SEDIMENTARY PROCESSES/Aeolian Processes 627 identified (Figure 16) The changes in system state are manifested as episodic accumulation of aeolian deposits, resulting, for example, in sequences of loess accumulation interspersed by palaeosols (Figure 8), or formation of different dune generations in aeolian sand seas and dune fields (Figure 14) Consideration of variations in the supply of sediment for dune construction or loess accumulation, together with changes in the availability and mobility of this sediment, has prompted new explanations of regional variations in loess stratigraphy in North America and periods of aeolian accumulation in the Mojave and Arabian deserts For example, loess accumulation was low during the last glacial maximum in Alaska, despite high rates of sediment supply and mobility, because tundra vegetation is ineffective at trapping sediment This is in contrast to areas in the Great Plains and Central Lowlands, where accumulations of thick sequences of loess during the last glacial period were favoured by high rates of sediment supply from glacial outwash and high rates of accumulation in the boreal forest that then covered these areas In the Mojave Desert, high rates of aeolian accumulation and dune construction took place during times when palaeolake systems were drying out seasonally or annually Sediment deposited in these basins during wetter periods was mobilized during periods of drier climates Aeolian construction ceased when these supplies of sediment were exhausted (Figure 16) In addition to being influenced by climate and sealevel change, aeolian sediments and landforms may also provide evidence for past climate changes Examples include loess–palaeosol sequences, as well as dune systems, now vegetated and inactive, indicating the former extent of arid conditions and past wind regimes in what are today areas of semi-arid or subhumid climates (Figure 17), and increased rates of aeolian dust deposition in ocean sediments and ice cores (Figure 18) See Also Sedimentary Environments: Deserts Sedimentary Processes: Erosional Sedimentary Structures; Depositional Sedimentary Structures; Deposition from Suspension Soils: Palaeosols Further Reading Bagnold RA (1941) The Physics of Blown Sand and Desert Dunes London: Chapman and Hall Bristow CS, Bailey SD, and Lancaster N (2000) Sediment ary structure of linear sand dunes Nature 406: 56 59 Fryberger SG (1979) Dune forms and wind regimes In: McKee ED (ed.) A Study of Global Sand Seas: United States Geological Survey, Professional Paper, 1052, pp 137 140 Reston, VA: USGS Goudie AS, Livingstone I, and Stokes S (eds.) (1999) Ae olian Environments, Sediments, and Landforms New York: Wiley Kocurek G (1998) Aeolian system response to external for cing factors a sequence stratigraphic view of the Saharan region In: Alsharan AS, Glennie KW, Whittle GL, and Kendall CGSC (eds.) Quaternary Deserts and Climatic Change, pp 327 338 Rotterdam/Brookfield: Balkema Kocurek G and Lancaster N (1999) Aeolian sediment states: theory and Mojave Desert Kelso Dunefield example Sedimentology 46(3): 505 516 Laity JE (1994) Landforms of aeolian erosion In: Abrahams AD and Parsons AJ (eds.) Geomorphology of Desert Environments, pp 506 535 London: Chapman and Hall Lancaster N (1983) Controls of dune morphology in the Namib sand sea In: Ahlbrandt TS and Brookfield ME (eds.) Eolian Sediments and Processes Developments in Sedimentology, pp 261 289 Amsterdam: Elsevier Lancaster N (1995) Geomorphology of Desert Dunes London: Routledge Lancaster N (2000) Eolian deposits In: Partridge TC and Maud RR (eds.) The Cenozoic of Southern Africa, pp 73 87 Cape Town, South Africa: Oxford University Press Livingstone I and Warren A (1996) Aeolian Geomorphology: An Introduction Harlow: Addison Wesley Longman Muhs DR and Bettis EA III (2003) Quaternary loess paleosol sequences as examples of climate driven sedi mentary events In: Chan MA and Archer AW (eds.) Extreme Depositional Environments, Mega End Mem bers in Geologic Time, pp 53 74 Boulder, Colorado: Geological Society of America Pye K (1987) Aeolian Dust and Dust Deposits London: Academic Press Pye K and Tsoar H (1990) Aeolian Sand and Sand Dunes London: Unwin Hyman Wasson RJ and Hyde R (1983) Factors determining desert dune type Nature 304: 337 339 Wiggs GFS (2001) Desert dune processes and dynamics Progress in Physical Geography 25(1): 53 79