Hit or miss - Meteorite impacts in the Cretaceous Western Interior Sea: Sedimentological and paleoecological response

西部内海，西临落基山脉，东邻加拿大盾，在白垩纪是一个动态的陆表海，覆盖北美西部，以全球高海平面为标志。在整个白垩纪，海道的古地理界线变化很大。海洋群落对由古海洋和古地理变化(动物迁徙路线的开放和关闭)、底物和氧气变化所驱动的波动的古生态条件作出反应。在沉积物供应量低的地区，如盆地的东缘，广泛页岩包内的较粗颗粒段往往通过形成生物碎屑层的高浓度磷酸盐脊椎动物碎屑来识别。这些生物碎屑层或骨层的成因被解释为波浪侵蚀面或海侵滞后沉积，其中一些已在盆地范围内被识别。我们推测，这些骨床中的一些是海啸沉积的结果，这些沉积物是由两颗陨石产生的，这两颗陨石要么直接击中西部内海，要么落在附近。这些是阿尔伯塔省的斯蒂恩河陨石坑和萨斯喀彻温省的后海湾陨石坑，日期分别为91 Ma和99 Ma。对灾难性事件的生物反应将通过观察几个化石组进行研究，包括脊椎动物组合、有孔虫、钙质超微化石和甲藻。方法将包括详细的岩石学和地球化学分析，以寻找陨石撞击指标(冲击石英、玻璃陨石等)，脊椎动物遗骸的挖掘研究，以及高分辨率微型动物群分析，以确定这些事件的发生。我们在西部内海的研究将区分那些形成与海平面有关的重要层序界面、盆地范围的层序界面、用于电缆测井对比的层序边界和更多的随机事件层。人们将广泛研究最近发生在地球上的海啸事件对生态系统的影响。因此，认识古代海啸沉积、其范围和对盆地生态和海洋生物形式的影响成为一项令人兴奋的努力。**********

The Western Interior Sea bordered by the Rocky Mountains to the West and the Canadian Shield to the East was a dynamic epicontinental sea covering Western North America during the Cretaceous Period marked by global high sea levels. Throughout the Cretaceous the seaway's paleogeographic boundaries varied significantly. Marine communities responded to fluctuating paleoecological conditions that were driven by paleoceanographic and paleogeographic changes (opening and closing of faunal migration routes), substrate and oxygen variations. In areas of low sediment supply such as the eastern margin of the basin coarser grained intervals within extensive shale packages are often recognized by their high concentration of phosphatic vertebrate debris forming bioclastic layers. The origin of these bioclastic horizons or bonebeds, some of them recognized basinwide, has been explained as wave erosional surfaces or transgressive lag deposits. We hypothesize that some of these bonebeds are the result of tsunami deposits that were generated by two meteorites that either directly hit the Western Interior Seaway or landed in close proximity. These are the Steen River Crater in Alberta dated 91 MA and the Deep Bay Crater in Saskatchewan dated 99 MA. Biotic responses to a catastrophic event will be investigated by looking at several fossil groups including vertebrate assemblages, foraminifera, calcareous nannofossils and dinoflagellates. Methods will include detailed petrographic and geochemical analysis in the search of meteorite impact indicators (shocked quartz, tektites etc.), taphonomic studies of vertebrate remains, and high resolution microfaunal analysis in order to bracket these events. Our studies in the Western Interior Sea will distinguish between those horizons that form important sea level related, basin-wide sequence boundaries serving for wireline log correlations and more random event beds. Recent tsunami events on earth will be extensively studied for their impact on ecological systems. Consequently, recognition of ancient tsunami deposits, their extent and impact on basin ecology and marine life forms becomes an exciting endeavor. **********