RUI:Preliminary Foraminiferal Porosity-Based Niobrara Paleoceanographic Investigation

RUI：基于有孔虫孔隙度的 Niobrara 古海洋学初步调查

• 批准号: 0309086
• 负责人: Cynthia Fisher
• 金额: $ 4.76万
• 依托单位: West Chester University of Pennsylvania
• 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 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309086&HistoricalAwards=false
• 关键词: RUI; Preliminary; Foraminiferal; Porosity; Based

ABSTRACTSignificant progress has been made in understanding the water column and circulation of the mid-Cretaceous Western Interior Sea by utilizing planktic foraminiferal porosity of the species Hedbergella delrioensis as a proxy for water temperature and relative density (Fisher et al., 2003 and Fisher et al., in review). The water column was significantly stratified; thereby inhibiting wind- mixing. Water mass mixing occurred along oceanic-fronts resulting in the formation of endemic Western Interior waters. Fronts may explain the paradox of a stratified, highly productive ocean, where nutrient renewal to the photic zone should have been inhibited due to the density stratification. Mixing along fronts provided nutrients to the central, more normal marine waters, to stimulate and sustain the high primary productivity recorded by the high organic-carbon accumulation found in the strata. Mixing in the Western Interior Seaway produced relatively cool water that was exported out of the sea to the south at depth (Fisher, 2002; Fisher, in review). As the Greenhorn Sea evolved, the strata of the Hartland Shale and Bridge Creek Limestone members indicate that the sea became more stratified by the addition of warmer layers, some of which were produced within the seaway (Fisher, 2002; Fisher, in review).Although much has been learned about the evolution of this important epicontinental sea of the greenhouse Earth, much remains to be learned. Due to the indurated nature of the limestones of the Greenhorn Formation, no examination of the development of Milankovitch cyclicity has been possible using the porosity method. Conducting porosity analyses on foraminifers from the Niobrara Formation is expected to provide data that will assist in understanding how the astronomical orbital cycles may have amplified terrestrial processes such as increased runoff, delivery of detrital material to the sea, and changed the mixing ratio of Tethyan-sourced versus Boreal-sourced waters. This information could prove critical to a greater understanding of the development of Cretaceous source-rock strata. An improved understanding of the Cretaceous greenhouse ocean circulation could also assist in understanding how future climate changes impact Earth. There are three goals to this pilot project: 1) establish a new proxy species adequate for porosity analysis in rocks younger than early Santonian (Hedbergella delrioensis has its global extinction in the early Santonian (Caron, 1985) and therefore would not be available for the entire duration of the Niobrara); 2) determine if there are substantial differences in the temperature and water column stratification in the Niobrara as compared to the Greenhorn; and 3) determine the feasibility of investigating the origin of the bedding couplets found in the Niobrara. Results of the pilot project should not only establish the feasibility of conducting a large-scale geographic and stratigraphic porosity study of the Niobrara Formation and equivalents that can be used to reconstruct circulation of the Niobrara Sea through time; but should provide preliminary results about the origin of couplet formation and provide important insights into the development of the Western Interior Seaway over the longer time-frame of second-order sea-level changes.This research will have an impact on teaching and learning in that the investigation will be carried out by the PI and two undergraduate research assistants over a period of one year beginning in June, 2003. The undergraduate students will be involved in every aspect of the work. All will participate in sampling the Berthoud State No. 4 core at the Denver United States Geological Survey Core Research Center. The students will be involved in all aspects of data collection, including operating the new Environmental Scanning Electron Microscope, interpreting the data and disseminating results in professional presentations and publications. The results of the research will be integrated into the West Chester University Introduction to Oceanography laboratories on paleoceanographic reconstruction and geologic proxies. The strong established record of involving underrepresented groups in research will be continued. The selection for undergraduate research assistants will take into account the under-representation of women and minorities in the Geosciences.

摘要：利用Hedbergella delrioensis 物种的浮游有孔虫孔隙度作为水温和相对密度的代表，在了解白垩纪中期西部内海的水柱和环流方面取得了重大进展（Fisher 等，2003 年和 Fisher 等，综述）。水柱分层明显；从而抑制风的混合。水团混合沿着海洋前沿发生，导致西部内陆水域特有的形成。锋面可以解释分层、高产海洋的悖论，其中透光区的养分更新应该由于密度分层而受到抑制。沿锋面的混合为中心、更正常的海水提供了营养物质，以刺激和维持地层中发现的高有机碳积累所记录的高初级生产力。西部内陆海道的混合产生了相对凉爽的水，这些水从海洋深处输出到南部（Fisher，2002；Fisher，评论中）。随着新手海的演化，哈特兰页岩和布里奇溪石灰岩成员的地层表明，由于增加了较温暖的层，海洋变得更加分层，其中一些温暖层是在海道内产生的（Fisher，2002；Fisher，评论中）。尽管人们已经对温室地球这一重要的陆缘海洋的演化有了很多了解，但还有很多东西有待了解。由于 Greenhorn 地层石灰岩的硬化性质，无法使用孔隙度方法检查米兰科维奇循环的发展。对 Niobrara 地层的有孔虫进行孔隙度分析预计将提供数据，有助于了解天文轨道周期如何放大陆地过程，例如增加径流、向海洋输送碎屑物质，以及改变特提斯源水与北方源水的混合比。这些信息对于更好地了解白垩纪烃源岩地层的发育至关重要。更好地了解白垩纪温室海洋环流也有助于了解未来气候变化如何影响地球。该试点项目有三个目标：1）建立一个新的代理物种，足以对早于桑托尼世的岩石进行孔隙度分析（Hedbergella delrioensis 在桑托尼世早期就已全球灭绝（Caron，1985），因此在 Niobrara 的整个时期都无法使用）； 2) 确定 Niobrara 与 Greenhorn 相比，温度和水柱分层是否存在显着差异； 3）确定调查尼奥布拉拉发现的床上对联的起源的可行性。试点项目的结果不仅应确立对尼奥布拉拉地层和可用于重建尼奥布拉拉海随时间变化的环流进行大规模地理和地层孔隙度研究的可行性；但应提供关于对联形成起源的初步结果，并为在二级海平面变化的较长时间内西部内陆航道的发展提供重要见解。这项研究将对教学产生影响，因为调查将由 PI 和两名本科生研究助理在 2003 年 6 月开始的一年时间内进行。本科生将参与工作的各个方面。所有人都将参与丹佛美国地质调查局核心研究中心的 Berthoud State No. 4 核心取样工作。学生将参与数据收集的各个方面，包括操作新型环境扫描电子显微镜、解释数据以及在专业演示和出版物中传播结果。研究结果将被纳入西切斯特大学海洋学概论实验室的古海洋学重建和地质代理。让代表性不足的群体参与研究的良好记录将继续下去。本科生研究助理的选拔将考虑到地球科学领域女性和少数族裔代表性不足的情况。