Provenance of Loessite in Equatorial Pangea: Implications for Paleoclimatic Reconstructions

两种环流模型和一些地质资料都表明，盘古超大陆的特征是季风环流。然而，季风爆发的时间，以及关于古赤道纬度的风向、强度和季节性的数据，仍然没有得到很好的约束。这项研究的目的是描述北美西部(赤道盘古)古风成粉砂岩的物源，以圈定晚古生代时期的古扩散和古大气环流。为了实现这一目标，PLS和学生们将把基于岩石学的骨架矿物学和粒度分析与单晶碎屑锆石年龄测定相结合，以准确地建立粉砂来源和粒度谱，从而确定地表风向和强度。碎屑锆石年龄谱应反映其物源的年龄谱，即晚古生代/中生代早期暴露的基底地体和(或)含粉砂地层。我们将利用北美现有的碎屑锆石参考剖面，辅以关键的克拉通参考剖面，探讨泥沙再循环的可能性和影响。初步结果表明，碎屑锆石和粒度数据可以用来约束当时和从属的风向和风力，并提供季节性信息。碎屑岩锆石年代学的结果特别表明，这项工作还可能有助于改善对目标红层和晚古生代阶段界线的最大年龄的限制。最终，研究结果还将有助于(1)更好地了解晚古生代西部盘古气候的低纬古气候和潜在的古构造作用，以及(2)我们对气候变化的理解，以及对气候模型的总体校准。

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.