GL4 E1 Key Idea 2 b ii SEDIMENTARY ROCKS The mineralogy and texture of sedimentary rocks are controlled by processes of weathering, erosion and deposition

GL4 E1 KI2 b (ii) Erosion EROSION: removal of material Acts together with weathering (weathering loosens the grains, erosion carries them away) Processes: Mass movement Air flow (wind transport) Water flow (rivers and sea) Ice flow (glaciation) (Perhaps sensible to read up on these “physical geography” areas)

Erosion (cont’d) Sorts the insoluble and soluble raw materials of weathering by a variety of physical and chemical processes And further breaks down the insoluble fraction by: abrasion, corrosion, saltation/suspension of particulate grains and the effect of grain composition, weight, density and shape (perhaps sensible to read up on these terms!)

What effect do you think the factors have? Composition? Weight? Density? Shape of grains?

Some suggestions…. Composition – resistance of minerals, how well they are joined/stuck together Weight and Density – bed load, requires strong current to move, easily deposited Shape of grains – plates (==) travel differently to spheres (oo)

Lab investigations: Size reduction or shape change – start with measured objects, apply simulated transport forces (eg. via shaking in a container so fragments knock together), measure fragments after “transport”, can be done as air or water transport. This has been done successfully with shells, baked clay cubes shaken in empty Pringles tubes but take care to number the fragments to record data carefully. Others have modelled rivers to see at what speed particles are picked up.