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

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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.