Collaborative Research: Refinement of the Late Permian and Early Triassic Time Scale through Integrated Ar/Ar and U/Pb Radioisotopic Dating and Magnetostratigraphy

9614324 Renne古生代末期的环境危机表现为海洋深度退化、动植物严重灭绝以及地球化学和同位素异常。由于缺乏可靠的地质年代学数据，寻找一个或多个原因以及确定观测到的现象之间的遗传联系受到阻碍。虽然二叠纪-三叠纪（P-T）界线的年代已经相当清楚，但仍有许多工作要做，以检验界线事件是否在全球等时，并建立界线前后事件的时间尺度。灭绝是持续的还是快速的，或者是脉冲式的，这取决于对时间尺度更好的校准。本研究将结合磁地层资料，为岩浆岩和锆石提供高精度的Ar/Ar和U/Pb测年，大大提高了时间尺度的分辨率。为Kiaman超年表之后的“Illawara”逆转建立一个校准良好的磁极时间尺度，将有助于促进全球对比，并有助于消除动物地方性和生物地层边界可能的历时性问题。拟议中的研究将集中在美国西部（德克萨斯州、新墨西哥州和怀俄明州）可接近的、研究充分的部分，这些部分已经获得了许多样本和一些数据。本项目提出了额外的可行性研究，费用很少或不需要，这将有助于确定南极洲、阿根廷、中国和南非的部分地区是否值得为实现本项目目标而进行进一步的研究。

9614324 Renne Environmental crises at the end of the Paleozoic are indicated by evidence for profound marine regression, severe faunal and floral extinctions, and geochemical and isotopic anomalies. The search for a cause or causes, as well as establishing genetic links between the observed phenomena, is hindered by a paucity of reliable geochronologic data. Though the Permian-Triassic (P-T) boundary is now reasonably well dated, much work remains to test whether the boundary events were globally isochronous and to establish the time scale of events before and after the boundary. Whether the extinctions were protracted or rapid, or occurred in pulses, relies on better calibration of the time scale. The research proposed herein would provide high-precision Ar/Ar an U/Pb dates for sanidine and zircon from tephras combined with magnetostratigraphic data, which would vastly improve the resolution of the time scale. Establishing a well-calibrated magnetic polarity time scale for the "Illawara" reversals after the Kiaman Superchron will facilitate global correlations and help obviate problems arising from faunal provincialism and possible diachronism of biostratigraphic boundaries. The proposed research would concentrate on accessible, well-studied sections in the western U.S. (Texas, New Mexico, and Wyoming) for which many samples and some data have already been obtained. Additional feasibility studies are proposed, at little or no cost to this project, which would help determine whether sections in Antarctica, Argentina, China, and South Africa merit future research towards the goals of this project.