Post on 22-Dec-2015
GE0-3112GE0-3112 Sedimentary processes and products Sedimentary processes and products
Lecture 7. Aeolian sedimentsLecture 7. Aeolian sediments
Geoff CornerGeoff CornerDepartment of GeologyDepartment of GeologyUniversity of TromsøUniversity of Tromsø20062006
Literature:Literature:- Leeder 1999. Ch. 16 - Leeder 1999. Ch. 16 Aeolian sediments in low-latitude desertsAeolian sediments in low-latitude deserts(See also Ch. 8 & Ch. 13). (See also Ch. 8 & Ch. 13).
ContentsContents
►7.1 Aeolian environments7.1 Aeolian environments►7.2 Desert types and distribution7.2 Desert types and distribution►7.3 Sediment flow paths7.3 Sediment flow paths►7.4 Dunes and draas7.4 Dunes and draas►7.5 Desert facies and architecture7.5 Desert facies and architecture
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Aeolian environmentsAeolian environments
►Types:Types: Deserts and semi-arid regionsDeserts and semi-arid regions Beaches and sabkasBeaches and sabkas Sandy river banksSandy river banks Periglacial regionsPeriglacial regions
►Characteristics:Characteristics: Lack of vegetationLack of vegetation Moderate to strong windsModerate to strong winds Mobile sand and silt sedimentMobile sand and silt sediment
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DefinitionsDefinitions
►Desert: arid zone having a large deficit Desert: arid zone having a large deficit of precipitation (P) in relation to of precipitation (P) in relation to evaotranspiration (ET)evaotranspiration (ET)
►Definitions/subdivision (P/ET ratios):Definitions/subdivision (P/ET ratios): Hyperarid:Hyperarid: <0.03 <0.03 Arid: Arid: 0.03-0.20.03-0.2 Semiarid:Semiarid: 0.2-0.50.2-0.5 Subhumid:Subhumid: 0.5-0.70.5-0.7
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World distribution of deserts (arid, hyperarid) and other dry areas.
Sahara
Arabia
Gobi
KalahariNamib
Patagonia(Argentina))
Atacama (Chile)
South-centralAustralia
SouthwestN. America
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Desert types and distributionDesert types and distribution
►Trade wind deserts (subtropical high-Trade wind deserts (subtropical high-pressure)pressure) N. Africa, Arabia, south-central Australia.N. Africa, Arabia, south-central Australia. Atacama, Namib (cool offshore current).Atacama, Namib (cool offshore current).
►Continental desertsContinental deserts Central asia.Central asia.
►Rain shadow/continentalRain shadow/continental western N. America, western N. America,
sub-Andean S. America.sub-Andean S. America.
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► Sub-tropical high pressure cells and trade winds.Sub-tropical high pressure cells and trade winds.
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► Rain shadow effect (lower precipitation E of Rain shadow effect (lower precipitation E of mountains)mountains)
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Deserts and aeolian depositsDeserts and aeolian deposits
►Rocky desertsRocky deserts►Sandy desertsSandy deserts►Most deserts contain rock outcrops Most deserts contain rock outcrops
and aeolian, lake or playa, and alluvial and aeolian, lake or playa, and alluvial depositsdeposits
►Loess deposits in and beyond desertsLoess deposits in and beyond deserts
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► Presently active sand dunes.Presently active sand dunes.
► Glacial maximum sand dunes.Glacial maximum sand dunes.
► Loess (mostly glacial maximum).Loess (mostly glacial maximum).
Distribution of Distribution of aeolian depositsaeolian deposits
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Sediment transportSediment transport
Sand-flow map for Saharan ergs
►SandSand
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Aerosol dust budgets for the Sahara and adjacent Atlantic Oceann.
►DustDust
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Dune types and interdune Dune types and interdune terrainterrain
►Bedrock and erosional forms (yardangs)Bedrock and erosional forms (yardangs)►DunesDunes
BarchansBarchans Transverse dunesTransverse dunes Linear dunesLinear dunes Star dunesStar dunes
►Lakes and (saline) playasLakes and (saline) playas►Alluvial fans and stream bedsAlluvial fans and stream beds
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Linear and compound dunes
Star dunes
Linear dunes
Interdune and intererg areas
Barchan dunes
Saharan dunes
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Star dunes
Barchan dunes
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Linear dunes
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Linear and compound dunes
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Star dunes
Namib desert
Transverse dunes?
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Uluru (Ayer’s Rock),Central Australia
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Controls on sand depositionControls on sand deposition
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Facies and architectureFacies and architecture
Facies sequencesat the marginsof an erg.
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Aeolian architectureAeolian architecture
Dune Interdune
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► U. Jurassic Entrada U. Jurassic Entrada sandstone, W. USA. sandstone, W. USA.
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► Permian Rotliegendes, Permian Rotliegendes, NW EuropeNW Europe
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Active dry phase
Wet phase
Formation of ’supersurface’
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Further readingFurther reading
►Galloway & Hobday 1996. Ch. 10. Galloway & Hobday 1996. Ch. 10. Eolian systems.Eolian systems.
►Kocurek, in Reading (ed.), 1996. Ch. 5. Kocurek, in Reading (ed.), 1996. Ch. 5. Desert aeolian systems. Desert aeolian systems.