐新世过渡，并在最近的冰川冰碛，表明冰川循环增强了交付放射性大陆的Os（高187 Os/188 Os）的海洋。本研究将寻找与推定的早期马斯特里赫特冰期相一致的高海水187 Os/188 Os的证据。如果找到这样的证据，这将加强白垩纪冰川作用的情况，这是一个有争议的说法，对我们理解地球气候演变有广泛的影响。这也将为寻找更古老的白垩纪冰川事件的锇同位素证据奠定基础。这一研究工作的更广泛影响包括非常重视研究生教育，并为本科生提供参与夏威夷大学（一所文化和种族多样性大学）研究的机会。