Late Cretaceous Osmium Isotope Stratigraphy

为了重建马斯特里赫斯和晚寒武世期间海水的187Os/188Os变化，将对一套海洋沉积物样品进行Os同位素分析。这套样本将提供所需的全球覆盖范围，以经验性地确定所产生的复合Os同位素记录是否代表187Os/188os期间的全洋变化。具体的研究地点将包括从意大利亚平宁地区的经典Scaglia Rossa剖面收集的露头样本，以及从西太平洋、南大西洋和南大洋恢复的ODP/DSDP存档材料的样本。OS同位素分析将由夏威夷大学的单收集器磁扇区电感耦合等离子体质谱仪进行。为了达到解决特定地质事件影响所需的高时间分辨率，这种高通量方法对于本研究是必不可少的。提案正文中报告的初步结果证明了这种方法的可行性，并表明在K-T边界事件之前的马斯特里赫特时代的最后300万年期间，沉积物的187Os/188Os比值有大约50%的逐步下降。这项研究关注的具体现象是：(1)德干圈闭在马斯特里赫特晚期侵位；(2)马斯特里赫斯早期推测海平面下降。大量对底栖和浮游有孔虫的稳定同位素研究表明，在K-T界线之前200-30万年，全球变暖曾短暂发生过。一些研究人员认为，这种变暖是由德干火山活动引起的。由于与德干火山作用有关的非放射性成因、地幔来源的Os(低的187Os/188Os)，海洋中的187Os/188Os比率预计将下降。通过直接比较同一岩心的Os同位素和氧同位素数据，将有可能检验德干火山作用对全球变暖起到了致因作用的假设。新泽西大陆边缘公布的层序地层学数据表明，在磁控管C31R底部附近发生了显著的退变。这种海平面较低的状态与几个公布的浮游生物和海底有孔虫记录中氧同位素比率向更高的转变相吻合，这种联系暗示着大陆冰川作用。以前在始新世-渐新世过渡时期和最近冰川冰川中进行的Os同位素研究表明，冰川旋回增强了放射性成因大陆Os(高187Os/188Os)向海洋的输送。这项研究将寻找高海水187Os/188Os与推测的早期马斯特里赫特冰川重合的证据。如果这样的证据被发现，这将加强白垩纪冰川作用的理由，这一有争议的说法对我们理解地球的气候演变具有广泛的影响。这也将为寻找白垩纪早期冰川事件的Os同位素证据奠定基础。这项研究的更广泛影响包括对研究生教育的高度重视，以及为本科生参与夏威夷大学的研究提供机会，夏威夷大学是一所文化和种族多元化的大学。

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.