What is the source of the sediment (mud) that makes up salt marshes?
The source of any sediment is the weathering of rocks: The sand silt and clay is transported by water or wind and deposited elsewhere, or it may just be weathered in situ and not transported. The exception is carbonate mud, which is generated by biological action in warm shallow water. So it depends on where the salt marsh is, and what kind of sediment you are talking about. Sediment in salt marshes in Deltas will be sourced from upriver originally. The mud settles out in a quiet environment, like inter-distributary flood plains , and collects, trapped among the roots of vegetation, or is deposited off-shore of the delta front, while the sand and coarser material is deposited in the channels.
