Earth's climate during the late Paleozoic (ca. 300 Ma) was profoundly affected by both large-scale continental glaciation and monsoonal circulation. Accordingly, key elements of its climate exhibit parallels to Earth's modern climate, which has intrigued both those who model climate, and those who reconstruct climate using proxy data. Validation and further sophistication of climate models of this interval are hampered, however, by low-resolution geologic datasets. That is, although the broad strokes of Pangea's climate system are well established, many aspects remain unconstrained. Preliminary geochronologic and sedimentologic data collected by the PIs from a lower Permian loessite-paleosol couplet in the study region document a profound shift in equatorial wind direction and strength; the PIs hypothesize that this shift signals a geologically abrupt change in the intensity of monsoonal circulation of western Pangea between glacials, and interglacials. The objective of the proposed study, therefore, is to examine and characterize in detail the character, variability, and chronology of such high-frequency shifts in atmospheric circulation in western equatorial Pangea, just before 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 have targeted for study loessite-paleosol couplets that represent wide geographic coverage in western equatorial Pangea (western U.S.), and that date from (1) middle-late Pennsylvanian (zonal), and (2) early Permian (monsoonal) times. Each study couplet will be subjected to several previously-tested techniques including detrital-zircon based provenance analysis, magnetic susceptibility, whole-rock geochemistry, and grain-size analysis as proxies for various climatic parameters including wind direction, strength, and seasonality, 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 absolute age 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 Paleozoic icehouse 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 of the Pangean interval. Results will also provide improved age constraints on target strata, and durations of climatic fluctuations, and will enable further testing of the paleosol-carbonate dating technique. Broader Impacts Resulting from Proposed Activity "Project results will provide better constraints for climate models of the late Paleozoic and for natural variation in climatic conditions of interglacials over geologically long periods of time. Accordingly, results should further our understanding of Earth's climate system in general, ultimately contributing to improved climate predictions in our modern interglacial world. The PIs will fund and train at least two graduate students directly from this proposed research, and have a strong commitment to, and history of, involving undergraduate geoscience majors in their research, which they will continue in the proposed project. OU's formal agreement with Fort Valley State University (a Historically Black University), in which upperclassmen complete their geology degrees 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, and will actively recruit at least one such student to work on aspects of the proposed project. The project will enhance teaching and training at all levels (undergraduate through professional). MJS teaches an Earth System Science course for education majors, and GSS teaches advanced courses in Earth's Past Climate and Depositional Systems; both PIs regularly utilizes case examples from their own research to illustrate climate concepts. Furthermore, the project will enable significant cross-disciplinary training, and involves a mixed-gender research team of sedimentologists and geochronologists. Finally, the PIs and students will continue to disseminate results in high-profile journals and at national meetings.
