Provenance of Loessite in Equatorial Pangea: Implications for Paleoclimatic Reconstructions

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Both circulation models and some geologic data suggest that monsoonal circulation characterized the Pangean supercontinent. The timing of monsoon onset, however, and data on wind directions, intensities and seasonality at paleoequatorial latitudes, remain poorly constrained. The objective of this study is to characterize the provenance of ancient eolian siltstones of western North America (western equatorial Pangea) to delineate paleodispersal and thereby paleoatmospheric circulation in late Paleozoic time. To achieve the objective, the Pls and students will integrate petrographically based framework mineralogy and grain-size analyses with singlecrystal detrital zircon age dating to precisely establish both silt provenance and size spectra, and thereby identify surface wind directions and strengths. The detrital zircon age spectra should reflect the age spectra of their sources, i.e., basement terranes and/or silt-bearing strata exposed in late Paleozoic/earliest Mesozoic time. We will address the possibility and implications of silt recycling by using existing detlital zircon reference sections published for North America, supplemented by key cratonal reference sections.Preliminary results indicate that detrital zircon and grain-size data can be used to constrain prevailing and subordinate wind directions and strengths, and provide information on seasonality. Results of detrital zircon geochronology in particular suggest that this work may additionally contribute to improvements in constraints on maximum ages of the target redbeds and of late Paleozoic stage boundaries. Ultimately, study results should also contribute to (1) an improved understanding of the low-latitude paleoclimate and potentially paleotectonism of late Paleozoic western Pangea, and (2) our understanding of climate change, and calibration of climate models in general.