Presentation on theme: "Aeolian environments Lecture 9. Introduction Depositional environments. 1. Where? a. Wherever there is available sand and silt b. Availability requires."— Presentation transcript:
Introduction Depositional environments. 1. Where? a. Wherever there is available sand and silt b. Availability requires minimal vegetative cover c. Hence, beaches, glacial outwash plains, deserts, dry lakes, loess plains
2. Our focus today: deserts a. The predominant environment of aeolian processes b. Importance (paleoclimatic studies, desertification and soil erosion) c. Perspective: Environment “going to Hell” may just be climatic change (for example, the Sahel in the early 70’s)
Grain fall and grain flow processes Grain fall occurs as saltating grains on the stoss slope fly over the brink and come to rest on the lee face. Grain flow occurs as the upper lee face steepens from grainfall accumulation and then fails to static angle of repose.
Grain fall and grain flow processes Grain flow produces inverse sorting and shear sorting. Beds thicken downslope. Grain fall produces indistinct lamination. Beds thin downslope but may continue to base of dune if dune is small enough.
Grain fall and grain flow processes Ripples can occur as ornamentation on lee face. Slumps occur only on wet dunes, because cohesion is needed.
An example of seasonal effects on stratigraphy (wet vs. dry systems) Wintertime accumulations Summertime accumulations