bottomset bed

Bottomset beds are layers of sedimentary material found at the bottom of a body of water, near where a stream enters. These layers are formed by sediment carried by the stream and are subsequently covered by foreset and topset beds as a delta builds up.1

In deltas, where a river meets standing water, sediment is deposited. Coarser materials like gravel and sand form steeply inclined foreset beds at the river's mouth. Finer silts and clays are carried further into the water and settle as nearly flat-lying bottomset beds. These bottomset deposits often consist of clays swept beyond the delta front and dip at low angles, following the topography of the continental shelf or lake bottom.23