delta environments

• Deltas form where rivers meet the ocean.
• If there is little tidal/wave action, sediment will be deposited in the mouth of the river due to the loss of energy and build up over time.
• The channel becomes blocked and the river splits into new distributary channels.
• In between delta channels, swampy islands form, these contain lots of vegetation if the delta is in the tropics and are the main sources of old coal.
• On the islands, mudstone and coal is found.
• In the channels, either sand (arkose) or pebbles (conglomerates) are found depending on the length of the river.
• Foresets are composed of sandstone, cross bedding or asymmetrical ripple marks.
• Bottomsets contain the smallest grains (siltstone/mudstone).
• A coarsening up sequence, representing a delta building up to sea, is called a cyclotherm.