desert environments

• Wadis are the dry river channels, they have a steep gradient and high energy so transport coarse sediment.
• Deposition in wadis is poorly sorted and the clasts are angular to rounded depending on the distance they have travelled.
• Alluvial fans are located close to mountains (breccia) and transported sediment for a long distance, making the grains smaller.
• Feldspar and mica from granites high in the mountains are transported to alluvial fans, turning them into arkose.
• Desert sandstones are very well sorted and rounded, made entirely of quartz, and are red from iron oxide cement.
• Desert sandstones can be seen in large scale cross bedding.
• Playa lakes are temporary lakes where desert streams flow into before evaporating or soaking into the ground.
• Metal ions from weathered rock become more concentrated as the water evaporates and the ions precipitate out of solution.
• Structures that can be found in playa lakes include: siltstones, evaporites, salt pseudomorphs, desiccation cracks and ripple marks.
• Evaporites precipitate in order from least soluble to most soluble.
• The order of evaporites is: Calcite, Gypsum, Anhydrite, Halite, Potassium/magnesium salts.