Delta Deposits are sedimentary deposits that form in the shape of a triangle, or delta. They are created when rivers deposit sediment at their mouths, forming a fan-like shape. These deposits are often found in coastal areas and can be composed of sand, silt, clay, and other materials. Silt is a type of sedimentary material that is made up of very small particles, usually between 0.004 and 0.06 millimeters in diameter.