RUI:Preliminary Foraminiferal Porosity-Based Niobrara Paleoceanographic Investigation

通过利用黑藻的浮游有孔虫孔隙度作为水温和相对密度的替代物，在理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等人，2003和Fisher等人，在综述中)。水柱明显分层，从而抑制了风的混合。水团混合沿海洋锋面发生，形成特有的西部内陆水域。锋面可能解释了分层、高生产力海洋的悖论，在那里，由于密度分层，光层的营养更新本应受到抑制。沿锋面的混合为中部更正常的海洋水域提供了营养物质，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较冷的水，这些水从海洋深处输出到南方(Fisher，2002；Fisher，在回顾中)。随着格林霍恩海的演化，哈特兰页岩和桥溪石灰岩的地层表明，由于增加了更温暖的层，海洋变得更加分层，其中一些层是在海道内产生的(Fisher，2002；Fisher，在回顾中)。尽管关于这个重要的温室地球陆表海的演化已经了解了很多，但仍然有很多需要了解的东西。由于格林霍恩组石灰岩的硬化性质，无法用孔隙度方法检查米兰科维奇旋回性的发展。对来自Niobrara组的有孔虫进行孔隙度分析预计将提供有助于理解天文轨道循环如何可能放大陆地过程的数据，例如径流增加、向海洋输送碎屑物质以及改变来自特提斯的水和来自北方的水的混合比例。这些信息可能对更好地了解白垩纪生油岩地层的发育情况至关重要。更好地了解白垩纪温室海洋环流也有助于理解未来气候变化对地球的影响。这项试点项目有三个目标：1)建立一个新的替代物种，足以分析早于桑托世(Hedbergella Delrioensis)的岩石的孔隙度(Hedbergella delrioensis在桑东期早期(Caron，1985)就已经全球灭绝，因此不能在整个Niobrara时期内使用)；2)确定Niobrara的温度和水柱分层是否与Greenhorn相比有实质性的差异；以及3)确定研究Niobrara中发现的层状对联的起源的可行性。试验项目的结果不仅应该确定对Niobrara组进行大规模地理和地层孔隙度研究的可行性，以及可以用来重建Niobrara海随时间循环的等价物的可行性；而且应该提供关于对联形成的初步结果，并为西部内陆海道在较长时间内的二次海平面变化的发展提供重要的见解。这项研究将对教学产生影响，因为这项研究将由PI和两名本科生研究助理进行，从2003年6月开始，为期一年。本科生将参与到工作的方方面面。所有人都将在丹佛美国地质调查局岩芯研究中心参与伯特豪德州4号岩芯的采样。学生将参与数据收集的方方面面，包括操作新的环境扫描电子显微镜，解释数据，并在专业演示和出版物中传播结果。研究成果将纳入西切斯特大学关于古海洋重建和地质指标的海洋学实验室导论。让代表人数不足的群体参与研究的良好记录将继续下去。挑选本科生研究助理将考虑到妇女和少数群体在地球科学界任职人数不足的情况。

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.