fluvial environments

• Fluvial environments are generally high energy environments except for floodplains.
• Dry conditions result in less water, leading to less energy.
• Alluvial fans occur beneath high ground where a mountain stream flows into a flat valley floor.
• The decrease in gradient is deposited in a fan shape.
• Alluvial fans deposit mostly breccias towards the back of the fan, and conglomerates that are deposited in the streams with the finer material washed away.
• Further from the mountain, smaller grains of arkose sandstone are deposited.
• In a Meandering river, the river moves laterally, depositing sediment on the shallow inside bend.
• Conglomerates are found in the river itself often in imbricate structure.
• Sandstones form at the river beach, the grains are moderately to well sorted and sub-rounded.
• Cross bedding may be present from the migration of ripple marks.
• Clays and mudstones are deposited in low energy flood plains.
• Flood plain clays and silts are deposited from turbulent waters, mudstones may have desiccation cracks or fossils.
• Braided rivers are found in semi-arid areas where discharge is low but can have infrequent high rainfall levels.
• Banks of sand and gravel are deposited when the river loses energy and wide channels form from the constant flow of water.
• Braided rivers produce cross bedded sequences that increase in grain size from the channel to the banks.
• braided river

  
• alluvial fan

  
• a meander