Glacial-Interglacial Variations in Late Paleozoic Atmospheric Circulation Inferred from Loessite-Paleosol Couplets of Western Equatorial Pangea

晚古生代（约300 Ma）的地球气候深受大尺度大陆冰川作用和季风环流的影响。因此，其气候的关键要素与地球的现代气候表现出相似之处，这引起了那些模拟气候的人和那些利用代理数据重建气候的人的兴趣。然而，低分辨率地质数据集阻碍了该区间气候模型的验证和进一步完善。也就是说，尽管盘古大陆气候系统的大体特征已经确立，但许多方面仍未受到限制。pi在研究区下二叠纪—古土壤对中收集的初步地质年代学和沉积学资料表明，赤道风向和强度发生了深刻的变化；pi假设这种转变标志着西盘古大陆在冰期和间冰期之间季风环流强度的地质突变。因此，本研究的目的是详细研究和描述赤道盘古大陆西部季风条件发生前后大气环流高频变化的特征、变异性和年代学。为了实现这一目标，pi和学生将研究黄土（风成淤泥）和间冰期交替状态的间冰期古土壤。pi的目标是研究黄土-古土壤对联，这些对联代表了西赤道盘古大陆（美国西部）广泛的地理覆盖范围，并且可以追溯到(1)宾夕法尼亚中晚期（地带性）和(2)早二叠纪（季风性）时代。每个研究对联将接受几个先前测试过的技术，包括碎屑锆石的物源分析、磁化率、全岩地球化学和粒度分析，作为各种气候参数的代表，包括风向、强度、季节性和相对干旱。最年轻（火山）碎屑锆石的高精度放射性同位素（U-Pb）定年和一些成童碳酸盐岩的实验定年将用于改善对目标对联的绝对约束，并约束这些冰期-间冰期移动的持续时间。建议活动的智力价值——项目结果将使我们能够以前所未有的细节检查古生代晚期的大气环流变化，特别是在盘古宙间隔的纬向和季风状态下赤道环流的高分辨率（冰期-间冰期）变化。结果还将提供对目标地层的更好的年龄限制，以及气候波动的持续时间，并将使古土壤-碳酸盐定年技术的进一步测试成为可能。“项目结果将为晚古生代的气候模型和地质上较长时期间冰期气候条件的自然变化提供更好的约束。因此，这些结果将进一步加深我们对地球气候系统的总体理解，最终有助于改进我们现代间冰期世界的气候预测。pi将资助和培训至少两名直接来自该研究的研究生，并且有很强的承诺和历史，让本科地球科学专业的学生参与他们的研究，他们将在拟议的项目中继续研究。开放大学与州立堡谷大学（一所历史悠久的黑人大学）的正式协议，高年级学生在开放大学完成地质学学位，这为少数民族学生参与这项本科研究提供了一个极好的机会。MJS还使用NSF资金支持科学教育专业的本科生研究项目，并将积极招募至少一名此类学生参与拟议项目的各个方面。该项目将加强各级（从本科到专业）的教学和培训。MJS教授教育专业的地球系统科学课程，GSS教授地球过去气候和沉积系统的高级课程；这两个pi经常利用他们自己研究中的案例来说明气候概念。此外，该项目将提供重要的跨学科培训，并包括一个由沉积学家和地质年代学家组成的男女混合研究小组。最后，pi和学生将继续在高知名度的期刊和国家会议上传播结果。

Earth's climate during the late Paleozoic (ca. 300 Ma) was profoundly affected by both large-scalecontinental glaciation and monsoonal circulation. Accordingly, key elements of its climate exhibitparallels to Earth's modern climate, which has intrigued both those who model climate, and those whoreconstruct climate using proxy data. Validation and further sophistication of climate models of thisinterval are hampered, however, by low-resolution geologic datasets. That is, although the broad strokesof Pangea's climate system are well established, many aspects remain unconstrained.Preliminary geochronologic and sedimentologic data collected by the PIs from a lower Permianloessite-paleosol couplet in the study region document a profound shift in equatorial wind direction andstrength; the PIs hypothesize that this shift signals a geologically abrupt change in the intensity ofmonsoonal circulation of western Pangea between glacials, and interglacials. The objective of theproposed study, therefore, is to examine and characterize in detail the character, variability, andchronology of such high-frequency shifts in atmospheric circulation in western equatorial Pangea, justbefore and after onset of monsoonal conditions. To achieve this, the PIs and students will study loessite(eolian silt) and intercalated paleosols that record alternating glacial-interglacial states. The PIs havetargeted for study loessite-paleosol couplets that represent wide geographic coverage in westernequatorial Pangea (western U.S.), and that date from (1) middle-late Pennsylvanian (zonal), and (2) earlyPermian (monsoonal) times. Each study couplet will be subjected to several previously-tested techniquesincluding detrital-zircon based provenance analysis, magnetic susceptibility, whole-rock geochemistry,and grain-size analysis as proxies for various climatic parameters including wind direction, strength, andseasonality, and relative aridity. High-precision, radio-isotopic (U-Pb) dating of the youngest (volcanic)detrital zircons and some experimental dating of pedogenic carbonate will be used to improve absoluteage constraints on the target couplets, and constrain durations of these glacial-interglacial shifts.Intellectual Merit of Proposed Activity-- Project results will enable examination of late Paleozoicicehouse variations in atmospheric circulation at an unprecedented detail, and in particular, high-resolution(glacial-interglacial) shifts in equatorial circulation during both zonal and monsoonal states ofthe Pangean interval. Results will also provide improved age constraints on target strata, and durations ofclimatic fluctuations, and will enable further testing of the paleosol-carbonate dating technique.Broader Impacts Resulting from Proposed Activity "Project results will provide better constraints forclimate models of the late Paleozoic and for natural variation in climatic conditions of interglacials overgeologically long periods of time. Accordingly, results should further our understanding of Earth'sclimate system in general, ultimately contributing to improved climate predictions in our moderninterglacial world. The PIs will fund and train at least two graduate students directly from this proposedresearch, and have a strong commitment to, and history of, involving undergraduate geoscience majors intheir research, which they will continue in the proposed project. OU's formal agreement with Fort ValleyState University (a Historically Black University), in which upperclassmen complete their geologydegrees at OU, offers an excellent opportunity to involve minority students in this undergraduate research.MJS has also used NSF funds to support science-education majors in undergraduate research projects, andwill actively recruit at least one such student to work on aspects of the proposed project. The projectwill enhance teaching and training at all levels (undergraduate through professional). MJS teaches anEarth System Science course for education majors, and GSS teaches advanced courses in Earth's PastClimate and Depositional Systems; both PIs regularly utilizes case examples from their own research toillustrate climate concepts. Furthermore, the project will enable significant cross-disciplinary training, andinvolves a mixed-gender research team of sedimentologists and geochronologists. Finally, the PIs andstudents will continue to disseminate results in high-profile journals and at national meetings.