Collaborative Research: Testing the Early Late Ordovician Cool Water Hypothesis

合作研究：验证晚奥陶世早期冷水假说/ Achim Herrmann，路易斯安那州立大学/ kenneth MacLeod，密苏里大学/ stephen Leslie， James Madison大学/[-1324954，-1323444，- 13245774]晚奥陶世冰川作用（LOG）与显生宙第二次大灭绝事件有关。它标志着早古生代持续~150m的全球变暖条件的结束，发生在pCO2升高的条件下。最近，人们对LOG的持续时间、其潜在的驱动机制以及冰期前的长期温度变化提出了相当大的怀疑。例如，在LOG之前大约15 Ma，北美大陆板块位于热带至亚热带纬度，但沉积学和古生物学证据表明，从温水碳酸盐沉积到冷水碳酸盐沉积的转变。目前尚不清楚这种沉积学变化是否反映了全球变冷（表明早在晚奥陶世冰期之前就对全球气候系统产生了重大扰动），还是对构造活动的物理反应，而没有必要的气候影响。这些项目将通过广泛的地球化学研究来检验试图解释这一事件的相互竞争的假设。特别是，pi将利用牙形石磷灰石（delta18O和epsilonNd）和碳酸盐（DELTA48， delta18O和delta13C）的地球化学档案来解决早晚奥陶世的古海洋条件问题。他们期望这项研究将有助于1)澄清这一时期古生物学/沉积学变化的潜在原因，2)更好地理解陆表海流，并改进陆表低纬度碳酸盐岩台地的相模式（现代没有类似的台地），3)更好地记录奥陶纪温室期段的温度历史。本研究项目将由本科生、研究生和一名中学科学教师积极参与。因此，该项目不仅将影响当前的大学生和研究人员，还将通过加强地球科学中等教育教师的知识基础和科学课程，影响后代的学生。数据将提供给可公开访问的数据库，供古气候和古海洋学领域的进一步研究和一般教育使用。

Collaborative Research: Testing the Early Late Ordovician Cool Water Hypothesisby Achim Herrmann, Louisiana State UniversityKenneth MacLeod, University of MissouriStephen Leslie, James Madison UniversityEAR-1324954, -1323444, -1324577ABSTRACTThe Late Ordovician glaciation (LOG) is associated with the second largest mass extinction event of the Phanerozoic. It marks the end of the global warm conditions of the early Paleozoic that lasted ~150my and occurred under elevated pCO2 conditions. Considerable doubt has recently been raised with regard to the duration of the LOG, its potential driving mechanisms, and pre-glacial, long-term temperature variations. For instance approximately 15 Ma prior to LOG the North American continental plate was situated in tropical to subtropical latitudes, but sedimentological and paleontological evidence suggest a shift from deposition of warm water carbonates to deposition of cool water carbonates. It is not clear whether this sedimentological change reflects global cooling (indicating significant perturbation to the global climate system well before the Late Ordovician glaciation) or physical responses to tectonic activity with no requisite climatic implications. The projects will test competing hypotheses that try to explain this event through an extensive geochemical study. In particular, PIs will use the geochemical archive of conodont apatite (delta18O and epsilonNd) and carbonates (DELTA48, delta18O, and delta13C) to address questions about paleoceanographic conditions during the Early Late Ordovician. They expect that this research will lead 1) to clarification of potential causes for the paleontological/sedimentological changes during this interval, 2) to a better understanding of epicontinental sea circulation and an improved facies model for epicontinental low latitude carbonate platforms (for which no modern-day analogues exist), and 3) to better documentation of the temperature history of the Ordovician greenhouse interval.This research project will have active participation by undergraduate students, graduate students, and a secondary school science teacher. Therefore, the project will not only impact present university students and researchers, it will also impact future generations of students through enhancing an earth science secondary educations teacher¡¦s knowledge base and science curriculum. Data will be contributed to publicly accessible databases making them available for further research and general education in the fields of paleoclimate and paleoceanography.