Using paleowind data to reconstruct Pangean paleoclimateSupercontinent PangeaPaleomagnetismPaleoclimatologyColorado PlateauAeolian Sediment TransportWind Direction Controls Dune MorphologyWinds Interpreted from Aeolian DunesPaleoclimate from Loess Deposits: Early Permian Cutler GroupWinds Predicted from GCMsPaleoclimate ReconstructionsAlternate ReconstructionsThank youUsing paleowind data to reconstruct Pangean paleoclimateErin EastwoodGEO 387HDecember 2, 2008Supercontinent Pangea Extraordinary effect on global paleoclimate Global red beds and evaporites Monsoons: seasonal reversal in surface winds Past climate change key to futureLowCO2HighCO2Map by Ron BlakeyChart from Dr. Yang’s lecture notesPaleomagnetismDott and Prothero (2002)Earth’s magnetic fieldIron-bearing mineralsDetermine paleo-latitudeRequires multiple data points from each continentDetrital hematite in sedimentary rocksIgneous rocksPaleoclimatology Ancient climate change, various time-scales Establish range of natural climatic variability Type of proxy data used = function of geologic time period trying to construct Late Carboniferous-Jurassic: atmospheric circulation = loessites & aeolian dune deposits Paleo-latitude = paleomagnetismPermian Cutler Group, SE UtahAeolian loess = wind-blown dustPhoto by Lynn SoreghanAeolian dunes = wind-blown sandColorado PlateauPaleogeographic maps by Ron Blakey2500m aeolian sandstone deposits during time of PangeaPermian Cedar Mesa SandstoneAeolian Sediment TransportPermian Cedar Mesa Sandstone, Utah5mLiDAR image of White Sands, NMModern dune Ancient dunesCrescentic ridges, Saudi ArabiaWind Direction Controls Dune MorphologyBarchans, MoroccoLinears, Mauritania Stars, Algeria100m5 km5 km50 kmWinds Interpreted from Aeolian Dunes Each vector represents > 20 dip measurements Random sampling – statistical average Largest paleowind datasetPeterson (1988)Modified from Rowe et al. (2007)Paleoclimate from Loess Deposits: Early Permian Cutler Group U-Pb geochronology zircon crystals Summer=monsoonal westerly winds Winter=easterly winds (N or S direction not constrained) Loessite soils record seasonally wet conditions Loess lacks wind intensity informationWinds Predicted from GCMsModified from Rowe et al. (2007)NH summer windsNH winter windsParrish and Peterson (1988)Summer=subtropical H-P cell, dominate windsWinter=monsoon L-P cellPatzkowsky et al. (1991)•Summer=monsoon L-P cell•Winter=subtropical H-P trade windsRowe et al. (2007), Chandler et al. (1992) Subtropical H-P trade winds turn to tropical westerliesPaleoclimate ReconstructionsLoope et al. (2004) Paleo-latitudes using detrital hematite paleomagnetism Western US remains near-equatorial through Jurassic NE trade winds shift to tropical north-westerliesMap by Ron BlakeyRowe et al. (2007) Traditional paleomagnetism Western US 18N by Jurassic Assume paleowinds correctOne of the following must be true: Paleomagnetism & paleogeography incorrect Climate model incorrect – no shift from trades to westerlies Paleowind data imply circulation patterns different from todayPaleoclimate ReconstructionsMap by Ron BlakeyAlternate Reconstructions Multiple wind directions – seasonal winds Seasonal signature lost in statistical averaging Create detailed paleowind datasetNPermian Cedar Mesa SandstoneThank
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