What process was primarily responsible for the formation of a delta ?

Question:
What process was primarily responsible for the formation of a delta ?

Weathering, transport, and deposition.

Rock and soil erode, are carried by the water downriver until the motion of the water is too slow to support the load, which is usually at or near the mouth of the river.

A delta is formed where a major river enters the sea which has a small tidal range. If the tidal range is high then the sediment is washed away and an estuary is formed. The delta is named by its shape: it looks like the letter D in the Greek alphabet.

Hope this helped :D sorry for long answer