COLLABORATIVE RESEARCH: Testing hypotheses for Late Devonian biotic and climatic events via high-precision CA-TIMS U-Pb zircon dating and quantitative correlation tools

合作研究：通过高精度的CA-TIMS U-Pb锆石定年和定量相关工具测试晚泥盆世生物和气候事件的假说。杰弗里·奥弗，EAR-1124275SUNY Geneseo晚泥盆世发生了一系列全球性生物灭绝事件，其规模之大足以被算作显生界的主要大灭绝之一。然而，关于海洋沉积、生物地球化学循环、海平面和气候的灭绝和相关变化的起因机制尚未达成共识。对晚泥盆世灭绝的相互竞争的假说--包括海平面波动和退缩、气候冷却、海洋缺氧、闪电冲击和/或大规模火山作用--目前受到古生物、构造和替代气候记录缺乏足够的时间分辨率的阻碍。在这项研究中，一个由古生物学家、生物地层学家和同位素地球化学家组成的多学科研究小组将把关键地层层序中层间火山灰层的高精度U-Pb锆石年代学与定量生物地层学相结合，应用于全球晚泥盆世多分类数据库，该数据库是根据文献和新的高分辨率采样建立的。U-Pb年代学将利用化学磨损法和EARTHTIME四峰同位素稀释法测定约0.1 Ma的分辨率年龄，通过约束优化来标定第一个高分辨率的晚泥盆世复合标准的建立。利用这个高分辨率的年龄模型，研究小组将询问与晚泥盆世生物事件的突发性、它们的全球同步性和过程驱动因素有关的几个基本问题。需要解决的具体假设包括：地外影响或大规模火山活动与生物危机之间的同步性和因果关系，相关的海平面上升和下降的速率以及碳循环和温度的替代记录中的波动是否与米兰科维奇带轨道强迫一致，以及气候、冰川稳定、海洋缺氧和碳循环之间的反馈是否导致了晚泥盆世的生物危机。这项研究将通过本科生参加一个多学科的国际科学团队来影响STEM人力资源的开发；发展国际科学合作；支持EARTHTIME地球年代学倡议的科学任务，以及相关的研究和推广计划；为许多其他古生代气候研究提供根本改进的年表；并提高我们对深层气候状态转变的理解，这种转变可能类似于导致我们目前冰库的那些转变。拟议研究的科学过程和内容将由国家科学基金会资助的一项平行的STEM教育倡议记录下来，该倡议开发了一系列基于网络的学习对象，教授地质年代学和地球历史科学。

COLLABORATIVE RESEARCH: Testing hypotheses for Late Devonian biotic and climatic events via high-precision CA-TIMS U-Pb zircon dating and quantitative correlation toolsMark Schmitz, EAR-1124488Boise State UniversityD. Jeffrey Over, EAR-1124275SUNY GeneseoABSTRACT The Late Devonian period hosts a series of global biological extinction events of such magnitude as to be counted among the major mass extinctions of the Phanerozoic. Yet no consensus has yet been reached regarding the causative mechanisms of extinction and associated changes in marine sedimentation, biogeochemical cycling, sea level and climate. Testing of competing hypotheses for Late Devonian extinctions?which include sea-level fluctuations and regression, climatic cooling, ocean anoxia, bolide impact, and/or massive volcanism?is currently hampered by a lack of sufficient temporal resolution in paleobiological, tectonic and proxy climate records.In this study, a multi-disciplinary research team of paleontologists, biostratigraphers and isotope geochemists will combine high-precision U-Pb zircon geochronology on interstratified volcanic ash beds in key stratigraphic successions with quantitative biostratigraphy applied to a global Late Devonian multi-taxa database compiled from the literature and new high-resolution sampling. The U-Pb geochronology will utilize the chemical abrasion and EARTHTIME quadruple spike isotope dilution methods to measure ca 0.1 Ma resolution ages, which will calibrate the construction of the first highly resolved composite standard for the Late Devonian via constrained optimization. With this high resolution age model the research team will interrogate several fundamental questions relating to the abruptness of the late Devonian biotic events, their global synchrony, and process drivers. Specific hypotheses to be addressed include the synchrony and causality between extraterrestrial impacts or massive volcanism and biotic crises, whether the rates of associated eustatic rise and fall and fluctuations in proxy records of carbon cycling and temperature are consistent with Milankovich-band orbital forcing, and if feedbacks between climate, glacioeustasy, ocean anoxia, and the carbon cycle caused the Late Devonian biotic crises.This research will impact STEM human resource development via participation of undergraduate students in a multi-disciplinary international science team; develop international scientific collaborations; support the science mission of the EARTHTIME geochronology initiative, and its associated inreach and outreach programs; provide fundamentally improved chronologies for numerous other Paleozoic climate studies; and improve our understanding of deep time climate state transitions potentially analogous to those leading to our current icehouse. The scientific process and content of the proposed research will be captured by a parallel NSF-funded STEM education initiative developing a series of web-based learning objects to teach the science of geochronology and Earth history.