l9_eolian_system 沉积地质学.pdfVIP

Eolian Landscapes and Deposits Relevant differences in air versus water as the transporting fluid ρwater ρ ≈ density air 800 µwater µ ≈ dynamic viscosity air 55 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 Superposition of eolian topography Order Wavelength Height Suggested Name Possible Origin Orientation 1st 300-5500 m 20-450 m draas primary aerodynamic longitudinal or instability transverse 2nd 3-600 m 0.1-100 m dunes primary aerodynamic longitudinal or instability transverse 3rd 15-250 cm 0.2-5 cm aerodynamic primary aerodynamic longitudinal or ripples instability transverse