Eolian Landscapes and Deposits: Differences in Air and Water as Transporting Fluids, Study notes of Geology

Download Eolian Landscapes and Deposits: Differences in Air and Water as Transporting Fluids and more Study notes Geology in PDF only on Docsity! Eolian Landscapes and Deposits Relevant differences in air versus water as the transporting fluid 800 water air ρρ ≈ density 55 water air µµ ≈ dynamic viscosity Good match between present-day distribution of active eolian dune fields and worldwide distribution of deserts Aridity is define as P/ETp where P = precipitation and ETp = ability of solar radiation and vegetation to return moisture to the atmosphere by evaporation and evapotranspiration Correlation between aridity and eolian landforms make eolian deposits attractive candidates for paleoclimate studies. Complicating issue: Inherited source of wind blown sediment. These sources of sediment can overwhelm potential substrate stabilization by plants. Relatively unique aspect of eolian system: fluid is very thick/deep (atmosphere) and excursion lengths for small particles can be very long (e.g., breadth of Atlantic Ocean). 1 Docsity.com Superposition of eolian topography Erg = genetically related assemblage of draas Interdraa and interdune areas can be dry or wet and in some cases be sites of flowing water. In many cases there is not sufficient wind-blown sediment to completely cover landscape. Barchan dunes develop under these sediment-limited conditions. Great debate about whether inter-draa horizons represent: 1. Regional water-table surfaces (Implying preservation is connected to climate- change), or 2. Bedform climb. Climb model requires a lot of sediment coming into the depositional system. Foreset stratification associated with eolian dunes is the product of grain-flow and air-fall deposits. Air-fall sedimentation produces the tangential strata at bounding surfaces. Translatent ripple stratification is common in eolian ripple deposits. Stratification is produced by ripples climbing at angles << stoss-side angle. 2 Order Wavelength Height OrientationSuggested Name Possible Origin 1st 300-5500 m 20-450 m draas longitudinal or transverse primary aerodynamic instability 2nd 3-600 m 0.1-100 m dunes longitudinal or transverse primary aerodynamic instability 3rd 15-250 cm 0.2-5 cm aerodynamic ripples longitudinal or transverse primary aerodynamic instability 4th 0.5-2,000 cm 0.05-100 cm The classification of aeolian bedforms. impact ripples transverseimpact mechanism Figure by MIT OCW. Docsity.com 5 X X X X X X X X 100 1000 10000 Grain Diameter (microns) 0 20 40 60 80 100 P er ce nt F in er Troughs Crests Docsity.com 1 2 3 4 Immobile salt crust Coarsening of active surface layer associated with deflation. 100 1000 10000 Grain Diameter (microns) 0 20 40 60 80 100 P er ce nt F in er Crest 1 Crest 2 Trough 2 Crest 3 Trough 3 Crest 4 6 Docsity.com