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