Using paleowind data to reconstruct Pangean paleoclimate
Erin EastwoodGEO 387H
December 2, 2008
Supercontinent Pangea
Extraordinary effect on global paleoclimate
Global red beds and evaporites
Monsoons: seasonal reversal in surface winds
Past climate change key to future
LowCO2
HighCO2
Map by Ron Blakey
Chart from Dr. Yang’s lecture notes
Paleomagnetism
Dott and Prothero (2002)
Earth’s magnetic fieldIron-bearing mineralsDetermine paleo-latitudeRequires multiple data points from each continentDetrital hematite in sedimentary rocksIgneous rocks
Paleoclimatology
Ancient climate change, various time-scales Establish range of natural climatic variability Type of proxy data used = function of geologic time period trying to constructLate Carboniferous-Jurassic:
atmospheric circulation = loessites & aeolian dune depositsPaleo-latitude = paleomagnetism
Permian Cutler Group, SE Utah
Aeolian loess = wind-blown dust
Photo by Lynn Soreghan
Aeolian dunes = wind-blown sand
Colorado Plateau
Paleogeographic maps by Ron Blakey
2500m aeolian
sandstone deposits during time of Pangea
Permian Cedar Mesa Sandstone
Aeolian Sediment Transport
Permian Cedar Mesa Sandstone, Utah
5mLiDAR image of White Sands, NM
Modern dune Ancient dunes
Crescentic ridges, Saudi Arabia
Wind Direction Controls Dune Morphology
Barchans, Morocco
Linears, Mauritania Stars, Algeria
100m 5 km
5 km50 km
Winds Interpreted from Aeolian Dunes
Each vector represents > 20 dip measurementsRandom sampling – statistical averageLargest paleowind dataset
Peterson (1988)
Modified from Rowe et al. (2007)
Paleoclimate from Loess Deposits: Early Permian Cutler Group
U-Pb geochronology zircon crystalsSummer=monsoonal westerly windsWinter=easterly winds (N or S direction not constrained)Loessite soils record seasonally wet conditionsLoess lacks wind intensity information
Winds Predicted from GCMs
Modified from Rowe et al. (2007)
NH summer winds NH winter winds
Parrish and Peterson (1988)Summer=subtropical H-P cell, dominate windsWinter=monsoon L-P cell
Patzkowsky et al. (1991)•Summer=monsoon L-P cell•Winter=subtropical H-P trade winds
Rowe et al. (2007), Chandler et al. (1992)Subtropical H-P trade winds turn to tropical westerlies
Paleoclimate ReconstructionsLoope et al. (2004)
Paleo-latitudes using detrital hematite paleomagnetismWestern US remains near-equatorial through JurassicNE trade winds shift to tropical north-westerlies
Map by Ron Blakey
Rowe et al. (2007)Traditional paleomagnetismWestern US 18N by JurassicAssume paleowinds correct
One of the following must be true:Paleomagnetism & paleogeography incorrectClimate model incorrect – no shift from trades to westerliesPaleowind data imply circulation patterns different from today
Paleoclimate Reconstructions
Map by Ron Blakey
Alternate Reconstructions
Multiple wind directions – seasonal windsSeasonal signature lost in statistical averagingCreate detailed paleowind dataset
N
Permian Cedar Mesa Sandstone
Thank you