GE0-3112 Sedimentary processes and products Lecture 7. Aeolian sediments Geoff Corner Department of...

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

Aeolian GEO-3112 2006

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


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


World distribution of deserts (arid, hyperarid) and other dry areas.

Sahara

Arabia

Gobi

KalahariNamib

Patagonia(Argentina))

Atacama (Chile)

South-centralAustralia

SouthwestN. America


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.


► Sub-tropical high pressure cells and trade winds.Sub-tropical high pressure cells and trade winds.


► Rain shadow effect (lower precipitation E of Rain shadow effect (lower precipitation E of mountains)mountains)


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


► 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


Sediment transportSediment transport

Sand-flow map for Saharan ergs

►SandSand


Aerosol dust budgets for the Sahara and adjacent Atlantic Oceann.

►DustDust


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


Linear and compound dunes

Star dunes

Linear dunes

Interdune and intererg areas

Barchan dunes

Saharan dunes


Star dunes

Barchan dunes


Linear dunes


Linear and compound dunes


Star dunes

Namib desert

Transverse dunes?


Uluru (Ayer’s Rock),Central Australia


Controls on sand depositionControls on sand deposition


Facies and architectureFacies and architecture

Facies sequencesat the marginsof an erg.


Aeolian architectureAeolian architecture

Dune Interdune


► U. Jurassic Entrada U. Jurassic Entrada sandstone, W. USA. sandstone, W. USA.


► Permian Rotliegendes, Permian Rotliegendes, NW EuropeNW Europe


Active dry phase

Wet phase

Formation of ’supersurface’


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.

GE0-3112 Sedimentary processes and products Lecture 7. Aeolian sediments Geoff Corner Department of...

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